JSF - Managed Beans

Managed Bean is a regular Java Bean class registered with JSF. In other words, Managed Beans is a Java bean managed by JSF framework. Managed bean contains the getter and setter methods, business logic, or even a backing bean (a bean contains all the HTML form value).
Managed beans works as Model for UI component. Managed Bean can be accessed from JSF page.
In JSF 1.2, a managed bean had to register it in JSF configuration file such as facesconfig.xml. From JSF 2.0 onwards, managed beans can be easily registered using annotations. This approach keeps beans and its registration at one place hence it becomes easier to manage.
<managed-bean>
   <managed-bean-name>helloWorld</managed-bean-name>
   <managed-bean-class>com.tutorialspoint.test.HelloWorld</managed-bean-class>
   <managed-bean-scope>request</managed-bean-scope>
</managed-bean> 

<managed-bean>
   <managed-bean-name>message</managed-bean-name>
   <managed-bean-class>com.tutorialspoint.test.Message</managed-bean-class>
   <managed-bean-scope>request</managed-bean-scope>
</managed-bean> 
@ManagedBean(name = "helloWorld", eager = true)
@RequestScoped
public class HelloWorld {
   @ManagedProperty(value = "#{message}")
   private Message message;
   ...
}
@ManagedBean marks a bean to be a managed bean with the name specified in name attribute. If the name attribute is not specified, then the managed bean name will default to class name portion of the fully qualified class name. In our case, it would be helloWorld.
Another important attribute is eager. If eager = "true" then managed bean is created before it is requested for the first time otherwise "lazy" initialization is used in which bean will be created only when it is requested.
Scope annotations set the scope into which the managed bean will be placed. If the scope is not specified, then bean will default to request scope. Each scope is briefly discussed in the following table.
@RequestScoped
Bean lives as long as the HTTP request-response lives. It gets created upon a HTTP request and gets destroyed when the HTTP response associated with the HTTP request is finished.
@NoneScoped
Bean lives as long as a single EL evaluation. It gets created upon an EL evaluation and gets destroyed immediately after the EL evaluation.
@ViewScoped
Bean lives as long as the user is interacting with the same JSF view in the browser window/tab. It gets created upon a HTTP request and gets destroyed once the user postbacks to a different view.
@SessionScoped
Bean lives as long as the HTTP session lives. It gets created upon the first HTTP request involving this bean in the session and gets destroyed when the HTTP session is invalidated.
@ApplicationScoped
Bean lives as long as the web application lives. It gets created upon the first HTTP request involving this bean in the application (or when the web application starts up and the eager=true attribute is set in @ManagedBean) and gets destroyed when the web application shuts down.
@CustomScoped
Bean lives as long as the bean's entry in the custom Map, which is created for this scope lives.
JSF is a simple static Dependency Injection (DI) framework. Using @ManagedProperty annotation, a managed bean's property can be injected in another managed bean.
Let us create a test JSF application to test the above annotations for managed beans.
package com.tutorialspoint.test;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;
import javax.faces.bean.RequestScoped;

@ManagedBean(name = "helloWorld", eager = true)
@RequestScoped
public class HelloWorld {
   @ManagedProperty(value = "#{message}")
   private Message messageBean;
   private String message;
   
   public HelloWorld() {
      System.out.println("HelloWorld started!");   
   }
   
   public String getMessage() {
      
      if(messageBean != null) {
         message = messageBean.getMessage();
      }       
      return message;
   }
   
   public void setMessageBean(Message message) {
      this.messageBean = message;
   }
}
package com.tutorialspoint.test;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;

@ManagedBean(name = "message", eager = true)
@RequestScoped
public class Message {
   private String message = "Hello World!";
	
   public String getMessage() {
      return message;
   }
   public void setMessage(String message) {
      this.message = message;
   }
}
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns = "http://www.w3.org/1999/xhtml">
   <head>
      <title>JSF Tutorial!</title>
   </head>
   
   <body>
      #{helloWorld.message}
   </body>
</html>
Once you are ready with all the changes done, let us compile and run the application as we did in JSF - Create Application chapter. If everything is fine with your application, this will produce the following result.

    37 Lectures 
     3.5 hours 

 Chaand Sheikh
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