学步园

•commons-dbutils 是 Apache 组织提供的一个开源 JDBC工具类库，它是对JDBC的简单封装，学习成本极低，并且使用dbutils能极大简化jdbc编码的工作量，同时也不会影响程序的性能。

•API介绍：
–org.apache.commons.dbutils.QueryRunner
–org.apache.commons.dbutils.ResultSetHandler
–工具类
•org.apache.commons.dbutils.DbUtils。   

QueryRunner类有两类主要方法:

query() : 用于查询数据

update() : 用于增删改

ResultSetHandler接口用与将查询到的数据按要求转换为另一种格式。

QueryRunner.update()

<span style="font-size:14px;">	/**
	 * 测试 QueryRunner 类的 update 方法
	 * 该方法可用于 INSERT, UPDATE 和 DELETE
	 */
	@Test
	public void testQueryRunnerUpdate() {
		//1. 创建 QueryRunner 的实现类
		QueryRunner queryRunner = new QueryRunner();
		
		String sql = "DELETE FROM customers " +
				"WHERE id IN (?,?)";
		
		Connection connection = null;
		
		try {
			connection = JDBCTools.getConnection();
			//2. 使用其 update 方法
			queryRunner.update(connection, 
					sql, 12, 13);
		} catch (Exception e) {
			e.printStackTrace();
		} finally{
			JDBCTools.releaseDB(null, null, connection);
		}
		
	}</span>

BeanHandler:把结果集的第一条记录转为创建BeanHandler对象时传入的Class参数对应的对象.

<span style="font-family:SimSun;font-size:14px;"><span style="font-size:14px;font-weight: normal;">public void testBeanHandler() {

		QueryRunner queryRunner = new QueryRunner();
		Connection conn = null;

		try {
			conn = JDBCTools.getConnection();
			String sql = "SELECT id, name customerName, email, birth "
					+ "FROM customers WHERE id>=?";
			Customer customer = queryRunner.query(conn, sql, new BeanHandler(
					Customer.class), 5);

			System.out.println(customer);
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			JDBCTools.releaseDB(null, null, conn);
		}
	}</span></span>

BeanListHandler:把结果集转为一个List,该List不为null,但可能为空集合(即size()方法返回0)

<span style="font-family:SimSun;font-size:14px;">public void testBeanListHandler(){
		String sql = "SELECT id, name customerName, email, birth " +
				"FROM customers";
		
		
		QueryRunner queryRunner = new QueryRunner();
		
		Connection conn = null;
		
		try {
			conn = JDBCTools.getConnection();
			
			Object object = queryRunner.query(conn, sql, 
					new BeanListHandler<>(Customer.class)); 			
			
			System.out.println(object); 
		} catch (Exception e) {
			e.printStackTrace();
		} finally{
			JDBCTools.releaseDB(null, null, conn);
		}
	}</span>

MapHandler:返回SQL语句对应的第一条记录对应的Map对象.键:SQL查询的列名(不是列的别名),值:列的值.

<span style="font-family:SimSun;font-size:14px;"><span style="font-size:14px;font-weight: normal;">public void testMapHandler(){
		Connection connection = null;
		QueryRunner queryRunner = new QueryRunner();
		
		String sql = "SELECT id, name customerName, email, birth " +
				"FROM customers WHERE id = ?";
		
		try {
			connection = JDBCTools.getConnection();
			Map<String, Object> map = queryRunner.query(connection, 
					sql, new MapHandler(), 4);
			
			System.out.println(map); 
		} catch (Exception e) {
			e.printStackTrace();
		} finally{
			JDBCTools.releaseDB(null, null, connection);
		}
	}</span></span>

MapLiatHandler:将结果转化为一个Map的List. MapLiatHandler:返回的多条记录对应的Map的集合.

<span style="font-family:SimSun;font-size:14px;font-weight: normal;">public void testMapListHandler(){
		Connection connection = null;
		QueryRunner queryRunner = new QueryRunner();
		
		String sql = "SELECT id, name, email, birth " +
				"FROM customers";
		
		try {
			connection = JDBCTools.getConnection();
			List<Map<String, Object>> mapList = queryRunner.query(connection, 
					sql, new MapListHandler());
			
			System.out.println(mapList); 
		} catch (Exception e) {
			e.printStackTrace();
		} finally{
			JDBCTools.releaseDB(null, null, connection);
		}
	}</span>

ScalarHandler:把结果集转为一个数值(可以是任意类型)返回

<span style="font-family:SimSun;">public void testScalarHandler(){
		Connection connection = null;
		QueryRunner queryRunner = new QueryRunner();
		
		String sql = "SELECT name FROM customers " +
				"WHERE id = ?";
		
		try {
			connection = JDBCTools.getConnection();
			Object count = queryRunner.query(connection, sql, 
					new ScalarHandler(), 6);
			
			System.out.println(count); 
		} catch (Exception e) {
			e.printStackTrace();
		} finally{
			JDBCTools.releaseDB(null, null, connection);
		}
	}</span>