Servlet

在开始前，先把Tomcat的/lib/servlet-api.jar加入到项目依赖库中。

Servlet类继承HttpServlet类，提供以下方法相应客户端请求：

• doGet() 响应客户端的get请求
• doPost() 响应客户端的post请求
• doPut 和 doDelete，不常用，不去了解

另外，HttpServlet还有两个方法：

• init() 创建Servlet实例时调用该方法
• destroy() 销毁Servlet实例时调用该方法

练习######

配合JSP编写一个小页面，收集表单数据后打印在浏览器上。

form.jsp代码如下

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %>




    




用户名：

男
女
喜欢的颜色：

红
绿
红配绿
国籍：


    China
    Russia
    Vietname

FIrstServlet.java代码如下

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

/**
 * Created by FanXiao on 2017/5/11.
 */

@WebServlet(name="firstServlet",urlPatterns={"/firstServlet"})
public class FirstServlet extends HttpServlet{
    public void service(HttpServletRequest request, HttpServletResponse response) throws IOException {
        //设置解码方式
        request.setCharacterEncoding("GBK");
        response.setContentType("text/html;charSet=GBK");
        //获取name、gender、color和country等请求参数值
        String name = request.getParameter("name");
        String gender = request.getParameter("gender");
        String[] color = request.getParameterValues("color");
        String country = request.getParameter("country");
        //获取out
        PrintStream out = new PrintStream((response.getOutputStream()));
        //输出html页面
        out.println("");
        out.println("");
        out.println("
 
 
 

 
 
 <% if(request.getAttribute("err") != null){
 out.println(request.getAttribut("err") + "
);
 } %>
 
 
 
输入用户名与密码
 

 用户名：

 密码：

 

 
 
 
 
 
从login.jsp采集到用户名和密码后，调用JavaBean对比数据库，根据结果不同转发到不同的jsp。LoginServlet.java如下
 
 
import javax.servlet.RequestDispatcher;
 import javax.servlet.ServletConfig;
 import javax.servlet.ServletException;
 import javax.servlet.annotation.WebInitParam;
 import javax.servlet.annotation.WebServlet;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 import java.io.IOException;
 import java.sql.ResultSet;
 
 
@WebServlet(name="login", urlPatterns = {"/login"},
 initParams={
 @WebInitParam(name="driver", value="com.mysql.jdbc,Driver"),
 @WebInitParam(name="url", value="jdbc:mysql://localhost:3306/javaee"),
 @WebInitParam(name="user", value="root"),
 @WebInitParam(name="password", value="123456")})
 public class LoginServlet extends HttpServlet{
 
 
@Override
public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String errMessage = "";
    //Servlet本身并不输出响应到客户端，因此必须将请求转发
    RequestDispatcher rd;
    //获取请求参数
    String username = request.getParameter("uesrname");
    String pass = request.getParameter("pass");
    try{
        //获取初始化参数
        ServletConfig config = getServletConfig();
        String driver = config.getInitParameter("driver");
        String url = config.getInitParameter("url");
        String user = config.getInitParameter("user");
        String password = config.getInitParameter("password");
        //调用JavaBean,查询数据库
        DbDao dd = new DbDao(driver, url, user, password);
        String sql = "select pass from user_table where name = ";
        ResultSet rs = dd.query(sql + username);
        //将结果转发到不同的jsp
        if (rs.next()){
            if (rs.getString("pass").equals(pass)){
                //获取session对象
                HttpSession session = request.getSession(true);
                //设置sessions属性，跟踪用户会话状态
                session.setAttribute("name",username);
                //获取转发对象
                rd = request.getRequestDispatcher("/welcom.jsp");
                //转发请求
                rd.forward(request,response);
            }
            else{
                errMessage += "输入的用户名或密码不正确";
            }
        }
        else{
            errMessage += "用户名不存在";
        }
    }
    catch (Exception e){
        e.printStackTrace();
    }

    //如果出错，转发到重新登入
    if (errMessage != null && !errMessage.equals("")){
        rd = request.getRequestDispatcher("/login.jsp");
        request.setAttribute("err", errMessage);
        rd.forward(request,response);
    }
}
 
 
}
 
 
DbDao.java用于连接和操作数据库
 
 
import java.sql.*;
 
 
/**
 
 
 
  
 
封装了数据库的增删改查功能
 */
 public class DbDao {
 private Connection conn;
 private String driver;
 private String url;
 private String username;
 private String pass;
 
public DbDao(){
 
}
 
public DbDao(String driver, String url, String username, String pass){
 this.driver = driver;
 this.url = url;
 this.username = username;
 this.pass = pass;
 }
 
public String getDriver() {
 return driver;
 }
 
public void setDriver(String driver) {
 this.driver = driver;
 }
 
public String getUrl() {
 return url;
 }
 
public void setUrl(String url) {
 this.url = url;
 }
 
public String getUsername() {
 return username;
 }
 
public void setUsername(String username) {
 this.username = username;
 }
 
public String getPass() {
 return pass;
 }
 
public void setPass(String pass) {
 this.pass = pass;
 }
 
//获取数据库连接
 public Connection getConnection() throws ClassNotFoundException, SQLException {
 if (conn == null){
 Class.forName(this.driver);
 conn = DriverManager.getConnection(url, username, pass);
 }
 return conn;
 }
 
//插入
 public boolean insert(String sql, Object... args) throws SQLException, ClassNotFoundException {
 PreparedStatement pstmt = getConnection().prepareStatement(sql);
 for (int i = 0; i < args.length; i++ ){
 pstmt.setObject(i + 1, args[i]);
 }
 if (pstmt.executeUpdate() != 1){
 return false;
 }
 return true;
 }
 
//查询
 public ResultSet query(String sql, Object... args) throws SQLException, ClassNotFoundException {
 PreparedStatement pstmt = getConnection().prepareStatement(sql);
 for (int i = 0; i < args.length; i++ ){
 pstmt.setObject(i + 1, args[i]);
 }
 return pstmt.executeQuery();
 }
 
//修改
 public void modify(String sql, Object... args) throws SQLException, ClassNotFoundException {
 PreparedStatement pstmt = getConnection().prepareStatement(sql);
 for (int i =0; i < args.length; i++ ){
 pstmt.setObject( i + 1, args[i]);
 }
 pstmt.executeUpdate();
 pstmt.close();
 }
 
//关闭数据库连接
 public void closeConn() throws SQLException {
 if (conn != null && !conn.isClosed()){
 conn.close();
 }
 }
 }
 
 
 
 
 
如果输入的用户名和密码有错误，则转发到login.jsp，并展示错误信息。
否则，登陆成功，转到welcom.jsp，如下
 
 

 
 
 
 
 

 <% out.print(request.getParameter("username") + "，欢迎回来！"); %>