Problem background
You need to read the parameters from the yml configuration file, write a config entity class, add GET, SET methods, and report a null pointer when @Autowired injects this configuration class into other classes.
Cause one of the problem
1. Cannot call other classes in a timed task. 2. Cannot new a class.
Then inject the value, because the timed task will start a new process, and the spring value will be injected into the initial class, but this valued class is not used, but a valueless class is called.
Cause two of the problem
Google’s great reply
translating human words is: initialization sequence
Member variable initialization -> Constructor -> @Autowired
When calling get, it has not yet entered the life cycle of autowired, it is naturally empty, and the value cannot be obtained, and a null pointer error is reported.
solution
Introduce tools
/**
* @author [email protected]
* 此工具类用于从Spring的上下文中去获取到类，解决@autowird注入空指针的问题
* @version 1.0
* @date 2020/10/27 16:54
*/
@Component
public class ApplicationContextHelperUtil implements ApplicationContextAware {
private static ApplicationContext applicationContext;
@Override
public void setApplicationContext( ApplicationContext applicationContext1 ) throws BeansException {
applicationContext = applicationContext1;
}
public static ApplicationContext getApplicationContext(){
return applicationContext;
}
@SuppressWarnings("unchecked")
public static <T> T getBean(Class<T> clazz) {
return (T) applicationContext.getBean(clazz);
}
}
At the same time the method is called by
@Autowired
HeartbeatConfig heartbeatConfig;
To
private static HeartbeatConfig heartbeatConfig =(HeartbeatConfig) ApplicationContextHelperUtil.getBean(HeartbeatConfig.class);