Accessing spring beans in static method

Question

I have a Util class with static methods. Inside my Util class, I want to use spring beans so I included them in my util class. As far as I know it\'s not a good practice to

Answer 1

Generic Solution

You can create a class that will allow access to any Bean from a static context. Most other answers here only show how to access a single class statically.

The Proxy in the code below was added in case someone calls the getBean() method before the ApplicationContext is autowired (as this would result in a nullpointer). None of the other solutions posted here handle that nullpointer.

Details on my blog: https://tomcools.be/post/apr-2020-static-spring-bean/

Usage

UserRepository userRepo = StaticContextAccessor.getBean(UserRespository.class)

Full code of the StaticContextAccessor:

@Component
public class StaticContextAccessor {

    private static final Map classHandlers = new HashMap<>();
    private static ApplicationContext context;

    @Autowired
    public StaticContextAccessor(ApplicationContext applicationContext) {
        context = applicationContext;
    }

    public static  T getBean(Class clazz) {
        if (context == null) {
            return getProxy(clazz);
        }
        return context.getBean(clazz);
    }

    private static  T getProxy(Class clazz) {
        DynamicInvocationhandler invocationhandler = new DynamicInvocationhandler<>();
        classHandlers.put(clazz, invocationhandler);
        return (T) Proxy.newProxyInstance(
                clazz.getClassLoader(),
                new Class[]{clazz},
                invocationhandler
        );
    }

    //Use the context to get the actual beans and feed them to the invocationhandlers
    @PostConstruct
    private void init() {
        classHandlers.forEach((clazz, invocationHandler) -> {
            Object bean = context.getBean(clazz);
            invocationHandler.setActualBean(bean);
        });
    }

    static class DynamicInvocationhandler implements InvocationHandler {

        private T actualBean;

        public void setActualBean(T actualBean) {
            this.actualBean = actualBean;
        }

        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if (actualBean == null) {
                throw new RuntimeException("Not initialized yet! :(");
            }
            return method.invoke(actualBean, args);
        }
    }
}