动手学servlet(二) servlet基础

1、我们来试着向一个servlet提交一个表单，现在webcontent下新建一个login.html页面，其中action对应servelt类名,代码如下：

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<title>提交表单</title>
</head>
<body>
<form action="LoginServlet" method="post">
用户名：<input name="username" type="text"><br>
密码：<input name="password" type="password"><br>
<input value="提交" name="submit" type="submit">
</form>
</body>
</html>

代码

附：request.getParameter("username");可以读取用户名输入框的值，针对复选框需要调用request.getParameterValues(name);将返回一个字符串数组

2、新建一个servlet类LoginServlet，代码如下：

package servletdemo;

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

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

    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        System.out.print("loginservlet...");
        // TODO Auto-generated constructor stub
    }

    @Override
    public void init() throws ServletException {
        // TODO 自动生成的方法存根
        System.out.print("init...");
    }
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.print("doget...");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.print("dopost...");
    }

    @Override
    public void destroy() {
        // TODO 自动生成的方法存根
        System.out.print("destory...");
    }

}

代码

注意：右键新建一个servlet不会在web.xml生成对应的配置标签，是因为servlet类里已经有了@WebServlet注解

3、运行login.html，可以验证servlet的生命周期，效果如下：

4、有时候需要获得web.xml里一些配置信息，例如下面的配置，其中name相当于key，value就是对应的值

<context-param>
<param-name>henry</param-name>
<param-value>123</param-value>
</context-param>

用这行代码就可以获得KEY对应的值：String result=this.getServletContext().getInitParameter("henry");  

5、servlet在MVC中相当于controller，所以经常需要做一些页面的跳转，下面来看看页面导航的实现

• 请求重定向

直接跳转到其他的网站，response.sendRedirect("http://www.baidu.com");

• 请求包含

就是跳转到另外一个serlvet，但是也输出本servlet的内容，具体看例子

//需要跳转的servlet的doGet()方法

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        PrintWriter out=response.getWriter();
        out.print("<h1>LoginServlet</h1>");
        request.getRequestDispatcher("MyServlet").include(request, response);
    }

//跳转到的MyServlet的doGet()方法
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO 自动生成的方法存根
        String result=this.getServletContext().getInitParameter("henry");
        System.out.print(result);
        resp.setContentType("text/html;charset=gbk");
        PrintWriter pw=resp.getWriter();
        pw.write(result);
        pw.close();
    }

代码

• 请求跳转

也是跳转到另外一个servlet，但是不输出本servlet的内容

//需要跳转的servlet的doGet()方法

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        PrintWriter out=response.getWriter();
        out.print("<h1>LoginServlet</h1>");
        request.getRequestDispatcher("MyServlet").forward(request, response);
    }

//跳转到的MyServlet的doGet()方法
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO 自动生成的方法存根
        String result=this.getServletContext().getInitParameter("henry");
        System.out.print(result);
        resp.setContentType("text/html;charset=gbk");
        PrintWriter pw=resp.getWriter();
        pw.write(result);
        pw.close();
    }

代码

 注意：getRequestDispatcher()方法的参数不是servlet类名，而是web.xml里url-pattern节点中的值