springboot之BeanPostProcessor功能及例⼦（⼀）
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⼀、BeanPostProcessor
字⾯上的意思是bean的后置处理器，什么意思呢？其实就是说，在bean的⽣命周期中，可以对它⼲什么。再简单点就是，bean初始化之前⼲点什么，之后⼜⼲点什么。
public interface BeanPostProcessor {
@Nullable
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
//bean初始化之前，要⼲点什么或者什么都不⼲，但是⼲不⼲都要把⼈家给返回回去，不能⼀进来就出不去了~
return bean;
}
@Nullable
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
//bean已经初始化完了，这时候你想⼲点什么或者什么都不⼲，和上⾯⼀样，都要给⼈家返回回去
return bean;
}
}
简单⽰例
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
@Component
static class MyBeanPostProcessor1 implements BeanPostProcessor {
@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("bean 初始化之前");
return bean;
}
@Override
@Nullable
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("bean 初始化之后");
return bean;
}
}
}
⼆、InstantiationAwareBeanPostProcessor
字⾯上的意思是实例化bean后置处理器，什么意思呢？就是说你可以在bean实例化前后做⼀些事情。注意，是先实例化才到初始化的！
public interface InstantiationAwareBeanPostProcessor extends B民事诉讼立案流程
eanPostProcessor {
//the bean object to expo instead of a default instance of the target bean, or null to proceed with default instantiation
@Nullable
default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
//如果什么都不做，返回null，代表⾛默认实例化的逻辑
//如果在这⾥做了什么，那么就返回你指定实例化逻辑产⽣的对象
return null;
}
//true if properties should be t on the bean,fal if property population should be skipped. Normal implementations should return true
default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
//实例化完了之后，如果这⾥返回true，代表这个笔记本功率
bean的属性会被正常t进去，如果是fal，那么就会跳过，spring给的建议是⼀般都要返回true。
return true;
}
//the actual property values to apply to the given bean (can be the pasd-in PropertyValues instance), or null which proceeds with the existing properti es but specifically continues with a call to postProcessPropertyValues
@Nullable
default PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
throws BeansException {
//null，相当于什么都没做
//返回不是null，相当于将返回的变量值替换原来的变量赋值
return null;
}
//deprecated as of 5.1, in favor of {@link #postProcessProperties(PropertyValues, Object, String)}
@Deprecated
@Nullable
default PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
return pvs;
}
}
简单⽰例
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
@Component
static class MyBeanPostProcessor2 implements InstantiationAwareBeanPostProcessor {
@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("bean 初始化之前");
return bean;
}
@Override
@Nullable
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("bean 初始化之后");
return bean;
}
@Override
@Nullable
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
System.out.println("bean 实例化之前");
return null;
}
@Override
public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
System.out.println("bean 实例化之后");
return true;
}
@Override
@Nullable
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
throws BeansException {
System.out.println("bean 变量处理");
return null;
}
}
}
三、SmartInstantia历史资料
tionAwareBeanPostProcessor
字⾯意思就是智能实例化bean后置处理器，什么意思呢？其实就是⽐InstantiationAwareBeanPostProcessor多三个接⼝，在bean实例化之前，多做⼀些事情⽽已。
public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationAwareBeanPostProcessor {
//return the type of the bean, or null if not predictable
@Nullable
default Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException {
//实例化之前先预测bean的类型？？（我也不是很懂它的⽤途，下篇⽂章讲例⼦的时候再顺带解决）
return null;
}
//return the candidate constructors, or null if none specified
@Nullable
default Constructor<?>[] determineCandidateConstructors(Class<?> beanClass,九九歌谣
String beanName)
throws BeansException {
//说⽩了就是可以决定⽤哪个构造器来实例化这个bean
return null;
}
//return the object to expo as bean reference typically with the pasd-in bean instance as default)
default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
//这个就⽜逼了，可以解决循环引⽤的问题，例如A引⽤了B，B引⽤了A，A实例化的时候，需要先实例化B，B实例化的时候⼜需要去实例化A，当B->实例化A的时候，就会⾛到这个⽅法，提前把A的引⽤暴露出去，这时候B就可以完成实例化，最后A也完成的实例化。
return bean;
}
简单⽰例
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
@Component
static class MyBeanPostProcessor3 implements SmartInstantiationAwareBeanPostProcessor {
@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("bean 初始化之前");
return bean;
}
@Override
@Nullable
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("bean 初始化之后");
return bean;
}
@Override
@Nullable
public Object postProcessBeforeInstantia五年级上册手抄报
tion(Class<?> beanClass, String beanName) throws BeansException {
System.out.println("bean 实例化之前");
return null;
}
@O绿豆面条
verride
public boolean postProcessAfterInstantiation(Object bean, String b做老师
eanName) throws BeansException {
System.out.println("bean 实例化之后");
return true;
}
@Override
@Nullable
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
throws BeansException {
System.out.println("bean 变量处理");
return null;
}
@Override
@Nullable
public Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException {
System.out.println("预测 bean 类型");
return null;
}
@Override
@Nullable
public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName)
throws BeansException {
System.out.println("选择构造器");
return null;
}
@Override
public Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
System.out.println("提前暴露引⽤");
return bean;
}
}
@Component
static class B {
@Autowired
A a;
}
@Component
static class A {
@Autowired
B b;
}
}
四、DestructionAwareBeanPostProcessor
字⾯上的意思就是销毁bean后置处理器，什么意思呢？就是销毁bean之前，你还想⼲嘛。
public interface DestructionAwareBeanPostProcessor extends BeanPostProcessor {
void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException;
//return true} if postProcessBeforeDestruction is suppod to be called for this bean instance eventually, or fal if not needed default boolean requiresDestruction(Object bean) {
//默认是true，也就是需要销毁之前做点什么，会调⽤postProcessBeforeDestruction
//如果是fal，那么就不会调⽤
return true;
}
简单⽰例
