Servlet学习笔记实践

目标：

1、看看Servlet开发、部署、请求、执行、响应全过程。

2、理解HTTP请求，并能熟练使用get、post请求。

实践：

一、开发Servlet

package test;

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 TestServlet extends HttpServlet {

  /**
    * 构造方法
    */
  public TestServlet() {
    super();
  }

  /**
    * Servlet销毁方法. <br>
    */
  public void destroy() {
    super.destroy(); // Just puts "destroy" string in log
    // Put your code here
  }

  /**
    * The doDelete method of the servlet. <br>
    *
    * 当收到一个HTTP delete请求的时候执行该方法.
    *
    * @param request the request send by the client to the server
    * @param response the response send by the server to the client
    * @throws ServletException if an error occurred
    * @throws IOException if an error occurred
    */
  public void doDelete(HttpServletRequest request,
      HttpServletResponse response) throws ServletException, IOException {

    // Put your code here
  }

  /**
    * The doGet method of the servlet. <br>
    *
    * 当收到一个HTTP get请求的时候执行该方法.
    *
    * @param request the request send by the client to the server
    * @param response the response send by the server to the client
    * @throws ServletException if an error occurred
    * @throws IOException if an error occurred
    */
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    response.setContentType("text/html");
    request.setCharacterEncoding("GB18030");
    PrintWriter out = response.getWriter();
    out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
    out.println("<HTML>");
    out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
    out.println("    <BODY>");
    out.print("        This is ");
    out.print(this.getClass());
    out.println(", using the GET method");

    out.println("<br>");
    String x = request.getParameter("x");
    String y = request.getParameter("y");
    out.println("x="+x);
    out.println("<br>");
    out.println("y="+y);
    out.println("<br>");

    out.println("    </BODY>");
    out.println("</HTML>");
    out.flush();
    out.close();
  }

  /**
    * The doPost method of the servlet. <br>
    *
    * 当收到一个HTTP post请求的时候执行该方法.
    *
    * @param request the request send by the client to the server
    * @param response the response send by the server to the client
    * @throws ServletException if an error occurred
    * @throws IOException if an error occurred
    */
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    out
        .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
    out.println("<HTML>");
    out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
    out.println("    <BODY>");
    out.print("        This is ");
    out.print(this.getClass());
    out.println(", using the POST method");

    out.println("<br>");
    String x = request.getParameter("x");
    String y = request.getParameter("y");
    out.println("x="+x);
    out.println("<br>");
    out.println("y="+y);
    out.println("<br>");

    out.println("    </BODY>");
    out.println("</HTML>");
    out.flush();
    out.close();
  }

  /**
    * The doPut method of the servlet. <br>
    *
    * 当收到一个HTTP put请求的时候执行该方法.
    *
    * @param request the request send by the client to the server
    * @param response the response send by the server to the client
    * @throws ServletException if an error occurred
    * @throws IOException if an error occurred
    */
  public void doPut(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    // Put your code here
  }

  /**
    * Returns information about the servlet, such as
    * author, version, and copyright.
    *
    * @return String information about this servlet
    */
  public String getServletInfo() {
    return "This is my default servlet created by Eclipse";
  }

  /**
    * Servlet初始化. <br>
    *
    * @throws ServletException if an error occurs
    */
  public void init() throws ServletException {
    // Put your code here
  }

}

2、配置Servlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app 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
  [url]http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd[/url]">
    <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>TestServlet</servlet-name>
        <servlet-class>test.TestServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>TestServlet</servlet-name>
        <url-pattern>/testServlet</url-pattern>
    </servlet-mapping>

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

3、访问Servlet

部署web应用并启动Servlet容器Tomcat。然后分别用两种方式来访问Servlet

a、通过URL直接访问

[url]http://localhost:8080/HelloApp/testServlet?x=11222&y=13123421[/url]

注意：第一参数x之前要用"?"号，其余参数之间用"&"符号。

显示效果：

b、通过一个JSP来访问

<%@ page language="java" import="java.util.*" pageEncoding="GB18030"%>
<%
String path = request.getContextPath();
%>
<html>
    <body>
        test post Method<br>
        <form action="<%=path %>/testServlet" method="post">
          x:<input type="text" name="x"><br>
          y:<input type="text" name="y"><br>
          <input type="submit" value="submit">
          <input type="reset" value="reset">
        </form>

    </body>
</html>

如果将jsp中form的请求方式改为get，则点击submit按钮会显示：

二、简单总结下

HTTP请求有很多种，最常用的就是get和post。get请求的参数提交后会显示在url后面，而post请求不会。

get请求适合少量数据，post请求没有限制。

get请求参数会显示在rul后面，不安全。可以直接请求。

从安全角度考虑，应该使用post请求。

转载于:https://blog.51cto.com/trans/114569

Servlet学习笔记 实践

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