封装数据库操作BaseDao

这里涉及到反射，不过我忘记记录了。后面学习框架应该会在提到。只是简单的记录一下。

我们在针对不同的数据表/JavaBean实例操作的时候，有一些操作是通用的，即增、删、改、查。不同的只是sql语句和参数不同而已。这样我们把相同的操作封装到BaseDao中，其他Dao的操作直接继承这些方法，并且我们将方法设置为protected，则这些方法不对外提供，只供Dao类自身调用。由于它不是具体的类的映射，所以定位虚类。

/**
 * 
 */
package com.atguigu.dao;

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;

import com.alibaba.druid.pool.DruidPooledConnection;
import com.atguigu.tools.JdbcUtils;


/**
 * 
* @Title: BaseDao
* @Description:  
* @author NianHao.X
* @date 2020年3月31日
 */
public abstract class BaseDao {
 private QueryRunner queryRunner = new QueryRunner();
 /**
  * 
  * @Title: update
  * @Description: TODO
  * @param sql
  * @param args
  * @return int
  * @date 2020-03-31 08:44:14
  */
 protected int update(String sql,Object...args){ DruidPooledConnection connection = JdbcUtils.getConnection();
        try {
            return queryRunner.update(connection,sql, args);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JdbcUtils.closeConnection(connection);
        }
        return -1;
    }
    
    protected <T> T queryForOne(Class<T> type,String sql,Object...args) {
        DruidPooledConnection connection = JdbcUtils.getConnection();
        try {
            return queryRunner.query(connection,sql,new BeanHandler<T>(type),args );
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JdbcUtils.closeConnection(connection);
        }
        return null;
        
    }
    protected <T> List<T> queryForList(Class<T>type,String sql,Object...args ){
        DruidPooledConnection connection = JdbcUtils.getConnection();
        try {
            return queryRunner.query(connection,sql,new BeanListHandler<T>(type),args );
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JdbcUtils.closeConnection(connection);
        }
        return null;
    }
        
    protected Object queryForSingleValue(String sql, Object... args){
        DruidPooledConnection connection = JdbcUtils.getConnection();
        try {
            return queryRunner.query(connection, sql, new ScalarHandler(), args);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.closeConnection(connection);
        }
        return null;
    }


}

这里我们的连接是通过数据库连接池管理的。我们使用的是阿里的druid数据库连接池。

/**
 * 
 */
package com.atguigu.tools;

import java.io.InputStream;
import java.util.Properties;

import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.pool.DruidDataSourceFactory;
import com.alibaba.druid.pool.DruidPooledConnection;
import com.mysql.jdbc.Connection;

/**
 * @author nianhao
 *
 */
public class JdbcUtils {
    private static DruidDataSource dataSource;
    
    static {
        try {
            Properties properties = new Properties();
            InputStream inStream = JdbcUtils.class.getClassLoader().getResourceAsStream("jdbc.properties");
            properties.load(inStream);
            dataSource = (DruidDataSource)DruidDataSourceFactory.createDataSource(properties);
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
        
    }
    public static DruidPooledConnection getConnection() {
        DruidPooledConnection connection = null;
        try {
            
            connection = dataSource.getConnection();
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
        return connection;
        
    }
    public static void closeConnection(DruidPooledConnection connection) {
        try {
            if(connection!=null) {
                connection.close();
            }
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
    }

}