public static List<Map<String,Object>> queryForList(){  
    Connection connection = null;  
    ResultSet rs = null;  
    PreparedStatement stmt = null;  
    List<Map<String,Object>> resultList = new ArrayList<Map<String,Object>>();  

    try {  
        // 加载 JDBC 驱动  
        Class.forName("oracle.jdbc.driver.OracleDriver").newInstance();  
        String url = "jdbc:oracle:thin:@localhost:1521:ORACLEDB";  

        String user = "trainer";   
        String password = "trainer";   

        // 建立并获取数据库连接 
        connection = DriverManager.getConnection(url,user,password);   

        String sql = "select * from userinfo where user_id = ? ";  
        // 创建 JDBC Statements 对象（每一个Statement为一次数据库执行请求）  
        stmt = connection.prepareStatement(sql);  

        // 设置 SQL 语句的传入参数  
        stmt.setString(1, "zhangsan");  

        // 执行 SQL 语句并获得查询结果 
        rs = stmt.executeQuery();  

        // 对查询结果进行转换处理并将处理结果返回（将查询结果转换成List<Map>格式）  
        ResultSetMetaData rsmd = rs.getMetaData();  
        int num = rsmd.getColumnCount();  

        while(rs.next()){  
            Map map = new HashMap();  
            for(int i = 0;i < num;i++){  
                String columnName = rsmd.getColumnName(i+1);  
                map.put(columnName,rs.getString(columnName));  
            }  
            resultList.add(map);  
        }  

    } catch (Exception e) {  
        e.printStackTrace();  
    } finally {  
        try {  
            // 关闭 ResultSet 
            if (rs != null) {  
                rs.close();  
                rs = null;  
            }  
            // 关闭 Statement  
            if (stmt != null) {  
                stmt.close();  
                stmt = null;  
            }  
            //关闭 Connection
            if (connection != null) {  
                connection.close();  
                connection = null;  
            }  
        } catch (SQLException e) {  
            e.printStackTrace();  
        }  
    }        
    return resultList;  
}

package demo.yangxu.jdbc;

import java.io.Serializable;

public class User implements Serializable {
    private Integer id;
    private String username;
    private  Integer age;
    private String phone;
    private  String desc;

    //Getter和Setter方法略
    //toString方法略
}

package demo.yangxu.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DbUtil {
    /*
     * 打开数据库
     */
    private static String driver;//连接数据库的驱动
    private static String url;
    private static String username;
    private static String password;

    static {
        driver="com.mysql.jdbc.Driver";//需要的数据库驱动
        //url="jdbc:mysql://127.0.0.1:3306/mybatis_learn?characterEncoding=utf8&serverTimezone=UTC&useSSL=false";
        //url="jdbc:mysql://127.0.0.1:3306/mybatis_learn?characterEncoding=utf8&serverTimezone=UTC&useSSL=false";
        url="jdbc:mysql://127.0.0.1:3306/mybatis_learn";//数据库名路径
        username="root";
        password="root123456";
    }
    public static Connection open()
    {
        try {
            Class.forName(driver);
            return (Connection) DriverManager.getConnection(url,username, password);
        } catch (Exception e) {
            System.out.println("数据库连接失败！");
            e.printStackTrace();
        }//加载驱动

        return null;
    }

    /*
     * 关闭数据库
     */
    public static void close(Connection conn)
    {
        if(conn!=null)
        {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

package demo.yangxu.jdbc;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

/***
 * 非对象
 */
public class Jdbc01 {
    public static void main(String[] args) {

        insert("Yangxu002",30);
    }

    static void insert(String name,int age)
    {
        String sql="insert into mybatis_user(username,age) value(?,?)";
        Connection conn=DbUtil.open();
        try {
            PreparedStatement pstmt=(PreparedStatement) conn.prepareStatement(sql);
            pstmt.setString(1,name);
            pstmt.setInt(2,age);
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        finally {
            DbUtil.close(conn);
        }

    }
}

package demo.yangxu.jdbc;

import lombok.extern.slf4j.Slf4j;

import java.sql.Connection;
import java.sql.PreparedStatement;

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

/***
 * 面向对象
 */
@Slf4j
public class Jdbc02 {
    public static void main(String[] args) {
        User c=new User();
        c.setUsername("Yangxu005");
        c.setAge(30);
        insert(c);
        //查询
        c=query(11);
        log.info("userid:{},name:{}",c.getId(),c.getUsername());
    }

    static void insert(User c)
    {
        String sql="insert into mybatis_user(username,age) value(?,?)";
        Connection conn=DbUtil.open();
        try {
            PreparedStatement pstmt=(PreparedStatement) conn.prepareStatement(sql);
            pstmt.setString(1,c.getUsername());
            pstmt.setInt(2,c.getAge());
            pstmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        finally {
            DbUtil.close(conn);
        }


    }

    static User query(int id)
    {
        String sql="select * from mybatis_user where id=?";
        Connection conn=DbUtil.open();
        try {
            PreparedStatement pstmt=(PreparedStatement) conn.prepareStatement(sql);
            pstmt.setInt(1,id);
            ResultSet rs=pstmt.executeQuery();
            if(rs.next())
            {
                String name=rs.getString(2);
                User c=new User();
                c.setId(id);
                c.setUsername(name);
                return c;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        finally {
            DbUtil.close(conn);
        }
        return null;
    }
}