Как получить результат анализа в формате объекта (JSON) при использовании Xtext Web Integration

Question

Я учусь использовать Xtext

В модульном тесте есть функция с именем parseHelper.parse() для получения результата анализа в формате объекта:

@RunWith(XtextRunner)

@InjectWith(MyDslInjectorProvider)

class MyDslParsingTest {
@Inject
ParseHelper<Model> parseHelper

@Test
def void loadModel() {
    val result = parseHelper.parse('''
        Hello Xtext!
    ''')
    Assert.assertNotNull(result)
    Assert.assertTrue(result.eResource.errors.isEmpty)
}
}

Я хочу получить результат анализа при интеграции с веб-интерфейсом, поэтому добавляю следующий код в файл /org.xtext.example.mydsl.web/xtend-gen/org/xtext/example/mydsl/web/MyDslServlet.java

          MyDslParser myDslParser = new MyDslParser();
          CharSequence cs = "Hello Xtext!";
          IParseResult iParseResult = myDslParser.doParse(cs);
          log.info(iParseResult.getRootASTElement().toString());

Полный код:

package org.xtext.example.mydsl.web;

import com.google.inject.Injector;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.io.StringReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.xtext.util.DisposableRegistry;
import org.eclipse.xtext.web.server.XtextServiceDispatcher;
import org.eclipse.xtext.web.servlet.XtextServlet;
import org.eclipse.xtext.xbase.lib.Exceptions;
import org.xtext.example.mydsl.web.MyDslWebSetup;
import org.eclipse.emf.common.util.URI;
import org.eclipse.emf.ecore.EObject;
import org.eclipse.emf.ecore.resource.Resource;
import org.eclipse.jetty.util.log.Slf4jLog;
import org.eclipse.xtend2.lib.StringConcatenation;
import org.eclipse.xtext.parser.antlr.*;
import com.google.gson.Gson;

import org.xtext.example.mydsl.myDsl.Model;
import org.xtext.example.mydsl.parser.antlr.MyDslParser;
import org.eclipse.xtext.parser.IParseResult;
import org.eclipse.xtext.parser.antlr.AbstractAntlrParser;
import org.eclipse.xtext.parser.ParseResult;
import org.eclipse.xtext.resource.XtextResource;
import org.eclipse.xtext.resource.XtextResourceSet;

/**
 * Deploy this class into a servlet container to enable DSL-specific services.
 */
@WebServlet(name = "XtextServices", urlPatterns = "/xtext-service/*")
@SuppressWarnings("all")
public class MyDslServlet extends XtextServlet {
  private DisposableRegistry disposableRegistry;
  final Slf4jLog log = new Slf4jLog("datpm");

  private static Pattern _pattern2 = Pattern.compile("/parser/(\\w+)");
  private XtextResourceSet resourceSet = new XtextResourceSet();

  @Override
  public void init() {
      log.info("init");
    try {
      super.init();
      final Injector injector = new MyDslWebSetup().createInjectorAndDoEMFRegistration();
      this.disposableRegistry = injector.<DisposableRegistry>getInstance(DisposableRegistry.class);
    } catch (Throwable _e) {
      throw Exceptions.sneakyThrow(_e);
    }
  }

  @Override
  public void destroy() {
    if ((this.disposableRegistry != null)) {
      this.disposableRegistry.dispose();
      this.disposableRegistry = null;
    }
    super.destroy();
  }

  @Override
  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      String url =  req.getRequestURL().toString();
      Matcher _matcher = _pattern2.matcher(url);
      // parser
      if (_matcher.find()) {
          resp.setContentType("text/x-json");
          Gson gson = new Gson();
          MyDslParser myDslParser = new MyDslParser();
//        Reader reader = new StringReader("Hello Xtext!");
          CharSequence cs = "Hello Xtext!";

          IParseResult iParseResult = myDslParser.doParse(cs);

          log.info(iParseResult.getRootASTElement().toString());

          gson.toJson(iParseResult.getRootASTElement().toString(), resp.getWriter());         
      } else {
          XtextServiceDispatcher.ServiceDescriptor service = getService(req);
          if (!service.isHasConflict() && service.isHasSideEffects()) {
              super.doGet(req, resp);
          } else {
              doService(service, resp);
          }  
      } 
  }
}

Когда я запускаюServerLauncher.java и доступ http://localhost:8080/xtext-service/parser/aaaaaaaa, это дает мне эту ошибку:

[main] INFO org.eclipse.jetty.util.log - Logging initialized @91ms
[main] INFO org.eclipse.jetty.server.Server - jetty-9.3.8.v20160314
[main] INFO org.eclipse.jetty.webapp.StandardDescriptorProcessor - NO JSP Support for /, did not find org.eclipse.jetty.jsp.JettyJspServlet
[main] INFO org.eclipse.jetty.server.handler.ContextHandler - Started o.e.j.w.WebAppContext@3a5ed7a6{/,[file:///home/thangld_anm/eclipse-workspace/org.xtext.example.mydsl.parent/org.xtext.example.mydsl.web/WebRoot/, jar:file:///home/thangld_anm/.gradle/caches/modules-2/files-2.1/org.webjars/requirejs/2.3.2/f70d2efec834af46229ffd92231acc18fa7856a/requirejs-2.3.2.jar!/META-INF/resources, jar:file:///home/thangld_anm/.gradle/caches/modules-2/files-2.1/org.webjars/jquery/2.2.4/c3dc40b1b5f24c56afa36fd9a463bb9f378ac4ab/jquery-2.2.4.jar!/META-INF/resources, jar:file:///home/thangld_anm/.gradle/caches/modules-2/files-2.1/org.eclipse.xtext/org.eclipse.xtext.web/2.12.0/b51418291a072d6c7520b0237e447cb30eb9b711/org.eclipse.xtext.web-2.12.0.jar!/META-INF/resources, jar:file:///home/thangld_anm/.gradle/caches/modules-2/files-2.1/org.webjars/ace/1.2.3/c027fca9e205f9f4a6b154a725cf41dbeff21a89/ace-1.2.3.jar!/META-INF/resources],AVAILABLE}
[main] INFO org.eclipse.jetty.server.ServerConnector - Started ServerConnector@3cef309d{HTTP/1.1,[http/1.1]}{localhost:8080}
[main] INFO org.eclipse.jetty.server.Server - Started @1960ms
[main] INFO org.xtext.example.mydsl.web.ServerLauncher - Server started http://localhost:8080/...
[Thread-11] INFO org.xtext.example.mydsl.web.ServerLauncher - Press enter to stop the server...
[qtp1558600329-10] INFO datpm - init
[qtp1558600329-10] WARN org.eclipse.jetty.servlet.ServletHandler - /xtext-service/parser/aaaaaaaa
java.lang.NullPointerException
    at org.eclipse.xtext.parser.antlr.AbstractAntlrParser.parse(AbstractAntlrParser.java:84)
    at org.eclipse.xtext.parser.antlr.AbstractAntlrParser.doParse(AbstractAntlrParser.java:62)
    at org.eclipse.xtext.parser.antlr.AbstractAntlrParser.doParse(AbstractAntlrParser.java:70)
    at org.xtext.example.mydsl.web.MyDslServlet.doGet(MyDslServlet.java:87)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
    at org.eclipse.xtext.web.servlet.XtextServlet.service(XtextServlet.java:60)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:837)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:583)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1160)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1092)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134)
    at org.eclipse.jetty.server.Server.handle(Server.java:518)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:308)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:244)
    at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)
    at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95)
    at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceAndRun(ExecuteProduceConsume.java:246)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:156)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:654)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:572)
    at java.lang.Thread.run(Thread.java:748)

Можете ли вы сказать мне, как получить результат анализа?Является ли IParseResult подходящим модулем для работы?Большое вам спасибо.