Working with Struts 2 actions

In Struts 2, you’ll spend most of your time working with actions. The action class contains business logic, retrieve resource bundle, hold the data, validation, and select the view result page that should send back to the user. It’s the heart of the Struts 2, so you have to understand the basic concept of actions.

1. Action

Struts 2 actions don’t force you to implement any interface or extends class, it’s only required you to implement an

execute()

method that returns a string to indicate which result page should return.

package com.mkyong.user.action;

public class LoginAction{

//business logic
public String execute() {
return "success";
}

}

In the

struts.xml

, configure the action class with

action

tag and

class

attribute. Define which result page should return to the user with

result

tag and the name of the action you can use to access this action class with

name

attribute.

<package name="user" namespace="/User" extends="struts-default">

<action name="validateUser" class="com.mkyong.user.action.LoginAction">
<result name="success">pages/welcome.jsp</result>
</action>

<package>

Now you can access the action via a suffix of

.action

extension.

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

The default

.action

is configurable, just change the “

struts.action.extension

” value to suit your need.

2. Optional Action interface

Struts 2 comes with an optional action interface (

com.opensymphony.xwork2.Action

). By implements this interface, it bring some convenient benefits, see the source code :

package com.opensymphony.xwork2;

public interface Action {

public static final String SUCCESS = "success";

public static final String NONE = "none";

public static final String ERROR = "error";

public static final String INPUT = "input";

public static final String LOGIN = "login";

public String execute() throws Exception;

}

This interface is really simple, comes with 5 common used constant values :

success

,

error

,

none

,

input

and

logic

. Now the action class can use the constant value directly.

package com.mkyong.user.action;

import com.opensymphony.xwork2.Action;

public class LoginAction{

//business logic
public String execute() {
return SUCCESS;
}

}

I don’t understand why many Struts developers like to implement this Action interface, it better to extend the

ActionSupport

.

3. ActionSupport

Support class, a common practice to provide default implementations of interfaces.

The

ActionSupport

(

com.opensymphony.xwork2.ActionSupport

), a very powerful and convenience class that provides default implementation of few of the important interfaces :

public class ActionSupport implements Action, Validateable,
ValidationAware, TextProvider, LocaleProvider, Serializable {
...
}

The

ActionSupport

class give you the ability to do :

Validation – Declared a

validate()

method and put the validation code inside.

Text localization – Use

GetText()

method to get the message from resource bundle.

package com.mkyong.user.action;

import com.opensymphony.xwork2.ActionSupport;

public class LoginAction extends ActionSupport{

private String username;
private String password;

public String getPassword() {
return password;
}

public void setPassword(String password) {
this.password = password;
}

public String getUsername() {
return username;
}

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

//business logic
public String execute() {

return "SUCCESS";

}

//simple validation
public void validate(){
if("".equals(getUsername())){
addFieldError("username", getText("username.required"));
}
if("".equals(getPassword())){
addFieldError("password", getText("password.required"));
}
}
}

In most cases, you should extends this class for the ready convenient features, unless you have reason not to.

4. Action annotation

Struts 2 has very good support for annotations, you can get rid of the XML file and replace with

@action

in your action class.

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 ValidateUserAction extends ActionSupport{

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

return SUCCESS;

}
}

Conclusion

No brainer, just extends the

ActionSupport

class, it suits in most of the cases.