NullPointerException getting collection from MongoTemplate

Here is my problem. I have a Spring Boot application connected to a MongoDB. I created a RESTful API, and using MongoTemplate on the Controllers did not return any error. But now, I want to create a thread to analyze some data while running the app. The problem es that after that thread is initialized, it returns a NullPointerException when the code reaches the statement to connect to the database or to assign the collection to a variable.

The code that returns the error is the following:

public class TreatmentThread implements Runnable {

	@Autowired
	MongoTemplate mongoTemplate;
	
	MongoCollection<Document> measurements = mongoTemplate.getCollection("measurements");
	
	@Override
	public void run() {
		try {
			Date today = new Date(System.currentTimeMillis());
			
			List<Bson> pipeline = Arrays.asList(
					match(and(
						gte("date", new java.util.Date(1598464800000L)), 
						lte("date", new java.util.Date(1598540400000L)))), 
					sort(orderBy(descending("date"), descending("hour"))), 
					group(and(eq("device", "$device"), eq("plant", "$plant")), 
						push("measurements", "$$ROOT")), 
					project(exclude("measurements._id", "measurements.plant", "measurements.device", "measurements._class")));
			
			AggregateIterable<AnalyzeMeasurements> result = measurements.aggregate(pipeline, AnalyzeMeasurements.class);
			
			// TODO: Analyze results
		} catch (Exception e) {
			Log.logger.error("Some error ocurred " + e);
		}
	}
}

With that code, it returns the error:

> Exception in thread "restartedMain" java.lang.reflect.InvocationTargetException
> at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> at java.base/java.lang.reflect.Method.invoke(Method.java:564)
> at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49)
>Caused by: java.lang.NullPointerException
> at com.rainforest.eco.analytics.TreatmentThread.<init>(TreatmentThread.java:35)
> at com.rainforest.eco.Application.main(Application.java:25)
> ... 5 more

In case I directly try to get the collection in the code, it simply returns a NullPointerException, not giving any more details.

The thread is launched in the Application.java class:

@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
		
		Log.logger.info("Starting Thread: TreatmentThread");
		Log.logger.info("Starting Thread: Analyze pot measurements to schedule treatments");
		//  Create pool with 10 threads
		int numThreads = 10;
		final ScheduledExecutorService schExService = Executors.newScheduledThreadPool(numThreads);
		// Create runnable thread
		final Runnable treatmentAnalyzer = new TreatmentThread();
		// Thread scheduling
		int minute = 60;
		schExService.scheduleWithFixedDelay(treatmentAnalyzer, minute, 5 * minute, TimeUnit.SECONDS);
		Log.logger.info("Thread Started: Currently Running");
    }
}

Does anyone know where the error comes from?

Instantiating TreatmentThread using a new operator doesn't autowire the dependencies. Therefore MongoTemplate mongoTemplate is null and the subsequent call on it throws the NPE.

You need to autowire such object in the Application class as well as define it as a bean (either @Component on the class level or @Bean on the method level):

@Component
public class TreatmentThread implements Runnable {
...
}

@SpringBootApplication
public class Application {
@Autowired
TreatmentThread treatmentThread;
...
}