BeanPostProcessor是建立每個類時都會去執行的一個介面，postProcessBeforeInitialization是在類初始化之前呼叫的一個方法，建立的物件的引用會指向改方法的返回值物件。呼叫過程示例如下：

ClassA classA = new ClassA();
classA = postProcessBeforeInitialization(classA, "classA");

所以我們可以通過該方法就可以實現動態替換我們的bean。

package com.example.hellododo.data;

import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.stereotype.Component;

/**
 * @author Liangzhifeng
 * date: 2018/9/4
 */
@Slf4j
@Component
public class LocalProcessor implements BeanPostProcessor {

    @Autowired
    private DefaultListableBeanFactory defaultListableBeanFactory;

    private String targetBeanName = "test22";

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (StringUtils.endsWithIgnoreCase(beanName, targetBeanName)) {
            boolean containsBean = defaultListableBeanFactory.containsBean(targetBeanName);
            if (containsBean) {
                //移除bean的定義和例項
                defaultListableBeanFactory.removeBeanDefinition(targetBeanName);
            }
            //註冊新的bean定義和例項
            defaultListableBeanFactory.registerBeanDefinition(targetBeanName, BeanDefinitionBuilder.genericBeanDefinition(Test55.class).getBeanDefinition());
            bean = null;
            return new Test55();
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}
 

在事件監聽器中，分別注入和獲取Bean物件。分別列印兩個物件的類名，可以看到兩個類名都是com.example.hellododo.data.Test55

package com.example.hellododo.data;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;

/**
 * @author Liangzhifeng
 * date: 2018/9/12
 */
@Slf4j
@Component
public class LocalEventListener implements ApplicationListener<ContextRefreshedEvent> {

    @Autowired
    private DefaultListableBeanFactory defaultListableBeanFactory;

    private boolean doFist = true;

    @Autowired
    private Test22 test22;

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {

        Test22 bean = defaultListableBeanFactory.getBean(Test22.class);
        if (doFist) {
            if (bean != null) {
                log.info("autowiredClassName={}, beanClassName={}", test22.getClass().getName(), bean.getClass().getName());
                doFist = false;
            }
        }
    }
}

 

package com.example.hellododo.data;

import lombok.Data;

/**
 * @author Liangzhifeng
 * date: 2018/9/6
 */
@Data
public class Test {

    private String data;
}

@Component
package com.example.hellododo.data;

import org.springframework.stereotype.Component;

/**
 * @author Liangzhifeng
 * date: 2018/9/6
 */
@Component
public class Test22 extends Test{

}
 

package com.example.hellododo.data;

/**
 * @author Liangzhifeng
 * date: 2018/9/6
 */
public class Test55 extends Test22{
  
}