Servlet的生命周期

Servlet的生命周期是由tomcat服务器来控制的。

1 构造方法：

创建servlet对象的时候调用。默认情况下，第一访问servlet就会创建servlet对象只创建一次。说明servlet对象在tomcat中是单实例的。

2初始化 init方法

当创建完servlet对象的时候会调用init()方法,只调用一次。

　　1>ServletConfig对象

　　　　　　获取serlvet初始化参数

　　　　　　调用的时候用

　　　　　　this.getInitParameter(参数名)

　　2>ServletContext对象

　　　　获取上下文信息

　　　　 A 获取全局参数

　　　　　　ServletContext sc= this.getServletContext()

　　　　　　sc.getInitParameter("ecode");

　　　　　　 sc.getContextPath() 项目路径 --项目名字

　　　　　　sc.getRealPath() 发布路径 --发布后在tomcat中的路径

3 调用服务 service 方法其中就包含doGet doPost等方法

每次发送请求的时候调用。可以调用n次。

4 销毁 destory 方法

销毁servlet对象的时候调用，停止服务器或者重新部署的web项目的时候销毁servlet就会调用destory方法

package com.bw.reg.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;

import com.bw.reg.bean.Users;
import com.bw.reg.service.ServiceImpl;

public class LoginServlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public LoginServlet() {
		super();
		System.out.println("这里是构造方法");
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		System.out.println("销毁");
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @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");
		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("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @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
	 * 
	 */
	
	//这里是service方法
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
        
		boolean isLogin = false;
		
		//设置编码类型
		request.setCharacterEncoding("UTF-8");
		
		//获取登入时输入的用户名和密码
		String username = request.getParameter("username");
		String password = request.getParameter("pwd");
		
		//创建users的对象
		Users users = new Users();
		//给users的对象设置登入时输入的用户名和密码
		users.setUserName(username);
		users.setPwd(password);
		//登入时的查找
		ServiceImpl serImpl = new ServiceImpl();
		isLogin = serImpl.find(users);
	
		if(isLogin){
			System.out.println("登入成功！！");
		}else {
			System.out.println("登录失败");
		}
	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
		System.out.println("这里是初始化方法");
	}

}