Spring中提供了很多PostProcessor供开发者进行拓展，例如：BeanPostProcessor、BeanFactoryPostProcessor、BeanValidationPostProcessor等一系列后处理器。他们的使用方式大多类似，了解其中一个并掌握他的使用方式，其他的可以触类旁通。
这里以BeanPostProcessor为例展示其使用方式。
BeanPostProcessor接口提供了两个供开发者自定义的方法：postProcessBeforeInitialization、postProcessAfterInitialization。
postProcessBeforeInitialization：该方法主要针对spring在bean初始化时调用初始化方法前进行自定义处理。
postProcessAfterInitialization：该方法主要针对spring在bean初始化时调用初始化方法后进行自定义处理。
示例代码：
/**
* 测试bean
*/
public class Cat {
private String name;
private int age;
public void say() {
System.out.println("name:" + name);
System.out.println("age:" + age);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
/**
* 自定义后处理器
*/
public class CatBeanPostProcessor implements BeanPostProcessor {
@Nullable
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof Cat) {
//输出原始属性
Cat cat = (Cat) bean;
cat.say();
return bean;
}
return bean;
}
@Nullable
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof Cat) {
//修改属性值，并返回
Cat cat = (Cat) bean;
cat.setName("hello maomi");
cat.setAge(3);
return cat;
}
return bean;
}
}
/**
* 运行
*/
public class Run {
public static void main(String[] args) {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-bean.xml");
Cat cat = (Cat) applicationContext.getBean("cat");
cat.say();
}
}
xml配置信息
<!--配置bean并初始化-->
<bean id="cat" class="com.source.postprocessor.Cat" >
<property name="name" value="HelloKitty" />
<property name="age" value="1" />
</bean>
<bean id="catBeanPostProcessor" class="com.source.postprocessor.CatBeanPostProcessor" />
输出结果：
name:HelloKitty
age:1
name:hello maomi
age:3
可以看到通过后处理器处理过后的bean信息已经改变。最后，看看源码中如何调用自定义实现的。
在初始化bean方法中：AbstractAutowireCapableBeanFactory.java
/**
* 初始化bean
*/
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
//省略部分无关代码
Object wrappedBean = bean;
//初始化前
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//调用初始化方法初始化bean
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
//初始化后
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
//postProcessBeforeInitialization方法调用
@Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
//调用自定义postProcessBeforeInitialization方法
Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
//postProcessAfterInitialization方法调用
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
//自定义postProcessAfterInitialization方法调用
Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
以上就是spring对自定义方法实现的调用过程。希望对大家的学习有所帮助，也希望大家多多支持。
