Spring MVC对单例的多个请求

Question

I have a problem with Spring MVC. I am using Stanford NLP and I put initialization of it to singleton class.

@Component
@Scope("singleton")
public class JavaNLP implements NlpInterface
{
  private DependencyNLP nlp_object = null;

  @PostConstruct
  public void init()
  {
    if (nlp_object == null) {
      nlp_object = new DependencyNLP();
      nlp_object.init("tokenize, ssplit, pos, lemma, ner, parse, dcoref");
    }
  }
  @Override
  public void init(String name, DataContainer container)
  {
    this.container = container;
    nlp_object.annotate(container.getText());
  }
  @Override
  public void execute()
  {
     ...
  }
}

Every request is calling init(String name, DataContainer container) and execute . Problem is in 70% requests nlp_object is not initialized.

Inside of a controller:

@Autowired
@Qualifier("javaNLP")
private NlpInterface nlpInterface;

@RequestMapping(value = "/parse", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE, headers = {"Content-type=application/json"})
  public @ResponseBody
  String parseWithGazetteerinJSON(@RequestBody DataContainer container)
  {
    String name = "Parsing text";

    nlpInterface.init(name, container);
    nlpInterface.execute();
    JSONArray triples = nlpInterface.getTriplesAsJSON();

    return triples.toString();
  }

EDIT 1

Unfortunetly it is still not working. I think I found where is the problem, just dont know how to fix it.

I put configuration + calling init function into config

<mvc:annotation-driven />
<context:component-scan base-package="com.metadata.tripletws.model" />
<context:component-scan base-package="com.metadata.tripletws.controller" />
<bean id="nlp" class="com.metadata.tripletws.service.Nlp" init-method="init"></bean>

I have created new object called Nlp and it is just sort of envelope for DependencyNLP (external library)

@Component
public class Nlp
{

  private DependencyNLP nlp;

  public void init()
  {
    nlp = new DependencyNLP();
    nlp.init();
  }

  public DependencyNLP getInstance()
  {
    return nlp;
  }

  public void execute()
  {
     ...
  }
  ...
}

Then I added this code to the controller:

DependencyNLP nlpInstance = nlp.getInstance();
System.out.println(nlpInstance);
nlpInstance.annotate(container.getSection().getText());
nlpInstance.execute(...);

and defined private Autowired variable

@Autowired
private Nlp nlp;

Printed nlpInstance is always same. That makes sense in the end. But here is the problem I beliave. Requests are influencing each other.

Does somebody know how to make it run?

Thanks

Answer 1

Instead of initializing the nlp_object in a @PostConstruct method try injecting it as a resource to your implementation of NlpInterface

Not sure if this will solve your problem, but if it were me I'd give it a go.

Also, you init() method(if you must go that way) should be synhcronized with double if ( singletonObj == null) gates outside and inside the sync block.