1. 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。

2. 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：

代码语言：javascript代码运行次数：0运行复制@Servicepublic 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：

代码语言：javascript代码运行次数：0运行复制[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。

代码语言：javascript代码运行次数：0运行复制[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)3. 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。