Chat Application

The application works like a mini-BBS. Users login to the application with a nickname. The user session is saved in a session scoped component. Once logged in, they can leave quips or messages.

Action Classes

LoginAction extends ActionSupport, which has default implementations of some of the basic action methods and provides some validation support.

The two main methods we are concerned with in ActionSupport are validate() and execute().

Validation

Validation is performed on your Action class if it implements Validatable (ActionSupport does), and your DefaultWorkflowInterceptor is activated on that action. The default configuration includes the workflow interceptor.

Execution

execute() returns a String. This String will be used to determine which result is used.

The framework provides some default return Strings, namely:

Action.SUCCESS = "success"
Action.INPUT = "input"
Action.NONE = "none"
Action.ERROR = "error"
Action.LOGIN = "login"

For example, lets take a look at the relevant part of our struts.xml configuration for LoginAction...

struts.xml fragment

<action name="login" class="example.LoginAction"> 
  <result name="success" type="chain"> 
    <param name="actionName">viewMessages</param>
  </result>

  <result name="input" type="chain"> 
    <param name="actionName">viewMessages</param>
  </result>
</action>

If execute() returns a String of "success", the result with attribute "success" will be used. If execute() returns a String of "input", the result with attribute "input" will be used.

You can define your own return results. For example:

public String execute() {
  return "resetPassword";
}

We need only configure a result for the "resetPassword" name:

<action name="login" class="example.LoginAction"> 
  <result name="resetPassword" type="chain"> 
    <param name="actionName">viewResetPassword</param>
  </result>
</action>

Context Variables / Mapping

LoginAction.java

public class LoginAction extends ActionSupport {

    private String loginName;

    public String getLoginName() {
        return loginName;
    }

    public void setLoginName(String loginName) {
        this.loginName = loginName;
    }
}

LoginAction has a bean property loginName. This property will be set automatically by Struts 2 from forms containing a loginName element.

<form method="POST" action="login.action">
  <input type="text" name="loginName" size="20">
  <input type="submit" value="Login">
</form>

Also, the bean property is available to your views. In Velocity, this accessible via the VelocityContext.

$loginName

which is mapped to getLoginName() in our LoginAction class.

You can map any other object you wish. For example, I could have a User object:

class User {
   private Account account;
   private String name;
   // with the relevant getX() methods...
}

We add a user property to an action class:

class MyExampleAction {
   //...
   User getUser() {
      returns user;
   }
   //...
}

In our Velocity template we can access User properties as expected:

Welcome, $user.name.
You last logged on at $user.lastLogin.
You currently have $user.account.balance left in your account.

Components

components.xml

<components> 
    <component> 
        <scope>application</scope>
        <class>example.data.MessageList</class>
        <enabler>example.data.MessageListAware</enabler>
    </component>

    <component> 
        <scope>session</scope>
        <class>example.web.UserSession</class>
        <enabler>example.web.UserSessionAware</enabler>
    </component>
</components>

Two components, one to hold the application scoped chat messages, another to hold the user's session information (login account name, etc.) For all practical purposes, you can replace the application scoped component with a database. i.e. instead of reading/writing to the component, read/write to the database.

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