Interceptor可以使用Annotation或使用Deployment Descriptor來宣告，下面的範例包含了一個Singleton Session Bean、一個要做為Interceptor的類別、一個宣告Interceptor的Deployment Descriptor文件，另外還有一個做為客戶端程式的Servlet，我使用GlassFish 3.1來做為我的伺服器，並使用Deployment Descriptor來宣告Interceptor。
SingletonSessionBean.java
package jk.idv.ssb;
import java.util.Date;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.ejb.LocalBean;
import javax.ejb.Singleton;
@Singleton(name="SingletonSessionBean")
@LocalBean
public class SingletonSessionBean
{
private final static String MY_NAME = "SingletonSessionBean";
private String username = "[no man]";
@PostConstruct
private void init()
{
System.out.println(" " + MY_NAME + " - Initialized");
}
@PreDestroy
private void destroy()
{
System.out.println("*** " + MY_NAME + " - Destroyed");
}
public String retrieveMessage()
{
Date theCurrentTime = new Date();
return "Name saved in " + MY_NAME + " is " + username + " "
+ theCurrentTime;
}
public void saveName(final String inName)
{
this.username = inName;
}
}
上列程式碼中，未使用@Interceptors來宣告這個Singleton Session Bean相關的Interceptor。
LogInterceptor.java
package idv.jk.interceptor;
package idv.jk.interceptor;
import javax.interceptor.InvocationContext;
public class LogInterceptor
{
public Object logMethod(InvocationContext inCtx) throws Exception
{
System.out.println(" LogInterceptor intercepting: " +
inCtx.getTarget().getClass().getSimpleName() +
"." + inCtx.getMethod().getName());
return inCtx.proceed();
}
}
上列的程式碼中，也沒有使用@Interceptor來宣告此類別為一個Interceptor。
SingletonClientServlet.java
package idv.jk.client;
import java.io.IOException;
import java.io.PrintWriter;
import javax.ejb.EJB;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import jk.idv.ssb.SingletonSessionBean;
/**
* Servlet implementation class SingletonClientServlet
*/
@WebServlet("/SingletonClientServlet")
public class SingletonClientServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@EJB
private SingletonSessionBean singletonSessionBean;
/**
* @see HttpServlet#HttpServlet()
*/
public SingletonClientServlet() {
super();
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String theParam = request.getParameter("name");
PrintWriter pw = response.getWriter();
String msg = singletonSessionBean.retrieveMessage();
pw.println("Get message from singleton session bean: ");
pw.println(msg);
if(theParam != null)
{
singletonSessionBean.saveName(theParam);
}
msg = singletonSessionBean.retrieveMessage();
pw.println("Check message from singleton session bean: ");
pw.println(msg);
pw.println("Finished invoking singleton session beans!");
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
上列的Servlet使用注入的方式來使用Singleton Session Bean的方法，並在瀏覽器中印出一些我需要的資訊。
最後是名為ejb-jar.xml的Deployment Descriptor：
idv.jk.interceptor.LogInterceptor logMethod SingletonSessionBean idv.jk.interceptor.LogInterceptor
將Web應用程式部署到GlassFish後，再打開瀏覽器輸入：http://localhost:8888/BusinessMethodInterceptorsDD/SingletonClientServlet?name=Javakid，應該可以看到下列的結果：
Get message from singleton session bean: Name saved in SingletonSessionBean is [no man] Fri Jan 24 00:05:32 CST 2014 Check message from singleton session bean: Name saved in SingletonSessionBean is Javakid Fri Jan 24 00:05:32 CST 2014 Finished invoking singleton session beans!
在Console中，也會看到一些訊息被印出來：
完整的程式由此下載。
參考資料：
http://www.slideshare.net/krizsan/ocp-jbcd-6-study-notes，p.97
