利用java语言查询数据库的工具类

准备工作：导入需要的包c3p0-0.9.1.2.jar，commons-dbutils-1.4.jar，commons-io-2.2.jar，commons-pool-1.5.6.jar，mysql-connector-java-5.0.8-bin.jar

其次需要导入配置文件c3p0-config.xml

然后开始编写工具类，里边包含连接数据可的方法，开启事务，提交事务，回滚事务的方法，以及关闭资源的方法，代码如下：

package com.qf.utils;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import com.mchange.v2.c3p0.ComboPooledDataSource;
//从连接池中获取连接
//获取连接池子对象
//获取连接
//关闭资源
public class DataSourceUtiles {
	private static ComboPooledDataSource dataSource = new ComboPooledDataSource();
     //返回连接池对象的方法
	private static ThreadLocal<Connection> th= new ThreadLocal<Connection>();
	public static ComboPooledDataSource getDataSource() {
		return dataSource;//出问题的地方
		//写的时候，自己调自己，造成内存溢出
	}
	public static Connection getConnection() {
         
		Connection connection = th.get();
		if(connection==null){
		try {//连接池中获取连接的方法
			connection = dataSource.getConnection();
			th.set(connection);//这儿做了一次修改，原来是th.set(getconnection());
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		}
		return connection;
	}
	
	//开启事务
	public static void startTransaction(){
		
		try {
			getConnection().setAutoCommit(false);
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	//提交事务
	public static void commit(){
		try {
			getConnection().commit();
			getConnection().close();
			th.remove();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
	}
	//回滚事务
	public static void rollback(){
		try {
			getConnection().rollback();
			getConnection().close();
			th.remove();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
//关闭资源的方法
	public static void close(Connection connection) {
		if (connection != null) {
			try {
				connection.close();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public static void close(ResultSet set) {
		if (set != null) {
			try {
				set.close();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public static void close(Statement statement) {
		if (statement != null) {
			try {
				statement.close();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public static void close(Connection connection, Statement statement) {
		close(connection);
		close(statement);
	}

	public static void close(Connection connection, ResultSet set) {

		close(connection);
		close(set);
	}

	public static void close(Statement statement, ResultSet set) {
		close(statement);
		close(set);

	}

	public static void close(Connection connection, Statement statement, ResultSet set) {
		close(connection);
		close(statement);
		close(set);

	}

}