jsp之servlet初识

2016-09-08

Study

java, servlet

最近几天，天气阴晴不定，雨时断时续，心情也是不太好，老是犯困，效率也不太高，看来是放松了自己，肚子上的肉还是没有减下来，学习的动力也没有以前足了。看到妹子在备战即将到来的教

师资格证的考试，心里也是对自己的放松感到愧疚，那就学习吧。前段时间学习了web请求的类型，以及请求和响应的相关知识。现在大部分针对的都是B/

S结构的，通过浏览器去与用户交互。现在更深入的去了解下整个请求响应的过程。

现在我们已经通过MyEclipse新建了一个web-project，src目录里面存放servlet相关java文件，在容器配置好后，将会编译后存放在webapps-webINF-classes里面。WebRoot目录下放置资源文件，也会存放在容器webapps中。
接下来我们来分析下一个请求怎样输出在浏览器，以简单的登录注册为例。首先，在浏览器访问一个地址localhost:8080/blog/login;然后请求会在web.xml文件中解析，里面servlet映射里面的url-partting有没有对应的/login地址，有的话找出对应的servlet-name，然后根据servlet-name（servlet注册）找到对应的包下面的servlet程序地址，然后执行doGet或者doPost方法。

具体实现代码：
LoginResServlet.java

package com.xieth.javaweb;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginResServlet extends HttpServlet {
    sqlDemo sqlD = null;
    @Override
    public void init(ServletConfig config) throws ServletException {
        try {
            sqlD = new sqlDemo();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        req.setCharacterEncoding("utf-8");
        String action = req.getParameter("action");
        PrintWriter out = resp.getWriter();
        // 注册
        if (action.equals("Register")) {
            String name = req.getParameter("name");
            String password = req.getParameter("password");
            String passwordProblm = req.getParameter("passwordProblem");
            String problemResult = req.getParameter("problemResult");
            boolean isEmpty = (name != null && !name.equals("")
                    && password != null && !password.equals("")
                    && passwordProblm != null && !passwordProblm.equals("")
                    && problemResult != null && !problemResult.equals(""));
            System.out.println(isEmpty);
            if (isEmpty) {
                try {
                    boolean flag = sqlD.InsertData(name, password,
                            passwordProblm, problemResult);
                    if (flag) {
                        out.println("<h1>恭喜你" + name
                                + ":注册成功点击<a href='login.html'>登录</a></h1>");
                    } else {
                        out.println("<h1>Soory"
                                + name
                                + ":注册失败,该用户已经存在,点击<a href='Register.html'>重新注册</a></h1>");
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            } else {
                out.println("<h1>所以选项均不可以为空！！！点击<a href='Register.html'>重新注册</h1>");
            }
        } else { // 登录
            String name = req.getParameter("name");
            String password = req.getParameter("password");
            try {
                boolean flag = sqlD.LoginCorrect(name, password);
                if (flag) {
                    out.println("<h1>欢迎你:" + name + "</h1>");
                } else {
                    out.println("<h1>SOrry密码错误！点击重新<a href='login.html'>登录</a></h1>");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        this.doGet(req, resp);
    }
}
class sqlDemo {
    private Connection conn = null;
    private Statement statement = null;
    public sqlDemo() throws Exception {
        conn = getConnection();
        statement = conn.createStatement();
    }
    // 查看登录用户名和密码是否正确
    public boolean LoginCorrect(String name, String password) throws Exception {
        String sql = "select * from logindemo where name = '" + name + "'";
        ResultSet rs = statement.executeQuery(sql);
        // 查看是否合法
        while (rs.next()) {
            if (name.equals(rs.getString("name"))
                    && password.equals(rs.getString("password")))
                return true;
        }
        rs.close();
        return false;
    }
    // 插入数据
    public boolean InsertData(String name, String password,
            String passwordProblm, String problemResult) throws Exception {
        String sql = "insert into logindemo values ('" + name + "','"
                + password + "','" + passwordProblm + "','" + problemResult
                + "')";
        String isAgainSql = "select name from logindemo where name = '" + name
                + "'";
        ResultSet rs = statement.executeQuery(isAgainSql);
        // 查看是否用户名重复
        while (rs.next()) {
            if (rs.getString("name").equals(name)) {
                return false;
            }
        }
        statement.executeUpdate(sql);
        rs.close();
        return true;
    }
    private Connection getConnection() throws Exception {
        String driverClass = "com.mysql.jdbc.Driver";
        String url = "jdbc:mysql:///hello?useUnicode=true&characterEncoding=utf8";
        String user = "root";
        String password = "123456";
        // 注册加载驱动
        Class.forName(driverClass);
        // 获取连接
        Connection conn = DriverManager.getConnection(url, user, password);
        System.out.println(conn);
        return conn;
    }
}

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="LoginResServlet" method="post">
        用户名:<input type="text" name="name"> 密码:<input type="password"
            name="password"> 密码找回问题:<input type="text"
            name="passwordProblem"> 答案:<input type="text"
            name="problemResult"> <input type="submit" value="注册">
        <input type="hidden" name="action" value="Register">
    </form>
</body>
</html>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="LoginResServlet" method="post">
        用户名:<input type="text" name="name"> 密码:<input type="password"
            name="password"> <input type="submit" value="登录"> <input
            type="hidden" name="action" value="login">
    </form>
</body>
</html>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">
    <servlet>
		<!--servlet注册-->
        <servlet-name>LoginResServlet</servlet-name>
        <servlet-class>com.xieth.javaweb.LoginResServlet</servlet-class>
    </servlet>
	<!-- servlet映射 -->
    <servlet-mapping>
        <servlet-name>LoginResServlet</servlet-name>
        <url-pattern>/LoginResServlet</url-pattern>
    </servlet-mapping>
</web-app>