利用ThreadLocal建立高质量事务处理

ThreadLocal此类是一个以当前线程为key的map对象的构想。

当我们在web开发中，多个浏览器访问的时候，servlet为它们各开线程执行相应代码，而事务的执行依赖于特定的一个Connection对象当中。所以用到了ThreadLocal类来封装<Connection>来取和放。

业务逻辑中不出现 Connection对象，代码风格好

数据库表

 create table account
 ( id int primary key,
   name varchar(20),
   float money(8,2)
   )

domain中

 package cn.itcast.domain;

 import java.io.Serializable;

 public class Account implements Serializable {

     private int id;
     private String name;
     private float money;
     public Account() {
     }
     public int getId() {
         return id;
     }
     public void setId(int id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public float getMoney() {
         return money;
     }
     public void setMoney(float money) {
         this.money = money;
     }
     @Override
     public String toString() {
         return "Account [id=" + id + ", name=" + name + ", money=" + money
                 + "]";
     }

 }

utils中TransactionUtil.java

 package cn.itcast.utils;

 import java.io.InputStream;
 import java.sql.Connection;
 import java.sql.SQLException;
 import java.util.Properties;

 import javax.sql.DataSource;

 import org.apache.commons.dbcp.BasicDataSourceFactory;

 public class TransactionUtil {
     private static ThreadLocal<Connection> t=new ThreadLocal<Connection>();

     private static DataSource ds;
     static{
         try {
             InputStream in = TransactionUtil.class.getClassLoader().getResourceAsStream("dbcpconfig.properties");
             Properties props = new Properties();
             props.load(in);
             ds = BasicDataSourceFactory.createDataSource(props);
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

     public static DataSource getDataSource(){
         return ds;
     }

     public static Connection getConnection()
     {
         Connection con=null;
         try {
             con = t.get();// 获取 value，为 Connection对象 用于事务的处理
             if(con==null)
             {
                 con=ds.getConnection();
                 t.set(con);
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
         return con;
     }
     public static void startTransaction() throws SQLException            //把异常抛出去 ，让后面调用 事务 获取异常然后rollback
     {
         Connection con=null;
         try {
             con = t.get();                            //如果前面调用过getConnection()，则con!=null,以下相同
             if(con==null)
             {
                 t.set(ds.getConnection());
             }
             con.setAutoCommit(false);            //开启事务
         } catch (SQLException e) {
             e.printStackTrace();
             throw e;
         }
     }
     public static void commitTransaction() throws SQLException
     {
         Connection con=null;
         try {
             con = t.get();
             if(con==null)
             {
                 t.set(ds.getConnection());
             }
             con.commit();
         } catch (SQLException e) {
             e.printStackTrace();
             throw e;
         }
     }
     public static void rollbackTransaction() throws SQLException
     {
         Connection con=null;
         try {
             con = t.get();
             if(con==null)
             {
                 t.set(ds.getConnection());
             }
             con.rollback();
         } catch (SQLException e) {
             e.printStackTrace();
             throw e;
         }
     }
     public static void release()
     {
         Connection con=null;

         try {
             con = t.get();
             if(con!=null)
             {
                 con.close();
                 t.remove();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }

     }

 }

daoImpl中

 package cn.itcast.dao.impl;

 import java.sql.SQLException;

 import org.apache.commons.dbutils.QueryRunner;
 import org.apache.commons.dbutils.handlers.BeanHandler;

 import cn.itcast.domain.Account;
 import cn.itcast.utils.TransactionUtil;

 public class AccountDaoImpl {
     private QueryRunner qr = new QueryRunner();
     public void updateAccount(Account c)
     {
         try {
             String sql="update  account_table set money=? where name=?";
             qr.update(TransactionUtil.getConnection(),sql,c.getMoney(),c.getName());
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }

     public Account findAccount(String accountName)
     {
         try {
             String sql="select * from account_table where name=?";
             return qr.query(TransactionUtil.getConnection(),sql, new BeanHandler<Account>(Account.class),accountName);
         } catch (SQLException e) {
             e.printStackTrace();
         }
         return null;
     }
 }

serviceImpl中

 package cn.itcast.ServiceImpl;

 import java.sql.SQLException;

 import cn.itcast.dao.impl.AccountDaoImpl;
 import cn.itcast.domain.Account;
 import cn.itcast.utils.TransactionUtil;

 public class AccountServeImpl {
     public AccountDaoImpl dao=new AccountDaoImpl();
     public void transe(String name1,String name2,int money)
     {
         Account c1=dao.findAccount(name1);
         Account c2=dao.findAccount(name2);

         c1.setMoney(c1.getMoney()-money);
         c2.setMoney(c2.getMoney()+money);

         try {
             TransactionUtil.startTransaction();
             dao.updateAccount(c1);
             int i=1/0;                    //发现异常
             dao.updateAccount(c2);
         } catch (Exception e) {                    //一定要用 捕获的异常来捕获
             try {
                 TransactionUtil.rollbackTransaction();
             } catch (SQLException e1) {
                 e1.printStackTrace();
             }
             e.printStackTrace();
         }
         finally
         {
             try {
                 TransactionUtil.commitTransaction();
                 TransactionUtil.release();
             } catch (SQLException e) {
                 e.printStackTrace();
             }
         }

     }
 }

测试

     @Test
     public void test() {
         AccountServeImpl service=new AccountServeImpl();
         service.transe("chenlongfei", "wangfang", 100);
     }