Field created in spring component in not initialized with new keyword - spring

Question

I have spring component class annotated with #Component and in it I have field ConcurrentHashMap map, which is init in constructor of component and used in spring stream listener:
#Component
public class FooService {
private ConcurrentHashMap<Long, String> fooMap;
public FooService () {
fooMap = new ConcurrentHashMap<>();
}
#StreamListener(value = Sink.INPUT)
private void handler(Foo foo) {
fooMap.put(foo.id, foo.body);
}
}
Listener handle messages sent by rest controller. Can you tell me why I always got there fooMap.put(...) NullPointerException because fooMap is null and not initialzied.
EDIT:
After #OlegZhurakousky answer I find out problem is with async method. When I add #Async on some method and add #EnableAsync I can't anymore use private modificator for my #StreamListener method. Do you have idea why and how to fix it?
https://github.com/schwantner92/spring-cloud-stream-issue
Thanks.

Answer 1

Could you try using #PostConstruct instead of constructor?
#PostConstruct
public void init(){
this.fooMap = new ConcurrentHashMap<>();
}

Answer 2

#Denis Stephanov
When I say bare minimum, here is what I mean. So try this as a start, you'll see that the map is not null and start evolving your app from there.
#SpringBootApplication
#EnableBinding(Processor.class)
public class DemoApplication {
private final Map<String, String> map;
public static void main(String[] args) {
SpringApplication.run(DemoRabbit174Application.class, args);
}
public DemoApplication() {
this.map = new HashMap<>();
}
#StreamListener(Processor.INPUT)
public void sink(String string) {
System.out.println(string);
}
}

Answer 3

With Spring everything has to be injected.
You need to declare a #Bean for the ConcurrentHashMap, that will be injected in you Component. So create a Configuration class like:
#Configuration
public class FooMapConfiguration {
#Bean("myFooMap")
public ConcurrentHashMap<Long, String> myFooMap() {
return new ConcurrentHashMap<>();
}
}
Then modify your Component:
#Component
public class FooService {
#Autowired
#Qualifier("myFooMap")
private ConcurrentHashMap<Long, String> fooMap;
public FooService () {
}
#StreamListener(value = Sink.INPUT)
private void handler(Foo foo) {
fooMap.put(foo.id, foo.body); // <= No more NPE here
}
}