spring注释一 : RequiredAnnotationBeanPostProcessor

使用案例

如果一个bean某些字段必须含有，则可以使用@Required注释

<bean id="" class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor">
</bean>

bean class定义

package com.javarticles.spring;

import org.springframework.beans.factory.annotation.Required;

public class Employee {
private String name;
private Company company;
private int age;

public String getName() {
return name;
}

@Required
public void setName(String name) {
this.name = name;
}

public Company getCompany() {
return company;
}

@Required
public void setCompany(Company company) {
this.company = company;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String toString() {
return "Employee(" + name + "), " + company;
}
}

如果一个bean不希望进行required检查

<bean id="dummy" class="com.javarticles.spring.Employee">
<meta
key="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.skipRequiredCheck"
value="true" />
</bean>

原理

继承InstantiationAwareBeanPostProcessorAdapter，在postProcessPropertyValues（）方法中进行校验

由于实现PriorityOrdered接口, Ordered.LOWEST_PRECEDENCE - 1，执行优先级比@Autowired、@Resource都要低

BeanPostProcessor具体实现类	处理注释	优先级(数字越低优先级越高)
AutowiredAnnotationBeanPostProcessor	@Autowoired	Integer.MAX -2
CommonAnnotationBeanPostProcessor	@Resource	Integer.MAX -3
RequiredAnnotationBeanPostProcessor	@Autowoired	Integer.MAX -1

待续….