Java事务之一——Java事务的基本问题
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关于加@Transactional注解的方法之间调用，事务是否生效的问题
https://blog.csdn.net/blacktal/article/details/79345902
之前面试被问过这个问题，回答基本靠猜，在此记录一下事务方法调用的问题。
- 不同类之间的方法调用，如类A的方法a()调用类B的方法b()，这种情况事务是正常起作用的。只要方法a()或b()配置了事务，运行中就会开启事务，产生代理。
若两个方法都配置了事务，两个事务具体以何种方式传播，取决于设置的事务传播特性。
- 同一个类内方法调用：重点来了，同一个类内的方法调用就没那么简单了，假定类A的方法a()调用方法b()
同一类内方法调用，无论被调用的b()方法是否配置了事务，此事务在被调用时都将不生效。
看一个例子：
@Service
public class UserServiceImpl implements UserService {
@Autowired
private UserDao userDao;
public int insertUser(User user) {
userDao.insertUser(user);
// 调用同类方法
this.selectUser(user.getId());
return 1;
}
@Transactional
public String selectUser(int id) {
throw new RuntimeException();
//return userDao.selectUser(id);
}
public int updateUser(User user) {
return userDao.updateUser(0, user);
}
}
service层中，insertUser()方法没有配置事务，selectUser()配置了事务，在insertUser()中调用selectUser()时，查看日志如下：
[DEBUG][2018-02-22 11:00:32] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:104) drop table if exists user
Hibernate: drop table if exists user
[DEBUG][2018-02-22 11:00:32] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:104) create table user (id integer not null auto_increment, createdDate datetime, email varchar(255), name varchar(20) not null, password varchar(255), phone varchar(255), updatedDate datetime, primary key (id))
Hibernate: create table user (id integer not null auto_increment, createdDate datetime, email varchar(255), name varchar(20) not null, password varchar(255), phone varchar(255), updatedDate datetime, primary key (id))
[INFO][2018-02-22 11:00:32] org.hibernate.tool.hbm2ddl.SchemaExport.execute(SchemaExport.java:406) HHH000230: Schema export complete
[DEBUG][2018-02-22 11:00:32] org.hibernate.internal.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:1073) Checking 0 named HQL queries
[DEBUG][2018-02-22 11:00:32] org.hibernate.internal.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:1096) Checking 0 named SQL queries
[DEBUG][2018-02-22 11:00:32] org.hibernate.stat.internal.StatisticsInitiator.initiateServiceInternal(StatisticsInitiator.java:110) Statistics initialized [enabled=false]
[INFO][2018-02-22 11:00:33] org.springframework.orm.hibernate4.HibernateTransactionManager.afterPropertiesSet(HibernateTransactionManager.java:360) Using DataSource [com.mchange.v2.c3p0.ComboPooledDataSource[ identityToken -> 1hge15x9t1g0fr98s704x1|72d1ad2e, dataSourceName -> 1hge15x9t1g0fr98s704x1|72d1ad2e ]] of Hibernate SessionFactory for HibernateTransactionManager
[DEBUG][2018-02-22 11:00:33] org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:228) Executing identity-insert immediately
[DEBUG][2018-02-22 11:00:33] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:104) insert into user (createdDate, email, name, password, phone, updatedDate) values (?, ?, ?, ?, ?, ?)
Hibernate: insert into user (createdDate, email, name, password, phone, updatedDate) values (?, ?, ?, ?, ?, ?)
[DEBUG][2018-02-22 11:00:33] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:212) Obtaining JDBC connection
[DEBUG][2018-02-22 11:00:33] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:218) Obtained JDBC connection
[DEBUG][2018-02-22 11:00:33] org.hibernate.id.IdentifierGeneratorHelper.getGeneratedIdentity(IdentifierGeneratorHelper.java:93) Natively generated identity: 1
[DEBUG][2018-02-22 11:00:33] org.hibernate.hql.internal.ast.QueryTranslatorImpl.parse(QueryTranslatorImpl.java:267) parse() - HQL: select name from com.wcl.pojo.User u where u.id = ?
[DEBUG][2018-02-22 11:00:33] org.hibernate.hql.internal.ast.QueryTranslatorImpl.showHqlAst(QueryTranslatorImpl.java:285) --- HQL
AST ---
可见没有开启事务，因此selectUser()的事务配置没有生效，抛异常后也不会回滚。
另一个例子：方法a()配置了事务，此时b()的事务虽然不生效，但a()的事务生效，对于b()中抛出的异常也会回滚。
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:104) drop table if exists user
Hibernate: drop table if exists user
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:104) create table user (id integer not null auto_increment, createdDate datetime, email varchar(255), name varchar(20) not null, password varchar(255), phone varchar(255), updatedDate datetime, primary key (id))
Hibernate: create table user (id integer not null auto_increment, createdDate datetime, email varchar(255), name varchar(20) not null, password varchar(255), phone varchar(255), updatedDate datetime, primary key (id))
[INFO][2018-02-22 11:08:50] org.hibernate.tool.hbm2ddl.SchemaExport.execute(SchemaExport.java:406) HHH000230: Schema export complete
[DEBUG][2018-02-22 11:08:50] org.hibernate.internal.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:1073) Checking 0 named HQL queries
[DEBUG][2018-02-22 11:08:50] org.hibernate.internal.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:1096) Checking 0 named SQL queries
[DEBUG][2018-02-22 11:08:50] org.hibernate.stat.internal.StatisticsInitiator.initiateServiceInternal(StatisticsInitiator.java:110) Statistics initialized [enabled=false]
[INFO][2018-02-22 11:08:50] org.springframework.orm.hibernate4.HibernateTransactionManager.afterPropertiesSet(HibernateTransactionManager.java:360) Using DataSource [com.mchange.v2.c3p0.ComboPooledDataSource[ identityToken -> 1hge15x9t1g0qf4c3bcmx8|399f45b1, dataSourceName -> 1hge15x9t1g0qf4c3bcmx8|399f45b1 ]] of Hibernate SessionFactory for HibernateTransactionManager
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:212) Obtaining JDBC connection
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:218) Obtained JDBC connection
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.transaction.spi.AbstractTransactionImpl.begin(AbstractTransactionImpl.java:158) begin
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doBegin(JdbcTransaction.java:69) initial autocommit status: true
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doBegin(JdbcTransaction.java:71) disabling autocommit
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:228) Executing identity-insert immediately
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.spi.SqlStatementLogger.logStatement(SqlStatementLogger.java:104) insert into user (createdDate, email, name, password, phone, updatedDate) values (?, ?, ?, ?, ?, ?)
Hibernate: insert into user (createdDate, email, name, password, phone, updatedDate) values (?, ?, ?, ?, ?, ?)
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:212) Obtaining JDBC connection
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:218) Obtained JDBC connection
[DEBUG][2018-02-22 11:08:50] org.hibernate.id.IdentifierGeneratorHelper.getGeneratedIdentity(IdentifierGeneratorHelper.java:93) Natively generated identity: 1
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.transaction.spi.AbstractTransactionImpl.rollback(AbstractTransactionImpl.java:203) rolling back
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doRollback(JdbcTransaction.java:164) rolled JDBC Connection
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.releaseManagedConnection(JdbcTransaction.java:126) re-enabling autocommit
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.releaseConnection(LogicalConnectionImpl.java:232) Releasing JDBC connection
[DEBUG][2018-02-22 11:08:50] org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.releaseConnection(LogicalConnectionImpl.java:250) Released JDBC connection
Exception in thread "main" java.lang.RuntimeException
at com.wcl.service.UserServiceImpl.selectUser(UserServiceImpl.java:26)
at com.wcl.service.UserServiceImpl.insertUser(UserServiceImpl.java:20)
- 不生效的原因？
有几篇文章探究了事务这个特性的原因，spring声明式事务 同一类内方法调用事务失效
个人理解，当从类外调用方法a()时，从spring容器获取到的serviceImpl对象实际是包装好的proxy对象，因此调用a()方法的对象是动态代理对象。而在类内部a()调用b()的过程中，实质执行的代码是this.b()，此处this对象是实际的serviceImpl对象而不是本该生成的代理对象，因此直接调用了b()方法。
aop原理跟事务一样，往大里说是动态代理，往小里说是反射机制。我又测试了两个方法，分别加上aop增强通知，类内调用的效果跟事务是一样的。这里最好研究一下spring aop和事务的源码，应该能搞得更清楚。
作者：blacktal
来源：CSDN
原文：https://blog.csdn.net/blacktal/article/details/79345902
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