One of the areas in which Spring excels is in the separation of view technologies from the rest of the MVC framework. For example, deciding to use Groovy Markup Templates or Thymeleaf in place of an existing JSP is primarily a matter of configuration. This chapter covers the major view technologies that work with Spring and touches briefly on how to add new ones. This chapter assumes you are already familiar with Section 21.5, “Resolving views” which covers the basics of how views in general are coupled to the MVC framework.
Thymeleaf is a good example of a view technology fitting perfectly in the MVC framework. Support for this integration is not provided by the Spring team but by the Thymeleaf team itself.
Configuring Thymeleaf for Spring usually requires a few beans defined, like a
ServletContextTemplateResolver
, a SpringTemplateEngine
and a ThymeleafViewResolver
.
Please refer to the Thymeleaf+Spring
documentation section for more details.
The Groovy Markup Template Engine is another view technology, supported by Spring. This template engine is a template engine primarily aimed at generating XML-like markup (XML, XHTML, HTML5, …), but that can be used to generate any text based content.
This requires Groovy 2.3.1+ on the the classpath.
Configuring the Groovy Markup Teplate Engine is quite easy:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureViewResolvers(ViewResolverRegistry registry) { registry.groovy(); } @Bean public GroovyMarkupConfigurer groovyMarkupConfigurer() { GroovyMarkupConfigurer configurer = new GroovyMarkupConfigurer(); configurer.setResourceLoaderPath("/WEB-INF/"); return configurer; } }
The XML counterpart using the MVC namespace is:
<mvc:annotation-driven /> <mvc:view-resolvers> <mvc:groovy /> </mvc:view-resolvers> <mvc:groovy-configurer resource-loader-path="/WEB-INF/" />
Unlike traditional template engines, this one relies on a DSL that uses the builder syntax. Here is a sample template for an HTML page:
yieldUnescaped '<!DOCTYPE html>' html(lang:'en') { head { meta('http-equiv':'"Content-Type" content="text/html; charset=utf-8"') title('My page') } body { p('This is an example of HTML contents') } }
Velocity and FreeMarker are two templating languages that can be used as view technologies within Spring MVC applications. The languages are quite similar and serve similar needs and so are considered together in this section. For semantic and syntactic differences between the two languages, see the FreeMarker web site.
Your web application will need to include velocity-1.x.x.jar
or freemarker-2.x.jar
in order to work with Velocity or FreeMarker respectively and commons-collections.jar
is required for Velocity. Typically they are included in the WEB-INF/lib
folder where
they are guaranteed to be found by a Java EE server and added to the classpath for your
application. It is of course assumed that you already have the spring-webmvc.jar
in
your 'WEB-INF/lib'
directory too! If you make use of Spring’s 'dateToolAttribute' or
'numberToolAttribute' in your Velocity views, you will also need to include the
velocity-tools-generic-1.x.jar
A suitable configuration is initialized by adding the relevant configurer bean
definition to your '*-servlet.xml'
as shown below:
<!-- This bean sets up the Velocity environment for us based on a root path for templates. Optionally, a properties file can be specified for more control over the Velocity environment, but the defaults are pretty sane for file based template loading. --> <bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"> <property name="resourceLoaderPath" value="/WEB-INF/velocity/"/> </bean> <!-- View resolvers can also be configured with ResourceBundles or XML files. If you need different view resolving based on Locale, you have to use the resource bundle resolver. --> <bean id="viewResolver" class="org.springframework.web.servlet.view.velocity.VelocityViewResolver"> <property name="cache" value="true"/> <property name="prefix" value=""/> <property name="suffix" value=".vm"/> </bean>
<!-- freemarker config --> <bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer"> <property name="templateLoaderPath" value="/WEB-INF/freemarker/"/> </bean> <!-- View resolvers can also be configured with ResourceBundles or XML files. If you need different view resolving based on Locale, you have to use the resource bundle resolver. --> <bean id="viewResolver" class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver"> <property name="cache" value="true"/> <property name="prefix" value=""/> <property name="suffix" value=".ftl"/> </bean>
![]() | Note |
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For non web-apps add a |
Your templates need to be stored in the directory specified by the *Configurer
bean
shown above. This document does not cover details of creating templates for the two
languages - please see their relevant websites for information. If you use the view
resolvers highlighted, then the logical view names relate to the template file names in
similar fashion to InternalResourceViewResolver
for JSP’s. So if your controller
returns a ModelAndView object containing a view name of "welcome" then the resolvers
will look for the /WEB-INF/freemarker/welcome.ftl
or /WEB-INF/velocity/welcome.vm
template as appropriate.
The basic configurations highlighted above will be suitable for most application requirements, however additional configuration options are available for when unusual or advanced requirements dictate.
This file is completely optional, but if specified, contains the values that are passed
to the Velocity runtime in order to configure velocity itself. Only required for
advanced configurations, if you need this file, specify its location on the
VelocityConfigurer
bean definition above.
<bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"> <property name="configLocation" value="/WEB-INF/velocity.properties"/> </bean>
Alternatively, you can specify velocity properties directly in the bean definition for the Velocity config bean by replacing the "configLocation" property with the following inline properties.
<bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"> <property name="velocityProperties"> <props> <prop key="resource.loader">file</prop> <prop key="file.resource.loader.class"> org.apache.velocity.runtime.resource.loader.FileResourceLoader </prop> <prop key="file.resource.loader.path">${webapp.root}/WEB-INF/velocity</prop> <prop key="file.resource.loader.cache">false</prop> </props> </property> </bean>
Refer to the
API
documentation for Spring configuration of Velocity, or the Velocity documentation for
examples and definitions of the 'velocity.properties'
file itself.
FreeMarker 'Settings' and 'SharedVariables' can be passed directly to the FreeMarker
Configuration
object managed by Spring by setting the appropriate bean properties on
the FreeMarkerConfigurer
bean. The freemarkerSettings
property requires a
java.util.Properties
object and the freemarkerVariables
property requires a
java.util.Map
.
<bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer"> <property name="templateLoaderPath" value="/WEB-INF/freemarker/"/> <property name="freemarkerVariables"> <map> <entry key="xml_escape" value-ref="fmXmlEscape"/> </map> </property> </bean> <bean id="fmXmlEscape" class="freemarker.template.utility.XmlEscape"/>
See the FreeMarker documentation for details of settings and variables as they apply to
the Configuration
object.
Spring provides a tag library for use in JSP’s that contains (amongst other things) a
<spring:bind/>
tag. This tag primarily enables forms to display values from form
backing objects and to show the results of failed validations from a Validator
in the
web or business tier. From version 1.1, Spring now has support for the same
functionality in both Velocity and FreeMarker, with additional convenience macros for
generating form input elements themselves.
A standard set of macros are maintained within the spring-webmvc.jar
file for both
languages, so they are always available to a suitably configured application.
Some of the macros defined in the Spring libraries are considered internal (private) but
no such scoping exists in the macro definitions making all macros visible to calling
code and user templates. The following sections concentrate only on the macros you need
to be directly calling from within your templates. If you wish to view the macro code
directly, the files are called spring.vm / spring.ftl and are in the packages
org.springframework.web.servlet.view.velocity
or
org.springframework.web.servlet.view.freemarker
respectively.
In your html forms (vm / ftl templates) that act as the 'formView' for a Spring form
controller, you can use code similar to the following to bind to field values and
display error messages for each input field in similar fashion to the JSP equivalent.
Note that the name of the command object is "command" by default, but can be overridden
in your MVC configuration by setting the 'commandName' bean property on your form
controller. Example code is shown below for the personFormV
and personFormF
views
configured earlier;
<!-- velocity macros are automatically available --> <html> ... <form action="" method="POST"> Name: #springBind( "command.name" ) <input type="text" name="${status.expression}" value="$!status.value" /><br> #foreach($error in $status.errorMessages) <b>$error</b> <br> #end <br> ... <input type="submit" value="submit"/> </form> ... </html>
<!-- freemarker macros have to be imported into a namespace. We strongly recommend sticking to 'spring' --> <#import "/spring.ftl" as spring /> <html> ... <form action="" method="POST"> Name: <@spring.bind "command.name" /> <input type="text" name="${spring.status.expression}" value="${spring.status.value?default("")}" /><br> <#list spring.status.errorMessages as error> <b>${error}</b> <br> </#list> <br> ... <input type="submit" value="submit"/> </form> ... </html>
#springBind
/ <@spring.bind>
requires a 'path' argument which consists of the name
of your command object (it will be 'command' unless you changed it in your
FormController properties) followed by a period and the name of the field on the command
object you wish to bind to. Nested fields can be used too such as
"command.address.street". The bind
macro assumes the default HTML escaping behavior
specified by the ServletContext parameter defaultHtmlEscape
in web.xml
The optional form of the macro called #springBindEscaped
/ <@spring.bindEscaped>
takes a second argument and explicitly specifies whether HTML escaping should be used in
the status error messages or values. Set to true or false as required. Additional form
handling macros simplify the use of HTML escaping and these macros should be used
wherever possible. They are explained in the next section.
Additional convenience macros for both languages simplify both binding and form generation (including validation error display). It is never necessary to use these macros to generate form input fields, and they can be mixed and matched with simple HTML or calls direct to the spring bind macros highlighted previously.
The following table of available macros show the VTL and FTL definitions and the parameter list that each takes.
Table 22.1. Table of macro definitions
macro | VTL definition | FTL definition |
---|---|---|
message (output a string from a resource bundle based on the code parameter) | #springMessage($code) | <@spring.message code/> |
messageText (output a string from a resource bundle based on the code parameter, falling back to the value of the default parameter) | #springMessageText($code $text) | <@spring.messageText code, text/> |
url (prefix a relative URL with the application’s context root) | #springUrl($relativeUrl) | <@spring.url relativeUrl/> |
formInput (standard input field for gathering user input) | #springFormInput($path $attributes) | <@spring.formInput path, attributes, fieldType/> |
formHiddenInput * (hidden input field for submitting non-user input) | #springFormHiddenInput($path $attributes) | <@spring.formHiddenInput path, attributes/> |
formPasswordInput * (standard input field for gathering passwords. Note that no value will ever be populated in fields of this type) | #springFormPasswordInput($path $attributes) | <@spring.formPasswordInput path, attributes/> |
formTextarea (large text field for gathering long, freeform text input) | #springFormTextarea($path $attributes) | <@spring.formTextarea path, attributes/> |
formSingleSelect (drop down box of options allowing a single required value to be selected) | #springFormSingleSelect( $path $options $attributes) | <@spring.formSingleSelect path, options, attributes/> |
formMultiSelect (a list box of options allowing the user to select 0 or more values) | #springFormMultiSelect($path $options $attributes) | <@spring.formMultiSelect path, options, attributes/> |
formRadioButtons (a set of radio buttons allowing a single selection to be made from the available choices) | #springFormRadioButtons($path $options $separator $attributes) | <@spring.formRadioButtons path, options separator, attributes/> |
formCheckboxes (a set of checkboxes allowing 0 or more values to be selected) | #springFormCheckboxes($path $options $separator $attributes) | <@spring.formCheckboxes path, options, separator, attributes/> |
formCheckbox (a single checkbox) | #springFormCheckbox($path $attributes) | <@spring.formCheckbox path, attributes/> |
showErrors (simplify display of validation errors for the bound field) | #springShowErrors($separator $classOrStyle) | <@spring.showErrors separator, classOrStyle/> |
formInput
macro, specifying ' hidden’ or ' `password’ as the value for the
`fieldType
parameter.
The parameters to any of the above macros have consistent meanings:
SortedMap
such as a TreeMap
with a suitable Comparator may
be used and for arbitrary Maps that should return values in insertion order, use a
LinkedHashMap
or a LinkedMap
from commons-collections.
Examples of the macros are outlined below some in FTL and some in VTL. Where usage differences exist between the two languages, they are explained in the notes.
<!-- the Name field example from above using form macros in VTL --> ... Name: #springFormInput("command.name" "")<br> #springShowErrors("<br>" "")<br>
The formInput macro takes the path parameter (command.name) and an additional attributes parameter which is empty in the example above. The macro, along with all other form generation macros, performs an implicit spring bind on the path parameter. The binding remains valid until a new bind occurs so the showErrors macro doesn’t need to pass the path parameter again - it simply operates on whichever field a bind was last created for.
The showErrors macro takes a separator parameter (the characters that will be used to separate multiple errors on a given field) and also accepts a second parameter, this time a class name or style attribute. Note that FreeMarker is able to specify default values for the attributes parameter, unlike Velocity, and the two macro calls above could be expressed as follows in FTL:
<@spring.formInput "command.name"/> <@spring.showErrors "<br>"/>
Output is shown below of the form fragment generating the name field, and displaying a validation error after the form was submitted with no value in the field. Validation occurs through Spring’s Validation framework.
The generated HTML looks like this:
Name: <input type="text" name="name" value=""> <br> <b>required</b> <br> <br>
The formTextarea macro works the same way as the formInput macro and accepts the same parameter list. Commonly, the second parameter (attributes) will be used to pass style information or rows and cols attributes for the textarea.
Four selection field macros can be used to generate common UI value selection inputs in your HTML forms.
Each of the four macros accepts a Map of options containing the value for the form field, and the label corresponding to that value. The value and the label can be the same.
An example of radio buttons in FTL is below. The form backing object specifies a default value of 'London' for this field and so no validation is necessary. When the form is rendered, the entire list of cities to choose from is supplied as reference data in the model under the name 'cityMap'.
... Town: <@spring.formRadioButtons "command.address.town", cityMap, "" /><br><br>
This renders a line of radio buttons, one for each value in cityMap
using the
separator "". No additional attributes are supplied (the last parameter to the macro is
missing). The cityMap uses the same String for each key-value pair in the map. The map’s
keys are what the form actually submits as POSTed request parameters, map values are the
labels that the user sees. In the example above, given a list of three well known cities
and a default value in the form backing object, the HTML would be
Town: <input type="radio" name="address.town" value="London">London</input> <input type="radio" name="address.town" value="Paris" checked="checked">Paris</input> <input type="radio" name="address.town" value="New York">New York</input>
If your application expects to handle cities by internal codes for example, the map of codes would be created with suitable keys like the example below.
protected Map referenceData(HttpServletRequest request) throws Exception { Map cityMap = new LinkedHashMap(); cityMap.put("LDN", "London"); cityMap.put("PRS", "Paris"); cityMap.put("NYC", "New York"); Map m = new HashMap(); m.put("cityMap", cityMap); return m; }
The code would now produce output where the radio values are the relevant codes but the user still sees the more user friendly city names.
Town: <input type="radio" name="address.town" value="LDN">London</input> <input type="radio" name="address.town" value="PRS" checked="checked">Paris</input> <input type="radio" name="address.town" value="NYC">New York</input>
Default usage of the form macros above will result in HTML tags that are HTML 4.01 compliant and that use the default value for HTML escaping defined in your web.xml as used by Spring’s bind support. In order to make the tags XHTML compliant or to override the default HTML escaping value, you can specify two variables in your template (or in your model where they will be visible to your templates). The advantage of specifying them in the templates is that they can be changed to different values later in the template processing to provide different behavior for different fields in your form.
To switch to XHTML compliance for your tags, specify a value of 'true' for a model/context variable named xhtmlCompliant:
# for Velocity..
#set($springXhtmlCompliant = true)
<-- for FreeMarker -->
<#assign xhtmlCompliant = true in spring>
Any tags generated by the Spring macros will now be XHTML compliant after processing this directive.
In similar fashion, HTML escaping can be specified per field:
<#-- until this point, default HTML escaping is used --> <#assign htmlEscape = true in spring> <#-- next field will use HTML escaping --> <@spring.formInput "command.name" /> <#assign htmlEscape = false in spring> <#-- all future fields will be bound with HTML escaping off -->
Spring provides a couple of out-of-the-box solutions for JSP and JSTL views. Using JSP
or JSTL is done using a normal view resolver defined in the WebApplicationContext
.
Furthermore, of course you need to write some JSPs that will actually render the view.
![]() | Note |
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Setting up your application to use JSTL is a common source of error, mainly caused by confusion over the different servlet spec., JSP and JSTL version numbers, what they mean and how to declare the taglibs correctly. The article How to Reference and Use JSTL in your Web Application provides a useful guide to the common pitfalls and how to avoid them. Note that as of Spring 3.0, the minimum supported servlet version is 2.4 (JSP 2.0 and JSTL 1.1), which reduces the scope for confusion somewhat. |
Just as with any other view technology you’re integrating with Spring, for JSPs you’ll
need a view resolver that will resolve your views. The most commonly used view resolvers
when developing with JSPs are the InternalResourceViewResolver
and the
ResourceBundleViewResolver
. Both are declared in the WebApplicationContext
:
<!-- the ResourceBundleViewResolver --> <bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> </bean> # And a sample properties file is uses (views.properties in WEB-INF/classes): welcome.(class)=org.springframework.web.servlet.view.JstlView welcome.url=/WEB-INF/jsp/welcome.jsp productList.(class)=org.springframework.web.servlet.view.JstlView productList.url=/WEB-INF/jsp/productlist.jsp
As you can see, the ResourceBundleViewResolver
needs a properties file defining the
view names mapped to 1) a class and 2) a URL. With a ResourceBundleViewResolver
you
can mix different types of views using only one resolver.
<bean id="viewResolver" 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>
The InternalResourceBundleViewResolver
can be configured for using JSPs as described
above. As a best practice, we strongly encourage placing your JSP files in a directory
under the 'WEB-INF'
directory, so there can be no direct access by clients.
When using the Java Standard Tag Library you must use a special view class, the
JstlView
, as JSTL needs some preparation before things such as the I18N features will
work.
Spring provides data binding of request parameters to command objects as described in earlier chapters. To facilitate the development of JSP pages in combination with those data binding features, Spring provides a few tags that make things even easier. All Spring tags haveHTML escaping features to enable or disable escaping of characters.
The tag library descriptor (TLD) is included in the spring-webmvc.jar
. Further
information about the individual tags can be found in the appendix entitled
???.
As of version 2.0, Spring provides a comprehensive set of data binding-aware tags for handling form elements when using JSP and Spring Web MVC. Each tag provides support for the set of attributes of its corresponding HTML tag counterpart, making the tags familiar and intuitive to use. The tag-generated HTML is HTML 4.01/XHTML 1.0 compliant.
Unlike other form/input tag libraries, Spring’s form tag library is integrated with Spring Web MVC, giving the tags access to the command object and reference data your controller deals with. As you will see in the following examples, the form tags make JSPs easier to develop, read and maintain.
Let’s go through the form tags and look at an example of how each tag is used. We have included generated HTML snippets where certain tags require further commentary.
The form tag library comes bundled in spring-webmvc.jar
. The library descriptor is
called spring-form.tld
.
To use the tags from this library, add the following directive to the top of your JSP page:
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
where form
is the tag name prefix you want to use for the tags from this library.
This tag renders an HTML 'form' tag and exposes a binding path to inner tags for
binding. It puts the command object in the PageContext
so that the command object can
be accessed by inner tags. All the other tags in this library are nested tags of the
form
tag.
Let’s assume we have a domain object called User
. It is a JavaBean with properties
such as firstName
and lastName
. We will use it as the form backing object of our
form controller which returns form.jsp
. Below is an example of what form.jsp
would
look like:
<form:form> <table> <tr> <td>First Name:</td> <td><form:input path="firstName" /></td> </tr> <tr> <td>Last Name:</td> <td><form:input path="lastName" /></td> </tr> <tr> <td colspan="2"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form:form>
The firstName
and lastName
values are retrieved from the command object placed in
the PageContext
by the page controller. Keep reading to see more complex examples of
how inner tags are used with the form
tag.
The generated HTML looks like a standard form:
<form method="POST"> <table> <tr> <td>First Name:</td> <td><input name="firstName" type="text" value="Harry"/></td> </tr> <tr> <td>Last Name:</td> <td><input name="lastName" type="text" value="Potter"/></td> </tr> <tr> <td colspan="2"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form>
The preceding JSP assumes that the variable name of the form backing object is
'command'
. If you have put the form backing object into the model under another name
(definitely a best practice), then you can bind the form to the named variable like so:
<form:form commandName="user"> <table> <tr> <td>First Name:</td> <td><form:input path="firstName" /></td> </tr> <tr> <td>Last Name:</td> <td><form:input path="lastName" /></td> </tr> <tr> <td colspan="2"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form:form>
This tag renders an HTML 'input' tag using the bound value and type='text' by default. For an example of this tag, see the section called “The form tag”. Starting with Spring 3.1 you can use other types such HTML5-specific types like 'email', 'tel', 'date', and others.
This tag renders an HTML 'input' tag with type 'checkbox'.
Let’s assume our User
has preferences such as newsletter subscription and a list of
hobbies. Below is an example of the Preferences
class:
public class Preferences { private boolean receiveNewsletter; private String[] interests; private String favouriteWord; public boolean isReceiveNewsletter() { return receiveNewsletter; } public void setReceiveNewsletter(boolean receiveNewsletter) { this.receiveNewsletter = receiveNewsletter; } public String[] getInterests() { return interests; } public void setInterests(String[] interests) { this.interests = interests; } public String getFavouriteWord() { return favouriteWord; } public void setFavouriteWord(String favouriteWord) { this.favouriteWord = favouriteWord; } }
The form.jsp
would look like:
<form:form> <table> <tr> <td>Subscribe to newsletter?:</td> <%-- Approach 1: Property is of type java.lang.Boolean --%> <td><form:checkbox path="preferences.receiveNewsletter"/></td> </tr> <tr> <td>Interests:</td> <%-- Approach 2: Property is of an array or of type java.util.Collection --%> <td> Quidditch: <form:checkbox path="preferences.interests" value="Quidditch"/> Herbology: <form:checkbox path="preferences.interests" value="Herbology"/> Defence Against the Dark Arts: <form:checkbox path="preferences.interests" value="Defence Against the Dark Arts"/> </td> </tr> <tr> <td>Favourite Word:</td> <%-- Approach 3: Property is of type java.lang.Object --%> <td> Magic: <form:checkbox path="preferences.favouriteWord" value="Magic"/> </td> </tr> </table> </form:form>
There are 3 approaches to the checkbox
tag which should meet all your checkbox needs.
java.lang.Boolean
, the
input(checkbox)
is marked as 'checked' if the bound value is true
. The value
attribute corresponds to the resolved value of the setValue(Object)
value property.
array
or java.util.Collection
, the
input(checkbox)
is marked as 'checked' if the configured setValue(Object)
value is
present in the bound Collection
.
input(checkbox)
is marked as
'checked' if the configured setValue(Object)
is equal to the bound value.
Note that regardless of the approach, the same HTML structure is generated. Below is an HTML snippet of some checkboxes:
<tr> <td>Interests:</td> <td> Quidditch: <input name="preferences.interests" type="checkbox" value="Quidditch"/> <input type="hidden" value="1" name="_preferences.interests"/> Herbology: <input name="preferences.interests" type="checkbox" value="Herbology"/> <input type="hidden" value="1" name="_preferences.interests"/> Defence Against the Dark Arts: <input name="preferences.interests" type="checkbox" value="Defence Against the Dark Arts"/> <input type="hidden" value="1" name="_preferences.interests"/> </td> </tr>
What you might not expect to see is the additional hidden field after each checkbox.
When a checkbox in an HTML page is not checked, its value will not be sent to the
server as part of the HTTP request parameters once the form is submitted, so we need a
workaround for this quirk in HTML in order for Spring form data binding to work. The
checkbox
tag follows the existing Spring convention of including a hidden parameter
prefixed by an underscore ("_") for each checkbox. By doing this, you are effectively
telling Spring that "the checkbox was visible in the form and I want my object to
which the form data will be bound to reflect the state of the checkbox no matter what".
This tag renders multiple HTML 'input' tags with type 'checkbox'.
Building on the example from the previous checkbox
tag section. Sometimes you prefer
not to have to list all the possible hobbies in your JSP page. You would rather provide
a list at runtime of the available options and pass that in to the tag. That is the
purpose of the checkboxes
tag. You pass in an Array
, a List
or a Map
containing
the available options in the "items" property. Typically the bound property is a
collection so it can hold multiple values selected by the user. Below is an example of
the JSP using this tag:
<form:form> <table> <tr> <td>Interests:</td> <td> <%-- Property is of an array or of type java.util.Collection --%> <form:checkboxes path="preferences.interests" items="${interestList}"/> </td> </tr> </table> </form:form>
This example assumes that the "interestList" is a List
available as a model attribute
containing strings of the values to be selected from. In the case where you use a Map,
the map entry key will be used as the value and the map entry’s value will be used as
the label to be displayed. You can also use a custom object where you can provide the
property names for the value using "itemValue" and the label using "itemLabel".
This tag renders an HTML 'input' tag with type 'radio'.
A typical usage pattern will involve multiple tag instances bound to the same property but with different values.
<tr> <td>Sex:</td> <td> Male: <form:radiobutton path="sex" value="M"/> <br/> Female: <form:radiobutton path="sex" value="F"/> </td> </tr>
This tag renders multiple HTML 'input' tags with type 'radio'.
Just like the checkboxes
tag above, you might want to pass in the available options as
a runtime variable. For this usage you would use the radiobuttons
tag. You pass in an
Array
, a List
or a Map
containing the available options in the "items" property.
In the case where you use a Map, the map entry key will be used as the value and the map
entry’s value will be used as the label to be displayed. You can also use a custom
object where you can provide the property names for the value using "itemValue" and the
label using "itemLabel".
<tr> <td>Sex:</td> <td><form:radiobuttons path="sex" items="${sexOptions}"/></td> </tr>
This tag renders an HTML 'input' tag with type 'password' using the bound value.
<tr> <td>Password:</td> <td> <form:password path="password" /> </td> </tr>
Please note that by default, the password value is not shown. If you do want the
password value to be shown, then set the value of the 'showPassword'
attribute to
true, like so.
<tr> <td>Password:</td> <td> <form:password path="password" value="^76525bvHGq" showPassword="true" /> </td> </tr>
This tag renders an HTML 'select' element. It supports data binding to the selected
option as well as the use of nested option
and options
tags.
Let’s assume a User
has a list of skills.
<tr> <td>Skills:</td> <td><form:select path="skills" items="${skills}"/></td> </tr>
If the User’s
skill were in Herbology, the HTML source of the 'Skills' row would look
like:
<tr> <td>Skills:</td> <td> <select name="skills" multiple="true"> <option value="Potions">Potions</option> <option value="Herbology" selected="selected">Herbology</option> <option value="Quidditch">Quidditch</option> </select> </td> </tr>
This tag renders an HTML 'option'. It sets 'selected' as appropriate based on the bound value.
<tr> <td>House:</td> <td> <form:select path="house"> <form:option value="Gryffindor"/> <form:option value="Hufflepuff"/> <form:option value="Ravenclaw"/> <form:option value="Slytherin"/> </form:select> </td> </tr>
If the User’s
house was in Gryffindor, the HTML source of the 'House' row would look
like:
<tr> <td>House:</td> <td> <select name="house"> <option value="Gryffindor" selected="selected">Gryffindor</option> <option value="Hufflepuff">Hufflepuff</option> <option value="Ravenclaw">Ravenclaw</option> <option value="Slytherin">Slytherin</option> </select> </td> </tr>
This tag renders a list of HTML 'option' tags. It sets the 'selected' attribute as appropriate based on the bound value.
<tr> <td>Country:</td> <td> <form:select path="country"> <form:option value="-" label="--Please Select"/> <form:options items="${countryList}" itemValue="code" itemLabel="name"/> </form:select> </td> </tr>
If the User
lived in the UK, the HTML source of the 'Country' row would look like:
<tr> <td>Country:</td> <td> <select name="country"> <option value="-">--Please Select</option> <option value="AT">Austria</option> <option value="UK" selected="selected">United Kingdom</option> <option value="US">United States</option> </select> </td> </tr>
As the example shows, the combined usage of an option
tag with the options
tag
generates the same standard HTML, but allows you to explicitly specify a value in the
JSP that is for display only (where it belongs) such as the default string in the
example: "-- Please Select".
The items
attribute is typically populated with a collection or array of item objects.
itemValue
and itemLabel
simply refer to bean properties of those item objects, if
specified; otherwise, the item objects themselves will be stringified. Alternatively,
you may specify a Map
of items, in which case the map keys are interpreted as option
values and the map values correspond to option labels. If itemValue
and/or itemLabel
happen to be specified as well, the item value property will apply to the map key and
the item label property will apply to the map value.
This tag renders an HTML 'textarea'.
<tr> <td>Notes:</td> <td><form:textarea path="notes" rows="3" cols="20" /></td> <td><form:errors path="notes" /></td> </tr>
This tag renders an HTML 'input' tag with type 'hidden' using the bound value. To submit
an unbound hidden value, use the HTML input
tag with type 'hidden'.
<form:hidden path="house" />
If we choose to submit the 'house' value as a hidden one, the HTML would look like:
<input name="house" type="hidden" value="Gryffindor"/>
This tag renders field errors in an HTML 'span' tag. It provides access to the errors created in your controller or those that were created by any validators associated with your controller.
Let’s assume we want to display all error messages for the firstName
and lastName
fields once we submit the form. We have a validator for instances of the User
class
called UserValidator
.
public class UserValidator implements Validator { public boolean supports(Class candidate) { return User.class.isAssignableFrom(candidate); } public void validate(Object obj, Errors errors) { ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "required", "Field is required."); ValidationUtils.rejectIfEmptyOrWhitespace(errors, "lastName", "required", "Field is required."); } }
The form.jsp
would look like:
<form:form> <table> <tr> <td>First Name:</td> <td><form:input path="firstName" /></td> <%-- Show errors for firstName field --%> <td><form:errors path="firstName" /></td> </tr> <tr> <td>Last Name:</td> <td><form:input path="lastName" /></td> <%-- Show errors for lastName field --%> <td><form:errors path="lastName" /></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form:form>
If we submit a form with empty values in the firstName
and lastName
fields, this is
what the HTML would look like:
<form method="POST"> <table> <tr> <td>First Name:</td> <td><input name="firstName" type="text" value=""/></td> <%-- Associated errors to firstName field displayed --%> <td><span name="firstName.errors">Field is required.</span></td> </tr> <tr> <td>Last Name:</td> <td><input name="lastName" type="text" value=""/></td> <%-- Associated errors to lastName field displayed --%> <td><span name="lastName.errors">Field is required.</span></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form>
What if we want to display the entire list of errors for a given page? The example below
shows that the errors
tag also supports some basic wildcarding functionality.
path="*"
- displays all errors
path="lastName"
- displays all errors associated with the lastName
field
path
is omitted - object errors only are displayed
The example below will display a list of errors at the top of the page, followed by field-specific errors next to the fields:
<form:form> <form:errors path="*" cssClass="errorBox" /> <table> <tr> <td>First Name:</td> <td><form:input path="firstName" /></td> <td><form:errors path="firstName" /></td> </tr> <tr> <td>Last Name:</td> <td><form:input path="lastName" /></td> <td><form:errors path="lastName" /></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </table> </form:form>
The HTML would look like:
<form method="POST"> <span name="*.errors" class="errorBox">Field is required.<br/>Field is required.</span> <table> <tr> <td>First Name:</td> <td><input name="firstName" type="text" value=""/></td> <td><span name="firstName.errors">Field is required.</span></td> </tr> <tr> <td>Last Name:</td> <td><input name="lastName" type="text" value=""/></td> <td><span name="lastName.errors">Field is required.</span></td> </tr> <tr> <td colspan="3"> <input type="submit" value="Save Changes" /> </td> </tr> </form>
A key principle of REST is the use of the Uniform Interface. This means that all
resources (URLs) can be manipulated using the same four HTTP methods: GET, PUT, POST,
and DELETE. For each method, the HTTP specification defines the exact semantics. For
instance, a GET should always be a safe operation, meaning that is has no side effects,
and a PUT or DELETE should be idempotent, meaning that you can repeat these operations
over and over again, but the end result should be the same. While HTTP defines these
four methods, HTML only supports two: GET and POST. Fortunately, there are two possible
workarounds: you can either use JavaScript to do your PUT or DELETE, or simply do a POST
with the 'real' method as an additional parameter (modeled as a hidden input field in an
HTML form). This latter trick is what Spring’s HiddenHttpMethodFilter
does. This
filter is a plain Servlet Filter and therefore it can be used in combination with any
web framework (not just Spring MVC). Simply add this filter to your web.xml, and a POST
with a hidden _method parameter will be converted into the corresponding HTTP method
request.
To support HTTP method conversion the Spring MVC form tag was updated to support setting the HTTP method. For example, the following snippet taken from the updated Petclinic sample
<form:form method="delete"> <p class="submit"><input type="submit" value="Delete Pet"/></p> </form:form>
This will actually perform an HTTP POST, with the 'real' DELETE method hidden behind a
request parameter, to be picked up by the HiddenHttpMethodFilter
, as defined in
web.xml:
<filter> <filter-name>httpMethodFilter</filter-name> <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class> </filter> <filter-mapping> <filter-name>httpMethodFilter</filter-name> <servlet-name>petclinic</servlet-name> </filter-mapping>
The corresponding @Controller
method is shown below:
@RequestMapping(method = RequestMethod.DELETE) public String deletePet(@PathVariable int ownerId, @PathVariable int petId) { this.clinic.deletePet(petId); return "redirect:/owners/" + ownerId; }
Starting with Spring 3, the Spring form tag library allows entering dynamic attributes, which means you can enter any HTML5 specific attributes.
In Spring 3.1, the form input tag supports entering a type attribute other than 'text'. This is intended to allow rendering new HTML5 specific input types such as 'email', 'date', 'range', and others. Note that entering type='text' is not required since 'text' is the default type.
It is possible to integrate any templating library running on top of a JSR-223
script engine in web applications using Spring. The following describes in a
broad way how to do this. The script engine must implement both ScriptEngine
and Invocable
interfaces.
It has been tested with:
To be able to use script templates integration, you need to have available in your classpath the script engine:
You should also need to add dependencies for your script based template engine. For example, for Javascript you can use WebJars to add Maven/Gradle dependencies in order to make your javascript libraries available in the classpath.
To be able to use script templates, you have to configure it in order to specify various parameters
like the script engine to use, the script files to load and what function should be called to
render the templates. This is done thanks to a ScriptTemplateConfigurer
bean and optional script
files.
For example, in order to render Mustache templates thanks to the Nashorn Javascript engine provided with Java 8+, you should declare the following configuration:
@Configuration @EnableWebMvc public class MustacheConfig extends WebMvcConfigurerAdapter { @Override public void configureViewResolvers(ViewResolverRegistry registry) { registry.scriptTemplate(); } @Bean public ScriptTemplateConfigurer configurer() { ScriptTemplateConfigurer configurer = new ScriptTemplateConfigurer(); configurer.setEngineName("nashorn"); configurer.setScripts("mustache.js"); configurer.setRenderObject("Mustache"); configurer.setRenderFunction("render"); return configurer; } }
The XML counterpart using MVC namespace is:
<mvc:annotation-driven /> <mvc:view-resolvers> <mvc:script-template /> </mvc:view-resolvers> <mvc:script-template-configurer engine-name="nashorn" render-object="Mustache" render-function="render"> <mvc:script location="mustache.js" /> </mvc:script-template-configurer>
The controller is exactly what you should expect:
@Controller public class SampleController { @RequestMapping public ModelAndView test() { ModelAndView mav = new ModelAndView(); mav.addObject("title", "Sample title").addObject("body", "Sample body"); mav.setViewName("template.html"); return mav; } }
And the Mustache template is:
<html> <head> <title>{{title}}</title> </head> <body> <p>{{body}}</p> </body> </html>
The render function is called with the following parameters:
Mustache.render()
is natively compatible with this signature, so you can call it directly.
If your templating technology requires some customization, you may provide a script that implements a custom render function. For example, Handlerbars needs to compile templates before using them, and requires a polyfill in order to emulate some browser facilities not available in the server-side script engine.
@Configuration @EnableWebMvc public class MustacheConfig extends WebMvcConfigurerAdapter { @Override public void configureViewResolvers(ViewResolverRegistry registry) { registry.scriptTemplate(); } @Bean public ScriptTemplateConfigurer configurer() { ScriptTemplateConfigurer configurer = new ScriptTemplateConfigurer(); configurer.setEngineName("nashorn"); configurer.setScripts("polyfill.js", "handlebars.js", "render.js"); configurer.setRenderFunction("render"); configurer.setSharedEngine(false); return configurer; } }
![]() | Note |
---|---|
Setting the |
polyfill.js
only defines the window
object needed by Handlebars to run properly:
var window = {};
This basic render.js
implementation compiles the template before using it. A production
ready implementation should also store and reused cached templates / pre-compiled templates.
This can be done on the script side, as well as any customization you need (managing
template engine configuration for example).
function render(template, model) { var compiledTemplate = Handlebars.compile(template); return compiledTemplate(model); }
Check out Spring script templates unit tests (java, resources) for more configuration examples.
The MarshallingView
uses an XML Marshaller
defined in the org.springframework.oxm
package to render the response content as XML. The object to be marshalled can be set
explicitly using MarhsallingView’s `modelKey
bean property. Alternatively, the view
will iterate over all model properties and marshal the first type that is supported
by the Marshaller
. For more information on the functionality in the
org.springframework.oxm
package refer to the chapter Marshalling XML using O/X
Mappers.
It is possible to integrate Tiles - just as any other view technology - in web applications using Spring. The following describes in a broad way how to do this.
![]() | Note |
---|---|
This section focuses on Spring’s support for Tiles v3 in the
|
To be able to use Tiles, you have to add a dependency on Tiles version 3.0.1 or higher and its transitive dependencies to your project.
To be able to use Tiles, you have to configure it using files containing definitions
(for basic information on definitions and other Tiles concepts, please have a look at
http://tiles.apache.org). In Spring this is done using the TilesConfigurer
. Have a
look at the following piece of example ApplicationContext configuration:
<bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles3.TilesConfigurer"> <property name="definitions"> <list> <value>/WEB-INF/defs/general.xml</value> <value>/WEB-INF/defs/widgets.xml</value> <value>/WEB-INF/defs/administrator.xml</value> <value>/WEB-INF/defs/customer.xml</value> <value>/WEB-INF/defs/templates.xml</value> </list> </property> </bean>
As you can see, there are five files containing definitions, which are all located in
the 'WEB-INF/defs'
directory. At initialization of the WebApplicationContext
, the
files will be loaded and the definitions factory will be initialized. After that has
been done, the Tiles includes in the definition files can be used as views within your
Spring web application. To be able to use the views you have to have a ViewResolver
just as with any other view technology used with Spring. Below you can find two
possibilities, the UrlBasedViewResolver
and the ResourceBundleViewResolver
.
You can specify locale specific Tiles definitions by adding an underscore and then the locale. For example:
<bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles3.TilesConfigurer"> <property name="definitions"> <list> <value>/WEB-INF/defs/tiles.xml</value> <value>/WEB-INF/defs/tiles_fr_FR.xml</value> </list> </property> </bean>
With this configuration, tiles_fr_FR.xml
will be used for requests with the fr_FR
locale,
and tiles.xml
will be used by default.
![]() | Note |
---|---|
Since underscores are used to indicate locales, it is recommended to avoid using them otherwise in the file names for Tiles definitions. |
The UrlBasedViewResolver
instantiates the given viewClass
for each view it has to
resolve.
<bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.tiles3.TilesView"/> </bean>
The ResourceBundleViewResolver
has to be provided with a property file containing
viewnames and viewclasses the resolver can use:
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> </bean>
... welcomeView.(class)=org.springframework.web.servlet.view.tiles3.TilesView welcomeView.url=welcome (this is the name of a Tiles definition) vetsView.(class)=org.springframework.web.servlet.view.tiles3.TilesView vetsView.url=vetsView (again, this is the name of a Tiles definition) findOwnersForm.(class)=org.springframework.web.servlet.view.JstlView findOwnersForm.url=/WEB-INF/jsp/findOwners.jsp ...
As you can see, when using the ResourceBundleViewResolver
, you can easily mix
different view technologies.
Note that the TilesView
class supports JSTL (the JSP Standard Tag Library) out of the
box.
As an advanced feature, Spring also supports two special Tiles PreparerFactory
implementations. Check out the Tiles documentation for details on how to use
ViewPreparer
references in your Tiles definition files.
Specify SimpleSpringPreparerFactory
to autowire ViewPreparer instances based on
specified preparer classes, applying Spring’s container callbacks as well as applying
configured Spring BeanPostProcessors. If Spring’s context-wide annotation-config has
been activated, annotations in ViewPreparer classes will be automatically detected and
applied. Note that this expects preparer classes in the Tiles definition files, just
like the default PreparerFactory
does.
Specify SpringBeanPreparerFactory
to operate on specified preparer names instead
of classes, obtaining the corresponding Spring bean from the DispatcherServlet’s
application context. The full bean creation process will be in the control of the Spring
application context in this case, allowing for the use of explicit dependency injection
configuration, scoped beans etc. Note that you need to define one Spring bean definition
per preparer name (as used in your Tiles definitions).
<bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles3.TilesConfigurer"> <property name="definitions"> <list> <value>/WEB-INF/defs/general.xml</value> <value>/WEB-INF/defs/widgets.xml</value> <value>/WEB-INF/defs/administrator.xml</value> <value>/WEB-INF/defs/customer.xml</value> <value>/WEB-INF/defs/templates.xml</value> </list> </property> <!-- resolving preparer names as Spring bean definition names --> <property name="preparerFactoryClass" value="org.springframework.web.servlet.view.tiles3.SpringBeanPreparerFactory"/> </bean>
XSLT is a transformation language for XML and is popular as a view technology within web applications. XSLT can be a good choice as a view technology if your application naturally deals with XML, or if your model can easily be converted to XML. The following section shows how to produce an XML document as model data and have it transformed with XSLT in a Spring Web MVC application.
This example is a trivial Spring application that creates a list of words in the
Controller
and adds them to the model map. The map is returned along with the view
name of our XSLT view. See Section 21.3, “Implementing Controllers” for details of Spring Web MVC’s
Controller
interface. The XSLT Controller will turn the list of words into a simple XML
document ready for transformation.
Configuration is standard for a simple Spring application.
The MVC configuration has to define a XsltViewResolver
bean and
regular MVC annotation configuration.
@EnableWebMvc @ComponentScan @Configuration public class WebConfig extends WebMvcConfigurerAdapter { @Bean public XsltViewResolver xsltViewResolver() { XsltViewResolver viewResolver = new XsltViewResolver(); viewResolver.setPrefix("/WEB-INF/xsl/"); viewResolver.setSuffix(".xslt"); return viewResolver; } }
And we need a Controller that encapsulates our word generation logic.
The controller logic is encapsulated in a @Controller
class, with the
handler method being defined like so…
@Controller public class XsltController { @RequestMapping("/") public String home(Model model) throws Exception { Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument(); Element root = document.createElement("wordList"); List<String> words = Arrays.asList("Hello", "Spring", "Framework"); for (String word : words) { Element wordNode = document.createElement("word"); Text textNode = document.createTextNode(word); wordNode.appendChild(textNode); root.appendChild(wordNode); } model.addAttribute("wordList", root); return "home"; } }
So far we’ve only created a DOM document and added it to the Model map. Note that you
can also load an XML file as a Resource
and use it instead of a custom DOM document.
Of course, there are software packages available that will automatically 'domify' an object graph, but within Spring, you have complete flexibility to create the DOM from your model in any way you choose. This prevents the transformation of XML playing too great a part in the structure of your model data which is a danger when using tools to manage the domification process.
Next, XsltViewResolver
will resolve the "home" XSLT template file and merge the
DOM document into it to generate our view.
Finally, the XsltViewResolver
will resolve the "home" XSLT template file and merge the
DOM document into it to generate our view. As shown in the XsltViewResolver
configuration, XSLT templates live in the war file in the 'WEB-INF/xsl'
directory
and end with a "xslt"
file extension.
<?xml version="1.0" encoding="utf-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="html" omit-xml-declaration="yes"/> <xsl:template match="/"> <html> <head><title>Hello!</title></head> <body> <h1>My First Words</h1> <ul> <xsl:apply-templates/> </ul> </body> </html> </xsl:template> <xsl:template match="word"> <li><xsl:value-of select="."/></li> </xsl:template> </xsl:stylesheet>
This is rendered as:
<html> <head> <META http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Hello!</title> </head> <body> <h1>My First Words</h1> <ul> <li>Hello</li> <li>Spring</li> <li>Framework</li> </ul> </body> </html>
Returning an HTML page isn’t always the best way for the user to view the model output, and Spring makes it simple to generate a PDF document or an Excel spreadsheet dynamically from the model data. The document is the view and will be streamed from the server with the correct content type to (hopefully) enable the client PC to run their spreadsheet or PDF viewer application in response.
In order to use Excel views, you need to add the 'poi' library to your classpath, and for PDF generation, the iText library.
Document based views are handled in an almost identical fashion to XSLT views, and the following sections build upon the previous one by demonstrating how the same controller used in the XSLT example is invoked to render the same model as both a PDF document and an Excel spreadsheet (which can also be viewed or manipulated in Open Office).
First, let’s amend the views.properties file (or xml equivalent) and add a simple view definition for both document types. The entire file now looks like this with the XSLT view shown from earlier:
home.(class)=xslt.HomePage home.stylesheetLocation=/WEB-INF/xsl/home.xslt home.root=words xl.(class)=excel.HomePage pdf.(class)=pdf.HomePage
If you want to start with a template spreadsheet or a fillable PDF form to add your model data to, specify the location as the 'url' property in the view definition
The controller code we’ll use remains exactly the same from the XSLT example earlier other than to change the name of the view to use. Of course, you could be clever and have this selected based on a URL parameter or some other logic - proof that Spring really is very good at decoupling the views from the controllers!
Exactly as we did for the XSLT example, we’ll subclass suitable abstract classes in
order to implement custom behavior in generating our output documents. For Excel, this
involves writing a subclass of
org.springframework.web.servlet.view.document.AbstractExcelView
(for Excel files
generated by POI) or org.springframework.web.servlet.view.document.AbstractJExcelView
(for JExcelApi-generated Excel files) and implementing the buildExcelDocument()
method.
Here’s the complete listing for our POI Excel view which displays the word list from the model map in consecutive rows of the first column of a new spreadsheet:
package excel; // imports omitted for brevity public class HomePage extends AbstractExcelView { protected void buildExcelDocument(Map model, HSSFWorkbook wb, HttpServletRequest req, HttpServletResponse resp) throws Exception { HSSFSheet sheet; HSSFRow sheetRow; HSSFCell cell; // Go to the first sheet // getSheetAt: only if wb is created from an existing document // sheet = wb.getSheetAt(0); sheet = wb.createSheet("Spring"); sheet.setDefaultColumnWidth((short) 12); // write a text at A1 cell = getCell(sheet, 0, 0); setText(cell, "Spring-Excel test"); List words = (List) model.get("wordList"); for (int i=0; i < words.size(); i++) { cell = getCell(sheet, 2+i, 0); setText(cell, (String) words.get(i)); } } }
And the following is a view generating the same Excel file, now using JExcelApi:
package excel; // imports omitted for brevity public class HomePage extends AbstractJExcelView { protected void buildExcelDocument(Map model, WritableWorkbook wb, HttpServletRequest request, HttpServletResponse response) throws Exception { WritableSheet sheet = wb.createSheet("Spring", 0); sheet.addCell(new Label(0, 0, "Spring-Excel test")); List words = (List) model.get("wordList"); for (int i = 0; i < words.size(); i++) { sheet.addCell(new Label(2+i, 0, (String) words.get(i))); } } }
Note the differences between the APIs. We’ve found that the JExcelApi is somewhat more intuitive, and furthermore, JExcelApi has slightly better image-handling capabilities. There have been memory problems with large Excel files when using JExcelApi however.
If you now amend the controller such that it returns xl
as the name of the view (
return new ModelAndView("xl", map);
) and run your application again, you should find
that the Excel spreadsheet is created and downloaded automatically when you request the
same page as before.
The PDF version of the word list is even simpler. This time, the class extends
org.springframework.web.servlet.view.document.AbstractPdfView
and implements the
buildPdfDocument()
method as follows:
package pdf; // imports omitted for brevity public class PDFPage extends AbstractPdfView { protected void buildPdfDocument(Map model, Document doc, PdfWriter writer, HttpServletRequest req, HttpServletResponse resp) throws Exception { List words = (List) model.get("wordList"); for (int i=0; i<words.size(); i++) { doc.add( new Paragraph((String) words.get(i))); } } }
Once again, amend the controller to return the pdf
view with return new
ModelAndView("pdf", map);
, and reload the URL in your application. This time a PDF
document should appear listing each of the words in the model map.
JasperReports ( http://jasperreports.sourceforge.net) is a powerful open-source reporting engine that supports the creation of report designs using an easily understood XML file format. JasperReports is capable of rendering reports in four different formats: CSV, Excel, HTML and PDF.
Your application will need to include the latest release of JasperReports, which at the time of writing was 0.6.1. JasperReports itself depends on the following projects:
JasperReports also requires a JAXP compliant XML parser.
To configure JasperReports views in your Spring container configuration you need to
define a ViewResolver
to map view names to the appropriate view class depending on
which format you want your report rendered in.
Typically, you will use the ResourceBundleViewResolver
to map view names to view
classes and files in a properties file.
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> </bean>
Here we’ve configured an instance of the ResourceBundleViewResolver
class that will
look for view mappings in the resource bundle with base name views
. (The content of
this file is described in the next section.)
The Spring Framework contains five different View
implementations for JasperReports,
four of which correspond to one of the four output formats supported by JasperReports,
and one that allows for the format to be determined at runtime:
Table 22.2. JasperReports View classes
Class Name | Render Format |
---|---|
| CSV |
| HTML |
| |
| Microsoft Excel |
| The view is decided upon at runtime |
Mapping one of these classes to a view name and a report file is a matter of adding the appropriate entries in the resource bundle configured in the previous section as shown here:
simpleReport.(class)=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper
Here you can see that the view with name simpleReport
is mapped to the
JasperReportsPdfView
class, causing the output of this report to be rendered in PDF
format. The url
property of the view is set to the location of the underlying report
file.
JasperReports has two distinct types of report file: the design file, which has a
.jrxml
extension, and the compiled report file, which has a .jasper
extension.
Typically, you use the JasperReports Ant task to compile your .jrxml
design file into
a .jasper
file before deploying it into your application. With the Spring Framework
you can map either of these files to your report file and the framework will take care
of compiling the .jrxml
file on the fly for you. You should note that after a .jrxml
file is compiled by the Spring Framework, the compiled report is cached for the lifetime
of the application. Thus, to make changes to the file you will need to restart your
application.
The JasperReportsMultiFormatView
allows for the report format to be specified at
runtime. The actual rendering of the report is delegated to one of the other
JasperReports view classes - the JasperReportsMultiFormatView
class simply adds a
wrapper layer that allows for the exact implementation to be specified at runtime.
The JasperReportsMultiFormatView
class introduces two concepts: the format key and the
discriminator key. The JasperReportsMultiFormatView
class uses the mapping key to look
up the actual view implementation class, and it uses the format key to lookup up the
mapping key. From a coding perspective you add an entry to your model with the format
key as the key and the mapping key as the value, for example:
public ModelAndView handleSimpleReportMulti(HttpServletRequest request, HttpServletResponse response) throws Exception { String uri = request.getRequestURI(); String format = uri.substring(uri.lastIndexOf(".") + 1); Map model = getModel(); model.put("format", format); return new ModelAndView("simpleReportMulti", model); }
In this example, the mapping key is determined from the extension of the request URI and
is added to the model under the default format key: format
. If you wish to use a
different format key then you can configure this using the formatKey
property of the
JasperReportsMultiFormatView
class.
By default the following mapping key mappings are configured in
JasperReportsMultiFormatView
:
Table 22.3. JasperReportsMultiFormatView Default Mapping Key Mappings
Mapping Key | View Class |
---|---|
csv |
|
html |
|
| |
xls |
|
So in the example above a request to URI /foo/myReport.pdf would be mapped to the
JasperReportsPdfView
class. You can override the mapping key to view class mappings
using the formatMappings
property of JasperReportsMultiFormatView
.
In order to render your report correctly in the format you have chosen, you must supply
Spring with all of the data needed to populate your report. For JasperReports this means
you must pass in all report parameters along with the report datasource. Report
parameters are simple name/value pairs and can be added to the Map
for your model as
you would add any name/value pair.
When adding the datasource to the model you have two approaches to choose from. The
first approach is to add an instance of JRDataSource
or a Collection
type to the
model Map
under any arbitrary key. Spring will then locate this object in the model
and treat it as the report datasource. For example, you may populate your model like so:
private Map getModel() { Map model = new HashMap(); Collection beanData = getBeanData(); model.put("myBeanData", beanData); return model; }
The second approach is to add the instance of JRDataSource
or Collection
under a
specific key and then configure this key using the reportDataKey
property of the view
class. In both cases Spring will wrap instances of Collection
in a
JRBeanCollectionDataSource
instance. For example:
private Map getModel() { Map model = new HashMap(); Collection beanData = getBeanData(); Collection someData = getSomeData(); model.put("myBeanData", beanData); model.put("someData", someData); return model; }
Here you can see that two Collection
instances are being added to the model. To ensure
that the correct one is used, we simply modify our view configuration as appropriate:
simpleReport.(class)=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper simpleReport.reportDataKey=myBeanData
Be aware that when using the first approach, Spring will use the first instance of
JRDataSource
or Collection
that it encounters. If you need to place multiple
instances of JRDataSource
or Collection
into the model you need to use the second
approach.
JasperReports provides support for embedded sub-reports within your master report files. There are a wide variety of mechanisms for including sub-reports in your report files. The easiest way is to hard code the report path and the SQL query for the sub report into your design files. The drawback of this approach is obvious: the values are hard-coded into your report files reducing reusability and making it harder to modify and update report designs. To overcome this you can configure sub-reports declaratively, and you can include additional data for these sub-reports directly from your controllers.
To control which sub-report files are included in a master report using Spring, your report file must be configured to accept sub-reports from an external source. To do this you declare a parameter in your report file like so:
<parameter name="ProductsSubReport" class="net.sf.jasperreports.engine.JasperReport"/>
Then, you define your sub-report to use this sub-report parameter:
<subreport> <reportElement isPrintRepeatedValues="false" x="5" y="25" width="325" height="20" isRemoveLineWhenBlank="true" backcolor="#ffcc99"/> <subreportParameter name="City"> <subreportParameterExpression><![CDATA[$F{city}]]></subreportParameterExpression> </subreportParameter> <dataSourceExpression><![CDATA[$P{SubReportData}]]></dataSourceExpression> <subreportExpression class="net.sf.jasperreports.engine.JasperReport"> <![CDATA[$P{ProductsSubReport}]]></subreportExpression> </subreport>
This defines a master report file that expects the sub-report to be passed in as an
instance of net.sf.jasperreports.engine.JasperReports
under the parameter
ProductsSubReport
. When configuring your Jasper view class, you can instruct Spring to
load a report file and pass it into the JasperReports engine as a sub-report using the
subReportUrls
property:
<property name="subReportUrls"> <map> <entry key="ProductsSubReport" value="/WEB-INF/reports/subReportChild.jrxml"/> </map> </property>
Here, the key of the Map
corresponds to the name of the sub-report parameter in the
report design file, and the entry is the URL of the report file. Spring will load this
report file, compiling it if necessary, and pass it into the JasperReports engine under
the given key.
This step is entirely optional when using Spring to configure your sub-reports. If you
wish, you can still configure the data source for your sub-reports using static queries.
However, if you want Spring to convert data returned in your ModelAndView
into
instances of JRDataSource
then you need to specify which of the parameters in your
ModelAndView
Spring should convert. To do this, configure the list of parameter names
using the subReportDataKeys
property of your chosen view class:
<property name="subReportDataKeys" value="SubReportData"/>
Here, the key you supply must correspond to both the key used in your ModelAndView
and the key used in your report design file.
If you have special requirements for exporter configuration — perhaps you want a
specific page size for your PDF report — you can configure these exporter parameters
declaratively in your Spring configuration file using the exporterParameters
property
of the view class. The exporterParameters
property is typed as a Map
. In your
configuration the key of an entry should be the fully-qualified name of a static field
that contains the exporter parameter definition, and the value of an entry should be the
value you want to assign to the parameter. An example of this is shown below:
<bean id="htmlReport" class="org.springframework.web.servlet.view.jasperreports.JasperReportsHtmlView"> <property name="url" value="/WEB-INF/reports/simpleReport.jrxml"/> <property name="exporterParameters"> <map> <entry key="net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER"> <value>Footer by Spring! </td><td width="50%">&nbsp; </td></tr> </table></body></html> </value> </entry> </map> </property> </bean>
Here you can see that the JasperReportsHtmlView
is configured with an exporter
parameter for net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER
which will output a footer in the resulting HTML.
Both AbstractAtomFeedView
and AbstractRssFeedView
inherit from the base class
AbstractFeedView
and are used to provide Atom and RSS Feed views respectfully. They
are based on java.net’s ROME project and are located in the
package org.springframework.web.servlet.view.feed
.
AbstractAtomFeedView
requires you to implement the buildFeedEntries()
method and
optionally override the buildFeedMetadata()
method (the default implementation is
empty), as shown below.
public class SampleContentAtomView extends AbstractAtomFeedView { @Override protected void buildFeedMetadata(Map<String, Object> model, Feed feed, HttpServletRequest request) { // implementation omitted } @Override protected List<Entry> buildFeedEntries(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception { // implementation omitted } }
Similar requirements apply for implementing AbstractRssFeedView
, as shown below.
public class SampleContentAtomView extends AbstractRssFeedView { @Override protected void buildFeedMetadata(Map<String, Object> model, Channel feed, HttpServletRequest request) { // implementation omitted } @Override protected List<Item> buildFeedItems(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception { // implementation omitted } }
The buildFeedItems()
and buildFeedEntires()
methods pass in the HTTP request in case
you need to access the Locale. The HTTP response is passed in only for the setting of
cookies or other HTTP headers. The feed will automatically be written to the response
object after the method returns.
For an example of creating an Atom view please refer to Alef Arendsen’s Spring Team Blog entry.
The MappingJackson2JsonView
uses the Jackson library’s ObjectMapper
to render the response
content as JSON. By default, the entire contents of the model map (with the exception of
framework-specific classes) will be encoded as JSON. For cases where the contents of the
map need to be filtered, users may specify a specific set of model attributes to encode
via the RenderedAttributes
property. The extractValueFromSingleKeyModel
property may
also be used to have the value in single-key models extracted and serialized directly
rather than as a map of model attributes.
JSON mapping can be customized as needed through the use of Jackson’s provided
annotations. When further control is needed, a custom ObjectMapper
can be injected
through the ObjectMapper
property for cases where custom JSON
serializers/deserializers need to be provided for specific types.
JSONP is supported and automatically enabled when
the request has a query parameter named jsonp
or callback
. The JSONP query parameter
name(s) could be customized through the jsonpParameterNames
property.
The MappingJackson2XmlView
uses the
Jackson XML extension's XmlMapper
to render the response content as XML. If the model contains multiples entries, the
object to be serialized should be set explicitly using MappingJackson2XmlView’s
`modelKey
bean property. If the model contains a single entry, it will be serialized
automatically.
XML mapping can be customized as needed through the use of JAXB or Jackson’s provided
annotations. When further control is needed, a custom XmlMapper
can be injected
through the ObjectMapper
property for cases where custom XML
serializers/deserializers need to be provided for specific types.