jabc访问数据库-查询

 实例一：

目录结构：

 

mysql：

 

代码实现：

package demo1;

import java.sql.*;

public class Test3 {
    public static void main(String[] args){
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;

        try {
            //加载驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.建立连接
            //url的格式：主协议:子协议:名称
            String url = "jdbc:mysql://127.0.0.1:3306/mysql_test?useUnicode=true&characterEncoding=utf8";
            connection = DriverManager.getConnection(url,"root","13474501003");
            //
            String sql = "SELECT * FROM student";
            statement = connection.createStatement();
            //执行
            //查询用excuteQuery方法
            resultSet = statement.executeQuery(sql);
            //处理结果
            //resultSet.next()：判断是否有下一行
            while (resultSet.next()){
                //rs.getXXXX()：参数可以是列号（不推荐使用）、列名
                int sno = resultSet.getInt("sno");
                String sname = resultSet.getString("sname");
                String sex = resultSet.getString("sex");
                int age = resultSet.getInt("age");
                String addr = resultSet.getString("addr");
                System.out.println(sno+"\t"+sname+"\t"+sex+"\t"+age+"\t"+addr);
            }
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }finally {
            //关闭
            try {
                if (resultSet != null){
                    resultSet.close();
                }
                if (statement != null){
                    statement.close();
                }
                if (connection != null){
                    connection.close();
                }
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}

 结果：

实例二：

目录结构：

 

mysql目录结构：

 

最初的student表：

代码实现：

Dbutil1：

package util;

import java.sql.*;

public class Dbuitl1 {

    static Connection connection = null;
    static PreparedStatement preparedStatement = null;
    static ResultSet resultSet = null;

    static{
        try{
            //加载驱动
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    //获取连接
    public static Connection getConnection(){
        try {
            //2.建立连接
            //url的格式：主协议:子协议:名称
            String url = "jdbc:mysql://127.0.0.1:3306/mysql_test?useUnicode=true&characterEncoding=utf8";
            connection = DriverManager.getConnection(url,"root","13474501003");
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return connection;
    }
    //创建PreparedStatement对象，并设置参数
    public static void createPreparedStatement(String sql,Object...arr){
        try {
            preparedStatement = connection.prepareStatement(sql);
            //设置参数
            int i;
            for (i = 0;i < arr.length;i++){
                preparedStatement.setObject(i+1,arr[i]);
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }
    //执行DML语句
    public static int executeUpdate(){
        int n = 0;
        try {
            n = preparedStatement.executeUpdate();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return n;
    }
    //执行查询语句，返回ResultSet对象
    public static ResultSet excuteQuery(){
        try {
            resultSet = preparedStatement.executeQuery();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return resultSet;
    }
    //关闭
    public static void close(){
        try {
            if (resultSet != null){
                resultSet.close();
            }
            if (preparedStatement != null){
                preparedStatement.close();
            }
            if (connection != null){
                connection.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }
}

 Test3：

package demo2;

import util.Dbuitl1;

import java.sql.ResultSet;
import java.sql.SQLException;

public class Test3 {
    public static void main(String[] args){
        Dbuitl1.getConnection();
        String sql = "SELECT * FROM student WHERE age>?";
        Dbuitl1.createPreparedStatement(sql,28);
        ResultSet resultSet = Dbuitl1.excuteQuery();
        try {
            while (resultSet.next()){
                int sno = resultSet.getInt("sno");
                String name = resultSet.getString("sname");
                System.out.println(sno+"\t"+name);
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        Dbuitl1.close();
    }
}

结果：

年龄大于28的