[大数据]JDBC之CRUD练习

JDBC连接常规步骤

package cn.jdbc;

import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.Statement;

public class Demo1 {
    public static void main(String[] args) throws Exception {
    	//注册驱动(可省略)
        Class.forName("com.mysql.jdbc.Driver");
        //定义sql语句
        String sql = "update stu set salary = 500 where id = 2";
        //获取Connection对象
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db1", "root", "");
        //获取执行sql的对象Statement
        Statement stmt = conn.createStatement();
        //执行sql，返回的是影响的行数
        int count = stmt.executeUpdate(sql);
        System.out.println(count);
        stmt.close();
        conn.close();

    }
}

添加、修改小实例

添加数据库表中数据

package cn.jdbc;

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

public class Demo2 {
    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String sql = "insert into stu values(null, '狗狗', 3000)";
            conn = DriverManager.getConnection("jdbc:mysql:///db1", "root", "");
            stmt = conn.createStatement();
            int count = stmt.executeUpdate(sql);
            System.out.println(count);
            if (count > 0) System.out.println("添加成功");
            else System.out.println("添加失败");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

修改表中信息

package cn.jdbc;

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

public class Demo3 {
    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        try {
            //1.注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取连接对象
            conn = DriverManager.getConnection("jdbc:mysql:///db1", "root", "");
            //3.定义sql
            String sql = "update stu set salary = 1500 where id = 4";
            //4.获取执行sql对象
            stmt = conn.createStatement();
            //5.执行sql
            int count = stmt.executeUpdate(sql);
            //6.处理结果
            System.out.println(count);
            if (count > 0) System.out.println("修改成功");
            else System.out.println("修改失败");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //7.释放资源，防止空指针异常
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

ResultSet：结果集对象，封装查询结果

不完全正确的使用

package cn.jdbc;

import java.sql.*;

public class Demo3 {
    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //1.注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取连接对象
            conn = DriverManager.getConnection("jdbc:mysql:///db1", "root", "");
            //3.定义sql
            String sql = "select * from stu";
            //4.获取执行sql对象
            stmt = conn.createStatement();
            //5.执行sql
            rs = stmt.executeQuery(sql);
            //6.处理结果
            //6.1 让游标向下移动一行，默认在表头
            rs.next();
            //6.2获取数据
            int id = rs.getInt(1);
            String name = rs.getString("name");
            int salary = rs.getInt(3);

            System.out.println(id + "---" + name + "---" + salary);

        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //7.释放资源，防止空指针异常
            if (rs != null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

while判断游标是否是最后一行末尾

package cn.jdbc;

import java.sql.*;

public class Demo3 {
    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //1.注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取连接对象
            conn = DriverManager.getConnection("jdbc:mysql:///db1", "root", "");
            //3.定义sql
            String sql = "select * from stu";
            //4.获取执行sql对象
            stmt = conn.createStatement();
            //5.执行sql
            rs = stmt.executeQuery(sql);
            //6.处理结果
            while (rs.next()) {
                int id = rs.getInt(1);
                String name = rs.getString("name");
                int salary = rs.getInt(3);
                System.out.println(id + "---" + name + "---" + salary);
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //7.释放资源，防止空指针异常
            if (rs != null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

抽取JDBC工具类

1、注册驱动
2、抽取一个方法获取连接对象
3、抽取一个方法释放资源

配置文件：jdbc.properties

url = jdbc:mysql:///db1
user = root
password =
driver = com.mysql.jdbc.Driver

使用工具类变化后的Demo代码

package cn.jdbc;

import cn.jdbc.util.JDBCUtils;

import java.sql.*;

public class Demo3 {
    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
//            //1.注册驱动
//            Class.forName("com.mysql.jdbc.Driver");
//            //2.获取连接对象
//            conn = DriverManager.getConnection("jdbc:mysql:///db1", "root", "");

            conn = JDBCUtils.getConnection();
            //3.定义sql
            String sql = "select * from stu";
            //4.获取执行sql对象
            stmt = conn.createStatement();
            //5.执行sql
            rs = stmt.executeQuery(sql);
            //6.处理结果
            while (rs.next()) {
                int id = rs.getInt(1);
                String name = rs.getString("name");
                int salary = rs.getInt(3);
                System.out.println(id + "---" + name + "---" + salary);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
//            //7.释放资源，防止空指针异常
//            if (rs != null) {
//                try {
//                    rs.close();
//                } catch (SQLException e) {
//                    e.printStackTrace();
//                }
//            }
//            if (stmt != null) {
//                try {
//                    stmt.close();
//                } catch (SQLException e) {
//                    e.printStackTrace();
//                }
//            }
//            if (conn != null) {
//                try {
//                    conn.close();
//                } catch (SQLException e) {
//                    e.printStackTrace();
//                }
//            }
            JDBCUtils.close(rs, stmt, conn);
        }
    }
}

工具类代码

package cn.jdbc.util;

import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.Properties;

/**
 * JDBC工具类
 */
public class JDBCUtils {
    private  static String url;
    private  static String user;
    private  static String password;
    private  static String driver;
    
    /**
     *配置文件的读取，只需要读取一次即可拿到这些值。
     * 使用静态代码块
     */
    static  {
        //读取资源文件，获取值。
        try {
            //1.创建Properties集合类。
            Properties pro = new Properties();

            //获取src路径下的文件的方式---->ClassLoader 类加载器
            ClassLoader classLoader = JDBCUtils.class.getClassLoader();
            URL res = classLoader.getResource("jdbc.properties");
            String path = res.getPath();
            System.out.println(path);
            //2.加载文件
            pro.load(new FileReader(path));

            //3.获取数据，赋值。
            url = pro.getProperty("url");
            user = pro.getProperty("user");
            password = pro.getProperty("password");
            driver = pro.getProperty("driver");

            Class.forName(driver);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }


    /**
     * 获取链接
     * 解决：配置文件实现传参数
     * @return 连接对象
     */
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, user, password);
    }

    /**
     * 释放资源
     * 2种
     * @param stmt
     * @param conn
     */
    public static void close(Statement stmt, Connection conn){
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public static void close(ResultSet rs, Statement stmt, Connection conn){
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}