关于spring:Spring事务传播行为

本文出处 Spring 事务流传行为
转载请阐明出处

在 Spring @Transactional 申明式事务有一个项属性 propagation 事务流传行为，是一个 Propagation 枚举类，有 7 种类型，对应不同应用场景。上面说下这些枚举代码含意，在联合代码加深了解，坚固学习。

事务流传级别生效

先做一个小试验，写一个长久化的 save 办法，设置成禁用事务，用事务办法去调用它，看会产生什么成果。

    @Transactional(propagation = Propagation.NEVER)
    public void save(Users users){usersRepository.save(users);
    }

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
    }

依照下面字段含意解析，save 办法不反对事务，在以后事务运行会抛出异样。可是执行后果不是意料那样，没有抛出异样，数据写入到数据库了。并且咱们能够在改一次 save 办法，间接抛出一个 RuntimeTime 异样，你会发现后果更加显著。

    @Transactional(propagation = Propagation.NEVER)
    public void save(Users users){usersRepository.save(users);
        throw new RuntimeException("4322");
    }

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
    }

你会发现 save 办法 数据回滚了。

在做多几次这种试验你就会发现，在同一个类中，最外层事务注解属性会笼罩办法内所有事务注解，比方你的外层设置默认事务流传行为，无论调用那种行为都会依照默认属性，外层没有设置事务，调用办法有事务也不会失效的。这个不难理解，实现 Spring 事务一个基于 AOP 的代理类，它依据指标办法注解来加强办法，这个是运行时动静执行的，办法内其余办法没有代理类的性能加强，就相当于一般办法成果了。千万不要在同一个类外面测试事务流传行为，否则你永远都都得不到论断的。

进入办法验证

默认事务

    @Transactional
    public void save(){Employee employee = new Employee();
        employee.setDepartmentId(2);
        employee.setName("Jorry");
        employee.setSalary(60000);
        repository.save(employee);
        throw new RuntimeException("33333");
    }

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
        employeeService.save();}

执行后果：users、employee 写入失败，employee 的办法抛出异样触发回滚，也会导致外层办法回滚。在同一个事务中，只有触发回滚，事务内所有数据操作都会回滚的。

反对事务

    @Transactional(propagation = Propagation.SUPPORTS)
    public void save(){Elimployee employee = new Employee();
        employee.setDepartmentId(2);
        employee.setName("Jorry");
        employee.setSalary(60000);
        repository.save(employee);
    }

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
        employeeService.save();
        throw new RuntimeException("3333");
    }

执行成果: Usres 和 Elimployee 都进行回滚了。SUPPORTS 会退出调用者事务中，和调用者事务是同一个事务，如果在事务中出现异常全副回滚。即便在employeeService.save() 抛出异样, 成果一样的。

开启新事务

    @Transactional(propagation = Propagation.REQUIRES_NEW)
    public void save(){Employee employee = new Employee();
        employee.setDepartmentId(2);
        employee.setName("Jorry");
        employee.setSalary(60000);
        repository.save(employee);
        throw new RuntimeException("3333");
    }

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
        try {employeeService.save();
        }catch (RuntimeException e){}

执行后果：empoyee 回滚，users 写入数据库胜利。要解决 employeeService.save()异样，不然异样会导致 multSave 出现异常事务回滚了。退出一个对照，在把 employeeService.save()改成默认属性，发现 users,employee 都会回滚了，还会抛出一个异样

org.springframework.transaction.UnexpectedRollbackException: Transaction silently rolled back because it has been marked as rollback-only

Spring 官网文档说到如果内部事务（内部调用者不晓得）将事务无提醒地标记为仅回滚，则内部调用者仍会调用 commit。内部调用者须要接管一个，UnexpectedRollbackException 以分明地批示已执行回滚。

强制不应用事务

    @Transactional(propagation = Propagation.NEVER)
    public void save(){Employee employee = new Employee();
        employee.setDepartmentId(2);
        employee.setName("Jorry");
        employee.setSalary(60000);
        repository.save(employee);
    }

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
        employeeService.save();}

执行后果: 两个表都写入失败，employeeService.save() 抛出异样

org.springframework.transaction.IllegalTransactionStateException: Existing transaction found for transaction marked with propagation ‘never’

不反对事务

    @Transactional(propagation = Propagation.NOT_SUPPORTED)
    public void save(){Employee employee = new Employee();
        employee.setDepartmentId(2);
        employee.setName("Jorry");
        employee.setSalary(60000);
        repository.save(employee);
        throw new RuntimeException("33333");
    }

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
        employeeService.save();}

执行后果：employee 胜利写入数据库，employee 将事务挂了，用无事务办法执行，users 受到异样抛出，触发事务回滚。如果你把 employeeService.save()解决一下，两种表操作都写入胜利了。

强制事务

    @Transactional(propagation = Propagation.MANDATORY)
    public void save(){Employee employee = new Employee();
        employee.setDepartmentId(2);
        employee.setName("Jorry");
        employee.setSalary(60000);
        repository.save(employee);
    }

    public void multSave(){Users users = getUsers();
        save(users);
        employeeService.save();}

执行后果: users 胜利写入数据库，employee 写入失败并且抛出异样

org.springframework.transaction.IllegalTransactionStateException: No existing transaction found for transaction marked with propagation ‘mandatory’

嵌套事务

    @Transactional
    public void multSave(){Users users = getUsers();
        save(users);
        employeeService.save();}

    @Transactional(propagation = Propagation.NESTED)
    public void save(){Employee employee = new Employee();
        employee.setDepartmentId(2);
        employee.setName("Jorry");
        employee.setSalary(60000);
        repository.save(employee);
    }

执行后果：employeeService.save()抛出一个异样，如同 JPA 的实现不反对嵌套执行，这个看不到成果了。

org.springframework.transaction.NestedTransactionNotSupportedException: JpaDialect does not support savepoints – check your JPA provider’s capabilities