java jdbc 查询与更新实现

package jdbc.demo;

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

public class Demo1 {

    private final static String username = "root";
    private final static String password = "tiger";
    private final static String url = "jdbc:mysql://localhost/test?characterEncoding=utf8&useSSL=false&serverTimezone=UTC ";
    Connection conn;// 连接引用
    PreparedStatement ps;

    public Connection getConnection() {

        try {
            Class.forName("com.mysql.cj.jdbc.Driver");// 加载jdbc驱动
            try {
                if (conn == null) {
                    // 加载完后可以通过DriverManager获取数据库连接
                    conn = DriverManager.getConnection(url, username, password);
                    conn.setAutoCommit(false);// 关闭事务自动提交
                }
            } catch (SQLException e) {
                System.out.println("连接不了数据库,或连接格式写错");
                e.printStackTrace();
                this.close();
                return null;
            }

        } catch (ClassNotFoundException e) {
            System.out.println("找不到驱动");
            e.printStackTrace();
            return null;
        }
        return conn;
    }

    public ResultSet find(Connection conn, String sql) {
        ResultSet result = null;
        try {
            ps = conn.prepareStatement(sql);
            result = ps.executeQuery();// 执行查询
        } catch (SQLException e) {
            // 查询一般没有事务要求
            this.close();
            e.printStackTrace();
        }
        return result;

    }

    public int updateInsertDelete(Connection conn, String sql) {
        int i = 0;
        try {
            ps = conn.prepareStatement(sql);
            i = ps.executeUpdate();// 执行表更新(插入,更新,删除都是表的更新操作)
        } catch (SQLException e) {
            try {
                conn.rollback();// 回滚事务
            } catch (SQLException e1) {
                System.out.println("回滚事务失败");
                e1.printStackTrace();
            }
            this.close();// 关闭资源
            e.printStackTrace();
        }
        return i;
    }

    public void close() {
        try {
            if (!ps.isClosed()) {
                ps.close();
            }
        } catch (SQLException e1) {
            e1.printStackTrace();
        }
        try {
            if (!conn.isClosed()) {
                conn.close();
            }
        } catch (SQLException e1) {
            e1.printStackTrace();
        }
    }

    public static void main(String[] args) throws SQLException {
        Demo1 jdbc = new Demo1();
        Connection conn = jdbc.getConnection();
        jdbc.updateInsertDelete(conn, "INSERT INTO test (username,create_time) VALUES ('user3',NOW());");
        conn.commit();// 更新操作要提交事务才能生效
        ResultSet result = jdbc.find(conn, "select id,username,update_time,create_time from test");
        int maxCol = result.getMetaData().getColumnCount();
        System.out.println("查询时指定列的数量,为*时则是表的列数maxCol: " + maxCol);

        while (result.next()) {// 通过result.next()遍历结果
            int row = result.getRow();
            System.out.print("当前遍历的行数: " + row + " ");
            // 第一列的列号为1,所以i最小为1
            for (int i = 1; i <= maxCol; i++) {
                System.out.print(result.getString(i) + " ");
            }
            System.out.println("");

        }
        jdbc.close();

    }

}
// 查询时指定列的数量,为*时则是表的列数maxCol: 4
// 当前遍历的行数: 1 1 user1 2017-05-29 10:19:39 2017-05-29 10:19:39
// 当前遍历的行数: 2 2 user2 2017-05-29 10:20:15 2017-05-29 10:20:15
// 当前遍历的行数: 3 5 user2 2017-05-29 10:22:12 2017-05-29 10:22:12
// 当前遍历的行数: 4 12 user3 2017-05-29 10:42:10 2017-05-29 10:42:10
// 当前遍历的行数: 5 13 user3 2017-05-29 10:42:12 2017-05-29 10:42:12
// 当前遍历的行数: 6 14 user3 2017-05-29 10:42:17 2017-05-29 10:42:17
// 当前遍历的行数: 7 15 user3 2017-05-29 10:43:34 2017-05-29 10:43:34
// 当前遍历的行数: 8 16 user3 2017-05-29 10:43:42 2017-05-29 10:43:42
// 当前遍历的行数: 9 17 user3 2017-05-29 10:44:33 2017-05-29 10:44:33
// 当前遍历的行数: 10 18 user3 2017-05-29 10:44:42 2017-05-29 10:44:42
// 当前遍历的行数: 11 19 user3 2017-05-29 10:56:58 2017-05-29 10:56:58
// 当前遍历的行数: 12 20 user3 2017-05-29 11:28:13 2017-05-29 11:28:13
// 当前遍历的行数: 13 21 user3 2017-05-29 11:29:02 2017-05-29 11:29:02

/*
 * CREATE TABLE test ( id INT(11) NOT NULL AUTO_INCREMENT , username VARCHAR(50)
 * NOT NULL , update_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE
 * CURRENT_TIMESTAMP, create_time DATETIME , PRIMARY KEY(id) )ENGINE=INNODB
 * DEFAULT CHARSET utf8mb4 COMMENT '测试表';
 * 
 * INSERT INTO test (username,create_time) VALUES ('user1',NOW());
 * 
 * 
 * 
 */