EJB有狀態Bean

有狀態對談Bean是一種企業bean儲存用戶端的對談狀態型別。有狀態對談bean作為每它的名字相關的用戶端狀態保持在它的範例變數。 EJB容器建立一個單獨的有狀態對談bean來處理用戶端的每個請求。只要請求範圍過，有狀態對談bean被銷毀。

以下是建立一個有狀態的EJB所需的步驟：

• 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.

遠端介面

import javax.ejb.Remote;
 
@Remote
public interface LibraryStatefulSessionBeanRemote {
   //add business method declarations
}

Stateful EJB

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

範例應用程式

讓我們建立一個測試測試狀態EJB的EJB應用程式。

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專案發現jboss的紀錄檔。

• JBoss已經自動建立一個JNDI條目對談bean-LibraryStatefulSessionBean/remote。

• 我們將使用這個查詢字串來獲得遠端型別的業務物件-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote

JBoss應用伺服器的紀錄檔輸出

...
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.

執行用戶端存取EJB

在專案資源管理器中找到EJBTester.java。右鍵單擊類EJBTester並選擇run file.

在Netbeans控制台驗證以下輸出。

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)

再次執行用戶端存取EJB

在專案資源管理器中找到EJBTester.java。右鍵單擊類EJBTester選擇run file.

在NetBeans控制台驗證以下輸出.

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)

• 輸出上面顯示的狀態，對於每個查詢不同狀態的EJB範例將被返回.

• 只適用於單個對談狀態EJB物件值。在第二次執行時，我們沒有得到任何值.