Servlet基础笔记_17-07-05

来源：互联网发布：excel数据分析占比编辑：程序博客网时间：2024/06/05 07:53

三个重写方法

1.Servlet的 init()方法:

默认情况下：当第一次访问该Servlet时，被调用（该Servlet被初始化），且只被调用一次【public void init() throws ServletException{

super.init();】(第一次访问只被调用一次)

2.Servlet的 servlet()方法:

servlet的主方法，每访问一次就被调用一次

【protected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException】

3.Servlert的destroy()方法:

【public void destroy() 】

在服务器被关闭时，被调用（该Servlet被销毁）

package com.yy.servlet.web.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 javax.xml.ws.Response;public class FirstServlet extends HttpServlet{@Override public void init() throws ServletException{super.init();System.out.println("第一次启动只调用一次");}@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {System.out.println("访问一次调用一次");}@Overridepublic void destroy() {super.destroy();System.out.println("被摧毁");}}

===========================================

Servlert也是单例模式，Servlert只被初始化一次

===========================================

通过Servlert判断接收的参数是否存在数据库

package com.yy.servlet.web.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 java.util.HashMap;import java.util.Map;import com.yy.servlet.dao.UserDao;import com.yy.servlet.po.User;public class FirstServlet extends HttpServlet {@Overridepublic void init() throws ServletException {System.out.println("FirstServlet这个servlet被初始化");}@Override protected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//接收参数String username = request.getParameter("username");String password = request.getParameter("password");response.setCharacterEncoding("UTF-8");response.setContentType("text/html");PrintWriter out = response.getWriter();out.print("用户名"+username);out.print("密码"+password);UserDao userDao = UserDao.getInstance();Mapmap = new HashMap();map.put("username", username);map.put("password",password);User user =userDao.getUserByMap(map);if(user !=null){out.print("在数据库中存在");}else{out.print("数据库中不存在");}out.flush();out.close();}@Overridepublic void destroy() {System.out.println("FirstServlet这个servlet被摧毁");}}

网页效果如下图

==========================================================

HttpServletRequest接口

获取请求的基本信息

1.getMethod()方法：返回客户端请求方式

2.getRequestURL()方法：返回端口后参数之前那部分内容，且为真实的资源名，而不一定与地址栏中相同

3.getQueryString()方法：返回资源路径?号后面所有的内容

4.getScheme()方法：返回协议名称

5.getContextPath()方法：返回情切url所属的web应用程序的路径

6.getrequestURL()方法：返回真实的资源路径，不一定与地址栏相同，但不包括参数部分，且返回类型SrtingBuffer

标准Servlert的写法：

1.新建一个Servlert

2.写上名字，选择doget()方法和doPost()方法

3.点next 给servlet配上在web.xml文件中的名字和URL，点finish 会在web.xml文件中自动配置Servlert

不需要 service()方法

实际上 service()方法就是先判断，请求的方式

get方式：Service()方法就调用doget()方法

psot方式：Service()方法就调用doPost()方法

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用servlet写一个注册登录的用户例子

第一个使用jsp文件建一个登录开头

              登录页面                  用户名：
  密码：

数据库中如果存在就能登录成功

不存在就会弹出注册然后跳转

注册成功后数据会保存在数据库

package com.yy.servlet.web.servlet;import java.io.IOException;import java.io.PrintWriter;import java.util.HashMap;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.yy.servlet.dao.UserDao;import com.yy.servlet.po.User;public class LonginServlet extends HttpServlet {@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html");response.setCharacterEncoding("UTF-8");String username = request.getParameter("username");String password = request.getParameter("password");PrintWriter out = response.getWriter();out.print("用户名"+username);out.print("密码"+password);UserDao userDao = UserDao.getInstance();Mapmap = new HashMap();map.put("username", username);map.put("password",password);User user =userDao.getUserByMap(map);if(user != null){out.print("登陆成功");}else{out.print("用户名不存在，请注册");out.print("");out.print("用户名
");out.print("密码
");out.print("
");}out.flush();out.close();}}

package com.yy.servlet.web.servlet;import java.io.IOException;import java.io.PrintWriter;import java.util.HashMap;import java.util.Map;import java.util.Set;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.yy.servlet.dao.UserDao;import com.yy.servlet.po.User;public class NextServlet extends HttpServlet{@Overridepublic void init()throws ServletException{super.init();}@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// TODO Auto-generated method stubresponse.setCharacterEncoding("UTF-8");response.setContentType("text/html");String username = request.getParameter("username");String password = request.getParameter("password");UserDao userDao=UserDao.getInstance();PrintWriter out = response.getWriter();out.print("用户名"+username);out.print("密码"+password);Map map= new HashMap();map.put("username",username);map.put("password",password);User user =userDao.getUserByMap(map);if(user != null){out.print("用户名已存在,请登录
");out.print("");out.print("用户名
");out.print("密码
");out.print("
");}else{User user2 = new User();user2.setUsername(username);user2.setPassword(password);boolean flag = UserDao.getInstance().saveUser2(user2);if(flag){out.print("OK");}else{out.print("NO");}} out.flush();out.close();}}

这是UserDao 中被调用的查询语句和插入语句

public User getUserByMap(Map map){User user = null;Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;String sql = "select * from user where username = ? ";try {conn = DBconnectionUitl.getConnection();ps = conn.prepareStatement(sql);ps.setString(1, map.get("username"));rs = ps.executeQuery();while(rs.next()){user = new User();user.setUserId(rs.getInt("userId"));user.setUsername(rs.getString("username"));user.setSex(rs.getInt("sex"));user.setPassword(rs.getString("password"));user.setFlag(rs.getInt("flag"));}} catch (SQLException e) {e.printStackTrace();} finally {DBconnectionUitl.closeAll(rs, ps, conn);}return user;}//查询数据库中是否存在数据public boolean saveUser2 (User user2){boolean flag = false;Connection conn = null;PreparedStatement ps = null;String sql = "insert into user (username,password) value (?,?)";try {conn = DBconnectionUitl.getConnection();ps = conn.prepareStatement(sql);ps.setString(1,user2.getUsername());ps.setString(2,user2.getPassword());int rows =ps.executeUpdate();if(rows != 0)flag =true;} catch (SQLException e) {e.printStackTrace();} finally {DBconnectionUitl.closeAll(null,ps,conn);}return flag;}}                    //注册时调用的插入语句

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