JavaWeb学习-DBUtils框架-6-ThreadLocal和转账版本3

骑猪看日落 2022-01-22 11:41 234阅读 0赞

上一篇我们发现还是有问题，不同把C3P0得到Connection对象的代码出现在业务层，这个只能出现在DAO层，这篇就来解决这个问题。

1.ThreadLocal

先看看ThreadLocal，叫线程局部变量，这个类有set和get方法，和当前线程绑定。

package com.anthony.threadlocal;
    
    public class TestThreadLocal {
    
    	public static void main(String[] args) {
    		ThreadLocal t = new ThreadLocal();
    		t.set("P");
    		//第二个线程
    		MyThread mt = new MyThread(t);
    		mt.start();
    		System.out.println(t.get());
    	}
    
    }

package com.anthony.threadlocal;
    
    public class MyThread extends Thread {
    	private ThreadLocal t1;
    	
    	public MyThread(ThreadLocal t1) {
    		this.t1 = t1;
    	}
    	
    	public void run() {
    		System.out.println(t1.get() + "aaaaaa");
    	}
    }

第一个线程是Main方法产生的，第二个线程MyThread，我这里想在第二个线程里面，想取出第一个线程中的set的值“P”，运行下

P
    nullaaaaaa

发现第二个线程是取不到第一个线程中set进去的P这个值，如果这里把P换成我们Connection对象，那么我们就可以在DAO层实现getConnection。

2.第三版转账(推荐)

2.1 在utils包（没有就新建一个）下新建一个MangerThreadLocal类

package com.anthony.utils;
    
    import java.sql.Connection;
    import java.sql.SQLException;
    
    import com.anthony.datasource.C3P0Utils;
    
    public class MangerThreadLocal {
    	
    	private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();
    	
    	// 得到连接对象
    	public static Connection getConnection() {
    		Connection conn = tl.get();
    		if(conn == null) {
    			conn = C3P0Utils.getConnection(); //从池中取出一个连接对象
    			tl.set(conn);
    		}
    		return conn;
    	}	
    	
    	// 开始事务
    	public static void startTransaction() {
    		try {
    			getConnection().setAutoCommit(false);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    	}
    	
    	// 提交事务
    	public static void commit() {
    		try {
    			getConnection().commit();
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    	}
    	
    	// 回滚事务
    	public static void rollback() {
    		try {
    			getConnection().rollback();
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    	}
    	
    	public static void close() {
    		try {
    			getConnection().close();
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    	}
    }

注意上面tl.set(conn)不要漏写。

2.2 AccountDaoImpl.java代码

package com.anthony.dao.impl;
     
    import org.apache.commons.dbutils.QueryRunner;
    import org.apache.commons.dbutils.handlers.BeanHandler;
     
    import com.anthony.dao.AccountDao;
    import com.anthony.datasource.C3P0Utils;
    import com.anthony.entity.Account;
    import com.anthony.utils.MangerThreadLocal;
     
    public class AccountDaoImpl implements AccountDao {
     
    	public void updateAccount(String fromName, String toName, double money) throws Exception {
    		//创建一个QueryRunner对象
    		QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
    		//转出
    		qr.update("update account set money=money-? where name=?", money, fromName);
    		qr.update("update account set money=money+? where name=?", money, toName);
    		
    	}
     
    	@Override
    	public void updateAccount(Account account) throws Exception {
    		
    		QueryRunner qr = new QueryRunner();
    		qr.update(MangerThreadLocal.getConnection(), "update account set money=? where name=?", account.getMoney(), account.getName());
    	}
     
    	
    	public Account findAccountByName(String name) throws Exception {
    		QueryRunner qr = new QueryRunner();
    		Account account = qr.query(MangerThreadLocal.getConnection(), "select * from account where name=?", new BeanHandler<Account>(Account.class), name);
    		return account;
    	}
    	
    }

注意这里conn的得到方式。

2.3 AccountServiceImpl.java代码

package com.anthony.service.impl;
     
    import java.sql.Connection;
    import java.sql.SQLException;
     
    import com.anthony.dao.AccountDao;
    import com.anthony.dao.impl.AccountDaoImpl;
    import com.anthony.datasource.C3P0Utils;
    import com.anthony.entity.Account;
    import com.anthony.service.AccountService;
    import com.anthony.utils.MangerThreadLocal;
     
    public class AccountServiceImpl implements AccountService {
    	AccountDao ad = new AccountDaoImpl();
    	
    	public void transfer(String fromName, String toName, double money) {
    		//ad.updateAccount(fromName, toName, money);
    		try {
    			MangerThreadLocal.startTransaction(); //开始事务
    			Account fromAccount = ad.findAccountByName(fromName);
    			Account toAccount = ad.findAccountByName(toName);
    			//设置各自账户金额
    			fromAccount.setMoney(fromAccount.getMoney()-money);
    			toAccount.setMoney(toAccount.getMoney()+money);
    			//完成转账操作
    			ad.updateAccount(fromAccount);
    			ad.updateAccount(toAccount);
    			MangerThreadLocal.commit(); //提交事务
    		} catch (Exception e) {
    			e.printStackTrace();
    			MangerThreadLocal.rollback(); //回滚事务
    		} finally {
    			MangerThreadLocal.close(); //释放连接资源
    		}
    	}
     
    }

运行下，转账没问题。