@Autowired 导致空指针报错 解决方式

Exception in thread "restartedMain" java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49)
Caused by: java.lang.NullPointerException

我的B类中，对A类型的变量加上了注解@Autowired，查到的解决方法大概有两种方式，通常可以由上下文获取类进行解决，于是我在B中由工具获取到A的类，并使用A的方法，还是空指针错误。

SpringBoot使用@Autowired注入静态变量报空指针异常_BBQ__XB的博客-CSDN博客

由于B类是在main 中以示例的方式声明的，那么由B的实例b去使用A的方法一定是错误的。

通过工具类在main中获取B的方式，就不会报错了。

Java变量的初始化顺序为：

静态变量或静态语句块–>实例变量或初始化语句块–>构造方法–>@Autowired

main方法里使用@Autowired注解报空指针错误_码农BookSea的博客-CSDN博客_main方法调用autowiredhttps://blog.csdn.net/bookssea/article/details/109196195?ops_request_misc=&request_id=&biz_id=102&utm_term=autowired%E6%B3%A8%E8%A7%A3%E6%8A%A5%E7%A9%BA%E6%8C%87%E9%92%88&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduweb~default-3-109196195.nonecase&spm=1018.2226.3001.4187

package main

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

import lombok.extern.slf4j.Slf4j;


@Component
@Slf4j
public class SpringUtil implements ApplicationContextAware {
    private static ApplicationContext context = null;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if (null == SpringUtil.context) {
            SpringUtil.context = applicationContext;
        }
    }

    public static ApplicationContext getApplicationContext() {
        return context;
    }

    public static Object getBean(String name) {
        return getApplicationContext().getBean(name);
    }

    public static  T getBean(Class clazz) {
        ApplicationContext applicationContext = getApplicationContext();
        log.info("SpringUtil getBean ApplicationContext is {}, class is {}", applicationContext, clazz.getName());
        return applicationContext.getBean(clazz);
    }

    public static  T getBean(String name, Class clazz) {
        ApplicationContext applicationContext = getApplicationContext();
        log.info("SpringUtil getBean ApplicationContext is {}, name is:{}, class is {}", applicationContext, name,
            clazz.getName());
        return applicationContext.getBean(name, clazz);
    }
}