package com.bjpowernode.drp.util;import java.sql.Connection;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import javax.naming.Context;import javax.naming.InitialContext;import javax.naming.NamingException;import javax.sql.DataSource;/** * 这是一个管理JDBC connection的类 (从连接池中拿Connection). * 浏览器的每一次访问服务器,服务器都会开启一个线程,即每一个request,对应一个线程. * 每一个线程即是一个ThreadLocal,放在ThreadLocal中的东西是属于同一线程共享的,所以在ThreadLocal放Connection, * 同一个request取出来的Connection是属于同一个的. * * @author Kevin * */public class ConnectionManager {/** * ThreadLocal存放Connection */private static ThreadLocal<Connection> connectionHolder = new ThreadLocal<Connection>();/** * 从连接池拿Connection * * getConnection和connectionHolder.get()的区别 * connectionHolder.get()是尝试从ThreadLocal中获取Connection,如果没有,返回null,如果有,直接返回. * getConnection也是尝试从ThreadLocal中获取Connection,如果没有,则创建一个,然后返回,如果有,直接返回. */public static Connection getConnection() {Connection connection = connectionHolder.get();if (connection == null) {// 1.连接池可以理解是一个java类,必须实现接口DateSource // 2.DBCP连接池也是一个java类,Tomcat为其new了对象并注册到JNDI,同时Tomcat实现了JavaEE规范之一的JNDI // 3.Context接口的lookup()可以从JNDI获取对象,通过名值对的形式;下面语句获取连接池对象(DateSource类型)Context context = null;try {context = new InitialContext();DataSource dataSource = (DataSource) context.lookup("java:comp/env/jdbc/drp");// 直接从连接池拿连接,不是此时才让Oracle去创建连接connection = dataSource.getConnection();connectionHolder.set(connection);} catch (NamingException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");}}return connection;}/** * Connection使用完毕,关闭 * 此处的Connection是从连接池中拿出来的,关闭Connection实质上是让Connection恢复空闲状态 */public static void closeConnection() {// 尝试从ThreadLocal获取Connection,如果没有,关闭Connection失去意义.Connection connection = connectionHolder.get();if (connection != null) {try {connection.close();connectionHolder.remove();} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!"); }}}/** * Statement使用完毕,关闭 */public static void closeStatement(Statement statement) {if (statement != null) {try {statement.close();} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");}}}/** * ResultSet使用完毕,关闭 */public static void closeResultSet(ResultSet resultSet) {if (resultSet != null) {try {resultSet.close();} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");}}}/** * 获取connection,把事务设置为手动提交,自己控制事务 */public static void manualCommitTransaction() {// 看看ThreadLocal中是否有Connection,如果没有(因为这是第一次跟Connection打交道,所以没有Connection),必须创建一个.// 如果此处不创建Connection,将无法保证事务.Connection connection = getConnection();if (connection != null) {try {if (connection.getAutoCommit()) {connection.setAutoCommit(false);}} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");}}}/** * 一切操作正常,提交事务 */public static void commitTransaction() {// 尝试从ThreadLocal获取Connection,如果没有,提交事务失去意义.Connection connection = connectionHolder.get();if (connection != null) {try {if (!connection.getAutoCommit()) {connection.commit();}} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");}}}/** * 操作发生异常,回滚事务 */public static void rollbackTransaction() {// 尝试从ThreadLocal获取Connection,如果没有,回滚事务失去意义.Connection connection = connectionHolder.get();if (connection != null) {try {if (!connection.getAutoCommit()) {connection.rollback();}} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");}}}/** * 重置事务,如果事务是手动提交的,重置为自动提交,如果是自动提交的,重置为手动提交. */public static void resetConnection() {// 尝试从ThreadLocal获取Connection,如果没有,重置事务失去意义.Connection connection = connectionHolder.get();if (connection != null) {try {if (connection.getAutoCommit()) {connection.setAutoCommit(false);} else {connection.setAutoCommit(true);}} catch (SQLException e) {e.printStackTrace();throw new ApplicationException("系统错误,请联系系统管理员!");}}}}
