Detailed explanation of the problem of injecting beans under Spring multi-threading

question

Multi-threaded injection userThreadService in Spring cannot be injected, showing that userThreadService is null exception

code show as below:

public class UserThreadTask implements Runnable {
  @Autowired
  private UserThreadService userThreadService;

  @Override
  public void run() {
    AdeUser user = userThreadService.get("0");
    System.out.println(user);
  }
}

 

Solution one

Pass the Service to be injected through the construction, the code is as follows:

public class UserThreadTask implements Runnable {
  private UserThreadService userThreadService;

  public UserThreadTask(UserThreadService userThreadService) {
    this.userThreadService = userThreadService;
  }

  @Override
  public void run() {
    AdeUser user = userThreadService.get("0");
    System.out.println(user);
  }
}

 

Thread t = new Thread(new UserThreadTask(userThreadService));
t.start();

 

Solution two

Obtain the Service that needs to be used through ApplicationContext

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

public class ApplicationContextHolder implements ApplicationContextAware {
  private static ApplicationContext context;
  @Override
  public void setApplicationContext(ApplicationContext context) throws BeansException {
    ApplicationContextHolder.context = context;
  }
  //根据bean name 获取实例
  public static Object getBeanByName(String beanName) {
    if (beanName == null || context == null) {
      return null;
    }
    return context.getBean(beanName);
  }
  //只适合一个class只被定义一次的bean（也就是说，根据class不能匹配出多个该class的实例）
  public static Object getBeanByType(Class clazz) {
    if (clazz == null || context == null) {
      return null;
    }
    return context.getBean(clazz);
  }
  public static String[] getBeanDefinitionNames() {
    return context.getBeanDefinitionNames();
  }
}

 

Spring loads its own defined ApplicationContextHolder class

<bean class = "cn.com.infcn.applicationcontext.ApplicationContextHolder"></bean>

Get instance by bean name

Copy code The code is as follows:
UserService user = (UserService) ApplicationContextHolder.getBeanByName("userService"); 

Get the instance according to the class of the bean (if there are multiple instances of the class, an error will be reported)

Copy code The code is as follows:
UserService user = (UserService) ApplicationContextHolder.getBeanByType(UserService.class); 

In this way, no matter whether it is multi-threaded or not, or a common class that does not accept spring management, you can use this method to obtain spring-managed beans.