How to Fix Spring Static Injection NPE: Real-World Demo & Solutions

Spring Static Injection Real-World Demo

Sometimes we wrap a bean into a utility class and expose it as a default method, but the static field ends up null, causing a NullPointerException in production.

Why does RemoteEBRpcInvoker.getEbFormIdUtil sometimes return NULL?

@Component
public class RemoteEBRpcInvoker {
    private static final String DEFAULT_RPC_GROUP = "ebuilderform";
    private static PublishKitRuntimeUtil publishKitRuntimeUtil;
    private static GetEbFormIdUtil getEbFormIdUtil;

    @Autowired
    public RemoteEBRpcInvoker(GetEbFormIdUtil getEbFormIdUtil,
                              PublishKitRuntimeUtil publishKitRuntimeUtil) {
        RemoteEBRpcInvoker.getEbFormIdUtil = getEbFormIdUtil;
        RemoteEBRpcInvoker.publishKitRuntimeUtil = publishKitRuntimeUtil;
    }

    /**
     * Build RPC service instance by appId.
     */
    public static <T> T newInstance(Class<T> tClass, Long appId) {
        Long appId = getEbFormIdUtil.getAppId(TagConstant.CS_APPID_TAG, tenantKey);
        return publishKitRuntimeUtil.buildRpcService(tClass, DEFAULT_RPC_GROUP, String.valueOf(appId));
    }
}

When calling newInstance(), getEbFormIdUtil is null because static injection failed.

Reason 1: Static variable initialization order

Static fields are initialized before instance fields; @Autowired works on instance creation, so static fields may remain null.

Reason 2: Spring lifecycle and static fields

Spring injects dependencies into instance fields; static fields are not tied to the bean lifecycle, leading to possible null values.

Solutions:

Solution

Method 1: Remove static fields (breaks original intent)

@Component
public class RemoteEBRpcInvoker {
    private static final String DEFAULT_RPC_GROUP = "ebuilderform";
    private PublishKitRuntimeUtil publishKitRuntimeUtil;
    private GetEbFormIdUtil getEbFormIdUtil;

    @Autowired
    public RemoteEBRpcInvoker(GetEbFormIdUtil getEbFormIdUtil,
                              PublishKitRuntimeUtil publishKitRuntimeUtil) {
        this.getEbFormIdUtil = getEbFormIdUtil;
        this.publishKitRuntimeUtil = publishKitRuntimeUtil;
    }
}

This works but defeats the goal of a static utility.

Method 2: Use @PostConstruct

Initialize static variables after injection.

@Component
public class RemoteEBRpcInvoker {
    private static final String DEFAULT_RPC_GROUP = "ebuilderform";
    private static PublishKitRuntimeUtil publishKitRuntimeUtil;
    private static GetEbFormIdUtil getEbFormIdUtil;

    @Autowired
    public RemoteEBRpcInvoker(GetEbFormIdUtil getEbFormIdUtil,
                              PublishKitRuntimeUtil publishKitRuntimeUtil) {
        this.getEbFormIdUtil = getEbFormIdUtil;
        this.publishKitRuntimeUtil = publishKitRuntimeUtil;
    }

    @PostConstruct
    public void init() {
        RemoteEBRpcInvoker.getEbFormIdUtil = this.getEbFormIdUtil;
        RemoteEBRpcInvoker.publishKitRuntimeUtil = this.publishKitRuntimeUtil;
    }
}

This ensures static variables are assigned after dependencies are injected.

Method 3: Use static @Autowired setter

@Component
public class RemoteEBRpcInvoker {
    private static final String DEFAULT_RPC_GROUP = "ebuilderform";
    private static PublishKitRuntimeUtil publishKitRuntimeUtil;
    private static GetEbFormIdUtil getEbFormIdUtil;

    @Autowired
    public static void setPublishKitRuntimeUtil(PublishKitRuntimeUtil publishKitRuntimeUtil) {
        RemoteEBRpcInvoker.publishKitRuntimeUtil = publishKitRuntimeUtil;
    }

    @Autowired
    public static void setGetEbFormIdUtil(GetEbFormIdUtil getEbFormIdUtil) {
        RemoteEBRpcInvoker.getEbFormIdUtil = getEbFormIdUtil;
    }
}

Static setter methods let Spring inject dependencies without relying on an instance.

Method 4: Use ApplicationContext to fetch beans

@Component
public class RemoteEBRpcInvoker implements ApplicationContextAware {
    private static final String DEFAULT_RPC_GROUP = "ebuilderform";
    private static ApplicationContext applicationContext;

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

    public static GetEbFormIdUtil getGetEbFormIdUtil() {
        return applicationContext.getBean(GetEbFormIdUtil.class);
    }

    public static PublishKitRuntimeUtil getPublishKitRuntimeUtil() {
        return applicationContext.getBean(PublishKitRuntimeUtil.class);
    }
}

Manually retrieve beans from the context in static methods.

Method 5: Singleton pattern with manual injection

@Component
public class RemoteEBRpcInvoker {
    private static final String DEFAULT_RPC_GROUP = "ebuilderform";
    private static RemoteEBRpcInvoker instance;

    private PublishKitRuntimeUtil publishKitRuntimeUtil;
    private GetEbFormIdUtil getEbFormIdUtil;

    @Autowired
    public RemoteEBRpcInvoker(GetEbFormIdUtil getEbFormIdUtil,
                              PublishKitRuntimeUtil publishKitRuntimeUtil) {
        this.getEbFormIdUtil = getEbFormIdUtil;
        this.publishKitRuntimeUtil = publishKitRuntimeUtil;
        instance = this;
    }

    public static RemoteEBRpcInvoker getInstance() {
        return instance;
    }

    public GetEbFormIdUtil getGetEbFormIdUtil() {
        return this.getEbFormIdUtil;
    }

    public PublishKitRuntimeUtil getPublishKitRuntimeUtil() {
        return this.publishKitRuntimeUtil;
    }
}

The singleton stores the bean instance in a static field, allowing static access to non‑static members.

Method 6: Use @Lazy for lazy loading

@Component
public class RemoteEBRpcInvoker {
    private static final String DEFAULT_RPC_GROUP = "ebuilderform";
    private static PublishKitRuntimeUtil publishKitRuntimeUtil;
    private static GetEbFormIdUtil getEbFormIdUtil;

    @Autowired
    @Lazy
    public RemoteEBRpcInvoker(GetEbFormIdUtil getEbFormIdUtil,
                              PublishKitRuntimeUtil publishKitRuntimeUtil) {
        RemoteEBRpcInvoker.getEbFormIdUtil = getEbFormIdUtil;
        RemoteEBRpcInvoker.publishKitRuntimeUtil = publishKitRuntimeUtil;
    }
}

@Lazy defers dependency initialization until the first actual use, preventing premature static initialization.

Summary

Avoid static fields; prefer instance fields (recommended).

Initialize static variables with @PostConstruct.

Inject static dependencies via static setter methods.

Manually obtain beans using ApplicationContext.

Apply a singleton pattern to access non‑static dependencies.

Use @Lazy to lazily load dependencies.