在J2EE环境下使用JNDI是非常简单的事，因为所有的J2EE容器都要实现JNDI服务，所以，在J2EE环境下使用JNDI，与使用Hashtable也没有什么太大区别。只有一点限制，那就是绑定对象时，对象所属的类必须实现java.io.Serializable接口，这一点也实在一点也不困难，几乎所有用到的Java类都实现了这个接口，对于自定义的类，在接口实现列表里把这个接口加进去也就是了。
下面，我将演示一下如何在J2EE环境下使用JNDI，为了保证代码的通用性，我不使用struts之类的框架，而是直接使用标准JSP和Servlet实现。我将该项目的名称定为jndi_test
要使用JNDI，需要先到SUN的网站上去下载jndi.jar。
2.1 JSP
本项目包括5个JSP，功能说明如下：
index.jsp：首页
bind.jsp：用于在JNDI中绑定对象
bind_result.jsp：绑定对象后的返回页面
lookup.jsp：用于在JNDI中检索对象
lookup_result.jsp：用于显示检索对象
本节中用到的JSP代码如下，代码都简单地很，就不多做解释了。
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
本例包括两个Servlet，功能说明如下：
BindServlet：用于在JNDI服务中绑定一个对象
LookupServlet：用于在JNDI服务中取出一个对象
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绑定对象是因为，使用bind时，如果已经有对象绑定到该键值上，则会抛出异常。
因为只是示例代码，所以我只是绑定了一个最简单的日期对象。
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，所有的代码都在这里了，部署到Tomcat下运行即可。