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Using Freemarker Templates
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Added by Musachy Barroso, last edited by Musachy Barroso on Feb 09, 2007 (view change)

FreeMarker is a Java-based template engine that is a great alternative to JSP. FreeMarker is ideal for situations where your action results can possibly be loaded from outside a Servlet container. For example, if you wished to support plugins in your application, you might wish to use FreeMarker so that the plugins could provide the entire action class and view in a single jar that is loaded from the classloader.

- Configure your action to use the "freemarker" result type
- Using properties
- Servlet / JSP Scoped Objects
  - Application Scope Attribute
  - Session Scope Attribute
  - Request Scope Attribute
  - Request Parameter
  - Context parameter
- Template Loading
- Variable Resolution
- FreeMarker configuration
- Tags
  - Using Struts tags
  - Using JSP tags
- Tips and Tricks
  - Type Conversion and Locales
  - String and Non String Values on tags
  - Extending
- FreeMarker alternative syntax
- FreeMarker links

## Configure your action to use the "freemarker" result type

Struts provides a result type "freemarker" which renders a FreeMarker template. This result type is defined in `struts-default.xml`. To create pages using FreeMarker, set the result type of the actions to "freemarker".

    <include file="struts-default.xml"/>
    ...
    <action name="test" class="package.Test">
      <result type="freemarker">/WEB-INF/views/testView.ftl</result>
    </action>
    ...

## Using properties

FreeMarker uses the ${...} notation to access properties. They are called interpolations. Properties on the actions (getter methods) will automatically be available on the FreeMarker templates. If an action has a "getName()" method, then its value can be inserted on the template like:

    Your name is: ${name}

| Be Careful By default, FreeMarker will throw an error if it finds a variable that is not defined, or has a null value. See this FAQ for details.

## Servlet / JSP Scoped Objects

The following are ways to obtained Application scope attributes, Session scope attributes, Request scope attributes, Request parameters, and framework Context scope parameters:-

### Application Scope Attribute

Assuming there's an attribute with name `myApplicationAttribute` in the Application scope.

    <#if Application.myApplicationAttribute?exists>
         ${Application.myApplicationAttribute}
    </#if>

or

    <@s.property value="%{#application.myApplicationAttribute}" />

### Session Scope Attribute

Assuming there's an attribute with name `mySessionAttribute` in the Session scope.

    <#if Session.mySessionAttribute?exists>
         ${Session.mySessionAttribute}
    </#if>

or

    <@s.property value="%{#session.mySessionAttribute}" />

### Request Scope Attribute

Assuming there's an attribute with name 'myRequestAttribute' in the Request scope.

    <#if Request.myRequestAttribute?exists>
          ${Request.myRequestAttribute}
    </#if>

or

    <@s.property value="%{#request.myRequestAttribute}" />

### Request Parameter

Assuming there's a request parameter myParameter (eg. http://host/myApp/myAction.action?myParameter=one).

    <#if Parameters.myParameter?exists>
         ${Parameters.myParameter}
    </#if>

or

    <@s.property value="%{#parameters.myParameter}" />

### Context parameter

Assuming there's a parameter with the name myContextParam in framework context.

    ${stack.findValue('#myContextParam')}

or

    <@s.property value="%{#myContextParam}" />

## Template Loading

The framework looks for FreeMarker templates in two locations (in this order):

1. Web application
2. Class path

This ordering makes it ideal for providing templates inside a fully-built jar, but allowing for overrides of those templates to be defined in your web application. In fact, this is how you can override the default UI tags and Form Tags included with the framework.

In addition, you can specify a location (directory on your file system) through the `templatePath` or `TemplatePath` context variable (in the `web.xml`. If a variable is specified, the content of the directory it points to will be searched first.

| This variable is currently NOT relative to the root of your application.

If a property is defined on the template with the same name as a property on the action, FreeMarker will use the property defined on the template.

## Variable Resolution

When using FreeMarker with the framework, variables are looked up in several different places, in this order:

1. Built-in variables
2. Value stack
3. Action context
4. Request scope
5. Session scope
6. Application scope

Note that the action context is looked up after the value stack. This means that you can reference the variable without the typical preceding has marker (#) like you would have to when using the JSP `s:property` tag. This is a nice convenience, though be careful because there is a small chance it could trip you up.

    <@s.url id="url" value="http://www.yahoo.com"/>
    Click <a xhref="${url}">here</a>!

The built-in variables that Struts-FreeMarker integration provides are:

Name | Description
--- | ---
stack | The value stack itself, useful for calls like ${stack.findString('ognl expr')}
action | The action most recently executed
response | The HttpServletResponse
res | Same as response
request | The HttpServletRequest
req | Same as request
session | The HttpSession
application | The ServletContext
base | The request's context path

## FreeMarker configuration

To configure the FreeMarker engine, just add a file `freemarker.properties` to the classpath. The supported properties are those that the FreeMarker Configuration object expects, see FreeMarker's documentation for more details.

freemarker.properties example

    default_encoding=ISO-8859-1
    template_update_delay=5
    locale=no_NO

## Tags

### Using Struts tags

Tags distributed with Struts are automatically made available to FreeMarker templates. To use any tag add "`@s.`" in front of the tag name. Like:

Using Struts tags on FreeMarker templates

    <@s.if test="printName">
        <@s.property value="myBeanProperty" />
    </@s.if>

### Using JSP tags

To use JSP tags that are not part of Struts you have to:

1. Add JspSupportSerlvet to web.xml

Adding JspSupportSerlvet to web.xml

    <servlet>
        <servlet-name>JspSupportServlet</servlet-name>
        <servlet-class>org.apache.struts2.views.JspSupportServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

2. Declare the tld on web.xml or use FreeMarker's "`assign`" directive. When using the "`assign`" directive, provide the absolute path to the tld file.

Using JSP tags on FreeMarker templates

    <#assign ex=JspTaglibs["/WEB-INF/example.tld"] />

    <@ex.mytag text="hello" />

## Tips and Tricks

There are some advanced features that may be useful when building Struts applications with FreeMarker.

### Type Conversion and Locales

FreeMarker has built in support for formatting dates and numbers. The formatting rules are based on the locale associated with the action request, which is by default set in struts.properties but can be over-ridden using the I18n Interceptor. This is normally perfect for your needs, but it is important to remember that these formatting rules are handled by FreeMarker and not by the framework's Type Conversion support.

If you want the framework to handle the formatting according to the Type Conversion you have specified, you shouldn't use the normal ${...} syntax. Instead, you should use the property tag. The difference is that the property tag is specifically designed to take an OGNL expression, evaluate it, and then convert it to a String using any Type Conversion rules you have specified. The normal ${...} syntax will use a FreeMarker expression language, evaluate it, and then convert it to a String using the built in formatting rules.

| The difference in how type conversion is handled under Freemarker is subtle but important to understand.

### String and Non String Values on tags

In FreeMarker it is incorrect to quote non string values. If a value is quoted, then an string will be passed, instead of the expected object, causing an exception. For example, the "textarea" tag expects the attributes "rows" and "cols" of type Integer:

Do not quote non string values in tag attributes!

    <@s.textarea rows=5 cols=40 />

### Extending

Sometimes you may with to extend the framework's FreeMarker support. For example, you might want to extend the Struts tags that come bundled with the framework.

To extend the Freemarker support, develop a class that extends `org.apache.struts2.views.freemarker.FreemarkerManager`, overriding methods as needed, and plugin the class through the struts.properties:

    struts.freemarker.manager.classname = com.yourcompany.YourFreeMarkerManager

## FreeMarker alternative syntax

FreeMarker by default uses the "<#directive />" syntax. FreeMarker supports an alternative syntax, where [ and ] are used instead of < and >. To enable the alternative syntax, add ftl at the beginning of the template. The alternative syntax makes it easier to differentiate between FreeMarker directives, and JSP or HTML tags.

Use alternative syntax

    [#ftl]
    <html>
       <head>FreeMarker Example</head>

       <body>
           <h1>Alternative Syntax</h1>
           [@s.if test="printName"]
              [@s.property value="myBeanProperty" /]
           [/@s.if]
       </body>
    </html>

## FreeMarker links

- Home Page
- Documentation
- IDE Integration