Java 使用BeanPostProcessor获取NullPointerException

我正在制作一个简单的程序来测试bean后处理器，但是得到了NullPointerException。这是我写的代码

人员类别：

public class Person {

private String name;

public String getName() {
    return name;
}

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

public void init(){
    System.out.println("Bean Initialize");
}

public void destroy(){
    System.out.println("Bean Destroy");
}
}

后处理器类：

public class Post implements BeanPostProcessor {

@Override
public Object postProcessAfterInitialization(Object bean, String beanName)
        throws BeansException {
    System.out.println("Before Initialization : " + beanName);
    return null;
}

@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
        throws BeansException {
    System.out.println("After Initialization : " + beanName);
    return null;
}
}

控制器类：

public class Controller {

public static void main(String[] args){
    @SuppressWarnings("resource")
    AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
    Person p = (Person)context.getBean("person");
    System.out.println(p.getName());
    context.registerShutdownHook();
}
}

Spring.xml：

<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-3.0.xsd">

<bean id="person" class="com.data.Person" init-method="init" destroy-method="destroy">
    <property name="name" value="Spring"></property>
</bean>

<bean class="com.postprocessor.Post"/>

Stack Trakce：

After Initialization : person
Apr 27, 2016 10:29:08 PM org.springframework.context.support.ClassPathXmlApplicationContext refresh
WARNING: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'person' defined in class path resource [spring.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'person' defined in class path resource [spring.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1578)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:772)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:839)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:538)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
at com.controller.Controller.main(Controller.java:12)
Caused by: java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeCustomInitMethod(AbstractAutowireCapableBeanFactory.java:1660)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1645)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1574)
... 12 more

初始化后：个人
2016年4月27日晚上10:29:08 org.springframework.context.support.ClassPathXmlApplicationContext刷新
警告：在上下文初始化过程中遇到异常-取消刷新尝试：org.springframework.beans.factory.BeanCreationException:创建在类路径资源[spring.xml]中定义了名为“person”的bean时出错：调用init方法失败；嵌套异常是java.lang.NullPointerException
线程“main”org.springframework.beans.factory.BeanCreationException中出现异常：创建类路径资源[spring.xml]中定义的名为“person”的bean时出错：调用init方法失败；嵌套异常是java.lang.NullPointerException
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean（AbstractAutowireCapableBeanFactory.java:1578）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean（AbstractAutowireCapableBeanFactory.java:545）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean（AbstractAutowireCapableBeanFactory.java:482）
位于org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject（AbstractBeanFactory.java:306）
位于org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton（DefaultSingletonBeanRegistry.java:230）
位于org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean（AbstractBeanFactory.java:302）
位于org.springframework.beans.factory.support.AbstractBeanFactory.getBean（AbstractBeanFactory.java:197）
位于org.springframework.beans.factory.support.DefaultListableBeanFactory.PreInstanceSingleton（DefaultListableBeanFactory.java:772）
位于org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization（AbstractApplicationContext.java:839）
位于org.springframework.context.support.AbstractApplicationContext.refresh（AbstractApplicationContext.java:538）
位于org.springframework.context.support.ClassPathXmlApplicationContext。（ClassPathXmlApplicationContext.java:139）
位于org.springframework.context.support.ClassPathXmlApplicationContext。（ClassPathXmlApplicationContext.java:83）
位于com.controller.controller.main（controller.java:12）
原因：java.lang.NullPointerException
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.InvokeCustominetMethod（AbstractAutowireCapableBeanFactory.java:1660）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods（AbstractAutowireCapableBeanFactory.java:1645）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean（AbstractAutowireCapableBeanFactory.java:1574）
... 还有12个

---

这就是我写的所有代码。有人能告诉我我在这里犯了什么错误吗。我很感激。

我不确定您想要实现什么，但为了正常运行，BeanPostProcessor应该在其方法中返回bean实例，而不是像您那样返回null。

解决方案 解释

BeanPostProcessor

是一个工厂钩子，允许自定义修改新的bean实例，例如检查标记接口或用代理包装它们

因此，此接口的目的是定义回调方法，您可以实现这些方法来提供自己的实例化逻辑，依赖项解析逻辑，修改新的bean实例等

例如，您可以在bean实例化时将bean包装在代理bean中

如果定义了

PostProcessor

方法，则

AbstractAutowireCapableBeanFactory

将调用

后处理器

方法以获取包装的bean，您将从

后处理器

方法返回

null

，该方法实质上创建了null指针异常

---

FYI发布堆栈跟踪中的相应代码。@shmosel我发布了堆栈跟踪

@Override
public Object postProcessAfterInitialization(Object bean, String beanName)
        throws BeansException {
    System.out.println("Before Initialization : " + beanName);
    return bean;
}

@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
        throws BeansException {
    System.out.println("After Initialization : " + beanName);
    return bean;
}