EJB 3.0提供了使用@AroundInvoke批注注释的方法来拦截业务方法调用的规范.在业务方法调用它被拦截之前,ejbContainer调用一个拦截器方法.以下是拦截器方法的示例签名
@AroundInvoke public Object methodInterceptor(InvocationContext ctx) throws Exception { System.out.println("*** Intercepting call to LibraryBean method: " + ctx.getMethod().getName()); return ctx.proceed(); }
拦截器方法可以在三个级别应用或绑定.
默认 : 部署中的每个bean都会调用默认拦截器.默认拦截器只能通过xml(ejb-jar.xml)应用.
类 : 为bean的每个方法调用类级别拦截器.类级别拦截器可以通过via xml(ejb-jar.xml)的注释来应用.
方法 : 为bean的特定方法调用方法级拦截器.方法级拦截器可以通过via xml(ejb-jar.xml)的注释来应用.
我们在这里讨论类级别拦截器.
package com.it1352.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(); } }
import javax.ejb.Remote; @Remote public interface LibraryBeanRemote { //add business method declarations }
@Interceptors ({BusinessInterceptor.class}) @Stateless public class LibraryBean implements LibraryBeanRemote { //implement business method }
让我们创建一个测试用于测试截获的无状态EJB的EJB应用程序.
Step | 描述 |
---|---|
1 | 在包 com.it1352.interceptor 下创建一个名为 EjbComponent 的项目,如 EJB - 创建应用程序中所述章节.您还可以使用在本章中 EJB - 创建应用程序章节中创建的项目来理解截获的EJB概念. |
2 | 创建 LibraryBean.java 和 LibraryBeanRemote 如 EJB - 创建应用程序章节中所述,在 com.it1352.interceptor 下.保持其余文件不变. |
3 | 清理并构建应用程序以确保业务逻辑按照要求运行. |
4 | 最后,在JBoss Application Server上以jar文件的形式部署应用程序.如果JBoss应用服务器尚未启动,它将自动启动. |
5 | 现在创建ejb客户端,一个基于控制台的应用程序,其方式与主题创建中的 EJB - 创建应用程序章节中所述的相同客户端访问EJB . |
package com.it1352.interceptor; import java.util.List; import javax.ejb.Remote; @Remote public interface LibraryBeanRemote { void addBook(String bookName); List getBooks(); }
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; } }
一旦部署EjbComponent关于JBOSS的项目,请注意jboss日志.
JBoss已自动为会话bean创建了一个JNDI条目 : LibraryBean/remote .
我们将使用此查找字符串来获取类型为&minus的远程业务对象; com.it1352.interceptor.LibraryBeanRemote
... 16:30:01,401 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: LibraryBean/remote - EJB3.x Default Remote Business Interface LibraryBean/remote-com.it1352.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.it1352.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.it1352.interceptor.LibraryBeanRemote - EJB3.x Remote Business Interface ...
java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces java.naming.provider.url=localhost
这些属性用于初始化java命名服务的InitialContext对象.
InitialContext对象将用于查找无状态会话bean.
package com.it1352.test; import com.it1352.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 \n1. Add Book\n2. Exit \nEnter 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执行以下任务 :
从jndi.properties加载属性并初始化InitialContext对象.
在testInterceptedEjb()方法中,使用名称"LibraryBean/remote"完成jndi查找以获取远程业务对象(无状态EJB).
然后向用户显示库存储用户界面,并要求他/她输入选项.
如果用户输入1,系统将要求输入书名和使用无状态会话bean addBook()方法保存本书.会话Bean将书存储在其实例变量中.
如果用户输入2,系统将使用无状态会话bean getBooks()方法检索书籍并退出.
在项目资源管理器中找到EJBTester.java.右键单击EJBTester类并选择运行文件.
在Netbeans控制台中验证以下输出.
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)
验证JBoss应用程序服务器日志输出中的以下输出.
.... 09:55:40,741 INFO [STDOUT] *** Intercepting call to LibraryBean method: addBook 09:55:43,661 INFO [STDOUT] *** Intercepting call to LibraryBean method: getBooks