Spring积累

爱被打了一巴掌 2022-01-28 11:51 270阅读 0赞

# [Spring积累][Spring] #

<tx:annotation-driven/>  （Spring的XML配置里两大Bean的声明之一）

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那我们是否就可以在程序中所有被spring管理的类(@Controller、@Service、@Component等等)上都可以使用@Transactional注解了呢，在Service上可以使用@Transactional 注解这个是肯定的了，那总有些人也想弄明白能否在Controller 使用？答案显然是“不一定”的（与时间配置有关），下面做下解释：

在 spring-framework-reference.pdf 文档上有这样一段话：

<tx:annotation-driven/> only looks for @Transactional on beans in the same application context it is defined in. This means that, if you put <tx:annotation-driven/> in a WebApplicationContext for a DispatcherServlet, it only checks for @Transactional beans in your controllers, and not your services.

意思就是：<tx:annoation-driven/>只会查找和它在相同的应用上下文件中定义的bean上面的@Transactional注解，如果你把它放在Dispatcher的应用上下文中，它只检查控制器（Controller）上的@Transactional注解，而不是你services上的@Transactional注解。

Bean初始化

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总结：

1、Spring为bean提供了两种初始化bean的方式，实现InitializingBean接口，实现afterPropertiesSet方法，或者在配置文件中通过init-method指定，两种方式可以同时使用。

2、实现InitializingBean接口是直接调用afterPropertiesSet方法，比通过反射调用init-method指定的方法效率要高一点，但是init-method方式消除了对spring的依赖。

3、如果调用afterPropertiesSet方法时出错，则不调用init-method指定的方法。

后置处理器：

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BeanPostProcessor API

public interface BeanPostProcessor { 
 
 /** 
 * Apply this BeanPostProcessor to the given new bean instance before any bean 
 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet} 
 * or a custom init-method). The bean will already be populated with property values. 
 */ 
 //实例化、依赖注入完毕，在调用显示的初始化之前完成一些定制的初始化任务 
 Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException; 
 
 
 /** 
 * Apply this BeanPostProcessor to the given new bean instance after any bean 
 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet} 
 * or a custom init-method). The bean will already be populated with property values. 
 */ 
 //实例化、依赖注入、初始化完毕时执行 
 Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException; 
 
 }

由API可以看出:
    1：后置处理器的postProcessorBeforeInitailization方法是在bean实例化，依赖注入之后及自定义初始化方法(例如：配置文件中bean标签添加init-method属性指定Java类中初始化方法、
    @PostConstruct注解指定初始化方法，Java类实现InitailztingBean接口)之前调用
    2：后置处理器的postProcessorAfterInitailization方法是在bean实例化、依赖注入及自定义初始化方法之后调用

注意：
       1.BeanFactory和ApplicationContext两个容器对待bean的后置处理器稍微有些不同。ApplicationContext容器会自动检测Spring配置文件中那些bean所对应的Java类实现了BeanPostProcessor
    接口，并自动把它们注册为后置处理器。在创建bean过程中调用它们，所以部署一个后置处理器跟普通的bean没有什么太大区别。

2.BeanFactory容器注册bean后置处理器时必须通过代码显示的注册，在IoC容器继承体系中的ConfigurableBeanFactory接口中定义了注册方法

/** 
 * Add a new BeanPostProcessor that will get applied to beans created 
 * by this factory. To be invoked during factory configuration. 
 * Note: Post-processors submitted here will be applied in the order of 
 * registration; any ordering semantics expressed through implementing the 
 * {@link org.springframework.core.Ordered} interface will be ignored. Note 
 * that autodetected post-processors (e.g. as beans in an ApplicationContext) 
 * will always be applied after programmatically registered ones. 
 * @param beanPostProcessor the post-processor to register 
 */ 
 void addBeanPostProcessor(BeanPostProcessor beanPostProcessor);

Spring如何调用多个BeanPostProcessor实现类：

我们可以在Spring配置文件中添加多个BeanPostProcessor(后置处理器)接口实现类，在默认情况下Spring容器会根据后置处理器的定义顺序来依次调用。

Spring配置文件：

xml版本

<?xml version="1.0" encoding="UTF-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans.xsd">
  
 <bean id="narCodeService" class="com.test.service.impl.NarCodeServiceImpl">
 </bean>
 <bean id="postProcessor" class="com.test.spring.PostProcessor"/>
 <bean id="postProcessorB" class="com.test.spring.PostProcessorB"/>
 </beans>

BeanPostProcessor实现类：

package com.test.spring;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    /**
     * bean后置处理器
     * @author zss
     *
     */
    public class PostProcessor implements BeanPostProcessor {
    
        @Override
        public Object postProcessBeforeInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器处理bean=【"+beanName+"】开始");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    
        @Override
        public Object postProcessAfterInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    }
    ----------------------------------------------------------------------------------------------------------------------------------------
    package com.test.spring;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    
    public class PostProcessorB implements BeanPostProcessor {
    
        @Override
        public Object postProcessBeforeInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器开始调用了");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    
        @Override
        public Object postProcessAfterInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器调用结束了");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    }

测试：

package com.test.spring;
    
    import org.junit.Before;
    import org.junit.Test;
    import org.springframework.context.support.AbstractApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class T {
        AbstractApplicationContext applicationcontext=null;
        @Before
        public void before() {
            System.out.println("》》》Spring ApplicationContext容器开始初始化了......");
            applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});
            System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");
        }
        @Test
        public void  test() {
            applicationcontext.registerShutdownHook();   
        }
    }

在Spring机制中可以指定后置处理器调用顺序，通过让BeanPostProcessor接口实现类实现Ordered接口getOrder方法，该方法返回一整数，默认值为 0，优先级最高，值越大优先级越低

package com.test.spring;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    import org.springframework.core.Ordered;
    /**
     * bean后置处理器
     * @author zss
     *
     */
    public class PostProcessor implements BeanPostProcessor,Ordered{
    
        @Override
        public Object postProcessBeforeInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器处理bean=【"+beanName+"】开始");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    
        @Override
        public Object postProcessAfterInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    
        @Override
        public int getOrder() {
            return 1;
        }
    }
    ----------------------------------------------------------------------------
    package com.test.spring;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    import org.springframework.core.Ordered;
    
    public class PostProcessorB implements BeanPostProcessor,Ordered {
    
        @Override
        public Object postProcessBeforeInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器开始调用了");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    
        @Override
        public Object postProcessAfterInitialization(Object bean,
                String beanName) throws BeansException {
            System.out.println("后置处理器调用结束了");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return bean;
        }
    
        @Override
        public int getOrder() {
            return 0;
        }
    }

测试结果：

[Spring]: https://www.cnblogs.com/toov5/p/10614359.html