The Spring Web model-view-controller (MVC) framework is designed
around a DispatcherServlet
that dispatches requests
to handlers, with configurable handler mappings, view resolution, locale
and theme resolution as well as support for uploading files. The default
handler is based on the @Controller
and
@RequestMapping
annotations, offering a
wide range of flexible handling methods. With the introduction of Spring
3.0, the @Controller
mechanism also allows
you to create RESTful Web sites and applications, through the
@PathVariable
annotation and other
features.
In Spring Web MVC you can use any object as a command or form-backing object; you do not need to implement a framework-specific interface or base class. Spring's data binding is highly flexible: for example, it treats type mismatches as validation errors that can be evaluated by the application, not as system errors. Thus you need not duplicate your business objects' properties as simple, untyped strings in your form objects simply to handle invalid submissions, or to convert the Strings properly. Instead, it is often preferable to bind directly to your business objects.
Spring's view resolution is extremely flexible. A
Controller
is typically responsible for
preparing a model Map
with data and selecting a
view name but it can also write directly to the response stream and
complete the request. View name resolution is highly configurable through
file extension or Accept header content type negotiation, through bean
names, a properties file, or even a custom
ViewResolver
implementation. The model (the
M in MVC) is a Map
interface, which allows
for the complete abstraction of the view technology. You can integrate
directly with template based rendering technologies such as JSP, Velocity
and Freemarker, or directly generate XML, JSON, Atom, and many other types
of content. The model Map
is simply
transformed into an appropriate format, such as JSP request attributes, a
Velocity template model.
Spring's web module includes many unique web support features:
Clear separation of roles. Each role —
controller, validator, command object, form object, model object,
DispatcherServlet
, handler mapping, view
resolver, and so on — can be fulfilled by a specialized
object.
Powerful and straightforward configuration of both framework and application classes as JavaBeans. This configuration capability includes easy referencing across contexts, such as from web controllers to business objects and validators.
Adaptability, non-intrusiveness, and flexibility. Define any controller method signature you need, possibly using one of the parameter annotations (such as @RequestParam, @RequestHeader, @PathVariable, and more) for a given scenario.
Reusable business code, no need for duplication. Use existing business objects as command or form objects instead of mirroring them to extend a particular framework base class.
Customizable binding and validation. Type mismatches as application-level validation errors that keep the offending value, localized date and number binding, and so on instead of String-only form objects with manual parsing and conversion to business objects.
Customizable handler mapping and view resolution. Handler mapping and view resolution strategies range from simple URL-based configuration, to sophisticated, purpose-built resolution strategies. Spring is more flexible than web MVC frameworks that mandate a particular technique.
Flexible model transfer. Model transfer
with a name/value Map
supports easy
integration with any view technology.
Customizable locale and theme resolution, support for JSPs with or without Spring tag library, support for JSTL, support for Velocity without the need for extra bridges, and so on.
A simple yet powerful JSP tag library known as the Spring tag library that provides support for features such as data binding and themes. The custom tags allow for maximum flexibility in terms of markup code. For information on the tag library descriptor, see the appendix entitled Appendix G, spring.tld
A JSP form tag library, introduced in Spring 2.0, that makes writing forms in JSP pages much easier. For information on the tag library descriptor, see the appendix entitled Appendix H, spring-form.tld
Beans whose lifecycle is scoped to the current HTTP
request or HTTP Session
.
This is not a specific feature of Spring MVC itself, but rather of
the WebApplicationContext
container(s) that Spring MVC uses. These bean scopes are described
in Section 5.5.4, “Request, session, and global session scopes”
Non-Spring MVC implementations are preferable for some projects. Many teams expect to leverage their existing investment in skills and tools. A large body of knowledge and experience exist for the Struts framework. If you can abide Struts' architectural flaws, it can be a viable choice for the web layer; the same applies to WebWork and other web MVC frameworks.
If you do not want to use Spring's web MVC, but intend to leverage
other solutions that Spring offers, you can integrate the web MVC
framework of your choice with Spring easily. Simply start up a Spring
root application context through its
ContextLoaderListener
, and access it through
its
ServletContext
attribute (or Spring's
respective helper method) from within a Struts or WebWork action. No
"plug-ins" are involved, so no dedicated integration is necessary. From
the web layer's point of view, you simply use Spring as a library, with
the root application context instance as the entry point.
Your registered beans and Spring's services can be at your fingertips even without Spring's Web MVC. Spring does not compete with Struts or WebWork in this scenario. It simply addresses the many areas that the pure web MVC frameworks do not, from bean configuration to data access and transaction handling. So you can enrich your application with a Spring middle tier and/or data access tier, even if you just want to use, for example, the transaction abstraction with JDBC or Hibernate.
Spring's web MVC framework is, like many other web MVC frameworks,
request-driven, designed around a central Servlet that dispatches requests
to controllers and offers other functionality that facilitates the
development of web applications. Spring's
DispatcherServlet
however, does more than just
that. It is completely integrated with the Spring IoC container and as
such allows you to use every other feature that Spring has.
The request processing workflow of the Spring Web MVC
DispatcherServlet
is illustrated in the following
diagram. The pattern-savvy reader will recognize that the
DispatcherServlet
is an expression of the
“Front Controller” design pattern (this is a pattern that
Spring Web MVC shares with many other leading web frameworks).
The DispatcherServlet
is an actual
Servlet
(it inherits from the
HttpServlet
base class), and as such is declared in
the web.xml
of your web application. You need to map
requests that you want the DispatcherServlet
to
handle, by using a URL mapping in the same web.xml
file. This is standard Java EE Servlet configuration; the following example
shows such a DispatcherServlet
declaration and
mapping:
<web-app> <servlet> <servlet-name>example</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>example</servlet-name> <url-pattern>/example/*</url-pattern> </servlet-mapping> </web-app>
In the preceding example, all requests starting with
/example
will be handled by the
DispatcherServlet
instance named
example
.
In a Servlet 3.0+ environment, you also have the
option of configuring the Servlet container programmatically. Below is the code
based equivalent of the above web.xml
example:
public class MyWebApplicationInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext container) { ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet()); registration.setLoadOnStartup(1); registration.addMapping("/example/*"); } }
WebApplicationInitializer
is an interface
provided by Spring MVC that ensures your code-based configuration is detected and
automatically used to initialize any Servlet 3 container. An abstract base class
implementation of this interace named
AbstractDispatcherServletInitializer
makes it even easier
to register the DispatcherServlet
by simply specifying
its servlet mapping. See
Code-based Servlet container initialization
for more details.
The above is only the first step in setting up
Spring Web MVC. You
now need to configure the various beans used by the Spring Web MVC
framework (over and above the DispatcherServlet
itself).
As detailed in Section 5.14, “Additional Capabilities of the
ApplicationContext
”,
ApplicationContext
instances in Spring can
be scoped. In the Web MVC framework, each
DispatcherServlet
has its own
WebApplicationContext
, which inherits all
the beans already defined in the root
WebApplicationContext
. These inherited
beans can be overridden in the servlet-specific scope, and you can define
new scope-specific beans local to a given Servlet instance.
Upon initialization of a DispatcherServlet
,
Spring MVC looks for a file named
[servlet-name]-servlet.xml
in the
WEB-INF
directory of your web application and creates
the beans defined there, overriding the definitions of any beans defined
with the same name in the global scope.
Consider the following DispatcherServlet
Servlet configuration (in the web.xml
file):
<web-app> <servlet> <servlet-name>golfing</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>golfing</servlet-name> <url-pattern>/golfing/*</url-pattern> </servlet-mapping> </web-app>
With the above Servlet configuration in place, you
will need to have a file called /WEB-INF/
golfing-servlet.xml
in your
application; this file will contain all of your Spring Web MVC-specific
components (beans). You can change the exact location of this
configuration file through a Servlet initialization parameter (see below
for details).
The WebApplicationContext
is an
extension of the plain ApplicationContext
that has some extra features necessary for web applications. It differs
from a normal ApplicationContext
in that it
is capable of resolving themes (see Section 17.9, “Using themes”),
and that it knows which Servlet it is associated with (by having a link to
the ServletContext
). The
WebApplicationContext
is bound in the
ServletContext
, and by using static methods
on the RequestContextUtils
class you can always
look up the WebApplicationContext
if you
need access to it.
The Spring DispatcherServlet
uses special
beans to process requests and render the appropriate views. These beans
are part of Spring MVC. You can choose which special beans to use
by simply configuring one or more of them in the
WebApplicationContext
.
However, you don't need to do that initially since Spring MVC
maintains a list of default beans to use if you don't configure any.
More on that in the next section. First see the table below
listing the special bean types the
DispatcherServlet
relies on.
Table 17.1. Special bean types in the
WebApplicationContext
Bean type | Explanation |
---|---|
HandlerMapping | Maps incoming requests to handlers and a list of
pre- and post-processors (handler interceptors) based on some
criteria the details of which vary by HandlerMapping
implementation. The most popular implementation supports
annotated controllers but other implementations exists as well. |
HandlerAdapter | Helps the DispatcherServlet to
invoke a handler mapped to a request regardless of the handler
is actually invoked. For example, invoking an annotated controller
requires resolving various annotations. Thus the main purpose
of a HandlerAdapter is to shield the
DispatcherServlet from such details. |
HandlerExceptionResolver | Maps exceptions to views also allowing for more complex exception handling code. |
ViewResolver | Resolves logical String-based view names to actual
View types. |
LocaleResolver | Resolves the locale a client is using, in order to be able to offer internationalized views |
ThemeResolver | Resolves themes your web application can use, for example, to offer personalized layouts |
MultipartResolver | Parses multi-part requests for example to support processing file uploads from HTML forms. |
FlashMapManager | Stores and retrieves the "input" and the "output"
FlashMap that can be used to pass attributes
from one request to another, usually across a redirect. |
As mentioned in the previous section for each special bean
the DispatcherServlet
maintains a list
of implementations to use by default. This information is
kept in the file DispatcherServlet.properties
in the package org.springframework.web.servlet
.
All special beans have some reasonable defaults of
their own. Sooner or later though you'll need to customize
one or more of the properties these beans provide.
For example it's quite common to configure
an InternalResourceViewResolver
settings its prefix
property to
the parent location of view files.
Regardless of the details, the important concept
to understand here is that once
you configure a special bean such as an
InternalResourceViewResolver
in your WebApplicationContext
, you
effectively override the list of default implementations
that would have been used otherwise for that special bean
type. For example if you configure an
InternalResourceViewResolver
,
the default list of ViewResolver
implementations is ignored.
In Section 17.15, “Configuring Spring MVC” you'll learn about other options for configuring Spring MVC including MVC Java config and the MVC XML namespace both of which provide a simple starting point and assume little knowledge of how Spring MVC works. Regardless of how you choose to configure your application, the concepts explained in this section are fundamental should be of help to you.
After you set up a DispatcherServlet
, and a
request comes in for that specific
DispatcherServlet
, the
DispatcherServlet
starts processing the request as
follows:
The WebApplicationContext
is
searched for and bound in the request as an attribute that the
controller and other elements in the process can use. It
is bound by default under the key
DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE
.
The locale resolver is bound to the request to enable elements in the process to resolve the locale to use when processing the request (rendering the view, preparing data, and so on). If you do not need locale resolving, you do not need it.
The theme resolver is bound to the request to let elements such as views determine which theme to use. If you do not use themes, you can ignore it.
If you specify a multipart file resolver, the request is
inspected for multiparts; if multiparts are found, the request is
wrapped in a MultipartHttpServletRequest
for
further processing by other elements in the process. See Section 17.10, “Spring's multipart (file upload) support” for further information about multipart
handling.
An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (preprocessors, postprocessors, and controllers) is executed in order to prepare a model or rendering.
If a model is returned, the view is rendered. If no model is returned, (may be due to a preprocessor or postprocessor intercepting the request, perhaps for security reasons), no view is rendered, because the request could already have been fulfilled.
Handler exception resolvers that are declared in the
WebApplicationContext
pick up exceptions
that are thrown during processing of the request. Using these exception
resolvers allows you to define custom behaviors to address
exceptions.
The Spring DispatcherServlet
also supports
the return of the last-modification-date, as
specified by the Servlet API. The process of determining the last
modification date for a specific request is straightforward: the
DispatcherServlet
looks up an appropriate handler
mapping and tests whether the handler that is found implements the
LastModified
interface. If so, the value of the long
getLastModified(request)
method of the
LastModified
interface is returned to the
client.
You can customize individual
DispatcherServlet
instances by adding Servlet
initialization parameters (init-param
elements) to the
Servlet declaration in the web.xml
file. See the
following table for the list of supported parameters.
Table 17.2. DispatcherServlet
initialization
parameters
Parameter | Explanation |
---|---|
contextClass | Class that implements
WebApplicationContext , which
instantiates the context used by this Servlet. By default, the
XmlWebApplicationContext is used. |
contextConfigLocation | String that is passed to the context instance (specified by
contextClass ) to indicate where context(s) can
be found. The string consists potentially of multiple strings
(using a comma as a delimiter) to support multiple contexts. In
case of multiple context locations with beans that are defined
twice, the latest location takes precedence. |
namespace | Namespace of the
WebApplicationContext . Defaults to
[servlet-name]-servlet . |
Controllers provide access to the application behavior that you typically define through a service interface. Controllers interpret user input and transform it into a model that is represented to the user by the view. Spring implements a controller in a very abstract way, which enables you to create a wide variety of controllers.
Spring 2.5 introduced an annotation-based programming model for MVC
controllers that uses annotations such as
@RequestMapping
,
@RequestParam
,
@ModelAttribute
, and so on. This annotation
support is available for both Servlet MVC and Portlet MVC. Controllers
implemented in this style do not have to extend specific base classes or
implement specific interfaces. Furthermore, they do not usually have
direct dependencies on Servlet or Portlet APIs, although you can easily
configure access to Servlet or Portlet facilities.
Tip | |
---|---|
Available in the samples repository, a number of web applications leverage the annotation support described in this section including MvcShowcase, MvcAjax, MvcBasic, PetClinic, PetCare, and others. |
@Controller public class HelloWorldController { @RequestMapping("/helloWorld") public String helloWorld(Model model) { model.addAttribute("message", "Hello World!"); return "helloWorld"; } }
As you can see, the @Controller
and
@RequestMapping
annotations allow flexible
method names and signatures. In this particular example the method accepts
a Model
and returns a view name as a
String
, but various other method parameters and
return values can be used as explained later in this section.
@Controller
and
@RequestMapping
and a number of other
annotations form the basis for the Spring MVC implementation. This section
documents these annotations and how they are most commonly used in a
Servlet environment.
The @Controller
annotation
indicates that a particular class serves the role of a
controller. Spring does not require you to extend
any controller base class or reference the Servlet API. However, you can
still reference Servlet-specific features if you need to.
The @Controller
annotation acts as
a stereotype for the annotated class, indicating its role. The
dispatcher scans such annotated classes for mapped methods and detects
@RequestMapping
annotations (see the next
section).
You can define annotated controller beans explicitly, using a
standard Spring bean definition in the dispatcher's context. However,
the @Controller
stereotype also allows
for autodetection, aligned with Spring general support for detecting
component classes in the classpath and auto-registering bean definitions
for them.
To enable autodetection of such annotated controllers, you add component scanning to your configuration. Use the spring-context schema as shown in the following XML snippet:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="org.springframework.samples.petclinic.web"/> <!-- ... --> </beans>
You use the @RequestMapping
annotation to map URLs such as /appointments
onto
an entire class or a particular handler method. Typically the
class-level annotation maps a specific request path (or path pattern)
onto a form controller, with additional method-level annotations
narrowing the primary mapping for a specific HTTP method request method
("GET", "POST", etc.) or an HTTP request parameter condition.
The following example from the Petcare sample shows a controller in a Spring MVC application that uses this annotation:
@Controller @RequestMapping("/appointments") public class AppointmentsController { private final AppointmentBook appointmentBook; @Autowired public AppointmentsController(AppointmentBook appointmentBook) { this.appointmentBook = appointmentBook; } @RequestMapping(method = RequestMethod.GET) public Map<String, Appointment> get() { return appointmentBook.getAppointmentsForToday(); } @RequestMapping(value="/{day}", method = RequestMethod.GET) public Map<String, Appointment> getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day, Model model) { return appointmentBook.getAppointmentsForDay(day); } @RequestMapping(value="/new", method = RequestMethod.GET) public AppointmentForm getNewForm() { return new AppointmentForm(); } @RequestMapping(method = RequestMethod.POST) public String add(@Valid AppointmentForm appointment, BindingResult result) { if (result.hasErrors()) { return "appointments/new"; } appointmentBook.addAppointment(appointment); return "redirect:/appointments"; } }
In the example, the @RequestMapping
is used in a number of places. The first usage is on the type (class)
level, which indicates that all handling methods on this controller are
relative to the /appointments
path. The
get()
method has a further
@RequestMapping
refinement: it only
accepts GET requests, meaning that an HTTP GET for
/appointments
invokes this method. The
post()
has a similar refinement, and the
getNewForm()
combines the definition of HTTP
method and path into one, so that GET requests for
appointments/new
are handled by that method.
The getForDay()
method shows another
usage of @RequestMapping
: URI templates.
(See the next
section ).
A @RequestMapping
on the class
level is not required. Without it, all paths are simply absolute, and
not relative. The following example from the
PetClinic sample application shows a multi-action
controller using @RequestMapping
:
@Controller public class ClinicController { private final Clinic clinic; @Autowired public ClinicController(Clinic clinic) { this.clinic = clinic; } @RequestMapping("/") public void welcomeHandler() { } @RequestMapping("/vets") public ModelMap vetsHandler() { return new ModelMap(this.clinic.getVets()); } }
Using @RequestMapping On
Interface Methods | |
---|---|
A common pitfall when working with annotated controller classes
happens when applying functionality that requires creating a proxy for
the controller object (e.g.
Note however that method argument annotations, e.g.
|
Spring 3.1 introduced a new set of support classes for
@RequestMapping
methods called
RequestMappingHandlerMapping
and
RequestMappingHandlerAdapter
respectively.
They are recommended for use and even required to take advantage of
new features in Spring MVC 3.1 and going forward. The new support
classes are enabled by default by the MVC namespace and the MVC Java
config but must be configured explicitly if using neither.
This section describes a few
important differences between the old and the new support classes.
Prior to Spring 3.1, type and method-level request mappings were
examined in two separate stages -- a controller was selected first
by the DefaultAnnotationHandlerMapping
and the
actual method to invoke was narrowed down second by
the AnnotationMethodHandlerAdapter
.
With the new support classes in Spring 3.1, the
RequestMappingHandlerMapping
is the only place
where a decision is made about which method should process the request.
Think of controller methods as a collection of unique endpoints
with mappings for each method derived from type and method-level
@RequestMapping
information.
This enables some new possibilities. For once a
HandlerInterceptor
or a
HandlerExceptionResolver
can now expect the
Object-based handler to be a HandlerMethod
,
which allows them to examine the exact method, its parameters and
associated annotations. The processing for a URL no longer needs to
be split across different controllers.
There are also several things no longer possible:
Select a controller first with a
SimpleUrlHandlerMapping
or
BeanNameUrlHandlerMapping
and then narrow
the method based on @RequestMapping
annotations.
Rely on method names as a fall-back mechanism to
disambiguate between two @RequestMapping
methods
that don't have an explicit path mapping URL path but otherwise
match equally, e.g. by HTTP method. In the new support classes
@RequestMapping
methods have to be mapped
uniquely.
Have a single default method (without an explicit path mapping) with which requests are processed if no other controller method matches more concretely. In the new support classes if a matching method is not found a 404 error is raised.
The above features are still supported with the existing support classes. However to take advantage of new Spring MVC 3.1 features you'll need to use the new support classes.
URI templates can be used for convenient
access to selected parts of a URL in a
@RequestMapping
method.
A URI Template is a URI-like string, containing one or more
variable names. When you substitute values for these variables, the
template becomes a URI. The proposed
RFC for URI Templates defines how a URI is parameterized. For
example, the URI Template
http://www.example.com/users/{userId}
contains the
variable userId. Assigning the value
fred to the variable yields
http://www.example.com/users/fred
.
In Spring MVC you can use the
@PathVariable
annotation on a method
argument to bind it to the value of a URI template variable:
@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable String ownerId, Model model) { Owner owner = ownerService.findOwner(ownerId); model.addAttribute("owner", owner); return "displayOwner"; }
The URI Template "/owners/{ownerId}
"
specifies the variable name ownerId
. When the
controller handles this request, the value of
ownerId
is set to the value found in the
appropriate part of the URI. For example, when a request comes in for
/owners/fred
, the value of ownerId
is
fred
.
Tip | |
---|---|
To process the @PathVariable annotation, Spring MVC needs to find the matching URI template variable by name. You can specify it in the annotation: @RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable("ownerId") String theOwner, Model model) { // implementation omitted } Or if the URI template variable name matches the method argument name you can omit that detail. As long as your code is not compiled without debugging information, Spring MVC will match the method argument name to the URI template variable name: @RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable String ownerId, Model model) { // implementation omitted } |
A method can have any number of
@PathVariable
annotations:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET) public String findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { Owner owner = ownerService.findOwner(ownerId); Pet pet = owner.getPet(petId); model.addAttribute("pet", pet); return "displayPet"; }
When a @PathVariable
annotation is
used on a Map<String, String>
argument, the
map is populated with all URI template variables.
A URI template can be assembled from type and path level
@RequestMapping annotations. As a result the
findPet()
method can be invoked with a URL
such as /owners/42/pets/21
.
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping("/pets/{petId}") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } }
A @PathVariable
argument can be
of any simple type such as int, long,
Date, etc. Spring automatically converts to the appropriate type or
throws a TypeMismatchException
if it fails to
do so. You can also register support for parsing additional data
types. See the section called “Method Parameters And Type Conversion” and the section called “Customizing WebDataBinder
initialization”.
Sometimes you need more precision in defining URI template
variables. Consider the URL
"/spring-web/spring-web-3.0.5.jar"
. How do you break it
down into multiple parts?
The @RequestMapping
annotation
supports the use of regular expressions in URI template variables. The
syntax is {varName:regex}
where the first part defines
the variable name and the second - the regular expression.For
example:
@RequestMapping("/spring-web/{symbolicName:[a-z-]+}-{version:\d\.\d\.\d}.{extension:\.[a-z]}") public void handle(@PathVariable String version, @PathVariable String extension) { // ... } }
In addition to URI templates, the
@RequestMapping
annotation also
supports Ant-style path patterns (for example,
/myPath/*.do
). A combination of URI templates and
Ant-style globs is also supported (for example,
/owners/*/pets/{petId}
).
Patterns in @RequestMapping
annotations
support ${...} placeholders against local properties and/or system properties
and environment variables. This may be useful in cases where the path a
controller is mapped to may need to be customized through configuration.
For more information on placeholders see the Javadoc for
PropertyPlaceholderConfigurer
.
The URI specification RFC 3986 defines the possibility of including name-value pairs within path segments. There is no specific term used in the spec. The general "URI path parameters" could be applied although the more unique "Matrix URIs", originating from an old post by Tim Berners-Lee, is also frequently used and fairly well known. Within Spring MVC these are referred to as matrix variables.
Matrix variables can appear in any path segment, each matrix variable
separated with a ";" (semicolon).
For example: "/cars;color=red;year=2012"
.
Multiple values may be either "," (comma) separated
"color=red,green,blue"
or the variable name may be repeated
"color=red;color=green;color=blue"
.
If a URL is expected to contain matrix variables, the request mapping pattern must represent them with a URI template. This ensures the request can be matched correctly regardless of whether matrix variables are present or not and in what order they are provided.
Below is an example of extracting the matrix variable "q":
// GET /pets/42;q=11;r=22 @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET) public void findPet(@PathVariable String petId, @MatrixVariable int q) { // petId == 42 // q == 11 }
Since all path segments may contain matrix variables, in some cases you need to be more specific to identify where the variable is expected to be:
// GET /owners/42;q=11/pets/21;q=22 @RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET) public void findPet( @MatrixVariable(value="q", pathVar="ownerId") int q1, @MatrixVariable(value="q", pathVar="petId") int q2) { // q1 == 11 // q2 == 22 }
A matrix variable may be defined as optional and a default value specified:
// GET /pets/42 @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET) public void findPet(@MatrixVariable(required=true, defaultValue="1") int q) { // q == 1 }
All matrix variables may be obtained in a Map:
// GET /owners/42;q=11;r=12/pets/21;q=22;s=23 @RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET) public void findPet( @MatrixVariable Map<String, String> matrixVars, @MatrixVariable(pathVar="petId"") Map<String, String> petMatrixVars) { // matrixVars: ["q" : [11,22], "r" : 12, "s" : 23] // petMatrixVars: ["q" : 11, "s" : 23] }
Note that to enable the use of matrix variables, you must set the
removeSemicolonContent
property of
RequestMappingHandlerMapping
to false
.
By default it is set to true
with the exception of the
MVC namespace and the MVC Java config both of which automatically enable
the use of matrix variables.
You can narrow the primary mapping by specifying a list of consumable media types. The request will be matched only if the Content-Type request header matches the specified media type. For example:
@Controller @RequestMapping(value = "/pets", method = RequestMethod.POST, consumes="application/json") public void addPet(@RequestBody Pet pet, Model model) { // implementation omitted }
Consumable media type expressions can also be negated as in !text/plain to match to all requests other than those with Content-Type of text/plain.
Tip | |
---|---|
The consumes condition is supported on the type and on the method level. Unlike most other conditions, when used at the type level, method-level consumable types override rather than extend type-level consumable types. |
You can narrow the primary mapping by specifying a list of producible media types. The request will be matched only if the Accept request header matches one of these values. Furthermore, use of the produces condition ensures the actual content type used to generate the response respects the media types specified in the produces condition. For example:
@Controller @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, produces="application/json") @ResponseBody public Pet getPet(@PathVariable String petId, Model model) { // implementation omitted }
Just like with consumes, producible media type expressions can be negated as in !text/plain to match to all requests other than those with an Accept header value of text/plain.
Tip | |
---|---|
The produces condition is supported on the type and on the method level. Unlike most other conditions, when used at the type level, method-level producible types override rather than extend type-level producible types. |
You can narrow request matching through request parameter
conditions such as "myParam"
, "!myParam"
, or
"myParam=myValue"
. The first two test for request
parameter presence/absence and the third for a specific parameter
value. Here is an example with a request parameter value
condition:
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, params="myParam=myValue") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } }
The same can be done to test for request header presence/absence or to match based on a specific request header value:
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping(value = "/pets", method = RequestMethod.GET, headers="myHeader=myValue") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } }
Tip | |
---|---|
Although you can match to Content-Type and Accept header values using media type wild cards (for example "content-type=text/*" will match to "text/plain" and "text/html"), it is recommended to use the consumes and produces conditions respectively instead. They are intended specifically for that purpose. |
An @RequestMapping
handler method can have
a very flexible signatures. The supported method arguments and return
values are described in the following section. Most arguments can be
used in arbitrary order with the only exception of
BindingResult
arguments. This is described in the
next section.
Note | |
---|---|
Spring 3.1 introduced a new set of support classes for
|
The following are the supported method arguments:
Request or response objects (Servlet API). Choose any
specific request or response type, for example
ServletRequest
or
HttpServletRequest
.
Session object (Servlet API): of type
HttpSession
. An argument of this
type enforces the presence of a corresponding session. As a
consequence, such an argument is never
null
.
Note | |
---|---|
Session access may not be thread-safe, in particular in
a Servlet environment. Consider setting the
|
org.springframework.web.context.request.WebRequest
or
org.springframework.web.context.request.NativeWebRequest
.
Allows for generic request parameter access as well as
request/session attribute access, without ties to the native
Servlet/Portlet API.
java.util.Locale
for the current
request locale, determined by the most specific locale resolver
available, in effect, the configured
LocaleResolver
in a Servlet
environment.
java.io.InputStream
/
java.io.Reader
for access to the
request's content. This value is the raw InputStream/Reader as
exposed by the Servlet API.
java.io.OutputStream
/
java.io.Writer
for generating the
response's content. This value is the raw OutputStream/Writer as
exposed by the Servlet API.
java.security.Principal
containing the currently authenticated user.
@PathVariable
annotated parameters
for access to URI template variables. See the section called “URI Template Patterns”.
@MatrixVariable
annotated parameters
for access to name-value pairs located in URI path segments.
See the section called “Matrix Variables”.
@RequestParam
annotated parameters
for access to specific Servlet request parameters. Parameter
values are converted to the declared method argument type. See
the section called “Binding request parameters to method parameters with
@RequestParam
”.
@RequestHeader
annotated
parameters for access to specific Servlet request HTTP headers.
Parameter values are converted to the declared method argument
type.
@RequestBody
annotated
parameters for access to the HTTP request body. Parameter values
are converted to the declared method argument type using
HttpMessageConverter
s. See the section called “Mapping the request body with the @RequestBody
annotation”.
@RequestPart
annotated
parameters for access to the content of a "multipart/form-data"
request part. See Section 17.10.5, “Handling a file upload request from programmatic clients” and Section 17.10, “Spring's multipart (file upload) support”.
HttpEntity<?>
parameters for
access to the Servlet request HTTP headers and contents. The
request stream will be converted to the entity body using
HttpMessageConverter
s. See the section called “Using HttpEntity<?>
”.
java.util.Map
/
org.springframework.ui.Model
/
org.springframework.ui.ModelMap
for
enriching the implicit model that is exposed to the web
view.
org.springframework.web.servlet.mvc.support.RedirectAttributes
to specify the exact set of attributes to use in case of a
redirect and also to add flash attributes (attributes stored
temporarily on the server-side to make them available to the
request after the redirect).
RedirectAttributes
is used instead of the
implicit model if the method returns a "redirect:" prefixed view
name or RedirectView
.
Command or form objects to bind request parameters to bean
properties (via setters) or directly to fields, with
customizable type conversion, depending on
@InitBinder
methods and/or the
HandlerAdapter configuration. See the
webBindingInitializer
property on
RequestMappingHandlerAdapter
. Such
command objects along with their validation results will be
exposed as model attributes by default, using the command class
class name - e.g. model attribute "orderAddress" for a command
object of type "some.package.OrderAddress". The
ModelAttribute
annotation can be used on
a method argument to customize the model attribute name
used.
org.springframework.validation.Errors
/
org.springframework.validation.BindingResult
validation results for a preceding command or form object (the
immediately preceding method argument).
org.springframework.web.bind.support.SessionStatus
status handle for marking form processing as complete, which
triggers the cleanup of session attributes that have been
indicated by the @SessionAttributes
annotation at the handler type level.
org.springframework.web.util.UriComponentsBuilder
a builder for preparing a URL relative to the current request's
host, port, scheme, context path, and the literal part of the
servlet mapping.
The Errors
or
BindingResult
parameters have to follow
the model object that is being bound immediately as the method
signature might have more that one model object and Spring will create
a separate BindingResult
instance for
each of them so the following sample won't work:
Example 17.1. Invalid ordering of BindingResult and @ModelAttribute
@RequestMapping(method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, Model model, BindingResult result) { … }
Note, that there is a Model
parameter in between Pet
and
BindingResult
. To get this working
you have to reorder the parameters as follows:
@RequestMapping(method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result, Model model) { … }
The following are the supported return types:
A ModelAndView
object, with the
model implicitly enriched with command objects and the results
of @ModelAttribute
annotated reference data
accessor methods.
A Model
object, with the
view name implicitly determined through a
RequestToViewNameTranslator
and
the model implicitly enriched with command objects and the
results of @ModelAttribute
annotated
reference data accessor methods.
A Map
object for exposing a
model, with the view name implicitly determined through a
RequestToViewNameTranslator
and
the model implicitly enriched with command objects and the
results of @ModelAttribute
annotated
reference data accessor methods.
A View
object, with the
model implicitly determined through command objects and
@ModelAttribute
annotated reference data
accessor methods. The handler method may also programmatically
enrich the model by declaring a
Model
argument (see above).
A String
value that is interpreted
as the logical view name, with the model implicitly determined
through command objects and @ModelAttribute
annotated reference data accessor methods. The handler method
may also programmatically enrich the model by declaring a
Model
argument (see
above).
void
if the method handles the response
itself (by writing the response content directly, declaring an
argument of type ServletResponse
/ HttpServletResponse
for that
purpose) or if the view name is supposed to be implicitly
determined through a
RequestToViewNameTranslator
(not
declaring a response argument in the handler method
signature).
If the method is annotated with
@ResponseBody
, the return type is
written to the response HTTP body. The return value will be
converted to the declared method argument type using
HttpMessageConverter
s. See the section called “Mapping the response body with the
@ResponseBody
annotation”.
A HttpEntity<?>
or
ResponseEntity<?>
object to provide
access to the Servlet response HTTP headers and contents. The
entity body will be converted to the response stream using
HttpMessageConverter
s. See the section called “Using HttpEntity<?>
”.
A Callable<?>
can
be returned when the application wants to produce the return
value asynchronously in a thread managed by Spring MVC.
A DeferredResult<?>
can
be returned when the application wants to produce the return
value from a thread of its own choosing.
Any other return type is considered to be a single model
attribute to be exposed to the view, using the attribute name
specified through @ModelAttribute
at the
method level (or the default attribute name based on the return
type class name). The model is implicitly enriched with command
objects and the results of @ModelAttribute
annotated reference data accessor methods.
Use the @RequestParam
annotation to bind
request parameters to a method parameter in your controller.
The following code snippet shows the usage:
@Controller @RequestMapping("/pets") @SessionAttributes("pet") public class EditPetForm { // ... @RequestMapping(method = RequestMethod.GET) public String setupForm(@RequestParam("petId") int petId, ModelMap model) { Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } // ...
Parameters using this annotation are required by default, but
you can specify that a parameter is optional by setting
@RequestParam
's
required
attribute to false
(e.g., @RequestParam(value="id",
required=false)
).
Type conversion is applied automatically if the target method
parameter type is not String
. See the section called “Method Parameters And Type Conversion”.
The @RequestBody
method parameter
annotation indicates that a method parameter should be bound to the
value of the HTTP request body. For example:
@RequestMapping(value = "/something", method = RequestMethod.PUT) public void handle(@RequestBody String body, Writer writer) throws IOException { writer.write(body); }
You convert the request body to the method argument by using an
HttpMessageConverter
.
HttpMessageConverter
is responsible for
converting from the HTTP request message to an object and converting
from an object to the HTTP response body. The
RequestMappingHandlerAdapter
supports the
@RequestBody
annotation with the following
default HttpMessageConverters
:
ByteArrayHttpMessageConverter
converts byte arrays.
StringHttpMessageConverter
converts
strings.
FormHttpMessageConverter
converts
form data to/from a MultiValueMap<String, String>.
SourceHttpMessageConverter
converts
to/from a javax.xml.transform.Source.
For more information on these converters, see Message Converters. Also note that if using the MVC namespace or the MVC Java config, a wider range of message converters are registered by default. See Enabling the MVC Java Config or the MVC XML Namespace for more information.
If you intend to read and write XML, you will need to configure
the MarshallingHttpMessageConverter
with a
specific Marshaller
and an
Unmarshaller
implementation from the
org.springframework.oxm
package. The example
below shows how to do that directly in your configuration but if
your application is configured through the MVC namespace or the
MVC Java config see Enabling
the MVC Java Config or the MVC XML Namespace instead.
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> <property name="messageConverters"> <util:list id="beanList"> <ref bean="stringHttpMessageConverter"/> <ref bean="marshallingHttpMessageConverter"/> </util:list> </property </bean> <bean id="stringHttpMessageConverter" class="org.springframework.http.converter.StringHttpMessageConverter"/> <bean id="marshallingHttpMessageConverter" class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter"> <property name="marshaller" ref="castorMarshaller" /> <property name="unmarshaller" ref="castorMarshaller" /> </bean> <bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/>
An @RequestBody
method parameter can be
annotated with @Valid
, in which case it will be
validated using the configured Validator
instance. When using the MVC namespace or the MVC Java config, a JSR-303 validator
is configured automatically assuming a JSR-303 implementation is
available on the classpath.
Just like with @ModelAttribute
parameters,
an Errors
argument can be used to examine the errors.
If such an argument is not declared, a
MethodArgumentNotValidException
will be raised.
The exception is handled in the
DefaultHandlerExceptionResolver
, which sends
a 400
error back to the client.
Note | |
---|---|
Also see Enabling the MVC Java Config or the MVC XML Namespace for information on configuring message converters and a validator through the MVC namespace or the MVC Java config. |
The @ResponseBody
annotation is
similar to @RequestBody
. This
annotation can be put on a method and indicates that the return type
should be written straight to the HTTP response body (and not placed
in a Model, or interpreted as a view name). For example:
@RequestMapping(value = "/something", method = RequestMethod.PUT) @ResponseBody public String helloWorld() { return "Hello World"; }
The above example will result in the text Hello
World
being written to the HTTP response stream.
As with @RequestBody
, Spring
converts the returned object to a response body by using an
HttpMessageConverter
. For more
information on these converters, see the previous section and Message Converters.
The HttpEntity
is similar to
@RequestBody
and
@ResponseBody
. Besides getting access
to the request and response body, HttpEntity
(and the response-specific subclass
ResponseEntity
) also allows access to the
request and response headers, like so:
@RequestMapping("/something") public ResponseEntity<String> handle(HttpEntity<byte[]> requestEntity) throws UnsupportedEncodingException { String requestHeader = requestEntity.getHeaders().getFirst("MyRequestHeader")); byte[] requestBody = requestEntity.getBody(); // do something with request header and body HttpHeaders responseHeaders = new HttpHeaders(); responseHeaders.set("MyResponseHeader", "MyValue"); return new ResponseEntity<String>("Hello World", responseHeaders, HttpStatus.CREATED); }
The above example gets the value of the
MyRequestHeader
request header, and reads the body
as a byte array. It adds the MyResponseHeader
to
the response, writes Hello World
to the response
stream, and sets the response status code to 201 (Created).
As with @RequestBody
and
@ResponseBody
, Spring uses
HttpMessageConverter
to convert from
and to the request and response streams. For more information on these
converters, see the previous section and Message Converters.
The @ModelAttribute
annotation
can be used on methods or on method arguments. This section explains
its usage on methods while the next section explains its usage on
method arguments.
An @ModelAttribute
on a method
indicates the purpose of that method is to add one or more model
attributes. Such methods support the same argument types as
@RequestMapping
methods but cannot be
mapped directly to requests. Instead
@ModelAttribute
methods in a controller
are invoked before @RequestMapping
methods, within the same controller. A couple of examples:
// Add one attribute // The return value of the method is added to the model under the name "account" // You can customize the name via @ModelAttribute("myAccount") @ModelAttribute public Account addAccount(@RequestParam String number) { return accountManager.findAccount(number); } // Add multiple attributes @ModelAttribute public void populateModel(@RequestParam String number, Model model) { model.addAttribute(accountManager.findAccount(number)); // add more ... }
@ModelAttribute
methods are used
to populate the model with commonly needed attributes for example to
fill a drop-down with states or with pet types, or to retrieve a
command object like Account in order to use it to represent the data
on an HTML form. The latter case is further discussed in the next
section.
Note the two styles of
@ModelAttribute
methods. In the first,
the method adds an attribute implicitly by returning it. In the
second, the method accepts a Model
and adds any
number of model attributes to it. You can choose between the two
styles depending on your needs.
A controller can have any number of
@ModelAttribute
methods. All such
methods are invoked before
@RequestMapping
methods of the same
controller.
@ModelAttribute
methods can also
be defined in an @ControllerAdvice
-annotated
class and such methods apply to all controllers.
The @ControllerAdvice
annotation is
a component annotation allowing implementation classes to be autodetected
through classpath scanning.
Tip | |
---|---|
What happens when a model attribute name is not explicitly
specified? In such cases a default name is assigned to the model
attribute based on its type. For example if the method returns an
object of type |
The @ModelAttribute
annotation
can be used on @RequestMapping
methods
as well. In that case the return value of the
@RequestMapping
method is interpreted
as a model attribute rather than as a view name. The view name is
derived from view name conventions instead much like for methods
returning void — see Section 17.12.3, “The View -
RequestToViewNameTranslator
”.
As explained in the previous section
@ModelAttribute
can be used on methods
or on method arguments. This section explains its usage on method
arguments.
An @ModelAttribute
on a method
argument indicates the argument should be retrieved from the model. If
not present in the model, the argument should be instantiated first
and then added to the model. Once present in the model, the argument's
fields should be populated from all request parameters that have
matching names. This is known as data binding in Spring MVC, a very
useful mechanism that saves you from having to parse each form field
individually.
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute Pet pet) { }
Given the above example where can the Pet instance come from? There are several options:
It may already be in the model due to use of
@SessionAttributes
— see the section called “Using @SessionAttributes
to store model
attributes in the HTTP session between requests”.
It may already be in the model due to an
@ModelAttribute
method in the same
controller — as explained in the previous section.
It may be retrieved based on a URI template variable and type converter (explained in more detail below).
It may be instantiated using its default constructor.
An @ModelAttribute
method is a
common way to to retrieve an attribute from the database, which may
optionally be stored between requests through the use of
@SessionAttributes
. In some cases it
may be convenient to retrieve the attribute by using an URI template
variable and a type converter. Here is an example:
@RequestMapping(value="/accounts/{account}", method = RequestMethod.PUT) public String save(@ModelAttribute("account") Account account) { }
In this example the name of the model attribute (i.e. "account")
matches the name of a URI template variable. If you register
Converter<String, Account>
that can turn
the String
account value into an
Account
instance, then the above example will
work without the need for an
@ModelAttribute
method.
The next step is data binding. The
WebDataBinder
class matches request parameter
names — including query string parameters and form fields — to model
attribute fields by name. Matching fields are populated after type
conversion (from String to the target field type) has been applied
where necessary. Data binding and validation are covered in Chapter 7, Validation, Data Binding, and Type Conversion. Customizing the data binding process for a
controller level is covered in the section called “Customizing WebDataBinder
initialization”.
As a result of data binding there may be errors such as missing
required fields or type conversion errors. To check for such errors
add a BindingResult
argument immediately
following the @ModelAttribute
argument:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { if (result.hasErrors()) { return "petForm"; } // ... }
With a BindingResult
you can check if
errors were found in which case it's common to render the same form
where the errors can be shown with the help of Spring's
<errors>
form tag.
In addition to data binding you can also invoke validation using
your own custom validator passing the same
BindingResult
that was used to record data
binding errors. That allows for data binding and validation errors to
be accumulated in one place and subsequently reported back to the
user:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { new PetValidator().validate(pet, result); if (result.hasErrors()) { return "petForm"; } // ... }
Or you can have validation invoked automatically by adding the
JSR-303 @Valid
annotation:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) { if (result.hasErrors()) { return "petForm"; } // ... }
See Section 7.8, “Spring 3 Validation” and Chapter 7, Validation, Data Binding, and Type Conversion for details on how to configure and use validation.
The type-level @SessionAttributes
annotation declares session attributes used by a specific handler.
This will typically list the names of model attributes or types of
model attributes which should be transparently stored in the session
or some conversational storage, serving as form-backing beans between
subsequent requests.
The following code snippet shows the usage of this annotation, specifying the model attribute name:
@Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { // ... }
Note | |
---|---|
When using controller interfaces (e.g., for AOP proxying),
make sure to consistently put all your mapping
annotations - such as |
By default all model attributes are considered to be exposed as URI template variables in the redirect URL. Of the remaining attributes those that are primitive types or collections/arrays of primitive types are automatically appended as query parameters.
In annotated controllers however the model may contain
additional attributes originally added for rendering purposes (e.g.
drop-down field values). To gain precise control over the attributes
used in a redirect scenario, an
@RequestMapping
method can declare an
argument of type RedirectAttributes
and
use it to add attributes for use in
RedirectView
. If the controller method does
redirect, the content of
RedirectAttributes
is used. Otherwise
the content of the default Model
is
used.
The RequestMappingHandlerAdapter
provides
a flag called "ignoreDefaultModelOnRedirect"
that
can be used to indicate the content of the default
Model
should never be used if a
controller method redirects. Instead the controller method should
declare an attribute of type
RedirectAttributes
or if it doesn't do
so no attributes should be passed on to
RedirectView
. Both the MVC namespace and the
MVC Java config keep this flag set to false
in order to maintain
backwards compatibility. However, for new applications we recommend
setting it to true
The RedirectAttributes
interface
can also be used to add flash attributes. Unlike other redirect
attributes, which end up in the target redirect URL, flash attributes
are saved in the HTTP session (and hence do not appear in the URL).
The model of the controller serving the target redirect URL
automatically receives these flash attributes after which they are
removed from the session. See Section 17.6, “Using flash attributes”
for an overview of the general support for flash attributes in Spring
MVC.
The previous sections covered use of
@ModelAttribute
to support form
submission requests from browser clients. The same annotation is
recommended for use with requests from non-browser clients as well.
However there is one notable difference when it comes to working with
HTTP PUT requests. Browsers can submit form data via HTTP GET or HTTP
POST. Non-browser clients can also submit forms via HTTP PUT. This
presents a challenge because the Servlet specification requires the
ServletRequest.getParameter*()
family of methods to
support form field access only for HTTP POST, not for HTTP PUT.
To support HTTP PUT and PATCH requests, the spring-web
module provides the filter
HttpPutFormContentFilter
, which can be
configured in web.xml
:
<filter> <filter-name>httpPutFormFilter</filter-name> <filter-class>org.springframework.web.filter.HttpPutFormContentFilter</filter-class> </filter> <filter-mapping> <filter-name>httpPutFormFilter</filter-name> <servlet-name>dispatcherServlet</servlet-name> </filter-mapping> <servlet> <servlet-name>dispatcherServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> </servlet>
The above filter intercepts HTTP PUT and PATCH requests with content type
application/x-www-form-urlencoded
, reads the form
data from the body of the request, and wraps the
ServletRequest
in order to make the form data
available through the
ServletRequest.getParameter*()
family of
methods.
The @CookieValue
annotation
allows a method parameter to be bound to the value of an HTTP
cookie.
Let us consider that the following cookie has been received with an http request:
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
The following code sample demonstrates how to get the value of
the JSESSIONID
cookie:
@RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) { //... }
Type conversion is applied automatically if the target method
parameter type is not String
. See the section called “Method Parameters And Type Conversion”.
This annotation is supported for annotated handler methods in Servlet and Portlet environments.
The @RequestHeader
annotation
allows a method parameter to be bound to a request header.
Here is a sample request header:
Host localhost:8080 Accept text/html,application/xhtml+xml,application/xml;q=0.9 Accept-Language fr,en-gb;q=0.7,en;q=0.3 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 300
The following code sample demonstrates how to get the value of
the Accept-Encoding
and
Keep-Alive
headers:
@RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding, @RequestHeader("Keep-Alive") long keepAlive) { //... }
Type conversion is applied automatically if the method parameter
is not String
. See the section called “Method Parameters And Type Conversion”.
Tip | |
---|---|
Built-in support is available for converting a comma-separated
string into an array/collection of strings or other types known to
the type conversion system. For example a method parameter annotated
with |
This annotation is supported for annotated handler methods in Servlet and Portlet environments.
String-based values extracted from the request including request
parameters, path variables, request headers, and cookie values may
need to be converted to the target type of the method parameter or
field (e.g., binding a request parameter to a field in an
@ModelAttribute
parameter) they're
bound to. If the target type is not String
,
Spring automatically converts to the appropriate type. All simple
types such as int, long, Date, etc. are supported. You can further
customize the conversion process through a
WebDataBinder
(see the section called “Customizing WebDataBinder
initialization”) or by registering
Formatters
with the
FormattingConversionService
(see Section 7.6, “Spring 3 Field Formatting”).
To customize request parameter binding with PropertyEditors
through Spring's WebDataBinder
, you can use
@InitBinder
-annotated methods within
your controller, @InitBinder
methods
within an @ControllerAdvice
class,
or provide a custom
WebBindingInitializer
.
Annotating controller methods with
@InitBinder
allows you to configure
web data binding directly within your controller class.
@InitBinder
identifies methods that
initialize the WebDataBinder
that will be
used to populate command and form object arguments of annotated
handler methods.
Such init-binder methods support all arguments that
@RequestMapping
supports, except for
command/form objects and corresponding validation result objects.
Init-binder methods must not have a return value. Thus, they are
usually declared as void
. Typical arguments
include WebDataBinder
in combination with
WebRequest
or
java.util.Locale
, allowing code to register
context-specific editors.
The following example demonstrates the use of
@InitBinder
to configure a
CustomDateEditor
for all
java.util.Date
form properties.
@Controller public class MyFormController { @InitBinder public void initBinder(WebDataBinder binder) { SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); dateFormat.setLenient(false); binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false)); } // ... }
To externalize data binding initialization, you can provide a
custom implementation of the
WebBindingInitializer
interface,
which you then enable by supplying a custom bean configuration for
an AnnotationMethodHandlerAdapter
, thus
overriding the default configuration.
The following example from the PetClinic application shows a
configuration using a custom implementation of the
WebBindingInitializer
interface,
org.springframework.samples.petclinic.web.ClinicBindingInitializer
,
which configures PropertyEditors required by several of the
PetClinic controllers.
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> <property name="cacheSeconds" value="0" /> <property name="webBindingInitializer"> <bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" /> </property> </bean>
@InitBinder
methods can also
be defined in an @ControllerAdvice
-annotated
class in which case they apply to all controllers. This provides an
alternative to using a WebBindingInitializer
.
The @ControllerAdvice
annotation is
a component annotation allowing implementation classes to be autodetected
through classpath scanning.
An @RequestMapping
method may
wish to support 'Last-Modified'
HTTP requests, as
defined in the contract for the Servlet API's
getLastModified
method, to facilitate content
caching. This involves calculating a lastModified
long
value for a given request, comparing it
against the 'If-Modified-Since'
request header
value, and potentially returning a response with status code 304 (Not
Modified). An annotated controller method can achieve that as
follows:
@RequestMapping public String myHandleMethod(WebRequest webRequest, Model model) { long lastModified = // 1. application-specific calculation if (request.checkNotModified(lastModified)) { // 2. shortcut exit - no further processing necessary return null; } // 3. or otherwise further request processing, actually preparing content model.addAttribute(...); return "myViewName"; }
There are two key elements to note: calling
request.checkNotModified(lastModified)
and returning
null
. The former sets the response status to 304
before it returns true
. The latter, in combination
with the former, causes Spring MVC to do no further processing of the
request.
Spring MVC 3.2 introduced Servlet 3 based asynchronous request
processing. Instead of returning a value, as usual, a controller method
can now return a java.util.concurrent.Callable
and produce the return value from a separate thread. Meanwhile the main Servlet
container thread is released and allowed to process other requests.
Spring MVC invokes the Callable
in a
separate thread with the help of a TaskExecutor
and when the Callable
returns, the
request is dispatched back to the Servlet container to resume
processing with the value returned by the
Callable
.
Here is an example controller method:
@RequestMapping(method=RequestMethod.POST) public Callable<String> processUpload(final MultipartFile file) { return new Callable<String>() { public Object call() throws Exception { // ... return "someView"; } }; }
A second option is for the controller to return an instance of
DeferredResult
. In this case the return value
will also be produced from a separate thread. However, that thread is not
known to Spring MVC. For example the result may be produced in response
to some external event such as a JMS message, a scheduled task, etc.
Here is an example controller method:
@RequestMapping("/quotes") @ResponseBody public DeferredResult<String> quotes() { DeferredResult<String> deferredResult = new DeferredResult<String>(); // Save the deferredResult in in-memory queue ... return deferredResult; } // In some other thread... deferredResult.setResult(data);
This may be difficult to understand without any knowledge of the Servlet 3 async processing feature. It would certainly help to read up on it. At a very minimum consider the following basic facts:
A ServletRequest
can be put in asynchronous mode by calling
request.startAsync()
. The main effect of doing so is
that the Servlet, as well as any Filters, can exit but the response
will remain open allowing some other thread to complete processing.
The call to request.startAsync()
returns an
AsyncContext
, which can be used for
further control over async processing. For example it provides
the method dispatch
, which can be called from an
application thread in order to "dispatch" the request back to
the Servlet container. An async dispatch is similar to a forward
except it is made from one (application) thread to another
(Servlet container) thread whereas a forward occurs synchronously
in the same (Servlet container) thread.
ServletRequest
provides access
to the current DispatcherType
, which
can be used to distinguish if a Servlet
or
a Filter
is processing on
the initial request processing thread and when it is processing in
an async dispatch.
With the above in mind, the following is the sequence
of events for async request processing with a Callable
:
(1) Controller returns a
Callable
, (2) Spring MVC starts async processing
and submits the Callable
to a TaskExecutor
for processing in a separate thread, (3) the DispatcherServlet
and all Filter's exit the request processing thread but the response
remains open, (4) the Callable
produces a result
and Spring MVC dispatches the request back to the Servlet container,
(5) the DispatcherServlet
is invoked again and processing
resumes with the asynchronously produced result from the
Callable
. The exact sequencing of (2),
(3), and (4) may vary depending on the speed of execution of the
concurrent threads.
The sequence of events for async request processing with a
DeferredResult
is the same in principal except
it's up to the application to produce the asynchronous result from some thread:
(1) Controller returns a DeferredResult
and saves it
in some in-memory queue or list where it can be accessed,
(2) Spring MVC starts async processing, (3) the DispatcherServlet
and all configured Filter's exit the request processing thread but the response
remains open, (4) the application sets the DeferredResult
from some thread and Spring MVC dispatches the request back to the Servlet container,
(5) the DispatcherServlet
is invoked again and processing
resumes with the asynchronously produced result.
Explaining the motivation for async request processing and when or why to use it are beyond the scope of this document. For further information you may wish to read this blog post series.
What happens if a Callable
returned
from a controller method raises an Exception while being executed?
The effect is similar to what happens when any controller method raises
an exception. It is handled by a matching
@ExceptionHandler
method in the same
controller or by one of the configured
HandlerExceptionResolver
instances.
Note | |
---|---|
Under the covers, when a |
When using a DeferredResult
, you have
a choice of calling its setErrorResult(Object)
method
and provide an Exception
or any other Object
you'd like to use as the result. If the result is an
Exception
, it will be processed with a
matching @ExceptionHandler
method in the
same controller or with any configured
HandlerExceptionResolver
instance.
An existing HandlerInterceptor
can
implement AsyncHandlerInterceptor
, which
provides one additional method afterConcurrentHandlingStarted
.
It is invoked after async processing starts and when the initial
request processing thread is being exited. See the Javadoc of
AsyncHandlerInterceptor
for more details
on that.
Further options for async request lifecycle callbacks are
provided directly on DeferredResult
,
which has the methods onTimeout(Runnable)
and
onCompletion(Runnable)
. Those are called when the
async request is about to time out or has completed respectively.
The timeout event can be handled by setting the
DeferredResult
to some value.
The completion callback however is final and the result can no
longer be set.
Similar callbacks are also available with a
Callable
. However, you will need to wrap
the Callable
in an instance of
WebAsyncTask
and then use that to register
the timeout and completion callbacks. Just like with
DeferredResult
, the timeout event can be
handled and a value can be returned while the completion event is final.
You can also register a
CallableProcessingInterceptor
or a
DeferredResultProcessingInterceptor
globally through the MVC Java config or the MVC namespace.
Those interceptors provide a full set of callbacks and apply every
time a Callable
or a
DeferredResult
is used.
To use Servlet 3 async request processing, you need to update
web.xml
to version 3.0:
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> ... <web-app>
The DispatcherServlet
and any
Filter
configuration need to have
the <async-supported>true</async-supported>
sub-element.
Additionally, any Filter
that also needs
to get involved in async dispatches should also be configured
to support the ASYNC dispatcher type. Note that it is safe
to enable the ASYNC dispatcher type for all filters provided with
the Spring Framework since they will not get involved in async
dispatches unless needed.
If using Servlet 3, Java based configuration, e.g. via
WebApplicationInitializer
, you'll
also need to set the "asyncSupported" flag as well as the
ASYNC dispatcher type just like with web.xml
.
To simplify all this configuration, consider
extending AbstractDispatcherServletInitializer
or AbstractAnnotationConfigDispatcherServletInitializer
,
which automatically set those options and make it very easy to register
Filter
instances.
The MVC Java config and the MVC namespace both provide options for
configuring async request processing.
WebMvcConfigurer
has the method
configureAsyncSupport
while <mvc:annotation-driven>
has an <async-support> sub-element.
Those allow you to configure the default timeout value to use for
async requests, which if not set depends on the underlying Servlet
container (e.g. 10 seconds on Tomcat). You can also configure an
AsyncTaskExecutor
to use for executing
Callable
instances returned from
controller methods. It is highly recommended to configure this property
since by default Spring MVC uses
SimpleAsyncTaskExecutor
. The MVC Java config
and the MVC namespace also allow you to register
CallableProcessingInterceptor
and
DeferredResultProcessingInterceptor
instances.
If you need to override the default timeout value for a
specific DeferredResult
, you can do so by using
the appropriate class constructor. Similarly, for a
Callable
, you can wrap it in a
WebAsyncTask
and use the appropriate class
constructor to customize the timeout value. The class constructor of
WebAsyncTask
also allows providing
an AsyncTaskExecutor
.
The spring-test
module offers first class support
for testing annotated controllers.
See Section 11.3.6, “Spring MVC Test Framework”.
In previous versions of Spring, users were required to define one or
more HandlerMapping
beans in the web
application context to map incoming web requests to appropriate handlers.
With the introduction of annotated controllers, you generally don't need
to do that because the RequestMappingHandlerMapping
automatically looks for @RequestMapping
annotations on all @Controller
beans.
However, do keep in mind that all HandlerMapping
classes extending from AbstractHandlerMapping
have
the following properties that you can use to customize their
behavior:
interceptors
List of interceptors to use.
HandlerInterceptor
s are discussed in
Section 17.4.1, “Intercepting requests with a
HandlerInterceptor
”.
defaultHandler
Default handler to use, when this handler mapping does not result in a matching handler.
order
Based on the value of the order property (see the
org.springframework.core.Ordered
interface),
Spring sorts all handler mappings available in the context and
applies the first matching handler.
alwaysUseFullPath
If true
, Spring uses the full path within
the current Servlet context to find an appropriate handler. If
false
(the default), the path within the current
Servlet mapping is used. For example, if a Servlet is mapped using
/testing/*
and the
alwaysUseFullPath
property is set to true,
/testing/viewPage.html
is used, whereas if the
property is set to false, /viewPage.html
is
used.
urlDecode
Defaults to true
, as of Spring 2.5. If you
prefer to compare encoded paths, set this flag to
false
. However, the
HttpServletRequest
always exposes the
Servlet path in decoded form. Be aware that the Servlet path will
not match when compared with encoded paths.
The following example shows how to configure an interceptor:
<beans> <bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"> <property name="interceptors"> <bean class="example.MyInterceptor"/> </property> </bean> <beans>
Spring's handler mapping mechanism includes handler interceptors, which are useful when you want to apply specific functionality to certain requests, for example, checking for a principal.
Interceptors located in the handler mapping must implement
HandlerInterceptor
from the
org.springframework.web.servlet
package. This
interface defines three methods: preHandle(..)
is
called before the actual handler is executed;
postHandle(..)
is called after
the handler is executed; and afterCompletion(..)
is
called after the complete request has finished.
These three methods should provide enough flexibility to do all kinds of
preprocessing and postprocessing.
The preHandle(..)
method returns a boolean
value. You can use this method to break or continue the processing of
the execution chain. When this method returns true
,
the handler execution chain will continue; when it returns false, the
DispatcherServlet
assumes the interceptor itself
has taken care of requests (and, for example, rendered an appropriate
view) and does not continue executing the other interceptors and the
actual handler in the execution chain.
Interceptors can be configured using the
interceptors
property, which is present on all
HandlerMapping
classes extending from
AbstractHandlerMapping
. This is shown in the
example below:
<beans> <bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"> <property name="interceptors"> <list> <ref bean="officeHoursInterceptor"/> </list> </property> </bean> <bean id="officeHoursInterceptor" class="samples.TimeBasedAccessInterceptor"> <property name="openingTime" value="9"/> <property name="closingTime" value="18"/> </bean> <beans>
package samples; public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter { private int openingTime; private int closingTime; public void setOpeningTime(int openingTime) { this.openingTime = openingTime; } public void setClosingTime(int closingTime) { this.closingTime = closingTime; } public boolean preHandle( HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { Calendar cal = Calendar.getInstance(); int hour = cal.get(HOUR_OF_DAY); if (openingTime <= hour && hour < closingTime) { return true; } else { response.sendRedirect("http://host.com/outsideOfficeHours.html"); return false; } } }
Any request handled by this mapping is intercepted by the
TimeBasedAccessInterceptor
. If the current time
is outside office hours, the user is redirected to a static HTML file
that says, for example, you can only access the website during office
hours.
Note | |
---|---|
When using the
|
As you can see, the Spring adapter class
HandlerInterceptorAdapter
makes it easier to
extend the HandlerInterceptor
interface.
Tip | |
---|---|
In the example above, the configured interceptor will apply to
all requests handled with annotated controller methods. If you want to
narrow down the URL paths to which an interceptor applies, you can use
the MVC namespace or the MVC Java config, or declare bean instances
of type |
All MVC frameworks for web applications provide a way to address views. Spring provides view resolvers, which enable you to render models in a browser without tying you to a specific view technology. Out of the box, Spring enables you to use JSPs, Velocity templates and XSLT views, for example. See Chapter 18, View technologies for a discussion of how to integrate and use a number of disparate view technologies.
The two interfaces that are important to the way Spring handles
views are ViewResolver
and
View
. The
ViewResolver
provides a mapping between
view names and actual views. The View
interface addresses the preparation of the request and hands the request
over to one of the view technologies.
As discussed in Section 17.3, “Implementing Controllers”, all handler
methods in the Spring Web MVC controllers must resolve to a logical view
name, either explicitly (e.g., by returning a String
,
View
, or ModelAndView
) or
implicitly (i.e., based on conventions). Views in Spring are addressed
by a logical view name and are resolved by a view resolver. Spring comes
with quite a few view resolvers. This table lists most of them; a couple
of examples follow.
Table 17.3. View resolvers
ViewResolver | Description |
---|---|
AbstractCachingViewResolver | Abstract view resolver that caches views. Often views need preparation before they can be used; extending this view resolver provides caching. |
XmlViewResolver | Implementation of
ViewResolver that accepts a
configuration file written in XML with the same DTD as Spring's
XML bean factories. The default configuration file is
/WEB-INF/views.xml . |
ResourceBundleViewResolver | Implementation of
ViewResolver that uses bean
definitions in a ResourceBundle ,
specified by the bundle base name. Typically you define the
bundle in a properties file, located in the classpath. The
default file name is
views.properties . |
UrlBasedViewResolver | Simple implementation of the
ViewResolver interface that
effects the direct resolution of logical view names to URLs,
without an explicit mapping definition. This is appropriate if
your logical names match the names of your view resources in a
straightforward manner, without the need for arbitrary
mappings. |
InternalResourceViewResolver | Convenient subclass of
UrlBasedViewResolver that supports
InternalResourceView (in effect, Servlets
and JSPs) and subclasses such as JstlView
and TilesView . You can specify the view
class for all views generated by this resolver by using
setViewClass(..) . See the Javadocs for the
UrlBasedViewResolver class for
details. |
VelocityViewResolver /
FreeMarkerViewResolver | Convenient subclass of
UrlBasedViewResolver that supports
VelocityView (in effect, Velocity
templates) or FreeMarkerView
,respectively, and custom subclasses of them. |
ContentNegotiatingViewResolver | Implementation of the
ViewResolver interface that
resolves a view based on the request file name or
Accept header. See Section 17.5.4, “ContentNegotiatingViewResolver ”. |
As an example, with JSP as a view technology, you can use the
UrlBasedViewResolver
. This view resolver
translates a view name to a URL and hands the request over to the
RequestDispatcher to render the view.
<bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean>
When returning test
as a logical view name,
this view resolver forwards the request to the
RequestDispatcher
that will send the request to
/WEB-INF/jsp/test.jsp
.
When you combine different view technologies in a web application,
you can use the
ResourceBundleViewResolver
:
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> <property name="defaultParentView" value="parentView"/> </bean>
The ResourceBundleViewResolver
inspects the
ResourceBundle
identified by the basename, and
for each view it is supposed to resolve, it uses the value of the
property [viewname].(class)
as the view class and the
value of the property [viewname].url
as the view url.
Examples can be found in the next chapter which covers view
technologies. As you can see, you can identify a parent view, from which
all views in the properties file “extend”. This way you can
specify a default view class, for example.
Note | |
---|---|
Subclasses of |
Spring supports multiple view resolvers. Thus you can chain
resolvers and, for example, override specific views in certain
circumstances. You chain view resolvers by adding more than one resolver
to your application context and, if necessary, by setting the
order
property to specify ordering. Remember, the
higher the order property, the later the view resolver is positioned in
the chain.
In the following example, the chain of view resolvers consists of
two resolvers, an InternalResourceViewResolver
,
which is always automatically positioned as the last resolver in the
chain, and an XmlViewResolver
for specifying
Excel views. Excel views are not supported by the
InternalResourceViewResolver
.
<bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> <bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver"> <property name="order" value="1"/> <property name="location" value="/WEB-INF/views.xml"/> </bean> <!-- in views.xml --> <beans> <bean name="report" class="org.springframework.example.ReportExcelView"/> </beans>
If a specific view resolver does not result in a view, Spring
examines the context for other view resolvers. If additional view
resolvers exist, Spring continues to inspect them until a view is
resolved. If no view resolver returns a view, Spring throws a
ServletException
.
The contract of a view resolver specifies that a view resolver
can return null to indicate the view could not be
found. Not all view resolvers do this, however, because in some cases,
the resolver simply cannot detect whether or not the view exists. For
example, the InternalResourceViewResolver
uses
the RequestDispatcher
internally, and dispatching
is the only way to figure out if a JSP exists, but this action can only
execute once. The same holds for the
VelocityViewResolver
and some others. Check the
Javadoc for the view resolver to see whether it reports non-existing
views. Thus, putting an
InternalResourceViewResolver
in the chain in a
place other than the last, results in the chain not being fully
inspected, because the
InternalResourceViewResolver
will
always return a view!
As mentioned previously, a controller typically returns a logical
view name, which a view resolver resolves to a particular view
technology. For view technologies such as JSPs that are processed
through the Servlet or JSP engine, this resolution is usually handled
through the combination of
InternalResourceViewResolver
and
InternalResourceView
, which issues an internal
forward or include via the Servlet API's
RequestDispatcher.forward(..)
method or
RequestDispatcher.include()
method. For other view
technologies, such as Velocity, XSLT, and so on, the view itself writes
the content directly to the response stream.
It is sometimes desirable to issue an HTTP redirect back to the
client, before the view is rendered. This is desirable, for example,
when one controller has been called with POST
ed data,
and the response is actually a delegation to another controller (for
example on a successful form submission). In this case, a normal
internal forward will mean that the other controller will also see the
same POST
data, which is potentially problematic if
it can confuse it with other expected data. Another reason to perform a
redirect before displaying the result is to eliminate the possibility of
the user submitting the form data multiple times. In this scenario, the
browser will first send an initial POST
; it will then
receive a response to redirect to a different URL; and finally the
browser will perform a subsequent GET
for the URL
named in the redirect response. Thus, from the perspective of the
browser, the current page does not reflect the result of a
POST
but rather of a GET
. The end
effect is that there is no way the user can accidentally
re-POST
the same data by performing a refresh. The
refresh forces a GET
of the result page, not a resend
of the initial POST
data.
One way to force a redirect as the result of a controller
response is for the controller to create and return an instance of
Spring's RedirectView
. In this case,
DispatcherServlet
does not use the normal view
resolution mechanism. Rather because it has been given the (redirect)
view already, the DispatcherServlet
simply
instructs the view to do its work.
The RedirectView
issues an
HttpServletResponse.sendRedirect()
call that
returns to the client browser as an HTTP redirect. By default all
model attributes are considered to be exposed as URI template
variables in the redirect URL. Of the remaining attributes those that
are primitive types or collections/arrays of primitive types are
automatically appended as query parameters.
Appending primitive type attributes as query parameters may be
the desired result if a model instance was prepared specifically for
the redirect. However, in annotated controllers the model may contain
additional attributes added for rendering purposes (e.g. drop-down
field values). To avoid the possibility of having such attributes
appear in the URL an annotated controller can declare an argument of
type RedirectAttributes
and use it to
specify the exact attributes to make available to
RedirectView
. If the controller method decides
to redirect, the content of
RedirectAttributes
is used. Otherwise
the content of the model is used.
Note that URI template variables from the present request are
automatically made available when expanding a redirect URL and do not
need to be added explicitly neither through
Model
nor
RedirectAttributes
. For example:
@RequestMapping(value = "/files/{path}", method = RequestMethod.POST) public String upload(...) { // ... return "redirect:files/{path}"; }
If you use RedirectView
and the view is
created by the controller itself, it is recommended that you configure
the redirect URL to be injected into the controller so that it is not
baked into the controller but configured in the context along with the
view names. The next section discusses this process.
While the use of RedirectView
works fine,
if the controller itself creates the
RedirectView
, there is no avoiding the fact
that the controller is aware that a redirection is happening. This is
really suboptimal and couples things too tightly. The controller
should not really care about how the response gets handled. In general
it should operate only in terms of view names that have been injected
into it.
The special redirect:
prefix allows you to
accomplish this. If a view name is returned that has the prefix
redirect:
, the
UrlBasedViewResolver
(and all subclasses) will
recognize this as a special indication that a redirect is needed. The
rest of the view name will be treated as the redirect URL.
The net effect is the same as if the controller had returned a
RedirectView
, but now the controller itself can
simply operate in terms of logical view names. A logical view name
such as redirect:/myapp/some/resource
will redirect
relative to the current Servlet context, while a name such as
redirect:http://myhost.com/some/arbitrary/path
will
redirect to an absolute URL.
It is also possible to use a special forward:
prefix for view names that are ultimately resolved by
UrlBasedViewResolver
and subclasses. This
creates an InternalResourceView
(which
ultimately does a RequestDispatcher.forward()
)
around the rest of the view name, which is considered a URL.
Therefore, this prefix is not useful with
InternalResourceViewResolver
and
InternalResourceView
(for JSPs for example).
But the prefix can be helpful when you are primarily using another
view technology, but still want to force a forward of a resource to be
handled by the Servlet/JSP engine. (Note that you may also chain
multiple view resolvers, instead.)
As with the redirect:
prefix, if the view
name with the forward:
prefix is injected into the
controller, the controller does not detect that anything special is
happening in terms of handling the response.
The ContentNegotiatingViewResolver
does not
resolve views itself but rather delegates to other view resolvers,
selecting the view that resembles the representation requested by the
client. Two strategies exist for a client to request a representation
from the server:
Use a distinct URI for each resource, typically by using a
different file extension in the URI. For example, the URI
http://www.example.com/users/fred.pdf
requests a PDF
representation of the user fred, and
http://www.example.com/users/fred.xml
requests an
XML representation.
Use the same URI for the client to locate the resource, but
set the Accept
HTTP request header to list the
media
types that it understands. For example, an HTTP request for
http://www.example.com/users/fred
with an
Accept
header set to application/pdf
requests a PDF representation of the user fred, while
http://www.example.com/users/fred
with an
Accept
header set to text/xml
requests an XML representation. This strategy is known as content
negotiation.
Note | |
---|---|
One issue with the Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 For this reason it is common to see the use of a distinct URI for each representation when developing browser based web applications. |
To support multiple representations of a resource, Spring provides
the ContentNegotiatingViewResolver
to resolve a
view based on the file extension or Accept
header of
the HTTP request. ContentNegotiatingViewResolver
does not perform the view resolution itself but instead delegates to a
list of view resolvers that you specify through the bean property
ViewResolvers
.
The ContentNegotiatingViewResolver
selects
an appropriate View
to handle the request by
comparing the request media type(s) with the media type (also known as
Content-Type
) supported by the
View
associated with each of its
ViewResolvers
. The first
View
in the list that has a compatible
Content-Type
returns the representation to the
client. If a compatible view cannot be supplied by the
ViewResolver
chain, then the list of views
specified through the DefaultViews
property will be
consulted. This latter option is appropriate for singleton
Views
that can render an appropriate
representation of the current resource regardless of the logical view
name. The Accept
header may include wild cards, for
example text/*
, in which case a
View
whose Content-Type was
text/xml
is a compatible match.
To support the resolution of a view based on a file extension, use
the ContentNegotiatingViewResolver
bean property
mediaTypes
to specify a mapping of file extensions to
media types. For more information on the algorithm used to determine the
request media type, refer to the API documentation for
ContentNegotiatingViewResolver
.
Here is an example configuration of a
ContentNegotiatingViewResolver:
<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver"> <property name="mediaTypes"> <map> <entry key="atom" value="application/atom+xml"/> <entry key="html" value="text/html"/> <entry key="json" value="application/json"/> </map> </property> <property name="viewResolvers"> <list> <bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </list> </property> <property name="defaultViews"> <list> <bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView" /> </list> </property> </bean> <bean id="content" class="com.springsource.samples.rest.SampleContentAtomView"/>
The InternalResourceViewResolver
handles
the translation of view names and JSP pages, while the
BeanNameViewResolver
returns a view based on the
name of a bean. (See "Resolving views with the
ViewResolver interface" for more details on how Spring looks up
and instantiates a view.) In this example, the
content
bean is a class that inherits from
AbstractAtomFeedView
, which returns an Atom RSS
feed. For more information on creating an Atom Feed representation, see
the section Atom Views.
In the above configuration, if a request is made with an
.html
extension, the view resolver looks for a view
that matches the text/html
media type. The
InternalResourceViewResolver
provides the
matching view for text/html
. If the request is made
with the file extension .atom
, the view resolver
looks for a view that matches the
application/atom+xml
media type. This view is
provided by the BeanNameViewResolver
that maps to
the SampleContentAtomView
if the view name
returned is content
. If the request is made with
the file extension .json
, the
MappingJackson2JsonView
instance from the
DefaultViews
list will be selected regardless of the
view name. Alternatively, client requests can be made without a file
extension but with the Accept
header set to the
preferred media-type, and the same resolution of request to views would
occur.
Note | |
---|---|
If |
The corresponding controller code that returns an Atom RSS feed
for a URI of the form http://localhost/content.atom
or http://localhost/content
with an
Accept
header of application/atom+xml is shown
below.
@Controller public class ContentController { private List<SampleContent> contentList = new ArrayList<SampleContent>(); @RequestMapping(value="/content", method=RequestMethod.GET) public ModelAndView getContent() { ModelAndView mav = new ModelAndView(); mav.setViewName("content"); mav.addObject("sampleContentList", contentList); return mav; } }
Flash attributes provide a way for one request to store attributes intended for use in another. This is most commonly needed when redirecting — for example, the Post/Redirect/Get pattern. Flash attributes are saved temporarily before the redirect (typically in the session) to be made available to the request after the redirect and removed immediately.
Spring MVC has two main abstractions in support of flash attributes.
FlashMap
is used to hold flash attributes while
FlashMapManager
is used to store, retrieve,
and manage FlashMap
instances.
Flash attribute support is always "on" and does not need to enabled
explicitly although if not used, it never causes HTTP session creation. On
each request there is an "input" FlashMap
with
attributes passed from a previous request (if any) and an "output"
FlashMap
with attributes to save for a subsequent
request. Both FlashMap
instances are accessible
from anywhere in Spring MVC through static methods in
RequestContextUtils
.
Annotated controllers typically do not need to work with
FlashMap
directly. Instead an
@RequestMapping
method can accept an
argument of type RedirectAttributes
and use
it to add flash attributes for a redirect scenario. Flash attributes added
via RedirectAttributes
are automatically
propagated to the "output" FlashMap. Similarly after the redirect
attributes from the "input" FlashMap
are
automatically added to the Model
of the
controller serving the target URL.
Spring MVC provides a mechanism for building and encoding a URI
using UriComponentsBuilder
and
UriComponents
.
For example you can expand and encode a URI template string:
UriComponents uriComponents = UriComponentsBuilder.fromUriString("http://example.com/hotels/{hotel}/bookings/{booking}").build(); URI uri = uriComponents.expand("42", "21").encode().toUri();
Note that UriComponents
is immutable and
the expand()
and encode()
operations return new instances if necessary.
You can also expand and encode using individual URI components:
UriComponents uriComponents = UriComponentsBuilder.newInstance() .scheme("http").host("example.com").path("/hotels/{hotel}/bookings/{booking}").build() .expand("42", "21") .encode();
In a Servlet environment the
ServletUriComponentsBuilder
sub-class provides
static factory methods to copy available URL information from a
Servlet requests:
HttpServletRequest request = ... // Re-use host, scheme, port, path and query string // Replace the "accountId" query param ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromRequest(request).replaceQueryParam("accountId", "{id}").build() .expand("123") .encode();
Alternatively, you may choose to copy a subset of the available information up to and including the context path:
// Re-use host, port and context path // Append "/accounts" to the path ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromContextPath(request).path("/accounts").build()
Or in cases where the DispatcherServlet
is mapped
by name (e.g. /main/*
), you can also have the literal part
of the servlet mapping included:
// Re-use host, port, context path // Append the literal part of the servlet mapping to the path // Append "/accounts" to the path ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromServletMapping(request).path("/accounts").build()
Most parts of Spring's architecture support internationalization,
just as the Spring web MVC framework does.
DispatcherServlet
enables you to automatically
resolve messages using the client's locale. This is done with
LocaleResolver
objects.
When a request comes in, the
DispatcherServlet
looks for a locale resolver, and
if it finds one it tries to use it to set the locale. Using the
RequestContext.getLocale()
method, you can always
retrieve the locale that was resolved by the locale resolver.
In addition to automatic locale resolution, you can also attach an
interceptor to the handler mapping (see Section 17.4.1, “Intercepting requests with a
HandlerInterceptor
” for more information on
handler mapping interceptors) to change the locale under specific
circumstances, for example, based on a parameter in the request.
Locale resolvers and interceptors are defined in the
org.springframework.web.servlet.i18n
package and are
configured in your application context in the normal way. Here is a
selection of the locale resolvers included in Spring.
This locale resolver inspects the
accept-language
header in the request that was sent
by the client (e.g., a web browser). Usually this header field contains
the locale of the client's operating system.
This locale resolver inspects a Cookie
that
might exist on the client to see if a locale is specified. If so, it
uses the specified locale. Using the properties of this locale resolver,
you can specify the name of the cookie as well as the maximum age. Find
below an example of defining a
CookieLocaleResolver
.
<bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"> <property name="cookieName" value="clientlanguage"/> <!-- in seconds. If set to -1, the cookie is not persisted (deleted when browser shuts down) --> <property name="cookieMaxAge" value="100000"> </bean>
Table 17.4. CookieLocaleResolver
properties
Property | Default | Description |
---|---|---|
cookieName | classname + LOCALE | The name of the cookie |
cookieMaxAge | Integer.MAX_INT | The maximum time a cookie will stay persistent on the client. If -1 is specified, the cookie will not be persisted; it will only be available until the client shuts down his or her browser. |
cookiePath | / | Limits the visibility of the cookie to a certain part of your site. When cookiePath is specified, the cookie will only be visible to that path and the paths below it. |
The SessionLocaleResolver
allows you to
retrieve locales from the session that might be associated with the
user's request.
You can enable changing of locales by adding the
LocaleChangeInterceptor
to one of the handler
mappings (see Section 17.4, “Handler mappings”). It will detect a
parameter in the request and change the locale. It calls
setLocale()
on the
LocaleResolver
that also exists in the
context. The following example shows that calls to all
*.view
resources containing a parameter named
siteLanguage
will now change the locale. So, for
example, a request for the following URL,
http://www.sf.net/home.view?siteLanguage=nl
will
change the site language to Dutch.
<bean id="localeChangeInterceptor" class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"> <property name="paramName" value="siteLanguage"/> </bean> <bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/> <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="interceptors"> <list> <ref bean="localeChangeInterceptor"/> </list> </property> <property name="mappings"> <value>/**/*.view=someController</value> </property> </bean>
You can apply Spring Web MVC framework themes to set the overall look-and-feel of your application, thereby enhancing user experience. A theme is a collection of static resources, typically style sheets and images, that affect the visual style of the application.
To use themes in your web application, you must set up an
implementation of the
org.springframework.ui.context.ThemeSource
interface. The WebApplicationContext
interface extends ThemeSource
but
delegates its responsibilities to a dedicated implementation. By default
the delegate will be an
org.springframework.ui.context.support.ResourceBundleThemeSource
implementation that loads properties files from the root of the
classpath. To use a custom ThemeSource
implementation or to configure the base name prefix of the
ResourceBundleThemeSource
, you can register a
bean in the application context with the reserved name
themeSource
. The web application context
automatically detects a bean with that name and uses it.
When using the ResourceBundleThemeSource
, a
theme is defined in a simple properties file. The
properties file lists the resources that make up the theme. Here is an
example:
styleSheet=/themes/cool/style.css background=/themes/cool/img/coolBg.jpg
The keys of the properties are the names that refer to the themed
elements from view code. For a JSP, you typically do this using the
spring:theme
custom tag, which is very similar to the
spring:message
tag. The following JSP fragment uses
the theme defined in the previous example to customize the look and
feel:
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%> <html> <head> <link rel="stylesheet" href="<spring:theme code='styleSheet'/>" type="text/css"/> </head> <body style="background=<spring:theme code='background'/>"> ... </body> </html>
By default, the ResourceBundleThemeSource
uses an empty base name prefix. As a result, the properties files are
loaded from the root of the classpath. Thus you would put the
cool.properties
theme definition in a directory at
the root of the classpath, for example, in
/WEB-INF/classes
. The
ResourceBundleThemeSource
uses the standard Java
resource bundle loading mechanism, allowing for full
internationalization of themes. For example, we could have a
/WEB-INF/classes/cool_nl.properties
that references a
special background image with Dutch text on it.
After you define themes, as in the preceding section, you decide
which theme to use. The DispatcherServlet
will
look for a bean named themeResolver
to find out
which ThemeResolver
implementation to
use. A theme resolver works in much the same way as a
LocaleResolver
. It detects the theme to
use for a particular request and can also alter the request's theme. The
following theme resolvers are provided by Spring:
Table 17.5. ThemeResolver
implementations
Class | Description |
---|---|
FixedThemeResolver | Selects a fixed theme, set using the
defaultThemeName property. |
SessionThemeResolver | The theme is maintained in the user's HTTP session. It only needs to be set once for each session, but is not persisted between sessions. |
CookieThemeResolver | The selected theme is stored in a cookie on the client. |
Spring also provides a
ThemeChangeInterceptor
that allows theme changes
on every request with a simple request parameter.
Spring's built-in multipart support handles file uploads in web
applications. You enable this multipart support with pluggable
MultipartResolver
objects, defined in the
org.springframework.web.multipart
package. Spring
provides one MultipartResolver
implementation for use with Commons
FileUpload and another for use with Servlet 3.0
multipart request parsing.
By default, Spring does no multipart handling, because some
developers want to handle multiparts themselves. You enable Spring
multipart handling by adding a multipart resolver to the web
application's context. Each request is inspected to see if it contains a
multipart. If no multipart is found, the request continues as expected.
If a multipart is found in the request, the
MultipartResolver
that has been declared in your
context is used. After that, the multipart attribute in your request is
treated like any other attribute.
The following example shows how to use the
CommonsMultipartResolver
:
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <!-- one of the properties available; the maximum file size in bytes --> <property name="maxUploadSize" value="100000"/> </bean>
Of course you also need to put the appropriate jars in your
classpath for the multipart resolver to work. In the case of the
CommonsMultipartResolver
, you need to use
commons-fileupload.jar
.
When the Spring DispatcherServlet
detects a
multi-part request, it activates the resolver that has been declared in
your context and hands over the request. The resolver then wraps the
current HttpServletRequest
into a
MultipartHttpServletRequest
that supports
multipart file uploads. Using the
MultipartHttpServletRequest
, you can get
information about the multiparts contained by this request and actually
get access to the multipart files themselves in your controllers.
In order to use Servlet 3.0 based multipart parsing, you need to
mark the DispatcherServlet
with a
"multipart-config"
section in
web.xml
, or with a
javax.servlet.MultipartConfigElement
in
programmatic Servlet registration, or in case of a custom Servlet class
possibly with a
javax.servlet.annotation.MultipartConfig
annotation on your Servlet class. Configuration settings such as maximum
sizes or storage locations need to be applied at that Servlet
registration level as Servlet 3.0 does not allow for those settings to
be done from the MultipartResolver.
Once Servlet 3.0 multipart parsing has been enabled in one of the
above mentioned ways you can add the
StandardServletMultipartResolver
to your Spring
configuration:
<bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"> </bean>
After the MultipartResolver
completes its
job, the request is processed like any other. First, create a form with
a file input that will allow the user to upload a form. The encoding
attribute (enctype="multipart/form-data"
) lets the
browser know how to encode the form as multipart request:
<html> <head> <title>Upload a file please</title> </head> <body> <h1>Please upload a file</h1> <form method="post" action="/form" enctype="multipart/form-data"> <input type="text" name="name"/> <input type="file" name="file"/> <input type="submit"/> </form> </body> </html>
The next step is to create a controller that handles the file
upload. This controller is very similar to a normal annotated
@Controller
, except that we use
MultipartHttpServletRequest
or
MultipartFile
in the method parameters:
@Controller public class FileUploadController { @RequestMapping(value = "/form", method = RequestMethod.POST) public String handleFormUpload(@RequestParam("name") String name, @RequestParam("file") MultipartFile file) { if (!file.isEmpty()) { byte[] bytes = file.getBytes(); // store the bytes somewhere return "redirect:uploadSuccess"; } else { return "redirect:uploadFailure"; } } }
Note how the @RequestParam
method
parameters map to the input elements declared in the form. In this
example, nothing is done with the byte[]
, but in
practice you can save it in a database, store it on the file system, and
so on.
When using Servlet 3.0 multipart parsing you can also use
javax.servlet.http.Part
for the method
parameter:
@Controller public class FileUploadController { @RequestMapping(value = "/form", method = RequestMethod.POST) public String handleFormUpload(@RequestParam("name") String name, @RequestParam("file") Part file) { InputStream inputStream = file.getInputStream(); // store bytes from uploaded file somewhere return "redirect:uploadSuccess"; } }
Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. All of the above examples and configuration apply here as well. However, unlike browsers that typically submit files and simple form fields, a programmatic client can also send more complex data of a specific content type — for example a multipart request with a file and second part with JSON formatted data:
POST /someUrl Content-Type: multipart/mixed --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="meta-data" Content-Type: application/json; charset=UTF-8 Content-Transfer-Encoding: 8bit { "name": "value" } --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="file-data"; filename="file.properties" Content-Type: text/xml Content-Transfer-Encoding: 8bit ... File Data ...
You could access the part named "meta-data" with a
@RequestParam("meta-data") String
metadata
controller method argument. However, you would
probably prefer to accept a strongly typed object initialized from the
JSON formatted data in the body of the request part, very similar to the
way @RequestBody
converts the body of a
non-multipart request to a target object with the help of an
HttpMessageConverter
.
You can use the @RequestPart
annotation instead of the @RequestParam
annotation for this purpose. It allows you to have the content of a
specific multipart passed through an
HttpMessageConverter
taking into consideration
the 'Content-Type'
header of the multipart:
@RequestMapping(value="/someUrl", method = RequestMethod.POST) public String onSubmit(@RequestPart("meta-data") MetaData metadata, @RequestPart("file-data") MultipartFile file) { // ... }
Notice how MultipartFile
method arguments
can be accessed with @RequestParam
or
with @RequestPart
interchangeably.
However, the @RequestPart("meta-data") MetaData
method argument in this case is read as JSON content based on its
'Content-Type'
header and converted with the help of
the MappingJackson2HttpMessageConverter
.
Spring HandlerExceptionResolver
implementations
deal with unexpected exceptions that occur during controller execution.
A HandlerExceptionResolver
somewhat resembles the
exception mappings you can define in the web application descriptor
web.xml
. However, they provide a more flexible way to
do so. For example they provide information about which handler was
executing when the exception was thrown. Furthermore, a programmatic way
of handling exceptions gives you more options for responding
appropriately before the request is forwarded to another URL (the same
end result as when you use the Servlet specific exception
mappings).
Besides implementing the
HandlerExceptionResolver
interface, which
is only a matter of implementing the
resolveException(Exception, Handler)
method and
returning a ModelAndView
, you may also use the provided
SimpleMappingExceptionResolver
or create
@ExceptionHandler
methods.
The SimpleMappingExceptionResolver
enables you to take the class name of any exception that might be thrown
and map it to a view name. This is functionally equivalent to the
exception mapping feature from the Servlet API, but it is also possible
to implement more finely grained mappings of exceptions from different
handlers. The @ExceptionHandler
annotation on
the other hand can be used on methods that should be invoked to handle an
exception. Such methods may be defined locally within an
@Controller
or may apply globally to all
@RequestMapping
methods when defined within
an @ControllerAdvice
class.
The following sections explain this in more detail.
The HandlerExceptionResolver
interface
and the SimpleMappingExceptionResolver
implementations
allow you to map Exceptions to specific views declaratively along with some
optional Java logic before forwarding to those views. However, in some cases,
especially when relying on @ResponseBody
methods
rather than on view resolution, it may be more convenient to directly set the
status of the response and optionally write error content to the body of the
response.
You can do that with @ExceptionHandler
methods. When declared within a controller such methods apply to exceptions
raised by @RequestMapping
methods of that
contoroller (or any of its sub-classes). You can also declare an
@ExceptionHandler
method within an
@ControllerAdvice
class in which case it
handles exceptions from @RequestMapping
methods from any controller.
The @ControllerAdvice
annotation is
a component annotation, which can be used with classpath scanning. It is
automatically enabled when using the MVC namespace and the MVC Java config,
or otherwise depending on whether the
ExceptionHandlerExceptionResolver
is configured or not.
Below is an example of a controller-local
@ExceptionHandler
method:
@Controller public class SimpleController { // @RequestMapping methods omitted ... @ExceptionHandler(IOException.class) public ResponseEntity<String> handleIOException(IOException ex) { // prepare responseEntity return responseEntity; } }
The @ExceptionHandler
value can be set to
an array of Exception types. If an exception is thrown that matches one of
the types in the list, then the method annotated with the matching
@ExceptionHandler
will be invoked. If the
annotation value is not set then the exception types listed as method
arguments are used.
Much like standard controller methods annotated with a
@RequestMapping
annotation, the method arguments
and return values of @ExceptionHandler
methods
can be flexible. For example, the
HttpServletRequest
can be accessed in Servlet
environments and the PortletRequest
in Portlet
environments. The return type can be a String
,
which is interpreted as a view name, a
ModelAndView
object, a
ResponseEntity
, or you can also add the
@ResponseBody
to have the method return value
converted with message converters and written to the response stream.
Spring MVC may raise a number of exceptions while processing
a request. The SimpleMappingExceptionResolver
can easily
map any exception to a default error view as needed.
However, when working with clients that interpret responses in an automated
way you will want to set specific status code on the response. Depending on
the exception raised the status code may indicate a client error (4xx) or a
server error (5xx).
The DefaultHandlerExceptionResolver
translates
Spring MVC exceptions to specific error status codes. It is registered
by default with the MVC namespace, the MVC Java config, and also by the
the DispatcherServlet
(i.e. when not using the MVC
namespace or Java config). Listed below are some of the exceptions handled
by this resolver and the corresponding status codes:
Exception | HTTP Status Code |
---|---|
BindException | 400 (Bad Request) |
ConversionNotSupportedException | 500 (Internal Server Error) |
HttpMediaTypeNotAcceptableException | 406 (Not Acceptable) |
HttpMediaTypeNotSupportedException | 415 (Unsupported Media Type) |
HttpMessageNotReadableException | 400 (Bad Request) |
HttpMessageNotWritableException | 500 (Internal Server Error) |
HttpRequestMethodNotSupportedException | 405 (Method Not Allowed) |
MethodArgumentNotValidException | 400 (Bad Request) |
MissingServletRequestParameterException | 400 (Bad Request) |
MissingServletRequestPartException | 400 (Bad Request) |
NoSuchRequestHandlingMethodException | 404 (Not Found) |
TypeMismatchException | 400 (Bad Request) |
The DefaultHandlerExceptionResolver
works
transparently by setting the status of the response. However, it stops short
of writing any error content to the body of the response while your
application may need to add developer-friendly content to every error
response for example when providing a REST API. You can prepare a
ModelAndView
and
render error content through view resolution -- i.e. by configuring a
ContentNeogitatingViewResolver
,
MappingJacksonJsonView
, and so on. However, you
may prefer to use @ExceptionHandler
methods instead.
If you prefer to write error content via
@ExceptionHandler
methods you can extend
ResponseEntityExceptionHandler
instead.
This is a convenient base for @ControllerAdvice
classes providing an @ExceptionHandler
method to handle standard Spring MVC exceptions and return
ResponseEntity
. That allows you to customize the response
and write error content with message converters. See the Javadoc of
ResponseEntityExceptionHandler
for more details.
A business exception can be annotated with
@ResponseStatus
. When the exception is raised,
the ResponseStatusExceptionResolver
handles it by
setting the status of the response accordingly.
By default the DispatcherServlet
registers
the ResponseStatusExceptionResolver
and it is
available for use.
When the status of the response is set to an error status code
and the body of the response is empty, Servlet containers commonly render
an HTML formatted error page.
To customize the default error page of the container, you can
declare an <error-page>
element in
web.xml
. Up until Servlet 3, that element had to
be mapped to a specific status code or exception type. Starting with
Servlet 3 an error page does not need to be mapped, which effectively
means the specified location customizes the default Servlet container
error page.
<error-page> <location>/error</location> </error-page>
Note that the actual location for the error page can be a
JSP page or some other URL within the container including one handled
through an @Controller
method:
When writing error information, the status code and the error message
set on the HttpServletResponse
can be
accessed through request attributes in a controller:
@Controller public class ErrorController { @RequestMapping(value="/error", produces="application/json") @ResponseBody public Map<String, Object> handle(HttpServletRequest request) { Map<String, Object> map = new HashMap<String, Object>(); map.put("status", request.getAttribute("javax.servlet.error.status_code")); map.put("reason", request.getAttribute("javax.servlet.error.message")); return map; } }
or in a JSP:
<%@ page contentType="application/json" pageEncoding="UTF-8"%> { status:<%=request.getAttribute("javax.servlet.error.status_code") %>, reason:<%=request.getAttribute("javax.servlet.error.message") %> }
For a lot of projects, sticking to established conventions and
having reasonable defaults is just what they (the projects) need, and
Spring Web MVC now has explicit support for convention over
configuration. What this means is that if you establish a set
of naming conventions and suchlike, you can
substantially cut down on the amount of configuration
that is required to set up handler mappings, view resolvers,
ModelAndView
instances, etc. This is a great boon
with regards to rapid prototyping, and can also lend a degree of (always
good-to-have) consistency across a codebase should you choose to move
forward with it into production.
Convention-over-configuration support addresses the three core areas of MVC: models, views, and controllers.
The ControllerClassNameHandlerMapping
class
is a HandlerMapping
implementation that
uses a convention to determine the mapping between request URLs and the
Controller
instances that are to handle
those requests.
Consider the following simple
Controller
implementation. Take special
notice of the name of the class.
public class ViewShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { // the implementation is not hugely important for this example... } }
Here is a snippet from the corresponding Spring Web MVC configuration file:
<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewShoppingCart" class="x.y.z.ViewShoppingCartController"> <!-- inject dependencies as required... --> </bean>
The ControllerClassNameHandlerMapping
finds
all of the various handler (or
Controller
) beans defined in its
application context and strips Controller
off the
name to define its handler mappings. Thus,
ViewShoppingCartController
maps to the
/viewshoppingcart*
request URL.
Let's look at some more examples so that the central idea becomes
immediately familiar. (Notice all lowercase in the URLs, in contrast to
camel-cased Controller
class
names.)
WelcomeController
maps to the
/welcome*
request URL
HomeController
maps to the
/home*
request URL
IndexController
maps to the
/index*
request URL
RegisterController
maps to the
/register*
request URL
In the case of MultiActionController
handler classes, the mappings generated are slightly more complex. The
Controller
names in the following
examples are assumed to be MultiActionController
implementations:
AdminController
maps to the
/admin/*
request URL
CatalogController
maps to the
/catalog/*
request URL
If you follow the convention of naming your
Controller
implementations as
xxx
Controller, the
ControllerClassNameHandlerMapping
saves you the
tedium of defining and maintaining a potentially
looooong
SimpleUrlHandlerMapping
(or suchlike).
The ControllerClassNameHandlerMapping
class
extends the AbstractHandlerMapping
base class so
you can define HandlerInterceptor
instances and everything else just as you would with many other
HandlerMapping
implementations.
The ModelMap
class is essentially a
glorified Map
that can make adding
objects that are to be displayed in (or on) a
View
adhere to a common naming
convention. Consider the following
Controller
implementation; notice that
objects are added to the ModelAndView
without any
associated name specified.
public class DisplayShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { List cartItems = // get a List of CartItem objects User user = // get the User doing the shopping ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name mav.addObject(cartItems); <-- look ma, no name, just the object mav.addObject(user); <-- and again ma! return mav; } }
The ModelAndView
class uses a
ModelMap
class that is a custom
Map
implementation that automatically
generates a key for an object when an object is added to it. The
strategy for determining the name for an added object is, in the case of
a scalar object such as User
, to use the short
class name of the object's class. The following examples are names that
are generated for scalar objects put into a
ModelMap
instance.
An x.y.User
instance added will have
the name user
generated.
An x.y.Registration
instance added will
have the name registration
generated.
An x.y.Foo
instance added will have the
name foo
generated.
A java.util.HashMap
instance added will
have the name hashMap
generated. You probably
want to be explicit about the name in this case because
hashMap
is less than intuitive.
Adding null
will result in an
IllegalArgumentException
being thrown. If the
object (or objects) that you are adding could be
null
, then you will also want to be explicit
about the name.
The strategy for generating a name after adding a
Set
or a
List
is to peek into the collection, take
the short class name of the first object in the collection, and use that
with List
appended to the name. The same applies to
arrays although with arrays it is not necessary to peek into the array
contents. A few examples will make the semantics of name generation for
collections clearer:
An x.y.User[]
array with zero or more
x.y.User
elements added will have the name
userList
generated.
An x.y.Foo[]
array with zero or more
x.y.User
elements added will have the name
fooList
generated.
A java.util.ArrayList
with one or more
x.y.User
elements added will have the name
userList
generated.
A java.util.HashSet
with one or more
x.y.Foo
elements added will have the name
fooList
generated.
An empty
java.util.ArrayList
will not be added at all
(in effect, the addObject(..)
call will
essentially be a no-op).
The RequestToViewNameTranslator
interface determines a logical View
name
when no such logical view name is explicitly supplied. It has just one
implementation, the
DefaultRequestToViewNameTranslator
class.
The DefaultRequestToViewNameTranslator
maps
request URLs to logical view names, as with this example:
public class RegistrationController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { // process the request... ModelAndView mav = new ModelAndView(); // add data as necessary to the model... return mav; // notice that no View or logical view name has been set } }
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- this bean with the well known name generates view names for us --> <bean id="viewNameTranslator" class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/> <bean class="x.y.RegistrationController"> <!-- inject dependencies as necessary --> </bean> <!-- maps request URLs to Controller names --> <bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </beans>
Notice how in the implementation of the
handleRequest(..)
method no
View
or logical view name is ever set on
the ModelAndView
that is returned. The
DefaultRequestToViewNameTranslator
is tasked with
generating a logical view name from the URL of the
request. In the case of the above
RegistrationController
, which is used in
conjunction with the
ControllerClassNameHandlerMapping
, a request URL
of http://localhost/registration.html
results in a
logical view name of registration
being generated by
the DefaultRequestToViewNameTranslator
. This
logical view name is then resolved into the
/WEB-INF/jsp/registration.jsp
view by the
InternalResourceViewResolver
bean.
Tip | |
---|---|
You do not need to define a
|
Of course, if you need to change the default settings, then you do
need to configure your own
DefaultRequestToViewNameTranslator
bean
explicitly. Consult the comprehensive Javadoc for the
DefaultRequestToViewNameTranslator
class for
details of the various properties that can be configured.
An ETag
(entity tag) is an HTTP response header returned by an HTTP/1.1 compliant
web server used to determine change in content at a given URL. It can be
considered to be the more sophisticated successor to the
Last-Modified
header. When a server returns a
representation with an ETag header, the client can use this header in
subsequent GETs, in an If-None-Match
header. If the
content has not changed, the server returns 304: Not
Modified
.
Support for ETags is provided by the Servlet filter
ShallowEtagHeaderFilter
. It is a plain Servlet
Filter, and thus can be used in combination with any web framework. The
ShallowEtagHeaderFilter
filter creates so-called
shallow ETags (as opposed to deep ETags, more about that later).The
filter caches the content of the rendered JSP (or other content),
generates an MD5 hash over that, and returns that as an ETag header in the
response. The next time a client sends a request for the same resource, it
uses that hash as the If-None-Match
value. The filter
detects this, renders the view again, and compares the two hashes. If they
are equal, a 304
is returned. This filter will not save
processing power, as the view is still rendered. The only thing it saves
is bandwidth, as the rendered response is not sent back over the
wire.
You configure the ShallowEtagHeaderFilter
in
web.xml
:
<filter> <filter-name>etagFilter</filter-name> <filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class> </filter> <filter-mapping> <filter-name>etagFilter</filter-name> <servlet-name>petclinic</servlet-name> </filter-mapping>
In a Servlet 3.0+ environment, you have the option of configuring the
Servlet container programmatically as an alternative or in combination with
a web.xml
file.
Below is an example of registering a DispatcherServlet
:
import org.springframework.web.WebApplicationInitializer; public class MyWebApplicationInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext container) { XmlWebApplicationContext appContext = new XmlWebApplicationContext(); appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml"); ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet(appContext)); registration.setLoadOnStartup(1); registration.addMapping("/"); } }
WebApplicationInitializer
is an interface
provided by Spring MVC that ensures your implementation is detected and
automatically used to initialize any Servlet 3 container. An abstract base
class implementation of WebApplicationInitializer
named
AbstractDispatcherServletInitializer
makes it even
easier to register the DispatcherServlet
by simply overriding
methods to specify the servlet mapping and the location of the
DispatcherServlet
configuration:
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer { @Override protected Class<?>[] getRootConfigClasses() { return null; } @Override protected Class<?>[] getServletConfigClasses() { return new Class[] { MyWebConfig.class }; } @Override protected String[] getServletMappings() { return new String[] { "/" }; } }
The above example is for an application that uses Java-based Spring
configuration. If using XML-based Spring configuration, extend directly from
AbstractDispatcherServletInitializer
:
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer { @Override protected WebApplicationContext createRootApplicationContext() { return null; } @Override protected WebApplicationContext createServletApplicationContext() { XmlWebApplicationContext cxt = new XmlWebApplicationContext(); cxt.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml"); return cxt; } @Override protected String[] getServletMappings() { return new String[] { "/" }; } }
AbstractDispatcherServletInitializer
also provides
a convenient way to add Filter
instances
and have them automatically mapped to the DispatcherServlet
:
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer { // ... @Override protected Filter[] getServletFilters() { return new Filter[] { new HiddenHttpMethodFilter(), new CharacterEncodingFilter() }; } }
Each filter is added with a default name based on its concrete type and
automatically mapped to the DispatcherServlet
.
The isAsyncSupported
protected method of
AbstractDispatcherServletInitializer
provides
a single place to enable async support on the DispatcherServlet
and all filters mapped to it. By default this flag is set to true
.
Section 17.2.1, “Special Bean Types In the WebApplicationContext
” and
Section 17.2.2, “Default DispatcherServlet Configuration” explained about
Spring MVC's special beans and the default implementations
used by the DispatcherServlet
.
In this section you'll learn about two additional ways of
configuring Spring MVC. Namely the MVC Java config and
the MVC XML namespace.
The MVC Java config and the MVC namespace provide
similar default configuration that overrides
the DispatcherServlet
defaults.
The goal is to spare most applications from having to
having to create the same configuration and also to
provide higher-level constructs for configuring
Spring MVC that serve as a simple starting point and
require little or no prior knowledge of the underlying
configuration.
You can choose either the MVC Java config or the MVC namespace depending on your preference. Also as you will see further below, with the MVC Java config it is easier to see the underlying configuration as well as to make fine-grained customizations directly to the created Spring MVC beans. But let's start from the beginning.
To enable MVC Java config add the annotation
@EnableWebMvc
to one of your
@Configuration
classes:
@Configuration @EnableWebMvc public class WebConfig { }
To achieve the same in XML use the mvc:annotation-driven
element:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> <mvc:annotation-driven /> </beans>
The above registers a
RequestMappingHandlerMapping
, a
RequestMappingHandlerAdapter
, and an
ExceptionHandlerExceptionResolver
(among others)
in support of processing requests with annotated controller methods using
annotations such as @RequestMapping
,
@ExceptionHandler
, and others.
It also enables the following:
Spring 3 style type conversion through a ConversionService instance in addition to the JavaBeans PropertyEditors used for Data Binding.
Support for formatting Number
fields using the @NumberFormat
annotation through the
ConversionService
.
Support for formatting Date,
Calendar, Long, and Joda Time fields using the
@DateTimeFormat
annotation.
Support for validating @Controller
inputs with @Valid
,
if a JSR-303 Provider is present on the classpath.
HttpMessageConverter support for
@RequestBody
method
parameters and @ResponseBody
method return values from
@RequestMapping
or
@ExceptionHandler
methods.
This is the complete list of HttpMessageConverters set up by mvc:annotation-driven:
ByteArrayHttpMessageConverter
converts byte arrays.
StringHttpMessageConverter
converts strings.
ResourceHttpMessageConverter
converts to/from
org.springframework.core.io.Resource
for all media types.
SourceHttpMessageConverter
converts to/from a
javax.xml.transform.Source
.
FormHttpMessageConverter
converts form data to/from a
MultiValueMap<String,
String>
.
Jaxb2RootElementHttpMessageConverter
converts Java objects to/from XML — added if JAXB2 is
present on the classpath.
MappingJackson2HttpMessageConverter
(or MappingJacksonHttpMessageConverter
)
converts to/from JSON — added if Jackson 2 (or Jackson) is present
on the classpath.
AtomFeedHttpMessageConverter
converts Atom feeds — added if Rome is present on the
classpath.
RssChannelHttpMessageConverter
converts RSS feeds — added if Rome is present on the
classpath.
To customize the default configuration in Java you simply
implement the WebMvcConfigurer
interface or more likely extend the class
WebMvcConfigurerAdapter
and override
the methods you need. Below is an example of some of the available
methods to override. See WebMvcConifgurer
for
a list of all methods and the Javadoc for further details:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override protected void addFormatters(FormatterRegistry registry) { // Add formatters and/or converters } @Override public void configureMessageConverters(List<HttpMessageConverter<?>> converters) { // Configure the list of HttpMessageConverters to use } }
To customize the default configuration of
<mvc:annotation-driven />
check what
attributes and sub-elements it supports. You can view the
Spring MVC XML schema
or use the code completion feature of your IDE to discover
what attributes and sub-elements are available.
The sample below shows a subset of what is available:
<mvc:annotation-driven conversion-service="conversionService"> <mvc:message-converters> <bean class="org.example.MyHttpMessageConverter"/> <bean class="org.example.MyOtherHttpMessageConverter"/> </mvc:message-converters> </mvc:annotation-driven> <bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean"> <property name="formatters"> <list> <bean class="org.example.MyFormatter"/> <bean class="org.example.MyOtherFormatter"/> </list> </property> </bean>
You can configure HandlerInterceptors
or WebRequestInterceptors
to be applied
to all incoming requests or restricted to specific URL path patterns.
An example of registering interceptors in Java:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(new LocaleInterceptor()); registry.addInterceptor(new ThemeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**"); registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*"); } }
And in XML use the <mvc:interceptors>
element:
<mvc:interceptors> <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor" /> <mvc:interceptor> <mapping path="/**"/> <exclude-mapping path="/admin/**"/> <bean class="org.springframework.web.servlet.theme.ThemeChangeInterceptor" /> </mvc:interceptor> <mvc:interceptor> <mapping path="/secure/*"/> <bean class="org.example.SecurityInterceptor" /> </mvc:interceptor> </mvc:interceptors>
Staring with Spring Framework 3.2, you can configure how Spring MVC determines the requested media types from the client for request mapping as well as for content negotiation purposes. The available options are to check the file extension in the request URI, the "Accept" header, a request parameter, as well as to fall back on a default content type. By default, file extension in the request URI is checked first and the "Accept" header is checked next.
For file extensions in the request URI, the MVC Java config and
the MVC namespace, automatically register extensions such as
.json
, .xml
,
.rss
, and .atom
if the
corresponding dependencies such as Jackson, JAXB2, or Rome
are present on the classpath. Additional extensions may be not need
to be registered explicitly if they can be discovered via
ServletContext.getMimeType(String)
or the
Java Activation Framework
(see javax.activation.MimetypesFileTypeMap
).
Below is an example of customizing content negotiation options through the MVC Java config:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureContentNegotiation(ContentNegotiationConfigurer configurer) { configurer.favorPathExtension(false).favorParameter(true); } }
In the MVC namespace, the <mvc:annotation-driven>
element
has a content-negotiation-manager
attribute, which expects a
ContentNegotiationManager
that in turn can be created
with a ContentNegotiationManagerFactoryBean
:
<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" /> <bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean"> <property name="favorPathExtension" value="false" /> <property name="favorParameter" value="true" /> <property name="mediaTypes" > <value> json=application/json xml=application/xml </value> </property> </bean>
If not using the MVC Java config or the MVC namespace, you'll need
to create an instance of ContentNegotiationManager
and use it to configure
RequestMappingHandlerMapping
for request mapping
purposes, and RequestMappingHandlerAdapter
and
ExceptionHandlerExceptionResolver
for
content negotiation purposes.
Note that ContentNegotiatingViewResolver
now can also be configured with a ContentNegotiatingViewResolver
,
so you can use one instance throughout Spring MVC.
In more advanced cases, it may be useful to configure
multiple ContentNegotiationManager
instances
that in turn may contain custom
ContentNegotiationStrategy
implementations.
For example you could configure
ExceptionHandlerExceptionResolver
with
a ContentNegotiationManager
that always
resolves the requested media type to "application/json"
.
Or you may want to plug a custom strategy that has some logic to select
a default content type (e.g. either XML or JSON) if no content
types were requested.
This is a shortcut for defining a
ParameterizableViewController
that immediately
forwards to a view when invoked. Use it in static cases when there is no
Java controller logic to execute before the view generates the
response.
An example of forwarding a request for "/"
to a view called "home"
in Java:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addViewControllers(ViewControllerRegistry registry) { registry.addViewController("/").setViewName("home"); } }
And the same in XML use the <mvc:view-controller>
element:
<mvc:view-controller path="/" view-name="home"/>
This option allows static resource requests following a particular
URL pattern to be served by a
ResourceHttpRequestHandler
from any of a list of
Resource
locations. This provides a convenient
way to serve static resources from locations other than the web
application root, including locations on the classpath. The
cache-period
property may be used to set far future
expiration headers (1 year is the recommendation of optimization tools
such as Page Speed and YSlow) so that they will be more efficiently
utilized by the client. The handler also properly evaluates the
Last-Modified
header (if present) so that a
304
status code will be returned as appropriate, avoiding
unnecessary overhead for resources that are already cached by the
client. For example, to serve resource requests with a URL pattern of
/resources/**
from a public-resources
directory within the web application root you would use:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/"); } }
And the same in XML:
<mvc:resources mapping="/resources/**" location="/public-resources/"/>
To serve these resources with a 1-year future expiration to ensure maximum use of the browser cache and a reduction in HTTP requests made by the browser:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/").setCachePeriod(31556926); } }
And in XML:
<mvc:resources mapping="/resources/**" location="/public-resources/" cache-period="31556926"/>
The mapping
attribute must be an Ant pattern that can
be used by SimpleUrlHandlerMapping
, and the
location
attribute must specify one or more valid resource
directory locations. Multiple resource locations may be specified using
a comma-separated list of values. The locations specified will be
checked in the specified order for the presence of the resource for any
given request. For example, to enable the serving of resources from both
the web application root and from a known path of
/META-INF/public-web-resources/
in any jar on the
classpath use:
@EnableWebMvc @Configuration public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**") .addResourceLocations("/", "classpath:/META-INF/public-web-resources/"); } }
And in XML:
<mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/public-web-resources/"/>
When serving resources that may change when a new version of the application is deployed, it is recommended that you incorporate a version string into the mapping pattern used to request the resources, so that you may force clients to request the newly deployed version of your application's resources. Such a version string can be parameterized and accessed using SpEL so that it may be easily managed in a single place when deploying new versions.
As an example, let's consider an application that uses a
performance-optimized custom build (as recommended) of the Dojo
JavaScript library in production, and that the build is generally
deployed within the web application at a path of
/public-resources/dojo/dojo.js
. Since different parts of
Dojo may be incorporated into the custom build for each new version of
the application, the client web browsers need to be forced to
re-download that custom-built dojo.js
resource any time a
new version of the application is deployed. A simple way to achieve this
would be to manage the version of the application in a properties file,
such as:
application.version=1.0.0
and then to make the properties file's values accessible to SpEL
as a bean using the util:properties
tag:
<util:properties id="applicationProps" location="/WEB-INF/spring/application.properties"/>
With the application version now accessible via SpEL, we can
incorporate this into the use of the resources
tag:
<mvc:resources mapping="/resources-#{applicationProps['application.version']}/**" location="/public-resources/"/>
In Java, you can use the @PropertySouce
annotation and then inject the Environment
abstraction for access to all defined properties:
@Configuration @EnableWebMvc @PropertySource("/WEB-INF/spring/application.properties") public class WebConfig extends WebMvcConfigurerAdapter { @Inject Environment env; @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources-" + env.getProperty("application.version") + "/**") .addResourceLocations("/public-resources/"); } }
and finally, to request the resource with the proper URL, we can take advantage of the Spring JSP tags:
<spring:eval expression="@applicationProps['application.version']" var="applicationVersion"/> <spring:url value="/resources-{applicationVersion}" var="resourceUrl"> <spring:param name="applicationVersion" value="${applicationVersion}"/> </spring:url> <script src="${resourceUrl}/dojo/dojo.js" type="text/javascript"> </script>
This tag allows for mapping the DispatcherServlet
to
"/" (thus overriding the mapping of the container's default Servlet),
while still allowing static resource requests to be handled by the
container's default Servlet. It configures a
DefaultServletHttpRequestHandler
with a URL mapping of
"/**" and the lowest priority relative to other URL mappings.
This handler will forward all requests to the default Servlet.
Therefore it is important that it remains last in the order of all other
URL HandlerMappings
. That will be the case if you use
<mvc:annotation-driven>
or alternatively if you are
setting up your own customized HandlerMapping
instance be
sure to set its order
property to a value lower than that
of the DefaultServletHttpRequestHandler
, which is
Integer.MAX_VALUE
.
To enable the feature using the default setup use:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) { configurer.enable(); } }
Or in XML:
<mvc:default-servlet-handler/>
The caveat to overriding the "/" Servlet mapping is that the
RequestDispatcher
for the default Servlet must be retrieved
by name rather than by path. The
DefaultServletHttpRequestHandler
will attempt to
auto-detect the default Servlet for the container at startup time, using
a list of known names for most of the major Servlet containers
(including Tomcat, Jetty, GlassFish, JBoss, Resin, WebLogic, and
WebSphere). If the default Servlet has been custom configured with a
different name, or if a different Servlet container is being used where
the default Servlet name is unknown, then the default Servlet's name
must be explicitly provided as in the following example:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) { configurer.enable("myCustomDefaultServlet"); } }
Or in XML:
<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>
See the following links and pointers for more resources about Spring Web MVC:
There are many excellent articles and tutorials that show how to build web applications with Spring MVC. Read them at the Spring Documentation page.
“Expert Spring Web MVC and Web Flow” by Seth Ladd and others (published by Apress) is an excellent hard copy source of Spring Web MVC goodness.
As you can see from the above examples, MVC Java config and the MVC namespace provide higher level constructs that do not require deep knowledge of the underlying beans created for you. Instead it helps you to focus on your application needs. However, at some point you may need more fine-grained control or you may simply wish to understand the underlying configuration.
The first step towards more fine-grained control is to see the
underlying beans created for you. In MVC Java config you can
see the Javadoc and the @Bean
methods in WebMvcConfigurationSupport
.
The configuration in this class is automatically imported
through the @EnableWebMvc
annotation.
In fact if you open @EnableWebMvc
you can
see the @Import
statement.
The next step towards more fine-grained control is to
customize a property on one of the beans created in
WebMvcConfigurationSupport
or perhaps
to provide your own instance. This requires two things --
remove the @EnableWebMvc
annotation in order to prevent the import and then
extend directly from WebMvcConfigurationSupport
.
Here is an example:
@Configuration public class WebConfig extends WebMvcConfigurationSupport { @Override public void addInterceptors(InterceptorRegistry registry){ // ... } @Override @Bean public RequestMappingHandlerAdapter requestMappingHandlerAdapter() { // Create or let "super" create the adapter // Then customize one of its properties } }
Note that modifying beans in this way does not prevent you from using any of the higher-level constructs shown earlier in this section.
Fine-grained control over the configuration created for you is a bit harder with the MVC namespace.
If you do need to do that, rather than replicating the
configuration it provides, consider configuring a
BeanPostProcessor
that detects
the bean you want to customize by type and then modifying its
properties as necessary. For example:
@Component public class MyPostProcessor implements BeanPostProcessor { public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException { if (bean instanceof RequestMappingHandlerAdapter) { // Modify properties of the adapter } } }
Note that MyPostProcessor
needs to be
included in an <component scan />
in order for it to be detected or if you prefer you can declare it
explicitly with an XML bean declaration.