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);
    }