Java scope和TransactionConfiguration

超、凢脫俗 2021-06-24 14:00 356阅读 0赞

Java注解scope和TransactionConfiguration经常要在项目中应用，对于scope的使用，我到现在还没有彻底弄明白，虽然我已经研究出是表示多例还是单例，然而我模糊的是何时我该用单例何时用多例，我会混淆，而TransactionConfiguration注解比较简单，用来配置使用哪一个事务管理器。

### scope ###

**在Java项目中，该注解表示该类的生命周期，其值为singleton（单例模式）和prototype（多例模式），简单来说，假如现在存在一个OrderService，该类使用单例模式**，那么按照如下测试，可以看出

@Service
    @Scope
    public class OrderService {
    	public void sayMyName() {
    		System.out.println("MyName: " + this);
    	}
    }

public static void main(String[] args) {
    		SpringUtils.getSpringContext();
    		SpringUtils.getBeansByClassType(OrderService.class).sayMyName();
    		SpringUtils.getBeansByClassType(OrderService.class).sayMyName();
    		SpringUtils.getBeansByClassType(OrderService.class).sayMyName();
    	}

debug日志：

DEBUG 2015-01-14 11:13:05,622 org.springframework.beans.factory.support.AbstractBeanFactory: Returning cached instance of singleton bean 'orderService'
    MyName: com.honzh.socket.server.business.test.OrderService@152bdc7
    DEBUG 2015-01-14 11:13:05,622 org.springframework.beans.factory.support.AbstractBeanFactory: Returning cached instance of singleton bean 'orderService'
    MyName: com.honzh.socket.server.business.test.OrderService@152bdc7
    DEBUG 2015-01-14 11:13:05,622 org.springframework.beans.factory.support.AbstractBeanFactory: Returning cached instance of singleton bean 'orderService'
    MyName: com.honzh.socket.server.business.test.OrderService@152bdc7

结论：service对象在单例情况下只有1个。

当参数为多例时：

@Service
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    public class OrderService {
    	public void sayMyName() {
    		System.out.println("MyName: " + this);
    	}
    }

DEBUG 2015-01-14 11:15:30,648 org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory: Finished creating instance of bean 'orderService'
    MyName: com.honzh.socket.server.business.test.OrderService@cab854
    DEBUG 2015-01-14 11:15:30,648 org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory: Creating instance of bean 'orderService'
    DEBUG 2015-01-14 11:15:30,648 org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory: Finished creating instance of bean 'orderService'
    MyName: com.honzh.socket.server.business.test.OrderService@10bbd42
    DEBUG 2015-01-14 11:15:30,648 org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory: Creating instance of bean 'orderService'
    DEBUG 2015-01-14 11:15:30,648 org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory: Finished creating instance of bean 'orderService'
    MyName: com.honzh.socket.server.business.test.OrderService@1b6772a

结论：prototype状态下，service在获取时会重新加载一个新的对象。

附上SpringUtils类，该类是为了通过applicationContext文件，加载对应的spring组件。

private static ApplicationContext factory;
    
    	private SpringUtils() {
    	};
    
    	public synchronized static ApplicationContext getSpringContext() throws BeansException {
    		if (factory == null) {
    			factory = new ClassPathXmlApplicationContext("/com/honzh/socket/server/business/applicationContext.xml");
    		}
    		return factory;
    	}
    
    	public synchronized static ApplicationContext getSpringContext(String appContextPath) throws BeansException {
    		if (factory == null) {
    			factory = new ClassPathXmlApplicationContext(appContextPath);
    		}
    		return factory;
    	}
    
    	public static <T> T getBeansByClassType(Class<T> requiredType) {
    		return factory.getBean(requiredType);
    	}

### TransactionConfiguration ###

**该注解主要是用于管理spring的事务管理器**，假如你的applicationContext.xml中对事务是这样配置的

那么同样对于Service对象时，假如你有一个需要启用事务Transactional的方法，那么你其实是不需要为该类指定 TransactionConfiguration注解配置的。

如果你xml中的配置，如上，可以满足基本的事务操作，那么是没有必要启用该注解，如果你的xml中配置了多个事务管理器，该service对象需要区分不同的事务管理器，那么你需要通过如下格式启用TransactionConfiguration

@TransactionConfiguration(transactionManager = "transactionManager1", defaultRollback = true)