Spring 依赖注入后行为实现

梦里梦外; 2022-08-20 04:16 167阅读 0赞

**主要有两种方式:**

**1.通过实现InitializingBean接口的afterPropertiesSet()方法,在方法中处理业务**

**2.在配置文件中配置init-method**

**实现方式1:InitializingBean**

<strong>@Component
    public class InitializingMyBean implements InitializingBean {
        @Autowired
    	private UserRepository userRepository;
    	
    	@Override
    	public void afterPropertiesSet() throws Exception {
    		System.out.println("》》》新增用户《《《 ");
    		User user =new User();
    		user.setName("admin");
    		user.setPassword("admin123");
    		user.setAge("23");
    		user.setSex("男");
    		User add  = userRepository.save(user);
    		if(!StringUtils.isEmpty(add)){
    			System.out.println("新增用户成功！");
    		}else{
    			System.out.println("新增用户失败！");
    		}
    	}
    
    
    }
    </strong>

2.配置文件 ：init-method

xml version="1.0" encoding="UTF-8"?>DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN""http://www.springframework.org/dtd/spring-beans.dtd"><beans><bean name="lifeBean" class="research.spring.beanfactory.ch4.LifeCycleBean"
     init-method="init">bean>beans>
    3.两种方式的区别:

实现InitializingBean接口是直接调用afterPropertiesSet方法，比通过反射调用init-method指定的方法效率相对来说要高点。但是init-method方式消除了对spring的依赖

4.注意:如果在spring初始化bean的时候，如果该bean是实现了InitializingBean接口，并且同时在配置文件中指定了init- method，

** \* 系统则是先调用afterPropertiesSet方法，然后在调用init-method中指定的方法**

**5.InitializingBean和init-mthod同时执行的原理:**

**详见：org.springframework.beans.factory.support包下的抽象类AbstractAutowireCapableBeanFactory**

**主要处理代码如下:**

/**
    		 * Give a bean a chance to react now all its properties are set,
    		 * and a chance to know about its owning bean factory (this object).
    		 * This means checking whether the bean implements InitializingBean or defines
    		 * a custom init method, and invoking the necessary callback(s) if it does.
    		 * @param beanName the bean name in the factory (for debugging purposes)
    		 * @param bean the new bean instance we may need to initialize
    		 * @param mbd the merged bean definition that the bean was created with
    		 * (can also be {@code null}, if given an existing bean instance)
    		 * @throws Throwable if thrown by init methods or by the invocation process
    		 * @see #invokeCustomInitMethod
    		 */
    		protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
    				throws Throwable {
                //获取当前bean是否实现了InitializingMyBean接口,如果实现了就执行afterPropertiesSet方法
    			boolean isInitializingBean = (bean instanceof InitializingBean);
    			if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
    				if (logger.isDebugEnabled()) {
    					logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
    				}
    				if (System.getSecurityManager() != null) {
    					try {
    						AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
    							@Override
    							public Object run() throws Exception {
    								//调用afterPropertiesSet()
    								((InitializingBean) bean).afterPropertiesSet();
    								return null;
    							}
    						}, getAccessControlContext());
    					}
    					catch (PrivilegedActionException pae) {
    						throw pae.getException();
    					}
    				}
    				else {
    					//调用afterPropertiesSet()
    					((InitializingBean) bean).afterPropertiesSet();
    				}
    			}
                //如果在配置文件中设置了init-mthod属性就通过反射调用init-method指定的方法
    			if (mbd != null) {
    				String initMethodName = mbd.getInitMethodName();
    				if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
    						!mbd.isExternallyManagedInitMethod(initMethodName)) {
    					invokeCustomInitMethod(beanName, bean, mbd);
    				}
    			}
    		}

/**
    		 * Invoke the specified custom init method on the given bean.
    		 * Called by invokeInitMethods.
    		 * <p>Can be overridden in subclasses for custom resolution of init
    		 * methods with arguments.
    		 * @see #invokeInitMethods
    		 */
    		protected void invokeCustomInitMethod(String beanName, final Object bean, RootBeanDefinition mbd) throws Throwable {
    			String initMethodName = mbd.getInitMethodName();
    			final Method initMethod = (mbd.isNonPublicAccessAllowed() ?
    					BeanUtils.findMethod(bean.getClass(), initMethodName) :
    					ClassUtils.getMethodIfAvailable(bean.getClass(), initMethodName));
    			if (initMethod == null) {
    				if (mbd.isEnforceInitMethod()) {
    					throw new BeanDefinitionValidationException("Couldn't find an init method named '" +
    							initMethodName + "' on bean with name '" + beanName + "'");
    				}
    				else {
    					if (logger.isDebugEnabled()) {
    						logger.debug("No default init method named '" + initMethodName +
    								"' found on bean with name '" + beanName + "'");
    					}
    					// Ignore non-existent default lifecycle methods.
    					return;
    				}
    			}
    
    			if (logger.isDebugEnabled()) {
    				logger.debug("Invoking init method  '" + initMethodName + "' on bean with name '" + beanName + "'");
    			}
    
    			if (System.getSecurityManager() != null) {
    				AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
    					@Override
    					public Object run() throws Exception {
    						ReflectionUtils.makeAccessible(initMethod);
    						return null;
    					}
    				});
    				try {
    					AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
    						@Override
    						public Object run() throws Exception {
    							initMethod.invoke(bean);
    							return null;
    						}
    					}, getAccessControlContext());
    				}
    				catch (PrivilegedActionException pae) {
    					InvocationTargetException ex = (InvocationTargetException) pae.getException();
    					throw ex.getTargetException();
    				}
    			}
    			else {
    				try {
    					ReflectionUtils.makeAccessible(initMethod);
    					initMethod.invoke(bean);
    				}
    				catch (InvocationTargetException ex) {
    					throw ex.getTargetException();
    				}
    			}
    		}