FreeMarker
Apache FreeMarker is a template engine for generating any kind of text output from HTML to email and others. The Spring Framework has built-in integration for using Spring MVC with FreeMarker templates.
View Configuration
The following example shows how to configure FreeMarker as a view technology:
-
Java
-
Kotlin
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureViewResolvers(ViewResolverRegistry registry) {
registry.freeMarker();
}
// Configure FreeMarker...
@Bean
public FreeMarkerConfigurer freeMarkerConfigurer() {
FreeMarkerConfigurer configurer = new FreeMarkerConfigurer();
configurer.setTemplateLoaderPath("/WEB-INF/freemarker");
return configurer;
}
}
@Configuration
@EnableWebMvc
class WebConfig : WebMvcConfigurer {
override fun configureViewResolvers(registry: ViewResolverRegistry) {
registry.freeMarker()
}
// Configure FreeMarker...
@Bean
fun freeMarkerConfigurer() = FreeMarkerConfigurer().apply {
setTemplateLoaderPath("/WEB-INF/freemarker")
}
}
The following example shows how to configure the same in XML:
<mvc:annotation-driven/>
<mvc:view-resolvers>
<mvc:freemarker/>
</mvc:view-resolvers>
<!-- Configure FreeMarker... -->
<mvc:freemarker-configurer>
<mvc:template-loader-path location="/WEB-INF/freemarker"/>
</mvc:freemarker-configurer>
Alternatively, you can also declare the FreeMarkerConfigurer
bean for full control over all
properties, as the following example shows:
<bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer">
<property name="templateLoaderPath" value="/WEB-INF/freemarker/"/>
</bean>
Your templates need to be stored in the directory specified by the FreeMarkerConfigurer
shown in the preceding example. Given the preceding configuration, if your controller
returns a view name of welcome
, the resolver looks for the
/WEB-INF/freemarker/welcome.ftl
template.
FreeMarker Configuration
You can pass FreeMarker 'Settings' and 'SharedVariables' directly to the FreeMarker
Configuration
object (which is 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
. The following example shows how to use a FreeMarkerConfigurer
:
<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.
Form Handling
Spring provides a tag library for use in JSPs that contains, among others, a
<spring:bind/>
element. This element primarily lets forms display values from
form-backing objects and show the results of failed validations from a Validator
in the
web or business tier. Spring also has support for the same functionality in FreeMarker,
with additional convenience macros for generating form input elements themselves.
The Bind Macros
A standard set of macros are maintained within the spring-webmvc.jar
file for
FreeMarker, so they are always available to a suitably configured application.
Some of the macros defined in the Spring templating 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 directly call from within your templates. If you wish to view the macro code
directly, the file is called spring.ftl
and is in the
org.springframework.web.servlet.view.freemarker
package.
Simple Binding
In your HTML forms based on FreeMarker templates that act as a form view for a Spring MVC
controller, you can use code similar to the next example to bind to field values and
display error messages for each input field in similar fashion to the JSP equivalent. The
following example shows a personForm
view:
<!-- 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 "personForm.name"/>
<input type="text"
name="${spring.status.expression}"
value="${spring.status.value?html}"/><br />
<#list spring.status.errorMessages as error> <b>${error}</b> <br /> </#list>
<br />
...
<input type="submit" value="submit"/>
</form>
...
</html>
<@spring.bind>
requires a 'path' argument, which consists of the name of your command
object (it is 'command', unless you changed it in your controller configuration) followed
by a period and the name of the field on the command object to which you wish to bind. You
can also use nested fields, such as command.address.street
. The bind
macro assumes the
default HTML escaping behavior specified by the ServletContext
parameter
defaultHtmlEscape
in web.xml
.
An alternative form of the macro called <@spring.bindEscaped>
takes a second argument
that explicitly specifies whether HTML escaping should be used in the status error
messages or values. You can set it to true
or false
as required. Additional form
handling macros simplify the use of HTML escaping, and you should use these macros
wherever possible. They are explained in the next section.
Input Macros
Additional convenience macros for FreeMarker simplify both binding and form generation (including validation error display). It is never necessary to use these macros to generate form input fields, and you can mix and match them with simple HTML or direct calls to the Spring bind macros that we highlighted previously.
The following table of available macros shows the FreeMarker Template (FTL) definitions and the parameter list that each takes:
macro | FTL definition |
---|---|
|
<@spring.message code/> |
|
<@spring.messageText code, text/> |
|
<@spring.url relativeUrl/> |
|
<@spring.formInput path, attributes, fieldType/> |
|
<@spring.formHiddenInput path, attributes/> |
|
<@spring.formPasswordInput path, attributes/> |
|
<@spring.formTextarea path, attributes/> |
|
<@spring.formSingleSelect path, options, attributes/> |
|
<@spring.formMultiSelect path, options, attributes/> |
|
<@spring.formRadioButtons path, options separator, attributes/> |
|
<@spring.formCheckboxes path, options, separator, attributes/> |
|
<@spring.formCheckbox path, attributes/> |
|
<@spring.showErrors separator, classOrStyle/> |
In FreeMarker templates, formHiddenInput and formPasswordInput are not actually
required, as you can use the normal formInput macro, specifying hidden or password
as the value for the fieldType parameter.
|
The parameters to any of the above macros have consistent meanings:
-
path
: The name of the field to bind to (for example, "command.name") -
options
: AMap
of all the available values that can be selected from in the input field. The keys to the map represent the values that are POSTed back from the form and bound to the command object. Map objects stored against the keys are the labels displayed on the form to the user and may be different from the corresponding values posted back by the form. Usually, such a map is supplied as reference data by the controller. You can use anyMap
implementation, depending on required behavior. For strictly sorted maps, you can use aSortedMap
(such as aTreeMap
) with a suitableComparator
and, for arbitrary Maps that should return values in insertion order, use aLinkedHashMap
or aLinkedMap
fromcommons-collections
. -
separator
: Where multiple options are available as discreet elements (radio buttons or checkboxes), the sequence of characters used to separate each one in the list (such as<br>
). -
attributes
: An additional string of arbitrary tags or text to be included within the HTML tag itself. This string is echoed literally by the macro. For example, in atextarea
field, you may supply attributes (such as 'rows="5" cols="60"'), or you could pass style information such as 'style="border:1px solid silver"'. -
classOrStyle
: For theshowErrors
macro, the name of the CSS class that thespan
element that wraps each error uses. If no information is supplied (or the value is empty), the errors are wrapped in<b></b>
tags.
The following sections outline examples of the macros.
Input Fields
The formInput
macro takes the path
parameter (command.name
) and an additional attributes
parameter (which is empty in the upcoming example). 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 does not need to pass the
path parameter again — it operates on the field for which a binding was last created.
The showErrors
macro takes a separator parameter (the characters that are 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 can specify default
values for the attributes parameter. The following example shows how to use the formInput
and showErrors
macros:
<@spring.formInput "command.name"/>
<@spring.showErrors "<br>"/>
The next example shows the output 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 resembles the following example:
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
) is used to pass style
information or rows
and cols
attributes for the textarea
.
Selection Fields
You can use four selection field macros to generate common UI value selection inputs in your HTML forms:
-
formSingleSelect
-
formMultiSelect
-
formRadioButtons
-
formCheckboxes
Each of the four macros accepts a Map
of options that contains the value for the form
field and the label that corresponds to that value. The value and the label can be the
same.
The next example is for radio buttons in FTL. The form-backing object specifies a default value of 'London' for this field, 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'. The following listing shows the example:
...
Town:
<@spring.formRadioButtons "command.address.town", cityMap, ""/><br><br>
The preceding listing renders a line of radio buttons, one for each value in cityMap
, and uses a
separator of ""
. 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 POST
request parameters. The map values are the
labels that the user sees. In the preceding example, given a list of three well known cities
and a default value in the form backing object, the HTML resembles the following:
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), you can create the map of codes with suitable keys, as the following example shows:
-
Java
-
Kotlin
protected Map<String, ?> referenceData(HttpServletRequest request) throws Exception {
Map<String, String> cityMap = new LinkedHashMap<>();
cityMap.put("LDN", "London");
cityMap.put("PRS", "Paris");
cityMap.put("NYC", "New York");
Map<String, Object> model = new HashMap<>();
model.put("cityMap", cityMap);
return model;
}
protected fun referenceData(request: HttpServletRequest): Map<String, *> {
val cityMap = linkedMapOf(
"LDN" to "London",
"PRS" to "Paris",
"NYC" to "New York"
)
return hashMapOf("cityMap" to cityMap)
}
The code now produces output where the radio values are the relevant codes, but the user still sees the more user-friendly city names, as follows:
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>
HTML Escaping
Default usage of the form macros described earlier results in HTML elements that are HTML 4.01
compliant and that use the default value for HTML escaping defined in your web.xml
file, as
used by Spring’s bind support. To make the elements be XHTML compliant or to override
the default HTML escaping value, you can specify two variables in your template (or in
your model, where they are 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 or context variable named xhtmlCompliant
, as the following example shows:
<#-- for FreeMarker -->
<#assign xhtmlCompliant = true>
After processing this directive, any elements generated by the Spring macros are now XHTML compliant.
In similar fashion, you can specify HTML escaping per field, as the following example shows:
<#-- until this point, default HTML escaping is used -->
<#assign htmlEscape = true>
<#-- 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 -->