JavaWeb连接并使用mysql数据库

  

不带参 

package JDBC_Web;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;

public class JDBC_Select extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //数据库使用：第一步装载驱动
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");//加载驱动器

            //第二步，建立数据库连接,con是建立好的一个数据库对象
            Connection con= DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbc","root","123456");

            //第三步，执行sql语句
            String sql="select * from tb_user";//定义一个查询语句出来
            Statement st=con.createStatement();//获取查询对象,注意这种查询不能带参数
            ResultSet rs=st.executeQuery(sql);//执行查询语句

            //第四步，把执行完查询语句的结果的数据提取出来，这里是输出到控制台上，正常是要输出到客户端的哦
//            while ((rs.next())){
//                System.out.println("id:"+rs.getString("id"));
//                System.out.println("name:"+rs.getString("name"));
//                System.out.println("age:"+rs.getString("age"));
//                System.out.println("interest:"+rs.getString("interest"));
//            }
            //向客户端输出例子
            response.setContentType("text/html;charset=UTF-8");
            PrintWriter out=response.getWriter();
            out.write("");
            out.write("");
            out.write("");
            out.write("");
            out.write("");
            out.write("");
            out.write("");

            while (rs.next()){
                out.write("");
                out.write("");
                out.write("");
                out.write("");
                out.write("");
                out.write("");
            }

            out.write("
id
name
age
interest
"+rs.getString("id")+"
"+rs.getString("name")+"
"+rs.getString("age")+"
"+rs.getString("interest")+"
");

            //第五步，关闭数据库连接
            con.close();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }

    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

下面是带参的，允许接收前端发过来的参数来查询，并在客户端显示出来

    
    




    请输入要查询的用户:
    

    

package JDBC_Web;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;

public class JDBC_Web_WithParameter extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String name=request.getParameter("name");
        try {
            //数据库使用：第一步装载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");//加载驱动器

            //第二步，建立数据库连接,con是建立好的一个数据库对象
            Connection con= DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbc","root","123456");

            //第三步，构建查询对象,这种Statement是带参的，允许接收前端传过来的参数
            PreparedStatement preparedStatement = con.prepareStatement("select * from tb_user where name =?");//这里的问号是暂定的意思，可以有很多个
            preparedStatement.setString(1, name);//1代表第一个问号，name就是给这个问号的值

            //获取结果
            ResultSet rs=preparedStatement.executeQuery();

            response.setContentType("text/html;charset=UTF-8");
            PrintWriter out=response.getWriter();
            out.write("");
            out.write("");
            out.write("");
            out.write("");
            out.write("");
            out.write("");
            out.write("");

            while (rs.next()){
                out.write("");
                out.write("");
                out.write("");
                out.write("");
                out.write("");
                out.write("");
            }

            out.write("
id
name
age
interest
"+rs.getString("id")+"
"+rs.getString("name")+"
"+rs.getString("age")+"
"+rs.getString("interest")+"
");

            //第五步，关闭数据库连接
            con.close();

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


    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}