JDBC（十一）利用DBUtils 封装访问数据库的Dao

1. 编写接口

package com.dason.jdbc;  
  
import java.sql.Connection;  
import java.sql.SQLException;  
import java.util.List;  
  
  
  /**
   *定义一个访问数据库的接口,只提供方法，不提供实现
   *
   *@params  :　类类型参数：在查询时告诉方法返回的bean是什么类型，
   *                           也就是将结果集封装成什么类型的类
   *
   */
public interface Dao {  
    
	// 批量处理
    void batch(Connection connection,String sql,Object [] ...args) throws SQLException;  
    
	// 查询一个值(返回的数据类型可以是任意类型,所以用泛型代替)
     E getForValue(Connection connection,String sql,Object...args) throws SQLException;  
	
	// 返回 T 类型对象的list 集合
    List getForList(Connection connection,String sql,Object...args) throws SQLException;  
      
	// 返回一个 T 类型的对象  
    T getBean(Connection connection,String sql,Object...args) throws SQLException;  
    
	// 更新操作 
    void update(Connection connection,String sql,Object...args) throws SQLException;  
}  

2. 编写实现类 JDBCDaoImpl

package com.dason.jdbc;  
  
import java.lang.reflect.ParameterizedType;  
import java.lang.reflect.Type;  
import java.sql.Connection;  
import java.sql.SQLException;  
import java.util.ArrayList;  
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;  
 
 /**
   * JDBCDaoImpl 实现接口Dao ,提供方法的具体实现
   *
   */
public class JDBCDaoImpl implements Dao {  
    
	// QueryRunner 类 是线程安全的,可作为全局变量
	private QueryRunner queryRunner;  
    	
    private Class type;  
	
    @SuppressWarnings("unchecked") 
	
	//在子类构造中有一个隐式的 supper(),所以子类在
	//实例化时都会链式调用父类构造方法初始化父类空间.
    public  JDBCDaoImpl() {  
        queryRunner  = new QueryRunner();  
		//getGenericSuperclass：利用反射获取获得带有泛型参数的父类
		//getActualTypeArguments()：返回该类的泛型参数 的数组
        type = (Class)((ParameterizedType)getClass().getGenericSuperclass())  
                .getActualTypeArguments()[0];    
    }  
      
    @Override  
    public void batch(Connection connection, String sql, Object[]... args) throws SQLException {  
        queryRunner.batch(connection, sql, args);  
    }  
  
    @Override  
    public  E getForValue(Connection connection, String sql, Object... args) throws SQLException {  
        return (E) queryRunner.query(connection, sql, new ScalarHandler(), args);  
    }  
  
    @Override  
    public List getForList(Connection connection, String sql, Object... args) throws SQLException {  
          
        return  queryRunner.query(connection, sql, new BeanListHandler<>(type), args);  
    }  
  
    @Override  
    public T getBean(Connection connection, String sql, Object... args) throws SQLException {  
          
        return queryRunner.query(connection, sql, new BeanHandler<>(type), args);   
    }  
  
    @Override  
    public void update(Connection connection, String sql, Object... args) throws SQLException {  
            queryRunner.update(connection, sql, args);  
    }  
  
}  

3. 继承JDBCDaoImpl ，传入类类型参数

ackage com.dason.jdbc;  
  
  /**
   *继承JDBCDaoImpl 并传入类类型参数
   *
   */
public class UserDao extends JDBCDaoImpl{  
      
}  

4. 单元测试

package com.dason.jdbc;  
  
import static org.junit.Assert.*;  
  
import java.sql.Connection;  
import java.util.List;  
  
import org.junit.Test;  
  
public class UserDaoTest {  
  
    UserDao userDao = new UserDao();  
    @Test  
    public void testBatch() {  
        Connection connection = null;  
        String sql ="insert into user(id,name,email) values(?,?,?)";  
        try {  
            connection = JDBCTools.getConnection();  
            Object[][] rowData = {{3,"c","c@123"},{7,"g","g@123"}};  
            userDao.batch(connection, sql,rowData);  
              
        } catch (Exception e) {  
            e.printStackTrace();  
        }   finally{  
            JDBCTools.releaseDB(null, null, connection);  
        }     
    }  
  
    @Test  
    public void testGetForValue() {  
        Connection connection = null;  
        String sql ="select * from user where id > ?";  
        try {  
            connection = JDBCTools.getConnection();  
            Object obj =  userDao.getForValue(connection, sql, 3);  
            System.out.println(obj);  
        } catch (Exception e) {  
            e.printStackTrace();  
        }   finally{  
            JDBCTools.releaseDB(null, null, connection);  
        }     
    }  
  
    @Test  
    public void testGetForList() {  
        Connection connection = null;  
        String sql ="select * from user where id > ?";  
        try {  
            connection = JDBCTools.getConnection();  
            List users =  userDao.getForList(connection, sql, 3);  
            System.out.println(users);  
        } catch (Exception e) {  
            e.printStackTrace();  
        }   finally{  
            JDBCTools.releaseDB(null, null, connection);  
        }  
    }  
  
    @Test  
    public void testGetBean() {  
        Connection connection = null;  
        String sql ="select * from user where id > ?";  
        try {  
            connection = JDBCTools.getConnection();  
            User user =  userDao.getBean(connection, sql, 3);  
            System.out.println(user);  
        } catch (Exception e) {  
            e.printStackTrace();  
        }   finally{  
            JDBCTools.releaseDB(null, null, connection);  
        }  
    }  
  
    @Test  
    public void testUpdate() {  
        Connection connection = null;  
        String sql ="delete from user where id = ?";  
        try {  
            connection = JDBCTools.getConnection();  
            userDao.update(connection, sql, 3);  
        } catch (Exception e) {  
            e.printStackTrace();  
        }   finally{  
            JDBCTools.releaseDB(null, null, connection);  
        }  
    }  
  
}  

5. 获取泛型参数利用的反射技术:  反射之Type