分析事务的问题【初探事务】

我们先实现一个可以转张的项目：
pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.qublog</groupId>
    <artifactId>spring03_account</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.0.2.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>commons-dbutils</groupId>
            <artifactId>commons-dbutils</artifactId>
            <version>1.4</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.16</version>
        </dependency>

        <dependency>
            <groupId>c3p0</groupId>
            <artifactId>c3p0</artifactId>
            <version>0.9.1.2</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>5.0.2.RELEASE</version>
        </dependency>
    </dependencies>
</project>

Account类：

package com.qublog.domain;


import java.io.Serializable;

//账户的实体类
public class Account implements Serializable {
    private Integer id;
    private String name;
    private Float money;

    public Integer getId() {
        return id;
    }

    public void setId(Integer 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 +
                '}';
    }
}

AccountDao接口：

package com.qublog.dao;

import com.qublog.domain.Account;

import java.util.List;

//账户的持久层接口
public interface AccountDao {
    //查询所有
    List<Account> findAllAccount();

    //查询一个
    Account findAccountById(Integer id);

    //保存
    void saveAccount(Account account);

    //更新
    void updateAccount(Account account);

    //删除
    void deleteAccount(Integer id);

    //根据名称查找账户，如果有唯一结果就返回，如果没有结果就返回null，如果结果集超过一个就抛异常
    Account findAccountByName(String accountName);
}

AccountDaoImpl类：

package com.qublog.dao.impl;

import com.qublog.dao.AccountDao;
import com.qublog.domain.Account;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;

import java.util.List;

//账户的持久层实现类
public class AccountDaoImpl implements AccountDao {

    private QueryRunner runner;

    public void setRunner(QueryRunner runner) {
        this.runner = runner;
    }

    public List<Account> findAllAccount() {
        try{
            return runner.query("select * from account;",new BeanListHandler<Account>(Account.class));
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public Account findAccountById(Integer id) {
        try{
            return runner.query("select * from account where id=?;",new BeanHandler<Account>(Account.class),id);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public void saveAccount(Account account) {
        try{
            runner.update("insert into account(name,money) values(?,?);", account.getName(), account.getMoney());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public void updateAccount(Account account) {
        try{
            runner.update("update account set name=?,money=? where id=?;", account.getName(), account.getMoney(),account.getId());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public void deleteAccount(Integer id) {
        try{
            runner.update("delete from account where id=?;",id);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public Account findAccountByName(String accountName) {
        try {
            List<Account> accounts = runner.query("select * from account where name = ?",new BeanListHandler<Account>(Account.class),accountName);
            if (accounts == null || accounts.size() == 0) {
                return null;
            }
            if (accounts.size() > 1) {
                throw new RuntimeException("结果集不唯一，数据有问题");
            }
            return accounts.get(0);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

AccountService接口：

package com.qublog.service;

import com.qublog.domain.Account;

import java.util.List;

//账户的业务层接口
public interface AccountService {

    //查询所有
    List<Account> findAllAccount();

    //查询一个
    Account findAccountById(Integer id);

    //保存
    void saveAccount(Account account);

    //更新
    void updateAccount(Account account);

    //删除
    void deleteAccount(Integer id);

    //转账
    void transfer(String sourceName, String targetName, Float money);
}

AccountServiceImpl类：

package com.qublog.service.impl;

import com.qublog.dao.AccountDao;
import com.qublog.domain.Account;
import com.qublog.service.AccountService;

import java.util.List;

//账户的业务层实现类
public class AccountServiceImpl implements AccountService {

    private AccountDao accountDao;

    public void setAccountDao(AccountDao accountDao) {
        this.accountDao = accountDao;
    }

    public List<Account> findAllAccount() {
        return accountDao.findAllAccount();
    }

    public Account findAccountById(Integer id) {
        return accountDao.findAccountById(id);
    }

    public void saveAccount(Account account) {
        accountDao.saveAccount(account);
    }

    public void updateAccount(Account account) {
        accountDao.updateAccount(account);
    }

    public void deleteAccount(Integer id) {
        accountDao.deleteAccount(id);
    }

    public void transfer(String sourceName, String targetName, Float money) {
        //根据名称查询转出账户
        Account source = accountDao.findAccountByName(sourceName);
        //根据名称查询转入账户
        Account target = accountDao.findAccountByName(targetName);
        //转出账户减钱
        source.setMoney(source.getMoney()-money);
        //转入账户加钱
        target.setMoney(target.getMoney()+money);
        //更新转出账户
        accountDao.updateAccount(source);
        //更新转入账户
        accountDao.updateAccount(target);
    }
}

AccountServiceTest类：

package com.qublog.test;

import com.qublog.service.AccountService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

//使用Junit单元测试，测试我们的配置
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:bean.xml")
public class AccountServiceTest {

    @Autowired
    private AccountService as;

    @Test
    public void testTransfer() {
        as.transfer("aaa","bbb",100f);
    }

}

执行结果为：

这时我们看数据发现没有任何问题，但当我们修改以下代码，如下：
AccountServiceImpl类：

    public void transfer(String sourceName, String targetName, Float money) {
        //根据名称查询转出账户
        Account source = accountDao.findAccountByName(sourceName);
        //根据名称查询转入账户
        Account target = accountDao.findAccountByName(targetName);
        //转出账户减钱
        source.setMoney(source.getMoney()-money);
        //转入账户加钱
        target.setMoney(target.getMoney()+money);
        //更新转出账户
        accountDao.updateAccount(source);
        int i=1/0;
        //更新转入账户
        accountDao.updateAccount(target);
    }

这时执行测试，打印输出：

mysql中结果为：

可以看出明显错误。

---

下面我们分析代码：
AccountServiceImpl类：

    public void transfer(String sourceName, String targetName, Float money) {
        //根据名称查询转出账户
        Account source = accountDao.findAccountByName(sourceName);
        //根据名称查询转入账户
        Account target = accountDao.findAccountByName(targetName);
        //转出账户减钱
        source.setMoney(source.getMoney()-money);
        //转入账户加钱
        target.setMoney(target.getMoney()+money);
        //更新转出账户
        accountDao.updateAccount(source);
        int i=1/0;
        //更新转入账户
        accountDao.updateAccount(target);
    }

代码中一共获取四个连接，前三个事务都成功了所以都提交了，但第四个事务前发生了除零异常，所以没有提交。
所以我们解决以上问题的思路就是：将transfer中的操作全放到一个连接中，所有操作要么全成功，要么全失败。
方法：使用ThreadLocal对象把Connection和当前线程绑定，从而使一个线程中只有一个能控制事务的对象。
注意：事务的控制应该都是在业务层。

修改后的代码：
pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.qublog</groupId>
    <artifactId>spring03_account</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.0.2.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>commons-dbutils</groupId>
            <artifactId>commons-dbutils</artifactId>
            <version>1.4</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.16</version>
        </dependency>

        <dependency>
            <groupId>c3p0</groupId>
            <artifactId>c3p0</artifactId>
            <version>0.9.1.2</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>5.0.2.RELEASE</version>
        </dependency>
    </dependencies>
</project>

Account类：

package com.qublog.domain;


import java.io.Serializable;

//账户的实体类
public class Account implements Serializable {
    private Integer id;
    private String name;
    private Float money;

    public Integer getId() {
        return id;
    }

    public void setId(Integer 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 +
                '}';
    }
}

AccountDao接口：

package com.qublog.dao;

import com.qublog.domain.Account;

import java.util.List;

//账户的持久层接口
public interface AccountDao {
    //查询所有
    List<Account> findAllAccount();

    //查询一个
    Account findAccountById(Integer id);

    //保存
    void saveAccount(Account account);

    //更新
    void updateAccount(Account account);

    //删除
    void deleteAccount(Integer id);

    //根据名称查找账户，如果有唯一结果就返回，如果没有结果就返回null，如果结果集超过一个就抛异常
    Account findAccountByName(String accountName);
}

AccountDaoImpl类：

package com.qublog.dao.impl;

import com.qublog.dao.AccountDao;
import com.qublog.domain.Account;
import com.qublog.utils.ConnectionUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;

import java.util.List;

//账户的持久层实现类
public class AccountDaoImpl implements AccountDao {

    private QueryRunner runner;

    private ConnectionUtils connectionUtils;

    public void setConnectionUtils(ConnectionUtils connectionUtils) {
        this.connectionUtils = connectionUtils;
    }

    public void setRunner(QueryRunner runner) {
        this.runner = runner;
    }

    public List<Account> findAllAccount() {
        try{
            return runner.query(connectionUtils.getThreadConnection(),"select * from account;",new BeanListHandler<Account>(Account.class));
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public Account findAccountById(Integer id) {
        try{
            return runner.query(connectionUtils.getThreadConnection(),"select * from account where id=?;",new BeanHandler<Account>(Account.class),id);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public void saveAccount(Account account) {
        try{
            runner.update(connectionUtils.getThreadConnection(),"insert into account(name,money) values(?,?);", account.getName(), account.getMoney());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public void updateAccount(Account account) {
        try{
            runner.update(connectionUtils.getThreadConnection(),"update account set name=?,money=? where id=?;", account.getName(), account.getMoney(),account.getId());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public void deleteAccount(Integer id) {
        try{
            runner.update(connectionUtils.getThreadConnection(),"delete from account where id=?;",id);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public Account findAccountByName(String accountName) {
        try {
            List<Account> accounts = runner.query(connectionUtils.getThreadConnection(),"select * from account where name = ?",new BeanListHandler<Account>(Account.class),accountName);
            if (accounts == null || accounts.size() == 0) {
                return null;
            }
            if (accounts.size() > 1) {
                throw new RuntimeException("结果集不唯一，数据有问题");
            }
            return accounts.get(0);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

AccountService接口：

package com.qublog.service;

import com.qublog.domain.Account;

import java.util.List;

//账户的业务层接口
public interface AccountService {

    //查询所有
    List<Account> findAllAccount();

    //查询一个
    Account findAccountById(Integer id);

    //保存
    void saveAccount(Account account);

    //更新
    void updateAccount(Account account);

    //删除
    void deleteAccount(Integer id);

    //转账
    void transfer(String sourceName, String targetName, Float money);
}

AccountServiceImpl类：

package com.qublog.service.impl;

import com.qublog.dao.AccountDao;
import com.qublog.domain.Account;
import com.qublog.service.AccountService;
import com.qublog.utils.TransactionManager;

import java.util.List;

//账户的业务层实现类
//事务的控制应该都是在业务层的
public class AccountServiceImpl implements AccountService {

    private AccountDao accountDao;

    private TransactionManager txManager;

    public void setTxManager(TransactionManager txManager) {
        this.txManager = txManager;
    }

    public void setAccountDao(AccountDao accountDao) {
        this.accountDao = accountDao;
    }

    public List<Account> findAllAccount() {
        try {
            //开启事务
            txManager.beginTransaction();
            //执行操作
            List<Account> accounts = accountDao.findAllAccount();
            //提交事务
            txManager.commit();
            //返回结果
            return accounts;
        } catch (Exception e) {
            //回滚操作
            txManager.rollback();
            throw new RuntimeException(e);
        } finally {
            //释放连接
            txManager.release();
        }
    }

    public Account findAccountById(Integer id) {
        try {
            //开启事务
            txManager.beginTransaction();
            //执行操作
            Account account = accountDao.findAccountById(id);
            //提交事务
            txManager.commit();
            //返回结果
            return account;
        } catch (Exception e) {
            //回滚操作
            txManager.rollback();
            throw new RuntimeException(e);
        } finally {
            //释放连接
            txManager.release();
        }
    }

    public void saveAccount(Account account) {
        try {
            //开启事务
            txManager.beginTransaction();
            //执行操作
            accountDao.saveAccount(account);
            //提交事务
            txManager.commit();
        } catch (Exception e) {
            //回滚操作
            txManager.rollback();
        } finally {
            //释放连接
            txManager.release();
        }
    }

    public void updateAccount(Account account) {
        try {
            //开启事务
            txManager.beginTransaction();
            //执行操作
            accountDao.updateAccount(account);
            //提交事务
            txManager.commit();
        } catch (Exception e) {
            //回滚操作
            txManager.rollback();
        } finally {
            //释放连接
            txManager.release();
        }
    }

    public void deleteAccount(Integer id) {
        try {
            //开启事务
            txManager.beginTransaction();
            //执行操作
            accountDao.deleteAccount(id);
            //提交事务
            txManager.commit();
        } catch (Exception e) {
            //回滚操作
            txManager.rollback();
        } finally {
            //释放连接
            txManager.release();
        }
    }

    public void transfer(String sourceName, String targetName, Float money) {
        try {
            //开启事务
            txManager.beginTransaction();
            //执行操作

            //根据名称查询转出账户
            Account source = accountDao.findAccountByName(sourceName);
            //根据名称查询转入账户
            Account target = accountDao.findAccountByName(targetName);
            //转出账户减钱
            source.setMoney(source.getMoney()-money);
            //转入账户加钱
            target.setMoney(target.getMoney()+money);
            //更新转出账户
            accountDao.updateAccount(source);
            int i=1/0;
            //更新转入账户
            accountDao.updateAccount(target);

            //提交事务
            txManager.commit();
        } catch (Exception e) {
            //回滚操作
            txManager.rollback();
            e.printStackTrace();
        } finally {
            //释放连接
            txManager.release();
        }
    }
}

ConnectionUtils类：

package com.qublog.utils;

import javax.sql.DataSource;
import java.sql.Connection;

//连接的工具类，它用于从数据源中获取一个连接，并且实现和线程的绑定
public class ConnectionUtils {
    private ThreadLocal<Connection> tl = new ThreadLocal<Connection>();

    private DataSource dataSource;

    public void setDataSource(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    //获取当前线程上的连接
    public Connection getThreadConnection() {
        try {
            //先从ThreadLocal上获取
            Connection conn = tl.get();
            //判断当前线程上是否有连接
            if (conn == null) {
                //从数据源中获取一个连接，并且存入ThreadLocal中
                conn = dataSource.getConnection();
                tl.set(conn);
            }
            //返回当前线程上的连接
            return conn;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    //把连接和线程解绑
    public void removeConnection() {
        tl.remove();
    }
}

TransactionManager类：

package com.qublog.utils;

//和事务管理相关的工具类，包含了，开启事务，提交事务，回滚事务，释放连接
public class TransactionManager {

    private ConnectionUtils connectionUtils;

    public void setConnectionUtils(ConnectionUtils connectionUtils) {
        this.connectionUtils = connectionUtils;
    }

    //开启事务
    public void beginTransaction() {
        try {
            connectionUtils.getThreadConnection().setAutoCommit(false);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //提交事务
    public void commit() {
        try {
            connectionUtils.getThreadConnection().commit();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //回滚事务
    public void rollback() {
        try {
            connectionUtils.getThreadConnection().rollback();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //释放连接
    public void release() {
        try {
            connectionUtils.getThreadConnection().close();//还回连接池中
            connectionUtils.removeConnection();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

AccountServiceTest类：

package com.qublog.test;

import com.qublog.service.AccountService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

//使用Junit单元测试，测试我们的配置
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:bean.xml")
public class AccountServiceTest {

    @Autowired
    private AccountService as;

    @Test
    public void testTransfer() {
        as.transfer("aaa","bbb",100f);
    }

}

这时再次测试，打印结果：

---

进一步分析代码，我们发现配置变得非常麻烦，依赖注入乱七八糟，各个类之间互相依赖，