EJB拦截

EJB3.0提供了拦截业务方法的规范使用@ AroundInvoke注释注释的方法调用。一个拦截器方法被称为包含EJBContainer的业务方法调用前拦截。下面的例子是一个拦截器方法签名

@AroundInvoke
public Object methodInterceptor(InvocationContext ctx) throws Exception
{
   System.out.println("*** Intercepting call to LibraryBean method: " 
   + ctx.getMethod().getName());
   return ctx.proceed();
}

拦截器方法可以应用在三个层面上的约束

• Default - 默认的拦截器被调用内deployment.Default拦截每个bean只能应用于通过XML（ejb-jar.xml）。

• Class - 类级别拦截所有的bean的方法被调用。类级别拦截器可以应用通过XML注释（ejb-jar.xml）。

• Method - 方法级别的拦截器是一个特定的bean的方法调用。方法级的拦截器可以应用通过XML注释（ejb-jar.xml）。

我们在这里讨论类级别拦截。

Interceptor class

package com.tutorialspoint.interceptor;

import javax.interceptor.AroundInvoke;
import javax.interceptor.InvocationContext;

public class BusinessInterceptor {
   @AroundInvoke
   public Object methodInterceptor(InvocationContext ctx) throws Exception
   {
      System.out.println("*** Intercepting call to LibraryBean method: " 
      + ctx.getMethod().getName());
      return ctx.proceed();
   }
}

Remote Interface

import javax.ejb.Remote;

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

Intercepted Stateless EJB

@Interceptors ({BusinessInterceptor.class})
@Stateless
public class LibraryBean implements LibraryBeanRemote {
   //implement business method 
}

示例应用程序

让我们创建一个测试测试截获的无状态EJB的EJB应用程序。

EJBComponent (EJB Module)

LibraryBeanRemote.java

package com.tutorialspoint.interceptor;

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

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

LibraryBean.java

package com.tutorialspoint.interceptor;

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

@Interceptors ({BusinessInterceptor.class})
@Stateless
public class LibraryBean implements LibraryBeanRemote {
    
   List<String> bookShelf;    

   public LibraryBean(){
      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，会注意到jboss的日志。

• JBoss已经自动为我们的会话bean创建一个JNDI条目 - LibraryBean/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.interceptor.LibraryBeanRemote

JBoss应用服务器的日志输出

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

   LibraryBean/remote - EJB3.x Default Remote Business Interface
   LibraryBean/remote-com.tutorialspoint.interceptor.LibraryBeanRemote - 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

• 这些属性是用来初始化InitialContext对象的Java命名服务

• InitialContext的对象将被用于查找无状态会话bean

EJBTester.java

package com.tutorialspoint.test;
   
import com.tutorialspoint.stateful.LibraryBeanRemote;
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.testInterceptedEjb();
   }
   
   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 testInterceptedEjb(){

      try {
         int choice = 1; 

         LibraryBeanRemote libraryBean =
         LibraryBeanRemote)ctx.lookup("LibraryBean/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++;
         }                
      } 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做以下任务。

• jndi.properties中加载和初始化的InitialContext对象。

• JNDI查找testInterceptedEjb（）方法，完成了名称 - “LibraryBean/remote”获得远程业务对象（无状态EJB）。

• 如果用户输入1，系统要求输入书籍名称和节约使用无状态的会话bean addBook（）方法的书。会话Bean存储在它的实例变量的书。

• 如果用户输入2，系统检索书使用状态会话Bean getBooks（）方法和退出。

Run Client to access 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: 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
BUILD SUCCESSFUL (total time: 13 seconds)

JBoss应用服务器的日志输出

验证下面的输出在JBoss应用服务器的日志输出。

....
09:55:40,741 INFO  [STDOUT] *** Intercepting call to LibraryBean method: addBook
09:55:43,661 INFO  [STDOUT] *** Intercepting call to LibraryBean method: getBooks