tomcat下jsp嵌入applet找不着类的解决方案

来源：互联网发布：arduino串口发送数据编辑：程序博客网时间：2024/06/05 11:21

背景：eclipse + tomcat + webProject
问题：webProject首页中使用了applet嵌入，结果提示applet类无法查找
解决方案：在应用程序根目录下新建 applet 文件夹，将编译好的 applet.class 文件考到该文件夹下。

详细情况：
1、新建项目 MyApplet, index.jsp 源码：
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>HelloWorld! Applet</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page">  </head> <body> This is my JSP page. <br> <applet code="com.defonds.applet.HelloApplet.class" width=200 height=100 ></applet> </body></html>
2、新建 applet 类 HelloApplet 源码：
package com.defonds.applet;import java.applet.Applet;import java.awt.Graphics;public class HelloApplet extends Applet { public void paint(Graphics g) { g.drawString("Hello,Defonds!", 5, 35); }}
3、将 MyApplet 部署到 tomcat 容器下。启动 tomcat，访问 MyApplet。页面提示错误信息如下：
载入：找不到类 com.defonds.applet.HelloApplet.class。java.lang.ClassNotFoundException: com.defonds.applet.HelloApplet.class at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source) at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source) at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source) at java.lang.Thread.run(Unknown Source)Caused by: java.io.IOException: open HTTP connection failed:http://localhost:9999/MyApplet/com/defonds/applet/HelloApplet/class.class at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source) at sun.plugin2.applet.Applet2ClassLoader.access$000(Unknown Source) at sun.plugin2.applet.Applet2ClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) ... 7 more异常：java.lang.ClassNotFoundException: com.defonds.applet.HelloApplet.class

分析：applet 的 class 文件最好不要放在 web-inf 目录下，因为这是个特殊目录，所以 http://localhost:9999/MyApplet/ 不能找到 com.defonds.applet.HelloApplet.class 这个文件。可以在 /webapps/MyApplet/ 下新建一个文件夹，将 applet 的 class 文件放在里面，在重新设置 codebase 属性。
这样，新的目录结构如下：
测试用的 jsp /webapps/MyApplet/index.jsp
jsp 中插入的applet class /webapps/MyApplet/applet/com/defonds/applet/HelloApplet.class
URL
http://localhost:9999/MyApplet/index.jsp
新的 index.jsp 源码如下：
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>HelloWorld! Applet</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page">  </head> <body> This is my JSP page. <br> <applet code="com.defonds.applet.HelloApplet.class" width=200 height=100 codebase="/MyApplet/applet/"></applet> </body></html>

redeploy 一下 tomcat，重新访问 MyApplet 项目，发现 applet 已经成功嵌入。