In addition to supporting conventional (servlet-based) Web development, Spring also supports JSR-168 Portlet development. As much as possible, the Portlet MVC framework is a mirror image of the Web MVC framework, and also uses the same underlying view abstractions and integration technology. So, be sure to review the chapters entitled Chapter 16, Web MVC framework and Chapter 17, View technologies before continuing with this chapter.
Note | |
---|---|
Bear in mind that while the concepts of Spring MVC are the same in Spring Portlet MVC, there are some notable differences created by the unique workflow of JSR-168 portlets. |
The main way in which portlet workflow differs from servlet workflow is that the request to the portlet can have two distinct phases: the action phase and the render phase. The action phase is executed only once and is where any backend changes or actions occur, such as making changes in a database. The render phase then produces what is displayed to the user each time the display is refreshed. The critical point here is that for a single overall request, the action phase is executed only once, but the render phase may be executed multiple times. This provides (and requires) a clean separation between the activities that modify the persistent state of your system and the activities that generate what is displayed to the user.
The dual phases of portlet requests are one of the real strengths of the JSR-168
specification. For example, dynamic search results can be updated routinely on the
display without the user explicitly rerunning the search. Most other portlet MVC
frameworks attempt to completely hide the two phases from the developer and make it look
as much like traditional servlet development as possible - we think this approach
removes one of the main benefits of using portlets. So, the separation of the two phases
is preserved throughout the Spring Portlet MVC framework. The primary manifestation of
this approach is that where the servlet version of the MVC classes will have one method
that deals with the request, the portlet version of the MVC classes will have two
methods that deal with the request: one for the action phase and one for the render
phase. For example, where the servlet version of AbstractController
has the
handleRequestInternal(..)
method, the portlet version of AbstractController
has
handleActionRequestInternal(..)
and handleRenderRequestInternal(..)
methods.
The framework is designed around a DispatcherPortlet
that dispatches requests to
handlers, with configurable handler mappings and view resolution, just as the
DispatcherServlet
in the web framework does. File upload is also supported in the same
way.
Locale resolution and theme resolution are not supported in Portlet MVC - these areas
are in the purview of the portal/portlet container and are not appropriate at the Spring
level. However, all mechanisms in Spring that depend on the locale (such as
internationalization of messages) will still function properly because
DispatcherPortlet
exposes the current locale in the same way as DispatcherServlet
.
The default handler is still a very simple Controller
interface, offering just two
methods:
void handleActionRequest(request,response)
ModelAndView handleRenderRequest(request,response)
The framework also includes most of the same controller implementation hierarchy, such
as AbstractController
, SimpleFormController
, and so on. Data binding, command object
usage, model handling, and view resolution are all the same as in the servlet framework.
All the view rendering capabilities of the servlet framework are used directly via a
special bridge servlet named ViewRendererServlet
. By using this servlet, the portlet
request is converted into a servlet request and the view can be rendered using the
entire normal servlet infrastructure. This means all the existing renderers, such as
JSP, Velocity, etc., can still be used within the portlet.
Spring Portlet MVC supports beans whose lifecycle is scoped to the current HTTP request
or HTTP Session
(both normal and global). This is not a specific feature of Spring
Portlet MVC itself, but rather of the WebApplicationContext
container(s) that Spring
Portlet MVC uses. These bean scopes are described in detail in
Section 4.5.4, “Request, session, and global session scopes”
Portlet MVC is a request-driven web MVC framework, designed around a portlet that
dispatches requests to controllers and offers other functionality facilitating the
development of portlet applications. Spring’s DispatcherPortlet
however, does more
than just that. It is completely integrated with the Spring ApplicationContext
and
allows you to use every other feature Spring has.
Like ordinary portlets, the DispatcherPortlet
is declared in the portlet.xml
file of
your web application:
<portlet> <portlet-name>sample</portlet-name> <portlet-class>org.springframework.web.portlet.DispatcherPortlet</portlet-class> <supports> <mime-type>text/html</mime-type> <portlet-mode>view</portlet-mode> </supports> <portlet-info> <title>Sample Portlet</title> </portlet-info> </portlet>
The DispatcherPortlet
now needs to be configured.
In the Portlet MVC framework, each DispatcherPortlet
has its own
WebApplicationContext
, which inherits all the beans already defined in the Root
WebApplicationContext
. These inherited beans can be overridden in the portlet-specific
scope, and new scope-specific beans can be defined local to a given portlet instance.
The framework will, on initialization of a DispatcherPortlet
, look for a file named
[portlet-name]-portlet.xml
in the WEB-INF
directory of your web application and
create the beans defined there (overriding the definitions of any beans defined with the
same name in the global scope).
The config location used by the DispatcherPortlet
can be modified through a portlet
initialization parameter (see below for details).
The Spring DispatcherPortlet
has a few special beans it uses, in order to be able to
process requests and render the appropriate views. These beans are included in the
Spring framework and can be configured in the WebApplicationContext
, just as any other
bean would be configured. Each of those beans is described in more detail below. Right
now, we’ll just mention them, just to let you know they exist and to enable us to go on
talking about the DispatcherPortlet
. For most of the beans, defaults are provided so
you don’t have to worry about configuring them.
Table 19.1. Special beans in the WebApplicationContext
Expression | Explanation |
---|---|
handler mapping(s) | (Section 19.5, “Handler mappings”) a list of pre- and post-processors and controllers that will be executed if they match certain criteria (for instance a matching portlet mode specified with the controller) |
controller(s) | (Section 19.4, “Controllers”) the beans providing the actual functionality (or at least, access to the functionality) as part of the MVC triad |
view resolver | (Section 19.6, “Views and resolving them”) capable of resolving view names to view definitions |
multipart resolver | (Section 19.7, “Multipart (file upload) support”) offers functionality to process file uploads from HTML forms |
handler exception resolver | (Section 19.8, “Handling exceptions”) offers functionality to map exceptions to views or implement other more complex exception handling code |
When a DispatcherPortlet
is setup for use and a request comes in for that specific
DispatcherPortlet
, it starts processing the request. The list below describes the
complete process a request goes through if handled by a DispatcherPortlet
:
PortletRequest.getLocale()
is bound to the request to let
elements in the process resolve the locale to use when processing the request (rendering
the view, preparing data, etc.).
ActionRequest
, the request is
inspected for multiparts and if they are found, it is wrapped in a
MultipartActionRequest
for further processing by other elements in the process. (See
Section 19.7, “Multipart (file upload) support” for further information about multipart handling).
WebApplicationContext
. If no model is returned (which could be due
to a pre- or post-processor intercepting the request, for example, for security
reasons), no view is rendered, since the request could already have been fulfilled.
Exceptions that are thrown during processing of the request get picked up by any of the
handler exception resolvers that are declared in the WebApplicationContext
. Using
these exception resolvers you can define custom behavior in case such exceptions get
thrown.
You can customize Spring’s DispatcherPortlet
by adding context parameters in the
portlet.xml
file or portlet init-parameters. The possibilities are listed below.
Table 19.2. DispatcherPortlet initialization parameters
Parameter | Explanation |
---|---|
| Class that implements |
| String which is passed to the context instance (specified by |
| The namespace of the |
| The URL at which |
The rendering process in Portlet MVC is a bit more complex than in Web MVC. In order to
reuse all the view technologies from Spring Web MVC, we must convert the
PortletRequest
/ PortletResponse
to HttpServletRequest
/ HttpServletResponse
and
then call the render
method of the View
. To do this, DispatcherPortlet
uses a
special servlet that exists for just this purpose: the ViewRendererServlet
.
In order for DispatcherPortlet
rendering to work, you must declare an instance of the
ViewRendererServlet
in the web.xml
file for your web application as follows:
<servlet> <servlet-name>ViewRendererServlet</servlet-name> <servlet-class>org.springframework.web.servlet.ViewRendererServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>ViewRendererServlet</servlet-name> <url-pattern>/WEB-INF/servlet/view</url-pattern> </servlet-mapping>
To perform the actual rendering, DispatcherPortlet
does the following:
WebApplicationContext
to the request as an attribute under the same
WEB_APPLICATION_CONTEXT_ATTRIBUTE
key that DispatcherServlet
uses.
Model
and View
objects to the request to make them available to the
ViewRendererServlet
.
PortletRequestDispatcher
and performs an include
using the /WEB-
INF/servlet/view
URL that is mapped to the ViewRendererServlet
.
The ViewRendererServlet
is then able to call the render
method on the View
with
the appropriate arguments.
The actual URL for the ViewRendererServlet
can be changed using DispatcherPortlet
's
viewRendererUrl
configuration parameter.
The controllers in Portlet MVC are very similar to the Web MVC Controllers, and porting code from one to the other should be simple.
The basis for the Portlet MVC controller architecture is the
org.springframework.web.portlet.mvc.Controller
interface, which is listed below.
public interface Controller { /** * Process the render request and return a ModelAndView object which the * DispatcherPortlet will render. */ ModelAndView handleRenderRequest(RenderRequest request, RenderResponse response) throws Exception; /** * Process the action request. There is nothing to return. */ void handleActionRequest(ActionRequest request, ActionResponse response) throws Exception; }
As you can see, the Portlet Controller
interface requires two methods that handle the
two phases of a portlet request: the action request and the render request. The action
phase should be capable of handling an action request, and the render phase should be
capable of handling a render request and returning an appropriate model and view. While
the Controller
interface is quite abstract, Spring Portlet MVC offers several
controllers that already contain a lot of the functionality you might need; most of
these are very similar to controllers from Spring Web MVC. The Controller
interface
just defines the most common functionality required of every controller: handling an
action request, handling a render request, and returning a model and a view.
Of course, just a Controller
interface isn’t enough. To provide a basic
infrastructure, all of Spring Portlet MVC’s Controller
s inherit from
AbstractController
, a class offering access to Spring’s ApplicationContext
and
control over caching.
Table 19.3. Features offered by the AbstractController
Parameter | Explanation |
---|---|
| Indicates whether or not this |
| Use this if you want handling by this controller to be synchronized on the user’s
session. To be more specific, the extending controller will override the
|
| If you want your controller to actually render the view when the portlet is in a minimized state, set this to true. By default, this is set to false so that portlets that are in a minimized state don’t display any content. |
| When you want a controller to override the default cache expiration defined for the
portlet, specify a positive integer here. By default it is set to |
The requireSession
and cacheSeconds
properties are declared on the
PortletContentGenerator
class, which is the superclass of AbstractController
) but
are included here for completeness.
When using the AbstractController
as a base class for your controllers (which is not
recommended since there are a lot of other controllers that might already do the job for
you) you only have to override either the handleActionRequestInternal(ActionRequest,
ActionResponse)
method or the handleRenderRequestInternal(RenderRequest,
RenderResponse)
method (or both), implement your logic, and return a ModelAndView
object (in the case of handleRenderRequestInternal
).
The default implementations of both handleActionRequestInternal(..)
and
handleRenderRequestInternal(..)
throw a PortletException
. This is consistent with
the behavior of GenericPortlet
from the JSR- 168 Specification API. So you only need
to override the method that your controller is intended to handle.
Here is short example consisting of a class and a declaration in the web application context.
package samples; import javax.portlet.RenderRequest; import javax.portlet.RenderResponse; import org.springframework.web.portlet.mvc.AbstractController; import org.springframework.web.portlet.ModelAndView; public class SampleController extends AbstractController { public ModelAndView handleRenderRequestInternal(RenderRequest request, RenderResponse response) { ModelAndView mav = new ModelAndView("foo"); mav.addObject("message", "Hello World!"); return mav; } }
<bean id="sampleController" class="samples.SampleController"> <property name="cacheSeconds" value="120"/> </bean>
The class above and the declaration in the web application context is all you need besides setting up a handler mapping (see Section 19.5, “Handler mappings”) to get this very simple controller working.
Although you can extend AbstractController
, Spring Portlet MVC provides a number of
concrete implementations which offer functionality that is commonly used in simple MVC
applications.
The ParameterizableViewController
is basically the same as the example above, except
for the fact that you can specify the view name that it will return in the web
application context (no need to hard-code the view name).
The PortletModeNameViewController
uses the current mode of the portlet as the view
name. So, if your portlet is in View mode (i.e. PortletMode.VIEW
) then it uses "view"
as the view name.
Spring Portlet MVC has the exact same hierarchy of command controllers as Spring Web
MVC. They provide a way to interact with data objects and dynamically bind parameters
from the PortletRequest
to the data object specified. Your data objects don’t have to
implement a framework-specific interface, so you can directly manipulate your persistent
objects if you desire. Let’s examine what command controllers are available, to get an
overview of what you can do with them:
AbstractCommandController
- a command controller you can use to create your own
command controller, capable of binding request parameters to a data object you
specify. This class does not offer form functionality, it does however offer
validation features and lets you specify in the controller itself what to do with the
command object that has been filled with the parameters from the request.
AbstractFormController
- an abstract controller offering form submission support.
Using this controller you can model forms and populate them using a command object you
retrieve in the controller. After a user has filled the form, AbstractFormController
binds the fields, validates, and hands the object back to the controller to take
appropriate action. Supported features are: invalid form submission (resubmission),
validation, and normal form workflow. You implement methods to determine which views
are used for form presentation and success. Use this controller if you need forms, but
don’t want to specify what views you’re going to show the user in the application
context.
SimpleFormController
- a concrete AbstractFormController
that provides even more
support when creating a form with a corresponding command object. The
SimpleFormController
lets you specify a command object, a viewname for the form, a
viewname for the page you want to show the user when form submission has succeeded,
and more.
AbstractWizardFormController
— a concrete AbstractFormController
that provides a
wizard-style interface for editing the contents of a command object across multiple
display pages. Supports multiple user actions: finish, cancel, or page change, all of
which are easily specified in request parameters from the view.
These command controllers are quite powerful, but they do require a detailed understanding of how they operate in order to use them efficiently. Carefully review the javadocs for this entire hierarchy and then look at some sample implementations before you start using them.
Instead of developing new controllers, it is possible to use existing portlets and map
requests to them from a DispatcherPortlet
. Using the PortletWrappingController
, you
can instantiate an existing Portlet
as a Controller
as follows:
<bean id="myPortlet" class="org.springframework.web.portlet.mvc.PortletWrappingController"> <property name="portletClass" value="sample.MyPortlet"/> <property name="portletName" value="my-portlet"/> <property name="initParameters"> <value>config=/WEB-INF/my-portlet-config.xml</value> </property> </bean>
This can be very valuable since you can then use interceptors to pre-process and
post-process requests going to these portlets. Since JSR-168 does not support any kind
of filter mechanism, this is quite handy. For example, this can be used to wrap the
Hibernate OpenSessionInViewInterceptor
around a MyFaces JSF Portlet.
Using a handler mapping you can map incoming portlet requests to appropriate handlers.
There are some handler mappings you can use out of the box, for example, the
PortletModeHandlerMapping
, but let’s first examine the general concept of a
HandlerMapping
.
Note: We are intentionally using the term "Handler" here instead of "Controller".
DispatcherPortlet
is designed to be used with other ways to process requests than just
Spring Portlet MVC’s own Controllers. A Handler is any Object that can handle portlet
requests. Controllers are an example of Handlers, and they are of course the default. To
use some other framework with DispatcherPortlet
, a corresponding implementation of
HandlerAdapter
is all that is needed.
The functionality a basic HandlerMapping
provides is the delivering of a
HandlerExecutionChain
, which must contain the handler that matches the incoming
request, and may also contain a list of handler interceptors that are applied to the
request. When a request comes in, the DispatcherPortlet
will hand it over to the
handler mapping to let it inspect the request and come up with an appropriate
HandlerExecutionChain
. Then the DispatcherPortlet
will execute the handler and
interceptors in the chain (if any). These concepts are all exactly the same as in Spring
Web MVC.
The concept of configurable handler mappings that can optionally contain interceptors
(executed before or after the actual handler was executed, or both) is extremely
powerful. A lot of supporting functionality can be built into a custom HandlerMapping
.
Think of a custom handler mapping that chooses a handler not only based on the portlet
mode of the request coming in, but also on a specific state of the session associated
with the request.
In Spring Web MVC, handler mappings are commonly based on URLs. Since there is really no such thing as a URL within a Portlet, we must use other mechanisms to control mappings. The two most common are the portlet mode and a request parameter, but anything available to the portlet request can be used in a custom handler mapping.
The rest of this section describes three of Spring Portlet MVC’s most commonly used
handler mappings. They all extend AbstractHandlerMapping
and share the following
properties:
interceptors
: The list of interceptors to use. HandlerInterceptor
s are discussed
in Section 19.5.4, “Adding HandlerInterceptors”.
defaultHandler
: The 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 will sort all handler mappings
available in the context and apply the first matching handler.
lazyInitHandlers
: Allows for lazy initialization of singleton handlers (prototype
handlers are always lazily initialized). Default value is false. This property is
directly implemented in the three concrete Handlers.
This is a simple handler mapping that maps incoming requests based on the current mode of the portlet (e.g. view, edit, help). An example:
<bean class="org.springframework.web.portlet.handler.PortletModeHandlerMapping"> <property name="portletModeMap"> <map> <entry key="view" value-ref="viewHandler"/> <entry key="edit" value-ref="editHandler"/> <entry key="help" value-ref="helpHandler"/> </map> </property> </bean>
If we need to navigate around to multiple controllers without changing portlet mode, the simplest way to do this is with a request parameter that is used as the key to control the mapping.
ParameterHandlerMapping
uses the value of a specific request parameter to control the
mapping. The default name of the parameter is 'action'
, but can be changed using the
'parameterName'
property.
The bean configuration for this mapping will look something like this:
<bean class="org.springframework.web.portlet.handler.ParameterHandlerMapping"> <property name="parameterMap"> <map> <entry key="add" value-ref="addItemHandler"/> <entry key="edit" value-ref="editItemHandler"/> <entry key="delete" value-ref="deleteItemHandler"/> </map> </property> </bean>
The most powerful built-in handler mapping, PortletModeParameterHandlerMapping
combines the capabilities of the two previous ones to allow different navigation within
each portlet mode.
Again the default name of the parameter is "action", but can be changed using the
parameterName
property.
By default, the same parameter value may not be used in two different portlet modes.
This is so that if the portal itself changes the portlet mode, the request will no
longer be valid in the mapping. This behavior can be changed by setting the
allowDupParameters
property to true. However, this is not recommended.
The bean configuration for this mapping will look something like this:
<bean class="org.springframework.web.portlet.handler.PortletModeParameterHandlerMapping"> <property name="portletModeParameterMap"> <map> <entry key="view"> <!-- view portlet mode --> <map> <entry key="add" value-ref="addItemHandler"/> <entry key="edit" value-ref="editItemHandler"/> <entry key="delete" value-ref="deleteItemHandler"/> </map> </entry> <entry key="edit"> <!-- edit portlet mode --> <map> <entry key="prefs" value-ref="prefsHandler"/> <entry key="resetPrefs" value-ref="resetPrefsHandler"/> </map> </entry> </map> </property> </bean>
This mapping can be chained ahead of a PortletModeHandlerMapping
, which can then
provide defaults for each mode and an overall default as well.
Spring’s handler mapping mechanism has a notion of handler interceptors, which can be extremely useful when you want to apply specific functionality to certain requests, for example, checking for a principal. Again Spring Portlet MVC implements these concepts in the same way as Web MVC.
Interceptors located in the handler mapping must implement HandlerInterceptor
from the
org.springframework.web.portlet
package. Just like the servlet version, this interface
defines three methods: one that will be called before the actual handler will be
executed ( preHandle
), one that will be called after the handler is executed (
postHandle
), and one that is called after the complete request has finished (
afterCompletion
). These three methods should provide enough flexibility to do all
kinds of pre- and post- processing.
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 DispatcherPortlet
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.
The postHandle
method is only called on a RenderRequest
. The preHandle
and
afterCompletion
methods are called on both an ActionRequest
and a RenderRequest
.
If you need to execute logic in these methods for just one type of request, be sure to
check what kind of request it is before processing it.
As with the servlet package, the portlet package has a concrete implementation of
HandlerInterceptor
called HandlerInterceptorAdapter
. This class has empty versions
of all the methods so that you can inherit from this class and implement just one or two
methods when that is all you need.
The portlet package also has a concrete interceptor named ParameterMappingInterceptor
that is meant to be used directly with ParameterHandlerMapping
and
PortletModeParameterHandlerMapping
. This interceptor will cause the parameter that is
being used to control the mapping to be forwarded from an ActionRequest
to the
subsequent RenderRequest
. This will help ensure that the RenderRequest
is mapped to
the same Handler as the ActionRequest
. This is done in the preHandle
method of the
interceptor, so you can still modify the parameter value in your handler to change where
the RenderRequest
will be mapped.
Be aware that this interceptor is calling setRenderParameter
on the ActionResponse
,
which means that you cannot call sendRedirect
in your handler when using this
interceptor. If you need to do external redirects then you will either need to forward
the mapping parameter manually or write a different interceptor to handle this for you.
As mentioned previously, Spring Portlet MVC directly reuses all the view technologies
from Spring Web MVC. This includes not only the various View
implementations
themselves, but also the ViewResolver
implementations. For more information, refer to
Chapter 17, View technologies and Section 16.5, “Resolving views” respectively.
A few items on using the existing View
and ViewResolver
implementations are worth
mentioning:
sendRedirect(..)
method of ActionResponse
cannot be used to stay within the
portal). So, RedirectView
and use of the 'redirect:'
prefix will not work
correctly from within Portlet MVC.
'forward:'
prefix from within Portlet MVC. However,
remember that since you are in a portlet, you have no idea what the current URL looks
like. This means you cannot use a relative URL to access other resources in your web
application and that you will have to use an absolute URL.
Also, for JSP development, the new Spring Taglib and the new Spring Form Taglib both work in portlet views in exactly the same way that they work in servlet views.
Spring Portlet MVC has built-in multipart support to handle file uploads in portlet
applications, just like Web MVC does. The design for the multipart support is done with
pluggable PortletMultipartResolver
objects, defined in the
org.springframework.web.portlet.multipart
package. Spring provides a
PortletMultipartResolver
for use with
Commons FileUpload. How uploading files is
supported will be described in the rest of this section.
By default, no multipart handling will be done by Spring Portlet MVC, as some developers
will want to handle multiparts themselves. You will have to enable it yourself by adding
a multipart resolver to the web application’s context. After you have done that,
DispatcherPortlet
will inspect each request to see if it contains a multipart. If no
multipart is found, the request will continue as expected. However, if a multipart is
found in the request, the PortletMultipartResolver
that has been declared in your
context will be used. After that, the multipart attribute in your request will be
treated like any other attribute.
Note | |
---|---|
Any configured |
The following example shows how to use the CommonsPortletMultipartResolver
:
<bean id="portletMultipartResolver" class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver"> <!-- 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
. Be sure to use at least version 1.1 of Commons FileUpload as
previous versions do not support JSR-168 Portlet applications.
Now that you have seen how to set Portlet MVC up to handle multipart requests, let’s
talk about how to actually use it. When DispatcherPortlet
detects a multipart request,
it activates the resolver that has been declared in your context and hands over the
request. What the resolver then does is wrap the current ActionRequest
in a
MultipartActionRequest
that has support for multipart file uploads. Using the
MultipartActionRequest
you can get information about the multiparts contained by this
request and actually get access to the multipart files themselves in your controllers.
Note that you can only receive multipart file uploads as part of an ActionRequest
, not
as part of a RenderRequest
.
After the PortletMultipartResolver
has finished doing its job, the request will be
processed like any other. To use the PortletMultipartResolver
, create a form with an
upload field (see example below), then let Spring bind the file onto your form (backing
object). To actually let the user upload a file, we have to create a (JSP/HTML) form:
<h1>Please upload a file</h1> <form method="post" action="<portlet:actionURL/>" enctype="multipart/form-data"> <input type="file" name="file"/> <input type="submit"/> </form>
As you can see, we’ve created a field named "file" that matches the property of the bean
that holds the byte[]
array. Furthermore we’ve added the encoding attribute (
enctype="multipart/form-data"
), which is necessary to let the browser know how to
encode the multipart fields (do not forget this!).
Just as with any other property that’s not automagically convertible to a string or
primitive type, to be able to put binary data in your objects you have to register a
custom editor with the PortletRequestDataBinder
. There are a couple of editors
available for handling files and setting the results on an object. There’s a
StringMultipartFileEditor
capable of converting files to Strings (using a user-defined
character set), and there is a ByteArrayMultipartFileEditor
which converts files to
byte arrays. They function analogous to the CustomDateEditor
.
So, to be able to upload files using a form, declare the resolver, a mapping to a controller that will process the bean, and the controller itself.
<bean id="portletMultipartResolver" class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver"/> <bean class="org.springframework.web.portlet.handler.PortletModeHandlerMapping"> <property name="portletModeMap"> <map> <entry key="view" value-ref="fileUploadController"/> </map> </property> </bean> <bean id="fileUploadController" class="examples.FileUploadController"> <property name="commandClass" value="examples.FileUploadBean"/> <property name="formView" value="fileuploadform"/> <property name="successView" value="confirmation"/> </bean>
After that, create the controller and the actual class to hold the file property.
public class FileUploadController extends SimpleFormController { public void onSubmitAction(ActionRequest request, ActionResponse response, Object command, BindException errors) throws Exception { // cast the bean FileUploadBean bean = (FileUploadBean) command; // let's see if there's content there byte[] file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // do something with the file here } protected void initBinder(PortletRequest request, PortletRequestDataBinder binder) throws Exception { // to actually be able to convert Multipart instance to byte[] // we have to register a custom editor binder.registerCustomEditor(byte[].class, new ByteArrayMultipartFileEditor()); // now Spring knows how to handle multipart object and convert } } public class FileUploadBean { private byte[] file; public void setFile(byte[] file) { this.file = file; } public byte[] getFile() { return file; } }
As you can see, the FileUploadBean
has a property of type byte[]
that holds the
file. The controller registers a custom editor to let Spring know how to actually
convert the multipart objects the resolver has found to properties specified by the
bean. In this example, nothing is done with the byte[]
property of the bean itself,
but in practice you can do whatever you want (save it in a database, mail it to
somebody, etc).
An equivalent example in which a file is bound straight to a String-typed property on a form backing object might look like this:
public class FileUploadController extends SimpleFormController { public void onSubmitAction(ActionRequest request, ActionResponse response, Object command, BindException errors) throws Exception { // cast the bean FileUploadBean bean = (FileUploadBean) command; // let's see if there's content there String file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // do something with the file here } protected void initBinder(PortletRequest request, PortletRequestDataBinder binder) throws Exception { // to actually be able to convert Multipart instance to a String // we have to register a custom editor binder.registerCustomEditor(String.class, new StringMultipartFileEditor()); // now Spring knows how to handle multipart objects and convert } } public class FileUploadBean { private String file; public void setFile(String file) { this.file = file; } public String getFile() { return file; } }
Of course, this last example only makes (logical) sense in the context of uploading a plain text file (it wouldn’t work so well in the case of uploading an image file).
The third (and final) option is where one binds directly to a MultipartFile
property
declared on the (form backing) object’s class. In this case one does not need to
register any custom property editor because there is no type conversion to be performed.
public class FileUploadController extends SimpleFormController { public void onSubmitAction(ActionRequest request, ActionResponse response, Object command, BindException errors) throws Exception { // cast the bean FileUploadBean bean = (FileUploadBean) command; // let's see if there's content there MultipartFile file = bean.getFile(); if (file == null) { // hmm, that's strange, the user did not upload anything } // do something with the file here } } public class FileUploadBean { private MultipartFile file; public void setFile(MultipartFile file) { this.file = file; } public MultipartFile getFile() { return file; } }
Just like Servlet MVC, Portlet MVC provides HandlerExceptionResolver
s to ease the
pain of unexpected exceptions that occur while your request is being processed by a
handler that matched the request. Portlet MVC also provides a portlet-specific, concrete
SimpleMappingExceptionResolver
that enables you to take the class name of any
exception that might be thrown and map it to a view name.
Spring 2.5 introduced an annotation-based programming model for MVC controllers, using
annotations such as @RequestMapping
, @RequestParam
, @ModelAttribute
, etc. 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 API’s, although they can easily get access to Servlet or Portlet
facilities if desired.
The following sections document these annotations and how they are most commonly used in a Portlet environment.
`@RequestMapping` will only be processed if a corresponding HandlerMapping
(for
type level annotations) and/or HandlerAdapter
(for method level annotations) is
present in the dispatcher. This is the case by default in both DispatcherServlet
and
DispatcherPortlet
.
However, if you are defining custom HandlerMappings
or HandlerAdapters
, then you
need to make sure that a corresponding custom DefaultAnnotationHandlerMapping
and/or
AnnotationMethodHandlerAdapter
is defined as well - provided that you intend to use
@RequestMapping
.
<?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"> <bean class="org.springframework.web.portlet.mvc.annotation.DefaultAnnotationHandlerMapping"/> <bean class="org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter"/> // ... (controller bean definitions) ... </beans>
Defining a DefaultAnnotationHandlerMapping
and/or AnnotationMethodHandlerAdapter
explicitly also makes sense if you would like to customize the mapping strategy, e.g.
specifying a custom WebBindingInitializer
(see below).
The @Controller
annotation indicates that a particular class serves the role of a
controller. There is no need to extend any controller base class or reference the
Portlet API. You are of course still able to reference Portlet-specific features if you
need to.
The basic purpose of the @Controller
annotation is to act as a stereotype for the
annotated class, indicating its role. The dispatcher will scan such annotated classes
for mapped methods, detecting @RequestMapping
annotations (see the next section).
Annotated controller beans may be defined explicitly, using a standard Spring bean
definition in the dispatcher’s context. However, the @Controller
stereotype also
allows for autodetection, aligned with Spring 2.5’s general support for detecting
component classes in the classpath and auto-registering bean definitions for them.
To enable autodetection of such annotated controllers, you have to add component scanning to your configuration. This is easily achieved by using 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.petportal.portlet"/> // ... </beans>
The @RequestMapping
annotation is used to map portlet modes like VIEW/EDIT onto an
entire class or a particular handler method. Typically the type-level annotation maps a
specific mode (or mode plus parameter condition) onto a form controller, with additional
method-level annotations narrowing the primary mapping for specific portlet request
parameters.
Tip | |
---|---|
In the following discussion, we’ll focus on controllers that are based on annotated handler methods. |
The following is an example of a form controller from the PetPortal sample application using this annotation:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { private Properties petSites; public void setPetSites(Properties petSites) { this.petSites = petSites; } @ModelAttribute("petSites") public Properties getPetSites() { return this.petSites; } @RequestMapping // default (action=list) public String showPetSites() { return "petSitesEdit"; } @RequestMapping(params = "action=add") // render phase public String showSiteForm(Model model) { // Used for the initial form as well as for redisplaying with errors. if (!model.containsAttribute("site")) { model.addAttribute("site", new PetSite()); } return "petSitesAdd"; } @RequestMapping(params = "action=add") // action phase public void populateSite(@ModelAttribute("site") PetSite petSite, BindingResult result, SessionStatus status, ActionResponse response) { new PetSiteValidator().validate(petSite, result); if (!result.hasErrors()) { this.petSites.put(petSite.getName(), petSite.getUrl()); status.setComplete(); response.setRenderParameter("action", "list"); } } @RequestMapping(params = "action=delete") public void removeSite(@RequestParam("site") String site, ActionResponse response) { this.petSites.remove(site); response.setRenderParameter("action", "list"); } }
Handler methods which are annotated with @RequestMapping
are allowed to have very
flexible signatures. They may have arguments of the following types, in arbitrary order
(except for validation results, which need to follow right after the corresponding
command object, if desired):
null
.
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 (the portal locale in a Portlet
environment).
java.util.TimeZone
/ java.time.ZoneId
for the current request time zone.
java.io.InputStream
/ java.io.Reader
for access to the request’s content. This
will be the raw InputStream/Reader as exposed by the Portlet API.
java.io.OutputStream
/ java.io.Writer
for generating the response’s content. This
will be the raw OutputStream/Writer as exposed by the Portlet API.
@RequestParam
annotated parameters for access to specific Portlet request
parameters. Parameter values will be converted to the declared method argument type.
java.util.Map
/ org.springframework.ui.Model
/ org.springframework.ui.ModelMap
for enriching the implicit model that will be exposed to the web view.
@InitBinder
methods and/or the
HandlerAdapter configuration - see the " webBindingInitializer
" property on
AnnotationMethodHandlerAdapter
. Such command objects along with their validation
results will be exposed as model attributes, by default using the non-qualified
command class name in property notation (e.g. "orderAddress" for type
"mypackage.OrderAddress"). Specify a parameter-level ModelAttribute
annotation for
declaring a specific model attribute name.
org.springframework.validation.Errors
/
org.springframework.validation.BindingResult
validation results for a preceding
command/form object (the immediate preceding argument).
org.springframework.web.bind.support.SessionStatus
status handle for marking form
processing as complete (triggering the cleanup of session attributes that have been
indicated by the @SessionAttributes
annotation at the handler type level).
The following return types are supported for handler methods:
ModelAndView
object, with the model implicitly enriched with command objects and
the results of @ModelAttribute
annotated reference data accessor methods.
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.
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.
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).
String
value which is interpreted as 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 (e.g. by writing the response content
directly).
@ModelAttribute
at the method level
(or the default attribute name based on the return type’s class name otherwise). The
model will be implicitly enriched with command objects and the results of
@ModelAttribute
annotated reference data accessor methods.
The @RequestParam
annotation is used to bind request parameters to a method parameter
in your controller.
The following code snippet from the PetPortal sample application shows the usage:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { // ... public void removeSite(@RequestParam("site") String site, ActionResponse response) { this.petSites.remove(site); response.setRenderParameter("action", "list"); } // ... }
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)
).
@ModelAttribute
has two usage scenarios in controllers. When placed on a method
parameter, @ModelAttribute
is used to map a model attribute to the specific, annotated
method parameter (see the populateSite()
method below). This is how the controller
gets a reference to the object holding the data entered in the form. In addition, the
parameter can be declared as the specific type of the form backing object rather than as
a generic java.lang.Object
, thus increasing type safety.
@ModelAttribute
is also used at the method level to provide reference data for the
model (see the getPetSites()
method below). For this usage the method signature can
contain the same types as documented above for the @RequestMapping
annotation.
Note | |
---|---|
|
The following code snippet shows these two usages of this annotation:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { // ... @ModelAttribute("petSites") public Properties getPetSites() { return this.petSites; } @RequestMapping(params = "action=add") // action phase public void populateSite( @ModelAttribute("site") PetSite petSite, BindingResult result, SessionStatus status, ActionResponse response) { new PetSiteValidator().validate(petSite, result); if (!result.hasErrors()) { this.petSites.put(petSite.getName(), petSite.getUrl()); status.setComplete(); response.setRenderParameter("action", "list"); } } }
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:
@Controller @RequestMapping("EDIT") @SessionAttributes("site") public class PetSitesEditController { // ... }
To customize request parameter binding with PropertyEditors, etc. via Spring’s
WebDataBinder
, you can either use @InitBinder
-annotated methods within your
controller or externalize your configuration by providing a custom
WebBindingInitializer
.
Annotating controller methods with @InitBinder
allows you to configure web data
binding directly within your controller class. @InitBinder
identifies methods which
initialize the WebDataBinder
which will be used for populating 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
for configuring 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 process of deploying a Spring Portlet MVC application is no different than deploying any JSR-168 Portlet application. However, this area is confusing enough in general that it is worth talking about here briefly.
Generally, the portal/portlet container runs in one webapp in your servlet container and
your portlets run in another webapp in your servlet container. In order for the portlet
container webapp to make calls into your portlet webapp it must make cross-context calls
to a well-known servlet that provides access to the portlet services defined in your
portlet.xml
file.
The JSR-168 specification does not specify exactly how this should happen, so each portlet container has its own mechanism for this, which usually involves some kind of "deployment process" that makes changes to the portlet webapp itself and then registers the portlets within the portlet container.
At a minimum, the web.xml
file in your portlet webapp is modified to inject the
well-known servlet that the portlet container will call. In some cases a single servlet
will service all portlets in the webapp, in other cases there will be an instance of the
servlet for each portlet.
Some portlet containers will also inject libraries and/or configuration files into the webapp as well. The portlet container must also make its implementation of the Portlet JSP Tag Library available to your webapp.
The bottom line is that it is important to understand the deployment needs of your target portal and make sure they are met (usually by following the automated deployment process it provides). Be sure to carefully review the documentation from your portal for this process.
Once you have deployed your portlet, review the resulting web.xml
file for sanity.
Some older portals have been known to corrupt the definition of the
ViewRendererServlet
, thus breaking the rendering of your portlets.