|Apache Struts 2 Documentation > Home > Guides > Plugin Developers Guide > REST Plugin|
|This plugin is only available with Struts 2.1.1 or later|
The REST Plugin 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.
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.
|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.
This Restful action mapper enforces Ruby-On-Rails Rest-style mappings. If the method is not specified (via '!' or 'method:' prefix), the method is "guessed" at using ReST-style conventions that examine the URL and the HTTP method. Special care has been given to ensure this mapper works correctly with the codebehind plugin so that XML configuration is unnecessary.
This mapper supports the following parameters:
struts.mapper.idParameterName- If set, this value will be the name of the parameter under which the id is stored. The id will then be removed from the action name. Whether or not the method is specified, the mapper will try to truncate the identifier from the url and store it as a parameter.
struts.mapper.indexMethodName- The method name to call for a GET request with no id parameter. Defaults to 'index'.
struts.mapper.getMethodName- The method name to call for a GET request with an id parameter. Defaults to 'show'.
struts.mapper.postMethodName- The method name to call for a POST request with no id parameter. Defaults to 'create'.
struts.mapper.putMethodName- The method name to call for a PUT request with an id parameter. Defaults to 'update'.
struts.mapper.deleteMethodName- The method name to call for a DELETE request with an id parameter. Defaults to 'destroy'.
struts.mapper.editMethodName- The method name to call for a GET request with an id parameter and the 'edit' view specified. Defaults to 'edit'.
struts.mapper.newMethodName- The method name to call for a GET request with no id parameter and the 'new' view specified. Defaults to 'editNew'.
The following URL's will invoke its methods:
GET: /movies => method="index"
GET: /movies/Thrillers => method="show", id="Thrillers"
GET: /movies/Thrillers;edit => method="edit", id="Thrillers"
GET: /movies/Thrillers/edit => method="edit", id="Thrillers"
GET: /movies/new => method="editNew"
POST: /movies => method="create"
PUT: /movies/Thrillers => method="update", id="Thrillers"
DELETE: /movies/Thrillers => method="destroy", id="Thrillers"
To simulate the HTTP methods PUT and DELETE, since they aren't supported by HTML, the HTTP parameter "_method" will be used.
Or, expressed as a table:
In addition to 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:
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
|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.|
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
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
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.
|As with all configuration of Struts 2, we prefer using <constant/> elements in our struts.xml.|
Instruct Struts to use the REST action mapper:
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:
|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.|
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.
|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.
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.
And, again, we're relying on the Convention plugin to find our controllers, so we need to configure the convention plugin a bit:
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.
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.
|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.
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.
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:
If the built-in content type handlers don't do what you need, you can override the handling of any extension by providing an alternate handler. First, define your own ContentTypeHandler and declare with its own alias. For example:
Then, tell the REST Plugin to override the handler for the desired extension with yours. In struts.properties, it would look like this:
|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||xhtml||Any extension|
|struts.rest.validationFailureStatusCode||The HTTP status code to return on validation failure||400||Any HTTP status code as an integer|
|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|
From Struts 2.1.1+