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HomeDatabaseMysql Tutorial三、第一个Servlet_MySQL

三、第一个Servlet_MySQL

Jun 01, 2016 pm 02:07 PM
importservletdesignationmethodask

servlet

3.1 Servlet基本结构

   下面的代码显示了一个简单Servlet的基本结构。该Servlet处理的是GET请求,所谓的GET请求,如果你不熟悉HTTP,可以把它看成是当用户在浏览器地址栏输入URL、点击Web页面中的链接、提交没有指定METHOD的表单时浏览器所发出的请求。Servlet也可以很方便地处理POST请求。POST请求是提交那些指定了METHOD=“POST”的表单时所发出的请求,具体请参见稍后几节的讨论。
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class SomeServlet extends HttpServlet {
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)

      throws ServletException, IOException {
      
  // 使用“request”读取和请求有关的信息(比如Cookies)
  // 和表单数据
    
    // 使用“response”指定HTTP应答状态代码和应答头
    // (比如指定内容类型,设置Cookie)
    
    PrintWriter out = response.getWriter();
    // 使用 "out"把应答内容发送到浏览器
  }
}




   如果某个类要成为Servlet,则它应该从HttpServlet 继承,根据数据是通过GET还是POST发送,覆盖doGet、doPost方法之一或全部。doGet和doPost方法都有两个参数,分别为HttpServletRequest 类型和HttpServletResponse 类型。HttpServletRequest提供访问有关请求的信息的方法,例如表单数据、HTTP请求头等等。HttpServletResponse除了提供用于指定HTTP应答状态(200,404等)、应答头(Content-Type,Set-Cookie等)的方法之外,最重要的是它提供了一个用于向客户端发送数据的PrintWriter 。对于简单的Servlet来说,它的大部分工作是通过println语句生成向客户端发送的页面。

   注意doGet和doPost抛出两个异常,因此你必须在声明中包含它们。另外,你还必须导入java.io包(要用到PrintWriter等类)、javax.servlet包(要用到HttpServlet等类)以及javax.servlet.http包(要用到HttpServletRequest类和HttpServletResponse类)。

   最后,doGet和doPost这两个方法是由service方法调用的,有时你可能需要直接覆盖service方法,比如Servlet要处理GET和POST两种请求时。

   3.2 输出纯文本的简单Servlet

   下面是一个输出纯文本的简单Servlet。

   3.2.1 HelloWorld.java
package hall;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class HelloWorld extends HttpServlet {

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