JDBC学习

	/*
	 * 此种方式的好处？
	 * 1.实现了数据与代码的分离。实现了解耦
	 * 2.如果需要修改配置文件信息，可以避免程序重新打包。
	 */
public void getConnection5() throws Exception{
		
		//1.读取配置文件中的4个基本信息
		InputStream is = ConnectionTest.class.getClassLoader().getResourceAsStream("jdbc.properties");
		
		Properties pros = new Properties();
		pros.load(is);
		
		String user = pros.getProperty("user");
		String password = pros.getProperty("password");
		String url = pros.getProperty("url");
		String driverClass = pros.getProperty("driverClass");
		
		//2.加载驱动
		Class.forName(driverClass);
    	//此时JVM查找并加载指定的类，也就是说JVM会执行该类的静态代码段
		
		//3.获取连接
		Connection conn = DriverManager.getConnection(url, user, password);
		System.out.println(conn);
		
		
	}

package com.atguigu.bookstore.dao;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;


/**
 * 定义一个用来被继承的对数据库进行基本操作的Dao
 * 
 * @author HanYanBing
 *
 * @param <T>
 */
public abstract class BaseDao<T> {
	private QueryRunner queryRunner = new QueryRunner();
	// 定义一个变量来接收泛型的类型
	private Class<T> type;

	// 获取T的Class对象，获取泛型的类型，泛型是在被子类继承时才确定
	public BaseDao() {
		// 获取子类的类型
		Class clazz = this.getClass();
		// 获取父类的类型
		// getGenericSuperclass()用来获取当前类的父类的类型
		// ParameterizedType表示的是带泛型的类型
		ParameterizedType parameterizedType = (ParameterizedType) clazz.getGenericSuperclass();
		// 获取具体的泛型类型 getActualTypeArguments获取具体的泛型的类型
		// 这个方法会返回一个Type的数组
		Type[] types = parameterizedType.getActualTypeArguments();
		// 获取具体的泛型的类型·
		this.type = (Class<T>) types[0];
	}

	/**
	 * 通用的增删改操作
	 * 
	 * @param sql
	 * @param params
	 * @return
	 */
	public int update(Connection conn,String sql, Object... params) {
		int count = 0;
		try {
			count = queryRunner.update(conn, sql, params);
		} catch (SQLException e) {
			e.printStackTrace();
		} 
		return count;
	}

	/**
	 * 获取一个对象
	 * 
	 * @param sql
	 * @param params
	 * @return
	 */
	public T getBean(Connection conn,String sql, Object... params) {
		T t = null;
		try {
			t = queryRunner.query(conn, sql, new BeanHandler<T>(type), params);
		} catch (SQLException e) {
			e.printStackTrace();
		} 
		return t;
	}

	/**
	 * 获取所有对象
	 * 
	 * @param sql
	 * @param params
	 * @return
	 */
	public List<T> getBeanList(Connection conn,String sql, Object... params) {
		List<T> list = null;
		try {
			list = queryRunner.query(conn, sql, new BeanListHandler<T>(type), params);
		} catch (SQLException e) {
			e.printStackTrace();
		} 
		return list;
	}

	/**
	 * 获取一个但一值得方法，专门用来执行像 select count(*)...这样的sql语句
	 * 
	 * @param sql
	 * @param params
	 * @return
	 */
	public Object getValue(Connection conn,String sql, Object... params) {
		Object count = null;
		try {
			// 调用queryRunner的query方法获取一个单一的值
			count = queryRunner.query(conn, sql, new ScalarHandler<>(), params);
		} catch (SQLException e) {
			e.printStackTrace();
		} 
		return count;
	}
}

public class Druidtest {
    @Test
    public void getConnection() throws Exception {
        Properties pros = new Properties();
        InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("druid.properties");
        pros.load(is);// 加载这个键值对的流is
        DataSource source = DruidDataSourceFactory.createDataSource(pros);
        Connection conn = source.getConnection();
        System.out.println(conn);
    }
}

// 测试添加
@Test
public void testInsert() throws Exception {
	QueryRunner runner = new QueryRunner();
	Connection conn = JDBCUtils.getConnection3();
	String sql = "insert into customers(name,email,birth)values(?,?,?)";
	int count = runner.update(conn, sql, "何成飞", "he@qq.com", "1992-09-08");

	System.out.println("添加了" + count + "条记录");
		
	JDBCUtils.closeResource(conn, null);

}

// 测试删除
@Test
public void testDelete() throws Exception {
	QueryRunner runner = new QueryRunner();
	Connection conn = JDBCUtils.getConnection3();
	String sql = "delete from customers where id < ?";
	int count = runner.update(conn, sql,3);

	System.out.println("删除了" + count + "条记录");
		
	JDBCUtils.closeResource(conn, null);

}

/*
 * 测试查询:查询一条记录
 * 
 * 使用ResultSetHandler的实现类：BeanHandler
 */
@Test
public void testQueryInstance() throws Exception{
	QueryRunner runner = new QueryRunner();

	Connection conn = JDBCUtils.getConnection3();
		
	String sql = "select id,name,email,birth from customers where id = ?";
		
	//
	BeanHandler<Customer> handler = new BeanHandler<>(Customer.class);
	Customer customer = runner.query(conn, sql, handler, 23);
	System.out.println(customer);	
	JDBCUtils.closeResource(conn, null);
}

/*
 * 测试查询:查询多条记录构成的集合
 * 
 * 使用ResultSetHandler的实现类：BeanListHandler
 */
@Test
public void testQueryList() throws Exception{
	QueryRunner runner = new QueryRunner();

	Connection conn = JDBCUtils.getConnection3();
		
	String sql = "select id,name,email,birth from customers where id < ?";
		
	//
	BeanListHandler<Customer> handler = new BeanListHandler<>(Customer.class);
	List<Customer> list = runner.query(conn, sql, handler, 23);
	list.forEach(System.out::println);
		
	JDBCUtils.closeResource(conn, null);
}

/*
 * 自定义ResultSetHandler的实现类
 */
@Test
public void testQueryInstance1() throws Exception{
	QueryRunner runner = new QueryRunner();

	Connection conn = JDBCUtils.getConnection3();
		
	String sql = "select id,name,email,birth from customers where id = ?";
		
	ResultSetHandler<Customer> handler = new ResultSetHandler<Customer>() {

		@Override
		public Customer handle(ResultSet rs) throws SQLException {
			System.out.println("handle");
//			return new Customer(1,"Tom","tom@126.com",new Date(123323432L));
				
			if(rs.next()){
				int id = rs.getInt("id");
				String name = rs.getString("name");
				String email = rs.getString("email");
				Date birth = rs.getDate("birth");
					
				return new Customer(id, name, email, birth);
			}
			return null;
				
		}
	};
		
	Customer customer = runner.query(conn, sql, handler, 23);
		
	System.out.println(customer);
		
	JDBCUtils.closeResource(conn, null);
}

/*
 * 如何查询类似于最大的，最小的，平均的，总和，个数相关的数据，
 * 使用ScalarHandler
 * 
 */
@Test
public void testQueryValue() throws Exception{
	QueryRunner runner = new QueryRunner();

	Connection conn = JDBCUtils.getConnection3();
		
	//测试一：
//	String sql = "select count(*) from customers where id < ?";
//	ScalarHandler handler = new ScalarHandler();
//	long count = (long) runner.query(conn, sql, handler, 20);
//	System.out.println(count);
		
	//测试二：
	String sql = "select max(birth) from customers";
	ScalarHandler handler = new ScalarHandler();
	Date birth = (Date) runner.query(conn, sql, handler);
	System.out.println(birth);
		
	JDBCUtils.closeResource(conn, null);
}