jsp+servlet+tomcat简单的数据库查询项目

JSP负责页面展现，其实jsp也是一个java类，最开始java为了在显示页面不得不分别out.println()方法输出标签，那样将显示与业务逻辑混合在一起很不好维护也不简洁。因此诞生了jsp技术。jsp全称为java server page。它是在服务端运行的程序。

• java web最经典的还是jsp + servlet +mysql + tomcat。
  接下来我们开始一个简单的java web项目。功能为查询数据库，输入学生号然后显示对应的学生姓名，输入姓名返回对应学生的学号，优先从姓名查找学号。

• 数据库为我昨天博客里建的请点击此处查看

目录结构为：

首先我们创建实体类：Student

package micro.entity;

public class Student {
    String name;
    int no;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getNo() {
        return no;
    }
    public void setNo(int no) {
        this.no = no;
    }

}

• 创建dao，负责数据库的连接与关闭：

package micro.dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import com.mysql.jdbc.PreparedStatement;

public class Dao {
    public static Connection getConnection() throws SQLException
    {
        String url = "jdbc:mysql://localhost:3306/micro";
        String username = "root";
        String password = "root";
        Connection conn = null;
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(url, username, password);
        }
        catch(ClassNotFoundException e)
        {
            e.printStackTrace();
        }
        return conn;
    }
    public static void close(ResultSet rs,PreparedStatement ps,Connection conn) throws SQLException
    {
        try
        {
            rs.close();
            ps.close();
            conn.close();
        }
        catch(SQLException e)
        {
            e.printStackTrace();
        }
    }
}

• 创建查询方法类（按名字查询和按学号查询）：

package micro.dao;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import micro.entity.Student;

import com.mysql.jdbc.PreparedStatement;

public class SearchDao {
    /** * @param micro * @return * @throws SQLException */
    // static String sql = "select * from Student where ? = ?";
    public static int getIdByName(String name) throws SQLException {
        int id = -1;
        try {
            Connection conn = Dao.getConnection();
            PreparedStatement ps = (PreparedStatement) conn
                    .prepareStatement("select * from Student where name = ?");
            // ps.setString(1, "name");
            ps.setString(1, name);
            ResultSet rs = ps.executeQuery();
            // List<Student> list = new ArrayList();
            while (rs.next()) {
                id = rs.getInt("id");
            }
            Dao.close(rs, ps, conn);

        } catch (SQLException e) {
            e.printStackTrace();
        }

        return id;
    }

    /** * @param id * @return * @throws SQLException */
    public static String getNameById(int id) throws SQLException {
        Connection conn;
        String name = null;
        try {
            conn = Dao.getConnection();
            PreparedStatement ps = (PreparedStatement) conn
                    .prepareStatement("select * from Student where id = ?");
            // ps.setString(1, "");
            ps.setInt(1, id);
            ResultSet rs = ps.executeQuery();
            while (rs.next()) {
                name = rs.getString("name");
            }
            Dao.close(rs, ps, conn);

        } catch (SQLException e) {
            e.printStackTrace();
        }
        return name;
    }
}

• 需要执行业务的servlet:

package micro.search;

import java.io.IOException;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import micro.dao.SearchDao;

/** * Servlet implementation class FindName */
@WebServlet("/FindName")
public class FindNameOrNo extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /** * @see HttpServlet#HttpServlet() */
    public FindNameOrNo() {
        super();
        // TODO Auto-generated constructor stub
    }

    /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        this.doPost(request, response);
    }

    /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String username = request.getParameter("username");
        int id = Integer.valueOf(request.getParameter("id"));

        if(!username.equals(""))
        {
            try
            {
                int no = SearchDao.getIdByName(username);
                request.setAttribute("id", no);
            }
            catch(SQLException e)
            {
                System.out.println("数据库出现异常");
                e.printStackTrace();
            }
            request.getRequestDispatcher("/WEB-INF/IdResult.jsp").forward(request, response);
        }
        else
        {
            try
            {
                String name = SearchDao.getNameById(id);
                request.setAttribute("name", name);
            }
            catch(SQLException e)
            {
                System.out.println("数据库出现异常");
                e.printStackTrace();
            }
            request.getRequestDispatcher("/WEB-INF/NameResult.jsp").forward(request, response);
        }
        }


}

• welcome.jsp页面：

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<!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="myQuery" method="post">
        请输入学生姓名：<input type="text" name="username" /> <br /> 请输入学生学号：<input  type="text" name="id" /> <br /> <input type="submit" value="查询" />
    </form>
</body>
</html>

• 返回学号的页面：

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<!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>
<h1>
查询结果对应的学号为:<%= request.getAttribute("id") %>
</h1>
<form action="welcome.jsp" method = "post" >
<input type = "submit" value = "返回" /> 
</form>
</body>
</html>

• 返回名字的页面：

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<!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>
    <h1>
        该学号的同学名字为：<%=request.getAttribute("name")%>
    </h1>
    <form action="welcome.jsp" method="post">
        <input type="submit" value="返回" />
    </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_2_5.xsd" version="2.5">
    <servlet>
        <servlet-name>Query</servlet-name>
        <servlet-class>micro.search.FindNameOrNo</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Query</servlet-name>
        <url-pattern>/myQuery</url-pattern>
    </servlet-mapping>
    <welcome-file-list>
        <welcome-file>welcome.jsp</welcome-file>
    </welcome-file-list>
</web-app>

• 需要的jar包：mysql-connector-java.jar
• build path只是个jar包的引用，部署的时候想不丢包最好还是手动拷贝到对应项目的lib文件下。
• 在try{}中定义的变量为局部变量。
• WEB-INF对于浏览器是无法直接通过url访问的，因此要想跳转到WEB-INF目录下必须采用服务端的foward方法而不能采用redirect方法。
• 注意网页的编码问题，一般全采用utf-8就没乱码了。
• 注意pageContext,request,session,application对象的scope，作用范围。