REST Plugin

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Table of Contents
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Overview

The REST Plugin

Excerpt

simplifies REST-style resources to be consumed by both human and machine clients

. The goals are to 100% follow Ruby on Rails-style REST URL conventions and enable XML-free resource development. It builds on the Convention Plugin to support automatic configuration of both actions and results.

provides high level support for the implementation of RESTful resource based web applications

. The REST plugin can cooperate with the Convention Plugin to support a zero configuration approach to declaring your actions and results, but you can always use the REST plugin with XML style configuration if you like.

If you prefer to see a working code example, instead of reading through an explanation, you can download the struts2 sample apps and check out the struts2-rest-showcase application, a complete WAR file, that demonstrates a simple REST web program.

Features

  • Ruby on Rails REST-style URLs
  • Zero XML config when used with Convention Plugin
  • Built-in serialization and deserialization support for XML and JSON
  • Automatic error handling
  • Type-safe configuration of the HTTP response
  • Automatic conditional GET support

Mapping REST URLs to Struts 2 Actions

The main functionality of the REST plugin lies in the interpretation of incoming request URL's according the RESTful rules. In the Struts 2 framework, this 'mapping' of request URL's to Actions is handled by in implementation of the ActionMapper interface. Out of the box, Struts 2 uses the DefaultActionMapper to map URL's to Actions via the logic you are probably already familiar with.

Note

Actions or Controllers? Most Struts 2 developers are familiar with the Action. They are the things that get executed by the incoming requests. In the context of the REST plugin, just to keep you on your toes, we'll adopt the RESTful lingo and refer to our Actions as Controllers. Don't be confused; it's just a name!

The REST plugin provides an alternative implementation, RestActionMapper, that provides the RESTful logic that maps a URL to a give action class ( aka 'controller' in RESTful terms ) and, more specifically, to the invocation of a method on that controller class. The following section, which comes from the Javadoc for the class, details this logic.

RESTful URL Mapping Logic

Wiki Markup
{snippet:url=rest-plugin/src/main/java/org/apache/struts2/rest/RestActionMapper.java|id=description|javadoc=true}

...

HTTP method

URI

Class.method

parameters

GET

/movie

Movie.index

 

POST

/movie

Movie.create

 

PUT

/movie/Thrillers

Movie.update

id="Thrillers"

DELETE

/movie/Thrillers

Movie.destroy

id="Thrillers"

GET

/movie/Thrillers

Movie.show

id="Thrillers"

GET

/movie/Thrillers/edit

Movie.edit

id="Thrillers"

GET

/movie/new

Movie.editNew

 

Content Types

In addition to being a REST-style URL mapper, this plugin provides built-in support for multiple content types, switchable through the URL extension. In this way, a single resource can be exposed as multiple content types without any extra work.For example, by exposing an "orders" resource, clients can immediately access it via:providing mapping of RESTful URL's to Controller ( Action ) invocations, the REST plugin also provides the ability to produce multiple representations of the resource data. By default, the plugin can return the resource in the following content types:

*HTML
*XML
*JSON

There is nothing configure here, just add the conent type extension to your RESTful URL. The framework will take care of the rest. So, for instance, assuming a Controller called Movies and a movie with the id of superman, the following URL's will all hit the

Code Block
http://my.company.com/myapp/ordersmovies/1superman
http://my.company.com/myapp/ordersmovies/1superman.xml
http://my.company.com/myapp/ordersmovies/1superman.xhtml
http://my.company.com/myapp/ordersmovies/1superman.json

The REST plugin automatically handles serialization to, and deserialization from, each format.

Features

  • Fully implements Ruby on Rails REST-style URLs
  • Supports XML-free development, without requiring annotations
  • Built-in serialization and deserialization support for XML and JSON
  • Automatic error handling
  • Type-safe configuration of the HTTP response
  • Automatic conditional GET support

Usage

...

Note

Note, these content types are supported as incoming data types as well. And, if you need, you can extend the functionality by writing your own implementations of org.apache.struts2.rest.handler.ContentTypeHandler and registering them with the system.

Usage

This section will walk you through a quick demo. Here are the steps in the sequence that we will follow.

*Setting Up your Project
*Configuring your Project
*Writing your Controllers

Setting Up

Assuming you have a normal Struts 2 application, all you need to do for this REST demo is to add the following two plugins:

*Struts 2 Rest Plugin
*Struts 2 Convention Plugin

Note, you can download the jars for these plugins from Maven Central

Configuration ( struts.xml )

Just dropping the plugin's into your application may not produce exactly the desired effect. There are a couple of considerations. The first consideration is whether you want to have any non-RESTful URL's coexisting with your RESTful URL's. We'll show two configurations. The first assumes all you want to do is REST. The second assumes you want to keep other non-RESTful URL's alive in the same Struts 2 application.

Note

As with all configuration of Struts 2, we prefer using <constant/> elements in our struts.xml.

REST Only Configuration

Instruct Struts to use the REST action mapper:

Code Block
xml

<constant name="struts.mapper.class" value="rest" />

At this point, the REST mapper has replaced the DefaultActionMapper so all incoming URL's will be interpreted as RESTful URL's.

We're relying on the Convention plugin to find our controllers, so we need to configure the convention plugin a bit:

Code Block
xml

<constant name="struts.convention.action.suffix" value="Controller"/>
<constant name="struts.convention.action.mapAllMatches" value="true"/>
<constant name="struts.convention.default.parent.package" value="rest-default"/>
<constant name="struts.convention.package.locators" value="example"/>
Note

Note, you don't have to use the Convention plugin just to use the REST plugin. The actions of your RESTful application can be defined in XML just as easily as by convention. The REST mapper doesn't care how the application came to know about your actions when it maps a URL to an invocation of one of it's methods.

REST and non-RESTful URL's Together Configuration

If you want to keep using some non-RESTful URL's alongside your REST stuff, then you'll have to provide for a configuration that utilizes to mappers.

Note

Plugins contain their own configuration. If you look in the Rest plugin jar, you'll see the struts-plugin.xml and in that you'll see some configuration settings made by the plugin. Often, the plugin just sets things the way it wants them. You may frequently need to override those settings in your own struts.xml.

First, you'll need to re-assert the extensions that struts knows about because the rest plugin will have thrown out the default action extension.

Code Block
xml

  <constant name="struts.action.extension" value="xhtml,,xml,json,action"/>

Next, we will configure the PrefixBasedActionMapper, which is part of the core Struts 2 distribution, to have some URL's routed to the Rest mapper and others to the default mapper.

Code Block
xml

  <constant name="struts.mapper.class" value="org.apache.struts2.dispatcher.mapper.PrefixBasedActionMapper" />
  <constant name="struts.mapper.prefixMapping" value="/rest:rest,:struts"/>

And, again, we're relying on the Convention plugin to find our controllers, so we need to configure the convention plugin a bit:

Code Block
xml

<constant name="struts.convention.action.suffix" value="Controller"/>
<constant name="struts.convention.action.mapAllMatches" value="true"/>
<constant name="struts.convention.default.parent.package" value="rest-default"/>
<constant name="struts.convention.package.locators" value="example"/>

Write Your Controller Actions

Once everything is configured, you need to create the controllers. Controllers are simply actions created with the purpose of handling requests for a give RESTful resource. As we saw in the mapping logic above, various REST URL's will hit different methods on the controller. Traditionally, normal Struts 2 actions expose the execute method as their target method. Here's a sample controller for a orders resource. Note, this sample doesn't implement all of the methods that can be hit via the RESTful action mapper's interpretation of URL's.

Code Block
langjava
package org.apache.struts2.rest.example;

public class OrdersController implements ModelDriven<Order> {

    private OrderManager orderManager;
    private String id;
    private Order model;

    // Handles /orders/{id} GET requests
    public HttpHeaders show() {
        model = orderManager.findOrder(id);
        return new DefaultHttpHeaders("show")
            .withETag(model.getUniqueStamp())
            .lastModified(model.getLastModified());
    }

    // Handles /orders/{id} PUT requests
    public String update() {
        orderManager.updateOrder(model);
        return "update";
    }

    // getters and setters
}

In this example, the ModelDriven interface is used to ensure that only my model, the Order object in this case, is returned to the client, otherwise, the whole OrdersController object would be serialized.

Note

Where's ActionSupport? Normally, you extend ActionSupport when writing Struts 2 actions. In these case, our controller doesn't do that. Why, you ask? ActionSupport provides a bunch of important functionality to our actions, including support for i18n and validation. All of this functionality, in the RESTful case, is provided by the default interceptor stack defined in the REST plugin's struts-plugin.xml file. Unless you willfully break your controller's membership in the rest-default package in which that stack is defined, then you'll get all that functionality you are used to inheriting from ActionSupport.

You may wonder why the show() method returns a HttpHeaders object and the update() method returns the expected result code String. The REST Plugin adds support for action methods that return HttpHeaders objects as a way for the action to have more control over the response. In this example, we wanted to ensure the response included the ETag header and a last modified date so that the information will be cached properly by the client. The HttpHeaders object is a convenient way to control the response in a type-safe way.

Also, notice we aren't returning the usual "success" result code in either method. This allows us to use the special features of the Codebehind Plugin to intuitively select the result template to process when this resource is accessed with the .xhtml extension. In this case, we can provide a customized XHTML view of the resource by creating /orders-show.jsp and /orders-update.jsp for the respective methods.

Advanced Topics

The following sections describe some of the non-standard bells and whistles that you might need to utilize for your application's more non-standard requirements.

Custom ContentTypeHandlers

If you need to handle extensions that aren't supported by the default handlers, you can create your own ContentTypeHandler implementation and define it in your struts.xml:

...

Code Block
struts.rest.handlerOverride.xml=myXml

struts.xml

Instruct Struts to use the REST action mapper:

...


<constant name="struts.mapper.class" value="rest" />

Because the REST plugin uses the Convention plugin, some settings need to be set in struts.xml:

...


<constant name="struts.convention.action.suffix" value="Controller"/>
<constant name="struts.convention.action.mapAllMatches" value="true"/>
<constant name="struts.convention.default.parent.package" value="rest-default"/>

and for this example:

...


<constant name="struts.convention.package.locators" value="example"/>

Example

The plugin ships with a struts2-rest-showcase application that demonstrates a simple REST web program.

Settings

The following settings can be customized. See the developer guide.
For more configuration options see the Convention Plugin Documentation

Setting

Description

Default

Possible Values

struts.rest.handlerOverride.EXTENSION

The alias for the ContentTypeHandler implementation that handles the EXTENSION value

N/A

Any declared alias for a ContentTypeHandler implementation

struts.rest.defaultExtension

The default extension to use when none is explicitly specified in the request

xml xhtml

Any extension

struts.rest.validationFailureStatusCode

The HTTP status code to return on validation failure

400

Any HTTP status code as an integer

Installation

...

struts.rest.namespace

Optional parameter to specify namespace for REST services

/

eg. /rest

struts.rest.content.restrictToGET

Optional parameter, if set to true blocks returning content from any other methods than GET, if set to false, the content can be returned for any kind of method

true

eg. put struts.rest.content.restrictToGET = false in struts.properties

Resources

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