A WebSocketSessionDecorator to listen for attribute changes

AttributeChangeEmitter.java

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.framework.ProxyFactory;
import org.springframework.lang.NonNull;
import org.springframework.lang.Nullable;
import org.springframework.web.socket.WebSocketSession;
import org.springframework.web.socket.handler.WebSocketSessionDecorator;

import java.util.Map;
import java.util.Objects;

public class AttributeChangeEmitter extends WebSocketSessionDecorator implements MethodInterceptor {
    @FunctionalInterface
    public interface ChangeListener {
        void onChange(String key, Object value);
    }

    @SuppressWarnings("unchecked")
    private final Map<String, Object> attributes = ProxyFactory.getProxy(Map.class, this);

    private final ChangeListener changeListener;


    public AttributeChangeEmitter(WebSocketSession session, ChangeListener changeListener) {
        super(session);
        this.changeListener = Objects.requireNonNull(changeListener);
    }

    @Override
    public Map<String, Object> getAttributes() {
        return attributes;
    }

    @Nullable
    @Override
    public Object invoke(@NonNull MethodInvocation invocation) throws Throwable {
        String name = invocation.getMethod().getName();
        if (name.equals("put") && invocation.getArguments().length == 2) {
            String key = (String) invocation.getArguments()[0];
            Object value = invocation.getArguments()[1];
            Object previous = super.getAttributes().get(key);
            if (!Objects.equals(previous, value)) {
                changeListener.onChange(key, value);
            }
        }
        return invocation.getMethod().invoke(super.getAttributes(), invocation.getArguments());
    }
}