EJB攔截

EJB3.0提供了攔截業務方法的規範使用@ AroundInvoke註釋註釋的方法調用。一個攔截器方法被稱爲包含EJBContainer的業務方法調用前攔截。下面的例子是一個攔截器方法簽名

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

攔截器方法可以應用在三個層面上的約束

• Default - 默認的攔截器被調用內deployment.Default攔截每個bean只能應用於通過XML（ejb-jar.xml）。

• Class - 類級別攔截所有的bean的方法被調用。類級別攔截器可以應用通過XML註釋（ejb-jar.xml）。

• Method - 方法級別的攔截器是一個特定的bean的方法調用。方法級的攔截器可以應用通過XML註釋（ejb-jar.xml）。

我們在這裏討論類級別攔截。

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 }

示例應用程序

讓我們創建一個測試測試截獲的無狀態EJB的EJB應用程序。

Step

描述

1

Create a project with a name EjbComponent under a package com.tutorialspoint.interceptoras explained in the EJB - Create Application chapter. You can also use the project created inEJB - Create Application chapter as such for this chapter to understand intercepted ejb concepts.

2

Create LibraryBean.java and LibraryBeanRemote under packagecom.tutorialspoint.interceptor 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)

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項目，會注意到jboss的日誌。

• JBoss已經自動爲我們的會話bean創建一個JNDI條目 - LibraryBean/remote.

• 我們將使用這個查詢字符串來獲得遠程類型的業務對象 -com.tutorialspoint.interceptor.LibraryBeanRemote

JBoss應用服務器的日誌輸出

...
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

• 這些屬性是用來初始化InitialContext對象的Java命名服務

• InitialContext的對象將被用於查找無狀態會話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做以下任務。

• jndi.properties中加載和初始化的InitialContext對象。

• JNDI查找testInterceptedEjb（）方法，完成了名稱 - 「LibraryBean/remote」獲得遠程業務對象（無狀態EJB）。

• 如果用戶輸入1，系統要求輸入書籍名稱和節約使用無狀態的會話bean addBook（）方法的書。會話Bean存儲在它的實例變量的書。

• 如果用戶輸入2，系統檢索書使用狀態會話Bean getBooks（）方法和退出。

Run Client to access EJB

在項目資源管理器中找到EJBTester.java。右鍵點擊上EJBTester類，並選擇run file.

在Netbeans控制檯驗證以下輸出。

run:
**********************
Welcome to Book Store
**********************
Options

1. Add Book
2. Exit
   Enter Choice: 1
   Enter book name: Learn Java
   **********************
   Welcome to Book Store
   **********************
   Options
3. Add Book
4. Exit
   Enter Choice: 2
   Book(s) entered so far: 1
5. Learn Java
   BUILD SUCCESSFUL (total time: 13 seconds)

JBoss應用服務器的日誌輸出

驗證下面的輸出在JBoss應用服務器的日誌輸出。

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