在J2EE環境下使用JNDI是非常簡單的事，因爲所有的J2EE容器都要實現JNDI服務，所以，在J2EE環境下使用JNDI，與使用Hashtable也沒有什麼太大區別。只有一點限制，那就是綁定對象時，對象所屬的類必須實現java.io.Serializable接口，這一點也實在一點也不困難，幾乎所有用到的Java類都實現了這個接口，對於自定義的類，在接口實現列表裏把這個接口加進去也就是了。
下面，我將演示一下如何在J2EE環境下使用JNDI，爲了保證代碼的通用性，我不使用struts之類的框架，而是直接使用標準JSP和Servlet實現。我將該項目的名稱定爲jndi_test
要使用JNDI，需要先到SUN的網站上去下載jndi.jar。
2.1 JSP
本項目包括5個JSP，功能說明如下：
- index.jsp：首頁
- bind.jsp：用於在JNDI中綁定對象
- bind_result.jsp：綁定對象後的返回頁面
- lookup.jsp：用於在JNDI中檢索對象
- lookup_result.jsp：用於顯示檢索對象
本節中用到的JSP代碼如下，代碼都簡單地很，就不多做解釋了。
2.1.1 index.jsp
<%...@ page language="java" contentType="text/html; charset=GB18030"
pageEncoding="GB18030"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=GB18030"><title>JNDI Test</title></head><body><a href="bind.jsp" target="_blank">bind.jsp</a><br /><a href="lookup.jsp" target="_blank">lookup.jsp</a></body></html>2.1.2 bind.jsp
<%...@ page language="java" contentType="text/html; charset=GB18030" pageEncoding="GB18030"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=GB18030"><title>JNDI Test - Bind</title></head><body><a href="bind.do">bind an object</a></body></html>2.1.3 bind_result.jsp
<%...@ page language="java" contentType="text/html; charset=GB18030" pageEncoding="GB18030"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=GB18030"><title>JNDI Test - Bind result</title></head><body><p>Binded successfully!</p></body></html>2.1.4 lookup.jsp
<%...@ page language="java" contentType="text/html; charset=GB18030" pageEncoding="GB18030"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=GB18030"><title>JNDI Test - lookup</title></head><body><a href="lookup.do">lookup the binded object</a></body></html>2.1.5 lookup_result.jsp
<%...@ page language="java" contentType="text/html; charset=GB18030" pageEncoding="GB18030"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=GB18030"><title>JNDI Test - Lookup result</title></head><body><%...
Object o = request.getAttribute("found_jndi_obj"); out.println(o);%></body></html>2.2 Servlet
本例包括兩個Servlet，功能說明如下：
- BindServlet：用於在JNDI服務中綁定一個對象
- LookupServlet：用於在JNDI服務中取出一個對象
2.2.1 BindServlet.java
package lld.test.jndi;import java.io.IOException;import java.util.Date;import javax.naming.Context;import javax.naming.InitialContext;import javax.servlet.RequestDispatcher;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.http.*;public class BindServlet extends HttpServlet...{ private static final long serialVersionUID = 5219969790998794367L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
...{ this.doPost(req, resp);
} @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException ...{ try ...{ Context jndi_ctx = new InitialContext(); String key = "jndi_object"; jndi_ctx.rebind(key, new Date()); }catch(Exception ex) ...{ ex.printStackTrace(); } ServletContext context = this.getServletContext(); RequestDispatcher dispatcher = context.getRequestDispatcher("/bind_result.jsp"); dispatcher.forward(req, resp); } }使用rebind而不是bind綁定對象是因爲，使用bind時，如果已經有對象綁定到該鍵值上，則會拋出異常。
因爲只是示例代碼，所以我只是綁定了一個最簡單的日期對象。
2.2.2 LookupServlet.java
package lld.test.jndi;import java.io.IOException;import javax.naming.Context;import javax.naming.InitialContext;import javax.servlet.RequestDispatcher;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class LookupServlet extends HttpServlet...{ private static final long serialVersionUID = 6677219828267184673L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException ...{ this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException ...{ try ...{ Context jndi_ctx = new InitialContext(); String key = "jndi_object"; Object o = jndi_ctx.lookup(key); req.setAttribute("found_jndi_obj", o); }catch(Exception ex) ...{ ex.printStackTrace(); } ServletContext context = this.getServletContext(); RequestDispatcher dispatcher = context.getRequestDispatcher("/lookup_result.jsp"); dispatcher.forward(req, resp); } }2.3 web.xml
在web.xml中，加入了servlet映射<?xml version="1.0" encoding="UTF-8"?><web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> <display-name>jndi_test</display-name> <servlet> <servlet-name>BindServlet</servlet-name> <servlet-class>lld.test.jndi.BindServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>BindServlet</servlet-name> <url-pattern>/bind.do</url-pattern> </servlet-mapping> <servlet> <servlet-name>LookupServlet</servlet-name> <servlet-class>lld.test.jndi.LookupServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LookupServlet</servlet-name> <url-pattern>/lookup.do</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list></web-app>OK，所有的代碼都在這裏了，部署到Tomcat下運行即可。
2.4 示例下載
嗯, 我不曉得如何上傳文件, 誰想要發我郵箱