调用 servlet 时出错

Question

我是 servlet.I 的新手，我正在尝试调用 Servlet 来验证用户名和密码。但是执行的时候，tomcat报错"The requested resource is not available"

代码如下

RequestServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.*;
import javax.servlet.ServletException;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class RequestServlet
 */
@WebServlet("/RequestServlet")
public class RequestServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    PrintWriter out;

    /**
     * @see HttpServlet#HttpServlet()
     */

    public void service(HttpServletRequest req,HttpServletResponse res)throws ServletException,IOException
    {
        ((ServletResponse) res).setContentType("text/html");
        out=((ServletResponse) res).getWriter();
        out.println("<html><body>");
        out.println(req.getMethod());

    String name=req.getParameter("name");
        String pass=req.getParameter("pass");
        if(name.equals("asad")&&pass.equals("123"))
            out.println("user is valid");
        else
            out.println("not valid");
        out.println("</body></html>");  
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>Learnserv</display-name>
  <servlet>
        <servlet-name>RequestServlet</servlet-name>
        <servlet-class>RequestServlet</servlet-class>
    </servlet> 

   <servlet-mapping>
        <servlet-name>RequestServlet</servlet-name>
        <url-pattern>/RequestServlet</url-pattern>
    </servlet-mapping>
  <welcome-file-list>

    <welcome-file>asd.html</welcome-file>
  </welcome-file-list>
</web-app>

asd.html

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form action="/RequestServlet"   method="GET">
<input type="text" name="name">
<input type="password" name="pass">
<input type="submit" value="ok">
</form>
</body>

Answer 1

尝试改变<form action="/RequestServlet" method="GET"> 至 <form action="RequestServlet" method="post"> 我认为 /RequestServlet 已被 localhost:port/RequestServlet 取代，但需要 localhost:port/context/RequestServlet（如果不为 Tomcat 在 webapps/ROOT 部署）

另外，如果使用 @WebServlet("/RequestServlet") 那么在 web.xml 中做同样的事情是重复的。或注解或web.xml.

并将 PrintWriter out 放在 service 内以确保线程安全。

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