EJB无状态Bean - EJB

无状态会话bean是一种企业bean,通常是用于执行独立操作。正如它的名字一样,无状态会话bean不具有任何关联的客户端的状态,但它可能会保持其实例的状态。 EJB容器通常创建一个容器池和几无状态的bean的对象,并使用这些对象来处理客户端的请求。由于有容器池,实例变量的值不能保证跨查找/方法调用同一个。

下面是创建一个无状态的EJB所需的步骤。

Remote Interface

import javax.ejb.Remote;

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

Stateless EJB

@Stateless
public class LibrarySessionBean implements LibrarySessionBeanRemote {
   //implement business method 
}

示例应用程序

让我们创建一个测试测试无状态EJB的EJB应用程序。

步骤 描述
1 Create a project with a name EjbComponent under a package com.tutorialspoint.stateless as explained in the EJB - Create Application chapter. You can also use the project created in EJB - Create Application chapter as such for this chapter to understand stateless ejb concepts.
2 Create LibrarySessionBean.java and LibrarySessionBeanRemote as explained in the EJB - Create Application chapter. Keep rest of the files unchanged.
3 Clean and Build the application to make sure business logic is working as per the requirements.
4 Finally, deploy the application in the form of jar file on JBoss Application Server. JBoss Application server will get started automatically if it is not started yet.
5 Now create the ejb client, a console based application in the same way as explained in theEJB - Create Application chapter under topic Create Client to access EJB.

EJBComponent (EJB Module)

LibrarySessionBeanRemote.java

package com.tutorialspoint.stateless;

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

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

LibrarySessionBean.java


package com.tutorialspoint.stateless;

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

@Stateless
public class LibrarySessionBean implements LibrarySessionBeanRemote {

   List<String> bookShelf;    

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

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

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

JBoss应用服务器的日志输出

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

   LibrarySessionBean/remote - EJB3.x Default Remote Business Interface
   LibrarySessionBean/remote-com.tutorialspoint.stateless.LibrarySessionBeanRemote - 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

EJBTester.java

package com.tutorialspoint.test;

import com.tutorialspoint.stateful.LibrarySessionBeanRemote;
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; 

         LibrarySessionBeanRemote libraryBean =
         LibrarySessionBeanRemote)ctx.lookup("LibrarySessionBean/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++;
         }       
         LibrarySessionBeanRemote libraryBean1 = 
            (LibrarySessionBeanRemote)ctx.lookup("LibrarySessionBean/remote");
         List<String> booksList1 = libraryBean1.getBooks();
         System.out.println(
            "***Using second lookup to get library stateless 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在执行以下任务。

运行客户端访问EJB

Locate EJBTester.java in project explorer. Right click on EJBTester class and select run file.

Verify the following output in Netbeans console.

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 stateless 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。右键点击上EJBTester类,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: 2
Book(s) entered so far: 0
***Using second lookup to get library stateless object***
Book(s) entered so far: 1
1\. Learn Java
BUILD SUCCESSFUL (total time: 12 seconds)

无状态EJB的bean实例变量的值是直到重新启动服务器才失效的。