ThreadLocal封装connection--隔离了相关资源，防止线程安全问题

线程安全问题的2种解决方法：

 

同步synchronized ，是一把锁，线程A操作变量X的时候，这把锁会锁住，此时其他线程B无法操作。

等线程A操作结束，锁打开，此时变量X可以被线程B操作 ----- 效果：多线程共享资源（变量）

 

另外，ThreadLocal是线程的本地变量，ThreadLocal隔离了相关资源，可以防止线程安全问题。---- 效果：一个线程对应一个ThreadLocal（独享资源），多线程不能共享资源（ThreadLocal可用于封装connection）

 

package com.qdsx.drp.util;

 

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.SQLException;

 

publicclass ConnectionManager {

   

   //ThreadLocal

   privatestatic ThreadLocal<Connection>connectionHolder =new ThreadLocal<Connection>();

   

   /**

    * 得到Connection

    * @return

    */

   publicstatic Connection getConnection(){

      

      //ThreadLocal

      Connection conn = connectionHolder.get();

      

      //ThreadLocal,如果在当前线程中没有绑定相应的Connection

      if(conn ==null){

          //取得jdbc配置信息

          try {

             JdbcInfo jdbcInfo = ConfigReader.getInstance().getJdbcInfo();

             Class.forName(jdbcInfo.getDriverName()).newInstance();

             conn = DriverManager.getConnection(jdbcInfo.getUrl(), jdbcInfo.getUsername(), jdbcInfo.getPassword());

             

             //ThreadLocal，将Connection设置(set)到线程变量（connectionHolder）中

             connectionHolder.set(conn);

             

          } catch (InstantiationException e) {

             e.printStackTrace();

             thrownew ApplicationException("系统错误，请联系系统管理员，qq:472989050");

          } catch (IllegalAccessException e) {

             e.printStackTrace();

             thrownew ApplicationException("系统错误，请联系系统管理员，qq:472989050");

          } catch (ClassNotFoundException e) {

             e.printStackTrace();

             thrownew ApplicationException("系统错误，请联系系统管理员，qq:472989050");

          } catch (SQLException e) {

             e.printStackTrace();

             thrownew ApplicationException("系统错误，请联系系统管理员，qq:472989050");

          }

      }

      return conn;     

   }

   

   publicstaticvoid closeConnection(){

      Connection conn = connectionHolder.get();

      if(conn !=null){

          try {

             conn.close();

             //从ThreadLocal中清除Connection（如果不清楚，下次拿到的还是已经close的Connection，用不了）

             connectionHolder.remove();

          } catch (SQLException e) {

             e.printStackTrace();

          }

      }

   }

   

   //以下是事务处理的封装

   publicstaticvoid beginTransaction(Connection conn) {

      try {

          if(conn !=null){

             if(conn.getAutoCommit()){

                 conn.setAutoCommit(false);//手动提交

             }

          }

      } catch (SQLException e) {

          e.printStackTrace();

      }

   }

   

   publicstaticvoid commitTransaction(Connection conn) {

      try {

          if(conn !=null){

             if(!conn.getAutoCommit()){

                 conn.commit();

             }

          }

      } catch (SQLException e) {

          e.printStackTrace();

      }

   }

   

   publicstaticvoid rollbackTransaction(Connection conn) {

      try {

          if (conn !=null) {

             if(!conn.getAutoCommit()){

                 conn.rollback();

             }

          }

      } catch (SQLException e) {

          e.printStackTrace();

      }

   }

   

   publicstaticvoid resetConnection(Connection conn) {

      try {

          if(conn !=null){

             if(conn.getAutoCommit()){

                 conn.setAutoCommit(false);

             }else{

                 conn.setAutoCommit(true);

             }

          }

      } catch (SQLException e) {

          e.printStackTrace();

      }

   }

   

   publicstaticvoid setAutoCommit(Connection conn,boolean autoCommit) {

      if (conn !=null) {

          try {

             conn.setAutoCommit(autoCommit);

          } catch (SQLException e) {

             e.printStackTrace();

          }

      }

   }  

}

 

在service层的使用：

 

   publicvoid addFlowCard(FlowCard flowCard)throws ApplicationException {

      Connection conn = null;

      try {

          //取得

          conn = ConnectionManager.getConnection();

          

          //开启事务

          ConnectionManager.beginTransaction(conn);

          

          //生成流向单单号

          String flowCardVouNo = flowCardDao.generateVouNo();

          //添加流向单主信息

          flowCardDao.addFlowCardMaster(flowCardVouNo, flowCard);

          //添加流向单明细信息

          flowCardDao.addFlowCardDetail(flowCardVouNo, flowCard.getFlowCardDetailList());

      

          //提交事务

          ConnectionManager.commitTransaction(conn);

      } catch (DaoException e) {

          //异常，回滚事务

          ConnectionManager.rollbackTransaction(conn);

          e.printStackTrace();

          thrownew ApplicationException("添加流向单失败！");

      }finally{

          //关闭Connection，并从ThreadLocal中清除Connection

          ConnectionManager.closeConnection();

      }     

   }

 

 

在dao层使用：

   public StringgenerateVouNo() throws DaoException {

      Connection conn = ConnectionManager.getConnection();

      returnnull;

   }

 

   publicvoid addFlowCardMaster(String flowCardVouNo, FlowCard flowCard)

          throws DaoException {

      Connection conn = ConnectionManager.getConnection();

   }

 

   publicvoid addFlowCardDetail(String flowCardVouNo,

          List<FlowCardDetail> flowCardDetailList) throws DaoException {

      Connection conn = ConnectionManager.getConnection();

   }