Reputation:

Can you use @Autowired with static fields?

Is there some way to use @Autowired with the static fields? If not, are there some other ways to do this?

Upvotes: 212

Answers (13)

markhuang1994

Reputation: 71

I use private static inner Component: FieldSetter, to inject static field: MyBean, at last SelfDestroyBean will help me remove redundant FiledSetter bean

public final class MyClass {
    private static MyBean myBean;

    @Component
    private static class FieldSetter extends SelfDestroyBean {
          public FieldSetter(MyBean myBean) {
              MyClass.myBean = myBean;
          }
    }
}
    
@SuppressWarnings("SpringJavaAutowiredMembersInspection")
public abstract class SelfDestroyBean {
    @Autowired
    private ApplicationContext context;

    @PostConstruct
    public void destroy() {
        final String[] beanNames = context.getBeanNamesForType(this.getClass());

        final BeanDefinitionRegistry registry =
                ((BeanDefinitionRegistry) context.getAutowireCapableBeanFactory());
        for (String beanName : beanNames) {
            registry.removeBeanDefinition(beanName);
        }
    }
}

Upvotes: 0

Nisarg Patil

Reputation: 1639

Solution 1 : Using Constructor @Autowired For Static Field

@Component
public class MyClass {

    private static MyService service;

    @Autowired
    public MyClass(MyService service) {
        TestClass.service= service;
    }
}

Solution 2 : Using @PostConstruct to set the value to Static Field

@Component
public class MyClass {

    private static MyService service;

    @Autowired
    private MyService srv;

    @PostConstruct
    public void init() {
        this.service= srv;
    }
}

Refer here for more detail

Upvotes: 0

Adir Dayan

Reputation: 1617

Generally, setting static field by object instance is a bad practice.

to avoid optional issues you can add synchronized definition, and set it only if private static Logger logger;

@Autowired
public synchronized void setLogger(Logger logger)
{
    if (MyClass.logger == null)
    {
        MyClass.logger = logger;
    }
}

Upvotes: 0

Ori Marko

Reputation: 58774

Wanted to add to answers that auto wiring static field (or constant) will be ignored, but also won't create any error:

@Autowired
private static String staticField = "staticValue";

Upvotes: 5

jozsef morrissey

Reputation: 191

Disclaimer This is by no means standard and there could very well be a better spring way of doing this. None of the above answers address the issues of wiring a public static field.

I wanted to accomplish three things.

Use spring to "Autowire" (Im using @Value)
Expose a public static value
Prevent modification

My object looks like this

private static String BRANCH = "testBranch";

@Value("${content.client.branch}")
public void finalSetBranch(String branch) {
    BRANCH = branch;
}

public static String BRANCH() {
    return BRANCH;
}

We have checked off 1 & 2 already now how do we prevent calls to the setter, since we cannot hide it.

@Component
@Aspect
public class FinalAutowiredHelper {

@Before("finalMethods()")
public void beforeFinal(JoinPoint joinPoint) {
    throw new FinalAutowiredHelper().new ModifySudoFinalError("");
}

@Pointcut("execution(* com.free.content.client..*.finalSetBranch(..))")
public void finalMethods() {}


public class ModifySudoFinalError extends Error {
    private String msg;

    public ModifySudoFinalError(String msg) {
        this.msg = msg;
    }

    @Override
    public String getMessage() {
        return "Attempted modification of a final property: " + msg;
    }
}

This aspect will wrap all methods beginning with final and throw an error if they are called.

I dont think this is particularly useful, but if you are ocd and like to keep you peas and carrots separated this is one way to do it safely.

Important Spring does not call your aspects when it calls a function. Made this easier, to bad I worked out the logic before figuring that out.

Upvotes: 0

Shapur

Reputation: 567

You can use ApplicationContextAware

@Component
public class AppContext implements ApplicationContextAware{
    public static ApplicationContext applicationContext;

    public AppBeans(){
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

then

static ABean bean = AppContext.applicationContext.getBean("aBean",ABean.class);

Upvotes: 1

Amol Kakade

Reputation: 11

private static UserService userService = ApplicationContextHolder.getContext().getBean(UserService.class);

Upvotes: -1

Sedat Başar

Reputation: 3798

@Component("NewClass")
public class NewClass{
    private static SomeThing someThing;

    @Autowired
    public void setSomeThing(SomeThing someThing){
        NewClass.someThing = someThing;
    }
}

Upvotes: 160

ak-j

Reputation: 700

Init your autowired component in @PostConstruct method

@Component
public class TestClass {
   private static AutowiredTypeComponent component;

   @Autowired
   private AutowiredTypeComponent autowiredComponent;

   @PostConstruct
   private void init() {
      component = this.autowiredComponent;
   }

   public static void testMethod() {
      component.callTestMethod();
   }
}

Upvotes: 34

JARC

Reputation: 5328

You can achieve this using XML notation and the MethodInvokingFactoryBean. For an example look here.

private static StaticBean staticBean;

public void setStaticBean(StaticBean staticBean) {
   StaticBean.staticBean = staticBean;
}

You should aim to use spring injection where possible as this is the recommended approach but this is not always possible as I'm sure you can imagine as not everything can be pulled from the spring container or you maybe dealing with legacy systems.

Note testing can also be more difficult with this approach.

Upvotes: 3