EJB有状态Bean - EJB

有状态会话Bean是一种企业bean保存客户端的会话状态类型。有状态会话bean作为每它的名字相关的客户端状态保持在它的实例变量。 EJB容器创建一个单独的有状态会话bean来处理客户端的每个请求。只要请求范围过，有状态会话bean被销毁。

以下是创建一个有状态的EJB所需的步骤：

• Create a remote/local interface exposing the business methods.

• This interface will be used by the ejb client application.

• Use @Local annotation if ejb client is in same environment where ejb session bean is to be deployed.

• Use @Remote annotation if ejb client is in different environment where ejb session bean is to be deployed.

• Create a stateful session bean implementing the above interface.

• Use @Stateful annotation to signify it a stateful bean. EJB Container automatically creates the relevant configurations or interfaces required by reading this annotation during deployment.

远程接口

import javax.ejb.Remote;

@Remote
public interface LibraryStatefulSessionBeanRemote {
   //add business method declarations
}

Stateful EJB

@Stateful
public class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote {
   //implement business method 
}

示例应用程序

让我们创建一个测试测试状态EJB的EJB应用程序。

EJBComponent (EJB Module)

LibraryStatefulSessionBeanRemote.java

package com.tutorialspoint.stateful;

import java.util.List;
import javax.ejb.Remote;

@Remote
public interface LibraryStatefulSessionBeanRemote {
   void addBook(String bookName);
   List getBooks();
}

LibraryStatefulSessionBean.java

package com.tutorialspoint.stateful;

import java.util.ArrayList;
import java.util.List;
import javax.ejb.Stateful;

@Stateful
public class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote {

   List<String> bookShelf;    

   public LibraryStatefulSessionBean(){
      bookShelf = new ArrayList<String>();
   }

   public void addBook(String bookName) {
      bookShelf.add(bookName);
   }    

   public List<String> getBooks() {
      return bookShelf;
   }
}

• 只要你部署在JBoss EjbComponent项目发现jboss的日志。

• JBoss已经自动创建一个JNDI条目会话bean-LibraryStatefulSessionBean/remote。

• 我们将使用这个查询字符串来获得远程类型的业务对象-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote

JBoss应用服务器的日志输出

...
16:30:01,401 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
   LibraryStatefulSessionBean/remote - EJB3.x Default Remote Business Interface
   LibraryStatefulSessionBean/remote-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO  [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryStatefulSessionBean,service=EJB3
16:30:02,723 INFO  [EJBContainer] STARTED EJB: com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote ejbName: LibraryStatefulSessionBean
16:30:02,731 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:

   LibraryStatefulSessionBean/remote - EJB3.x Default Remote Business Interface
   LibraryStatefulSessionBean/remote-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote - EJB3.x Remote Business Interface
...

EJBTester (EJB Client)

jndi.properties

java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory
java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces
java.naming.provider.url=localhost

• These properties are used to initialize the InitialContext object of java naming service

• InitialContext object will be used to lookup stateful session bean

EJBTester.java

package com.tutorialspoint.test;

import com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.List;
import java.util.Properties;
import javax.naming.InitialContext;
import javax.naming.NamingException;

public class EJBTester {

   BufferedReader brConsoleReader = null; 
   Properties props;
   InitialContext ctx;
   {
      props = new Properties();
      try {
         props.load(new FileInputStream("jndi.properties"));
      } catch (IOException ex) {
         ex.printStackTrace();
      }
      try {
         ctx = new InitialContext(props);            
      } catch (NamingException ex) {
         ex.printStackTrace();
      }
      brConsoleReader = 
      new BufferedReader(new InputStreamReader(System.in));
   }

   public static void main(String[] args) {

      EJBTester ejbTester = new EJBTester();

      ejbTester.testStatelessEjb();
   }

   private void showGUI(){
      System.out.println("**********************");
      System.out.println("Welcome to Book Store");
      System.out.println("**********************");
      System.out.print("Options 
1\. Add Book
2\. Exit 
Enter Choice: ");
   }

   private void testStatelessEjb(){

      try {
         int choice = 1; 

         LibraryStatefulSessionBeanRemote libraryBean =
         LibraryStatefulSessionBeanRemote)ctx.lookup("LibraryStatefulSessionBean/remote");

         while (choice != 2) {
            String bookName;
            showGUI();
            String strChoice = brConsoleReader.readLine();
            choice = Integer.parseInt(strChoice);
            if (choice == 1) {
               System.out.print("Enter book name: ");
               bookName = brConsoleReader.readLine();
               Book book = new Book();
               book.setName(bookName);
               libraryBean.addBook(book);          
            } else if (choice == 2) {
               break;
            }
         }

         List<Book> booksList = libraryBean.getBooks();

         System.out.println("Book(s) entered so far: " + booksList.size());
         int i = 0;
         for (Book book:booksList) {
            System.out.println((i+1)+". " + book.getName());
            i++;
         }       
         LibraryStatefulSessionBeanRemote libraryBean1 = 
            (LibraryStatefulSessionBeanRemote)ctx.lookup("LibraryStatefulSessionBean/remote");
         List<String> booksList1 = libraryBean1.getBooks();
         System.out.println(
            "***Using second lookup to get library stateful object***");
         System.out.println(
            "Book(s) entered so far: " + booksList1.size());
         for (int i = 0; i < booksList1.size(); ++i) {
            System.out.println((i+1)+". " + booksList1.get(i));
         }         
      } catch (Exception e) {
         System.out.println(e.getMessage());
         e.printStackTrace();
      }finally {
         try {
            if(brConsoleReader !=null){
               brConsoleReader.close();
            }
         } catch (IOException ex) {
            System.out.println(ex.getMessage());
         }
      }
   }
}

EJBTester is doing the following tasks.

• Load properties from jndi.properties and initialize the InitialContext object.

• In testStatefulEjb() method, jndi lookup is done with name - "LibraryStatefulSessionBean/remote" to obtain the remote business object (stateful ejb).

• Then user is shown a library store User Interface and he/she is asked to enter choice.

• If user enters 1, system asks for book name and saves the book using stateful session bean addBook() method. Session Bean is storing the book in its instance variable.

• If user enters 2, system retrieves books using stateful session bean getBooks() method and exits.

• Then another jndi lookup is done with name - "LibraryStatefulSessionBean/remote" to obtain the remote business object (stateful ejb) again and listing of books is done.

运行客户端访问EJB

在项目资源管理器中找到EJBTester.java。右键单击类EJBTester并选择run file.

在Netbeans控制台验证以下输出。

run:
**********************
Welcome to Book Store
**********************
Options 
1\. Add Book
2\. Exit 
Enter Choice: 1
Enter book name: Learn Java
**********************
Welcome to Book Store
**********************
Options 
1\. Add Book
2\. Exit 
Enter Choice: 2
Book(s) entered so far: 1
1\. Learn Java
***Using second lookup to get library stateful object***
Book(s) entered so far: 0
BUILD SUCCESSFUL (total time: 13 seconds)

再次运行客户端访问EJB

在项目资源管理器中找到EJBTester.java。右键单击类EJBTester选择run file.

在NetBeans控制台验证以下输出.

run:
**********************
Welcome to Book Store
**********************
Options 
1\. Add Book
2\. Exit 
Enter Choice: 2
Book(s) entered so far: 0
***Using second lookup to get library stateful object***
Book(s) entered so far: 0
BUILD SUCCESSFUL (total time: 12 seconds)

• 输出上面显示的状态，对于每个查询不同状态的EJB实例将被返回.

• 只适用于单个会话状态EJB对象值。在第二次运行时，我们没有得到任何值.