演示ResultSetHandler实现类

axinawang

于 2024-11-28 13:34:25 发布

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分类专栏： javaweb 文章标签： java 数据库算法

本文链接：https://blog.youkuaiyun.com/daqi1983/article/details/144109071

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4.1.搭建数据库环境

CREATE DATABASE IF NOT EXISTS `jdbc`;
USE `jdbc`;
DROP TABLE IF EXISTS `users`;
CREATE TABLE `users` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `username` VARCHAR(40) DEFAULT NULL,
  `password` VARCHAR(40) DEFAULT NULL,
  `email` VARCHAR(60) DEFAULT NULL,
  `birthday` DATE DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT  INTO `users`(`id`,`username`,`password`,`email`,`birthday`) 
	VALUES (1,'zs','123456','zs@qq.com','2021-11-26'),
		(2,'lisi','123456','lisi@sina.com','2021-10-01'),
		(3,'wangyu','123456','wangyu@sina.com','2021-09-01');

4.2.添加dbutils依赖的坐标并且需要JDBCUtils.java

              <dependency>
                    <groupId>commons-dbutils</groupId>
                    <artifactId>commons-dbutils</artifactId>
                    <version>1.8.1</version>
                </dependency>

4.3.创建BaseDao类，用来模拟QueryRunner

public class BaseDao {
 	// 优化查询
 	public static Object query(String sql, ResultSetHandler<?> rsh, 
              Object... params) throws SQLException {
 		    Connection conn = null;
 		    PreparedStatement pstmt = null;
 		    ResultSet rs = null;
 		    try {
 				// 获得连接
 				conn = JDBCUtils.getConnection();
 				// 预编译sql
 				pstmt = conn.prepareStatement(sql);
 				// 将参数设置进去
 				for (int i = 0; params != null && i < params.length; i++) 
                  {
 					pstmt.setObject(i + 1, params[i]);
 				}
 				// 发送sql
 				rs = pstmt.executeQuery();
 				// 让调用者去实现对结果集的处理
 				Object obj = rsh.handle(rs);
 				return obj;
 			} catch (Exception e) {
 				e.printStackTrace();
 			}finally {
 				// 释放资源
 				JDBCUtils.release(rs, pstmt, conn);
 		 	}
 			return rs;
 		}
 }

4.4.创建实体类User

public class User {
	private int id;
	private String username;
	private String password;
	private String email;
	private Date birthday;
//补充getter setter

4.5.创建测试类ResultSetTest1

public class ResultSetTest1 {
	public static void testBeanHandler() throws SQLException {
		BaseDao basedao = new BaseDao();
		String sql = "select * from users where id=?";
		User user = (User) basedao.query(sql, new BeanHandler(User.class), 1);
		System.out.print("id为1的User对象的name值为：" + user.getUsername());
	}
	public static void main(String[] args) throws SQLException {
		testBeanHandler();
	}
}

4.6.ResultSetTest2

public class ResultSetTest2 {
	public static void testBeanListHandler() throws SQLException {
		BaseDao basedao = new BaseDao();
		String sql = "select * from users ";
		ArrayList<User> list = (ArrayList<User>) basedao.query(sql,
				new BeanListHandler(User.class));
		for (int i = 0; i < list.size(); i++) {
			System.out.println("第" + (i + 1) + "条数据的username值为:"
					+ list.get(i).getUsername());
		}
	}
	public static void main(String[] args) throws SQLException {
		testBeanListHandler();
	}
}

4.7.ResultSetTest3

    public static void testScalarHandler() throws SQLException {
	    BaseDao basedao = new BaseDao();
	    String sql = "select * from users where id=?";
	    Object arr = (Object) basedao.query(sql, 
                           new ScalarHandler("username"), 1);
		System.out.println(arr);
	}
	public static void main(String[] args) throws SQLException {
		testScalarHandler();
	}