Struts 2 Hello World Annotation Example

In this tutorials, it will reuse the previous Strust 2 Hello World (XML version) example, and convert it into annotation version.

Struts 2 Annotation Concept

The Struts 2 annotation is supported by Struts 2 convention plugin, So, you have to understand the magic behind its “Scanning Methodology” and “Naming Converter” mechanism.

1. Scanning Methodology

Many Struts 2 articles or books stated that you can configure the filter’s “

init-param

” or “

struts.convention.action.packages

” to tell Struts 2 where to scan the annotated classes. For example,

web.xml

<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
<init-param>
<param-name>actionPackages</param-name>
<param-value>com.mkyong.common</param-value>
</init-param>
</filter>

From my testing (Struts2 version 2.1.6 and 2.1.8), this is not true, no matter what you put in the “

param-value

” or “

struts.convention.action.packages

“, Struts 2 will just ignore it and scan the specified folders named struts, struts2, action or actions only.

Here’s how the scanning work

Scan the annotated classes which located at the packaged named “struts, struts2, action or actions“.

Next, scan the file which match either of the following criteria :

Implemented the

com.opensymphony.xwork2.Action

interface.

Extends the

com.opensymphony.xwork2.ActionSupport

class.

File name ends with Action (e.g

UserAction

,

LoginAction

).

2. Naming Converter

Struts 2 convention plugin will convert all the annotated action file name to a specified format.

For example :

LoginAction.java

First, remove the “

Action

” word at the end of the file name, if present.

Second, convert the first letter of the file name to lowercase.

So, After removing the ending and converting the case of the first letter, the

LoginAction.action

will change to

login.action

.

The Struts 2 convention plugin’s “scanning methodology” and “naming converter” features are really bring a lot of conveniences and benefits, only if your Struts 2 project is following the naming convention properly; otherwise it will be a total disaster.

Struts 2 Annotation example

It’s time to start the conversion process.

Final project structure

1. Update

pom.xml

To use the Struts 2 annotation feature, you need to download the

struts2-convention-plugin.jar

.

pom.xml

...
<dependency>
<groupId>org.apache.struts</groupId>
<artifactId>struts2-core</artifactId>
<version>2.1.8</version>
</dependency>

<dependency>
<groupId>org.apache.struts</groupId>
<artifactId>struts2-convention-plugin</artifactId>
<version>2.1.8</version>
</dependency>
...

2.

LoginAction

Create a

LoginAction

extends

ActionSupport

and do nothing, the

ActionSupport

default return a “

success

” string, which will match the

@Result

and redirect to “

pages/login.jsp

“.

Annotation version

package com.mkyong.user.action;

import org.apache.struts2.convention.annotation.Namespace;
import org.apache.struts2.convention.annotation.Result;
import org.apache.struts2.convention.annotation.ResultPath;

import com.opensymphony.xwork2.ActionSupport;

@Namespace("/User")
@ResultPath(value="/")
@Result(name="success",location="pages/login.jsp")
public class LoginAction extends ActionSupport{

}
##XML equivalent

pages/login.jsp

##3. `WelcomeUserAction`
Override the `execute()` method and specified the `@Action` and `@Result` annotation.

Annotation version

package com.mkyong.user.action;

import org.apache.struts2.convention.annotation.Action;

import org.apache.struts2.convention.annotation.Namespace;

import org.apache.struts2.convention.annotation.Result;

import org.apache.struts2.convention.annotation.ResultPath;

import com.opensymphony.xwork2.ActionSupport;

@Namespace(“/User”)

@ResultPath(value=”/”)

public class WelcomeUserAction extends ActionSupport{

private String username;

public String getUsername() {
return username;
}

public void setUsername(String username) {
this.username = username;
}

@Action(value="Welcome", results={
@Result(name="success",location="pages/welcome_user.jsp")
})
public String execute() {

return SUCCESS;

}

}

““

XML equivalent

<package name="user" namespace="/User" extends="struts-default">
<action name="Welcome" class="com.mkyong.user.action.WelcomeUserAction">
<result name="SUCCESS">pages/welcome_user.jsp</result>
</action>
</package>

The Struts 2 annotations –

@Action

,

@Result

and

@Namespace

are self-explanatory, you can always compare it with the XML equivalent. The

@ResultPath

may need a bit explanation, see this

@ResultPath

example.

4. JSP view pages

Normal JSP view pages to accept a username and password, and redirect to a welcome page once the submit button is clicked.

login.jsp

<%@ page contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>

Struts 2 Hello World Annotation Example

welcome_user.jsp

<%@ page contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>

Struts 2 Hello World Annotation ExampleHello

5.

struts.xml

No need to create

struts.xml

file, all classes are annotated.

6.

web.xml

Just create a classic

web.xml

file and declared the

FilterDispatcher

filter as normal.

<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
<display-name>Struts 2 Web Application</display-name>

<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
</filter>

<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

</web-app>

7. Run it

The

LoginAction.action

is changed to login.action, see “Naming Converter” above.

http://localhost:8080/Struts2Example/User/login.action



http://localhost:8080/Struts2Example/User/Welcome.action