数据库的增删改查

Text类

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

public class Test {

	public static void delete() {//删除
		String sql = "delete from user_info";
		if(new DBLink().update(sql)) {//处理结果
			System.out.println("OK");
			return;
		}
		System.out.println("ON");
	}
	
	public static void insert() {//添加
		String sql = "insert into user_info(id, name, mobile, address) values('5458','Tim','1111111125','河南')";
		if(new DBLink().update(sql)) {//处理结果
			System.out.println("OK");
			return;
		}
		System.out.println("ON");
	}
	
	public static void update() {//修改
		String sql = "update user_info set id = '5457' where id = '5451'";
		if(new DBLink().update(sql)) {//处理结果
			System.out.println("OK");
			return;
		}
		System.out.println("ON");
	}
	
	public static void select() {//查询
		Connection connection = null;
		Statement statement = null;
		ResultSet resultSet = null;
		try {
			Class.forName("com.mysql.jdbc.Driver");//加载驱动
			String url = "jdbc:mysql://127.0.0.1:3306/one";
			connection = DriverManager.getConnection(url, "root", "585");//获取链接
			statement = connection.createStatement();
			resultSet = statement.executeQuery("select id,name,mobile,address from user_info");//执行sql，将查询的数据存到ResultSet类
			while(resultSet.next()) {//next方法“指针”至一行数据，有数据为 true 没有数据为 false
				String id = resultSet.getString("id");
				String name = resultSet.getString("name");
				String mobile = resultSet.getString("mobile");
				String address = resultSet.getString("address");
				System.out.println(id+","+name+","+mobile+","+address);
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if(resultSet != null) {
					resultSet.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}
			try {
				if(statement != null) {
					statement.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}
			try {
				if(connection != null) {
					connection.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
	
	public static void main(String[] args) {
//		delete();//删除
//		insert();//添加
//		update();//修改
//		select();//查询
	}
}

DBLink类

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

public class DBLink {

	public boolean update(String sql) {
		Connection connection = null;
		Statement statement = null;
		try {
			Class.forName("com.mysql.jdbc.Driver");//加载驱动
			String url = "jdbc:mysql://127.0.0.1:3306/one";//指定连接哪一台计算机上的哪一个数据库实例
			connection = DriverManager.getConnection(url, "root", "525");//获取数据库连接对象，一个对象表示一次数据库连接
			statement = connection.createStatement();//获取Statement对象
			int result = statement.executeUpdate(sql);//执行sql语句，返回受影响的行数，仅限于数据insert、update、和delete
//			statement.close();//这两行代码不能写在这个地方。因为如果上面代码出现异常，则其下面代码无法执行，所以资源无法释放；比如sql语句语法错误，则statement和connection资源都无法释放
//			connection.close();
			return result > 0;
		} catch (Exception e) {
			e.printStackTrace();
		} finally {//即便有异常，也会执行
			try {
				if(statement != null) {//有可能由于异常导致statement没有赋值，比如url出错
					statement.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}
			try {
				if(connection != null) {
					connection.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		return false;
	}
}