Name	Convention Plugin
Publisher	Brian Pontarelli
License	Open Source (ASL2)
Version	2.1.1-SNAPSHOT
Homepage	You're at the homepage
Download	Part of the Struts2 distribution

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The Convention is a code by convention and component plugin similar to the Codebehind and Zero-config plugins.

Introduction

The Convention Plugin provides the following features:

Action location by package naming conventions
Result (JSP, FreeMarker, etc) location by naming conventions
Class name to URL naming convention
Package name to namespace convention
SEO compliant URLs (i.e. my-action rather than MyAction)
Action name overrides using annotations
Namespace overrides using annotations
XWork package overrides using annotations
Default action and result handling (i.e. /products will try com.example.actions.Products as well as com.example.actions.products.Index)

The Convention Plugin should require no configuration to use. Many of the conventions can be controlled using configuration properties and many of the classes can be extended or overridden.

Setup

In order to use the Convention plugin, you first need to add the JAR file to the WEB-INF/lib directory of your application.

Hello world

Now that the Convention plugin has been added to your application, let's start with a very simple example. This example will use an actionless result that is identified by the URL. By default, the Convention plugin assumes that all of the results are stored in WEB-INF/content. This can be changed by setting the property struts.convention.result.path in the Struts properties file to the new location. Don't worry about trailing slashes, the Convention plugin handles this for you. Here is our hello world JSP:

WEB-INF/content/hello-world.jsp

<html>
<body>
Hello world!
</body>
</html>

If you start Tomcat (or whichever J2EE container you are using) and type in http://localhost:8080/hello-world into your browser you should get this result:

WEB-INF/content/hello-world.jsp

Hello world!

This illustrates that the Convention plugin will find results even when no action exists and it is all based on the URL passed to Struts.

Code behind hello world

Let's expand on this example and add a code behind class. In order to do this we need to ensure that the Convention plugin is able to find our action classes. By default, the Convention plugin will find all action classes that implement com.opensymphony.xwork2.Action or whose name ends with the word Action in specific packages.

These packages are located by the Convention plugin using a search methodology. First the Convention plugin finds packages named struts, struts2, action or actions. Any packages that match those names are considered the root packages for the Convention plugin. Next, the plugin looks at all of the classes in those packages as well as sub-packages and determines if the classes implement com.opensymphony.xwork2.Action or if their name ends with Action (i.e. FooAction). Here's an example of a few classes that the Convention plugin will find:

Classes

com.example.actions.MainAction
com.example.actions.products.Display (implements com.opensymphony.xwork2.Action)
com.example.struts.company.details.ShowCompanyDetailsAction

Each of the action classes that the plugin finds will be configured to respond to specific URLs. The URL is based on the package name that the class is defined in and the class name itself. First the plugin determines the namespace of the URL using the package names between the root package and the package the class is defined in. For our examples above, the namespaces would be:

Namespaces

com.example.actions.MainAction -> /
com.example.actions.products.Display -> /products
com.example.struts.company.details.ShowCompanyDetailsAction -> /company/details

Next, the plugin determines the resource of the URL using the class name. It first removes the word Action from the end of the class name and then converts camel case names to dashes. In our example the full URLs would be:

Full URLs

com.example.actions.MainAction -> /main
com.example.actions.products.Display -> /products/display
com.example.struts.company.details.ShowCompanyDetailsAction -> /company/details/show-company-details

You can tell the Convention plugin to ignore certain packages using the property struts.convention.exclude.packages. You can also tell the plugin to use different strings to locate root packages using the property struts.convention.package.locators. Finally, you can tell the plugin to search specific root packages using the property struts.convention.action.packages.

Here is our code behind action class:

com.example.actions.HelloWorld

package com.example.actions;

import com.opensymphony.xwork2.ActionSupport; 

public class HelloWorld extends ActionSupport {
  private String message;

  public String getMessage() {
    return message;
  }

  public String execute() {
    message = "Hello World!"
    return SUCCESS;
  }
}

If you compile this class and place it into your application in the WEB-INF/classes or WEB-INF/lib (inside a JAR file), the Convention plugin will find the class and map the URL /hello-world to it. Next, we need to update our JSP to print out the message we setup in the action class. Here is the new JSP:

WEB-INF/content/hello-world.jsp

<html>
<body>
The message is ${message}
</body>
</html>

If start up the application server and open up http://localhost:8080/hello-world in our browser, we should get this result:

Result

The message is Hello World!

Results and result codes

The Convention Plugin will pre-configure all of you action classes when Struts is started. By default, this configuration will also contain results for any JSPs that it can find within the application. The JSPs have an additional feature that allows different JSPs to be used based on the result code of the action. Since action methods return Strings and these Strings are traditionally used to locate results for the action, the Convention plugin allows you to define different results based on the result code.

Building on our example from above, let's say we want to provide a different result if the result code from our action is the String zero rather than success. First, we update the action class to return different result codes:

com.example.actions.HelloWorld

package com.example.actions;

import com.opensymphony.xwork2.ActionSupport; 

public class HelloWorld extends ActionSupport {
  private String message;

  public String getMessage() {
    return message;
  }

  public String execute() {
    if (System.currentTimeMillis() % 2 == 0) {
      message = "It's 0";
      return "zero";
    }

    message = "It's 1";
    return SUCCESS;
  }
}

Next, we add a new JSP to the application named WEB-INF/content/hello-world-zero.jsp. Notice that the first part of the file name is the same as the URL of the action and the last part of the name is the result code. This is the convention that the plugin uses to determine which results to render. Here is our new JSP:

WEB-INF/content/hello-world.jsp

<html>
<body>
The error message is ${message}
</body>
</html>

Now, if you compile the action and restart the application, based on the current time, you'll either see the result from WEB-INF/content/hello-world.jsp or WEB-INF/content/hello-world-zero.jsp.

Child pages

Introduction

Setup

Hello world

Code behind hello world

Results and result codes

Configuration reference

Annotation reference