自己为了测试servlet，用MyEclipse2015写了一个简单的登录程序。
1.登录页面index.jsp.
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String lUserName = (String)session.getAttribute("iUserName");
%> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta charset="utf-8">
<title>My JSP 'index.jsp' starting page</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>
<%
if (lUserName != ""&&lUserName!=null) {
%>
欢迎光临，<%=lUserName%>
<%
} else {
%>
<form name="loginfrm" action="loginserv" method="post">
用户名：<input type="text" name="username" value="zhangsan"><br>
密码:<input type="text" name="password" value="mm123456"><br>
<input type="submit" value="登录">
</form>
<%
}
%>
</body>
</html>
2.用模版写了一个servlet程序loginserv.java.
package com.kaly.servlet; import java.io.IOException;
import java.io.PrintWriter; import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse; public class loginserv extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
} public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html);charset=utf-8");
String getUser=request.getParameter("username");
String getpassword=request.getParameter("password");
PrintWriter pw=response.getWriter();
pw.print(getUser);
} }
这是一个很简单的程序，在收到请求后，把用户名打印出来。
3.运行出现问题：The requested resource is not available.
4.查找咨询，没有解决。后来查看web.xml。
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>loginserv</servlet-name>
<servlet-class>com.kaly.servlet.loginserv</servlet-class>
</servlet> <servlet-mapping>
<servlet-name>loginserv</servlet-name>
<url-pattern>/servlet/loginserv</url-pattern>
</servlet-mapping> </web-app>
因为这些都是自动生成，没有想到过会出现问题。不过记起以前写这个程序时<url-pattern>节点只是在<servlet-name>节点内容前多一个"/"，尝试将其改为/loginserv，重启服务运行页面。一些正常。
总结：这应该是这种问题出现的其中一种解决途径。