@Solutions to null pointer error caused by Autowired

Report errors

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

my B Class , Yes A Type variables are annotated @Autowired, There are probably two solutions found , Usually, it can be solved by the context acquisition class , So I am B From the tool A Class , And use A Methods , Or null pointer error .

SpringBoot Use @Autowired Inject static variable and report null pointer exception _BBQ__XB The blog of -CSDN Blog

resolvent ：

because B Class is in main Declared as an example in , So by the B Example b To use the A Your method must be wrong .

Through the tool class in main In order to get B The way , It won't be wrong .

Java The initialization order of variables is ：

Static variable or static statement block –> Instance variable or initialization statement block –> Construction method –>@Autowired

main Method @Autowired Comment null pointer error _ Code the agriculture BookSea The blog of -CSDN Blog _main Method call 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

Tool class

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;

/**
 *  Function description :  from Spring Get the class in the context , solve @Autowird Injection null pointer problem .
 *
 */
@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> T getBean(Class<T> clazz) {
        ApplicationContext applicationContext = getApplicationContext();
        log.info("SpringUtil getBean ApplicationContext is {}, class is {}", applicationContext, clazz.getName());
        return applicationContext.getBean(clazz);
    }

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