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Home » Eclipse Projects » Eclipse Scout » NullPointerException in AbstractRestClientHelper derived class(A derived class of the AbstractRestClientHelper class throws a NullPointerException when it is called)
NullPointerException in AbstractRestClientHelper derived class [message #1840755] Fri, 23 April 2021 12:26 Go to next message
J D is currently offline J DFriend
Messages: 99
Registered: February 2021
Member
Hi there everyone,

I am having a new problem.

I have an endpoint in my REST server that clients call to test if a handshake can be established between the clients and the server. When successful, the server sends the following JSON document to the client that called it:

{
  "result": [
    {
      "remoteip": "",
      "useragent": "insomnia/2021.2.2",
      "header": "",
      "servergreeting": "Bienvenue! Le serveur est en marche!. Vous pouvez envoyez vos rêquetes."
    }
  ],
  "id": 1
}


The user agent depends on what type of client called the server.

To call the server from an Eclipse Scout REST client, I created the following 4 classes:

a) YGHelloRestClientHelper.java
@Bean
public class YGHelloRestClientHelper extends AbstractRestClientHelper {

  @Override
  protected String getBaseUri() {
    return "http://localhost:28200/ygserver/v2/root";
  }

  @Override
  protected RuntimeException transformException(RuntimeException e, Response response) {
    if (response != null && response.hasEntity()) {
      ErrorDo error = response.readEntity(ErrorResponse.class).getError();
      throw new VetoException(error.getMessage()).withTitle(error.getTitle());
    }
    return e;
  }
}


b) YGHelloResourceClient.java
public class YGHelloResourceClient implements IRestResourceClient {

  protected static final String RESOURCE_PATH = "/sayhello";

  protected YGHelloRestClientHelper helper() {
    return BEANS.get(YGHelloRestClientHelper.class);
  }

  /**
   * Fetches the server greeting message
   */
  public YGHelloDoMapEntity getServerGreeting() {
    WebTarget target = helper().target(RESOURCE_PATH).queryParam("schema", "my_company");
    return target.request().accept(MediaType.APPLICATION_JSON).get(YGHelloDoMapEntity.class);
  }
}


c) YGHelloDoEntity.java
@TypeName("YGHelloDoEntity")
public class YGHelloDoEntity extends DoEntity {

  @AttributeName("remoteip")
  public DoValue<String> remoteIp() {
    return doValue("remoteip");
  }

  @AttributeName("useragent")
  public DoValue<String> userAgent() {
    return doValue("useragent");
  }

  @AttributeName("header")
  public DoValue<String> header() {
    return doValue("header");
  }

  @AttributeName("servergreeting")
  public DoValue<String> servergreeting() {
    return doValue("servergreeting");
  }
}


And finally
d) YGHelloDoMapEntity.java
// Builds a map of data objects (YGHelloDoMapEntity in this case)
@TypeName("YGHelloDoMapEntity")
public class YGHelloDoMapEntity extends DoMapEntity<YGHelloDoEntity> {
}


When I try to GET the server greeting using the following code:

      @Order(10000)
      public class GetMessageButton extends AbstractButton {

        @Override
        protected void execClickAction() {
          YGHelloDoMapEntity greeting = BEANS.get(YGHelloResourceClient.class).getServerGreeting();
          System.out.println(greeting);

        }
      }


it throws the following exception:
2021-04-23 13:41:11,005 ERROR [scout-model-thread-23 Processing JSON request] org.eclipse.scout.rt.platform.exception.ExceptionHandler.handleThrowable(ExceptionHandler.java:135) - NullPointerException:n/a - MDC[principal=jd, uiSession=1:do2658ks25e9niqa60336mv22p74af4br13ac8gluemjojthnja, scoutSession=1mkq0brl45dbs3mb2hlq5kbs2qaunb3lebenpcf1g4ml62frshqh, jobName=Processing JSON request, cid=NA8CV9ZA9tR/9]
java.lang.NullPointerException: null
	at org.eclipse.scout.apps.ygclient.client.rest.common.YGHelloRestClientHelper.transformException(YGHelloRestClientHelper.java:23)
	at org.eclipse.scout.rt.rest.client.proxy.RestClientProxyFactory$RestProxyInvcationHandler.transformException(RestClientProxyFactory.java:256)
	at org.eclipse.scout.rt.rest.client.proxy.RestClientProxyFactory$RestProxyInvcationHandler.invoke(RestClientProxyFactory.java:206)
	at com.sun.proxy.$Proxy66.get(Unknown Source)
	at org.eclipse.scout.apps.ygclient.client.rest.common.YGHelloResourceClient.getServerGreeting(YGHelloResourceClient.java:22)
	at org.eclipse.scout.apps.ygclient.client.integrationproject.employee.EmployeeForm$MainBox$ProjectExitDataBox$ProjectExitSaveButton.execClickAction(EmployeeForm.java:3184)
	at org.eclipse.scout.rt.client.ui.form.fields.button.AbstractButton$LocalButtonExtension.execClickAction(AbstractButton.java:583)
	at org.eclipse.scout.rt.client.extension.ui.form.fields.button.ButtonChains$ButtonClickActionChain$1.callMethod(ButtonChains.java:59)
	at org.eclipse.scout.rt.client.extension.ui.form.fields.button.ButtonChains$ButtonClickActionChain$1.callMethod(ButtonChains.java:1)
	at org.eclipse.scout.rt.shared.extension.AbstractExtensionChain.callChain(AbstractExtensionChain.java:113)
	at org.eclipse.scout.rt.client.extension.ui.form.fields.button.ButtonChains$ButtonClickActionChain.execClickAction(ButtonChains.java:62)
	at org.eclipse.scout.rt.client.ui.form.fields.button.AbstractButton.interceptClickAction(AbstractButton.java:567)
	at org.eclipse.scout.rt.client.ui.form.fields.button.AbstractButton.doClick(AbstractButton.java:409)
	at org.eclipse.scout.rt.client.ui.form.fields.button.AbstractButton$P_UIFacade.fireButtonClickFromUI(AbstractButton.java:537)
	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:566)
	at org.eclipse.scout.rt.client.ModelContextProxy.lambda$1(ModelContextProxy.java:49)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:227)
	at org.eclipse.scout.rt.platform.transaction.TransactionProcessor.runTxMandatory(TransactionProcessor.java:156)
	at org.eclipse.scout.rt.platform.transaction.TransactionProcessor.runTxRequired(TransactionProcessor.java:139)
	at org.eclipse.scout.rt.platform.transaction.TransactionProcessor.intercept(TransactionProcessor.java:78)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:222)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain.call(CallableChain.java:170)
	at org.eclipse.scout.rt.platform.context.RunContext.call(RunContext.java:158)
	at org.eclipse.scout.rt.client.ModelContextProxy.lambda$0(ModelContextProxy.java:49)
	at com.sun.proxy.$Proxy43.fireButtonClickFromUI(Unknown Source)
	at org.eclipse.scout.rt.ui.html.json.form.fields.button.JsonButton.handleUiEvent(JsonButton.java:170)
	at org.eclipse.scout.rt.ui.html.json.JsonEventProcessor.processEvent(JsonEventProcessor.java:52)
	at org.eclipse.scout.rt.ui.html.json.JsonEventProcessor.processEvents(JsonEventProcessor.java:37)
	at org.eclipse.scout.rt.ui.html.UiSession.processJsonRequestInternal(UiSession.java:817)
	at org.eclipse.scout.rt.platform.util.concurrent.Callables.lambda$0(Callables.java:31)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:227)
	at org.eclipse.scout.rt.platform.job.internal.ExceptionProcessor.intercept(ExceptionProcessor.java:41)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:222)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:227)
	at org.eclipse.scout.rt.platform.transaction.TransactionProcessor.runTxMandatory(TransactionProcessor.java:156)
	at org.eclipse.scout.rt.platform.transaction.TransactionProcessor.runTxRequired(TransactionProcessor.java:139)
	at org.eclipse.scout.rt.platform.transaction.TransactionProcessor.intercept(TransactionProcessor.java:78)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:222)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain.call(CallableChain.java:170)
	at org.eclipse.scout.rt.platform.context.RunContext.call(RunContext.java:158)
	at org.eclipse.scout.rt.platform.context.RunContextRunner.intercept(RunContextRunner.java:38)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:222)
	at org.eclipse.scout.rt.platform.job.internal.CallableChainExceptionHandler.intercept(CallableChainExceptionHandler.java:33)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain$Chain.continueChain(CallableChain.java:222)
	at org.eclipse.scout.rt.platform.chain.callable.CallableChain.call(CallableChain.java:170)
	at org.eclipse.scout.rt.platform.job.internal.JobFutureTask.lambda$0(JobFutureTask.java:106)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at org.eclipse.scout.rt.platform.job.internal.JobFutureTask.run(JobFutureTask.java:175)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:834)
	at org.eclipse.scout.rt.platform.job.internal.NamedThreadFactory$1.run(NamedThreadFactory.java:63)


There is a NullPointerException for YGHelloRestClientHelper.

What is it that I'm doing wrong?

Thanks a million.

Cheers,

JD

[Updated on: Fri, 23 April 2021 12:32]

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Re: NullPointerException in AbstractRestClientHelper derived class [message #1840769 is a reply to message #1840755] Fri, 23 April 2021 13:52 Go to previous messageGo to next message
Andre Wegmueller is currently offline Andre WegmuellerFriend
Messages: 204
Registered: September 2012
Location: Baden-Dättwil, Switzerla...
Senior Member
Hi JD

The Stacktrace says the exception happens in your own code, its probably the best thing to debug into your YGHelloRestClientHelper#transformException method and analyze on which method-call exactly the NPE occurs. This will give you (and us here in the forum) a better chance to find the source of the problem.

André


Eclipse Scout Homepage | Documentation | GitHub
Re: NullPointerException in AbstractRestClientHelper derived class [message #1840793 is a reply to message #1840769] Fri, 23 April 2021 18:31 Go to previous messageGo to next message
Paolo Bazzi is currently offline Paolo BazziFriend
Messages: 33
Registered: January 2017
Location: Switzerland
Member
Hi JD

Is the server also a Scout application providing the REST endpoint?

If it's not a Scout server, then you may not expect the server to send an ErrorResponse containing an ErrorDo object. Therefore your exception translator should be implemented expecting any kind of error (or just an http error status code without any further payload).

You could as a first step try to omit your own transformException method in your implementation of AbstractRestClientHelper or just implement by logging and re-throwing the exception.
Take a look at the basic implementation org.eclipse.scout.rt.rest.client.proxy.BasicRestClientExceptionTransformer for a simple exception transformer which does not rely on ErrorResponse/ErrorDo.

If your REST service returns a JSON object in case of an error, then implement a custom DoEntity class with the appropriate attributes available in case of an error.

Regards,
Paolo


Eclipse Scout Homepage | Documentation | GitHub
Re: NullPointerException in AbstractRestClientHelper derived class [message #1840797 is a reply to message #1840793] Fri, 23 April 2021 22:26 Go to previous messageGo to next message
J D is currently offline J DFriend
Messages: 99
Registered: February 2021
Member
Hi there Paolo & Andre,

Thanks for your suggestions. They were very helpful.

I finally found out the souce of the problem. It was the forward slash in RESOURCE_PATH = "/sayhello" Removing it cleared the NullPointerException.

I then cleaned up the code and tried again.

I got another exception: a java.lang.IllegalStateException: Entity input stream has already been closed.

Please be patient with me. I snooped around for a while and I discovered that the issue was the JSON object returned by the REST server (It is not a Scout server, it was developed in another programming language). The structure of the JSON object in general is:

{
  "result": [{ }],
  "id": a number
}


I use the EntityDo below for the server response:

@TypeName("YGBaseEntityDo")
public class YGBaseEntityDo extends DoEntity {

  @AttributeName("result")
  public DoList<String> result() {
    return doList("result");
  }

  @AttributeName("id")
  public DoValue<String> id() {
    return doValue("id");
  }
}


I added the methods below in my YGBaseRestResourceClient and tested again:

  public YGBaseEntityDo getServerGreeting() {
    WebTarget target = helper().target(RESOURCE_PATH).queryParam("schema", "mycompany");
    return target.request().accept(MediaType.APPLICATION_JSON).get(YGBaseEntityDo.class);
   }

  public String getGreeting() {
    WebTarget target = helper().target(RESOURCE_PATH).queryParam("schema", "mycompany");
    return target.request().accept(MediaType.APPLICATION_JSON).get(String.class);
  }


The getServerGreeting method above is the one that threw up the exception java.lang.IllegalStateException: Entity input stream has already been closed

The getGreeting method that just returns a plain Java String class worked!!!!

My Scout REST client received the following message from the server:

{
    "result": [
        {
            "remoteip": "",
            "useragent": "Jersey/2.31 (HttpUrlConnection 11.0.10)",
            "header": "",
            "servergreeting": "Bienvenue! Le serveur est en marche!. Vous pouvez envoyez vos rêquetes."
        }
    ],
    "id": 11
}


I do not understand why my EntityDo failed. Any ideas?

Thanks a lot.

Cheers,

JD



Re: NullPointerException in AbstractRestClientHelper derived class [message #1840798 is a reply to message #1840797] Fri, 23 April 2021 22:31 Go to previous messageGo to next message
J D is currently offline J DFriend
Messages: 99
Registered: February 2021
Member
I just found the answer.

  @AttributeName("result")
  public DoList<String> result() {
    return doList("result");
  }

should actually be
  @AttributeName("result")
  public DoList<Object> result() {
    return doList("result");
  }


JD

[Updated on: Fri, 23 April 2021 22:32]

Report message to a moderator

Re: NullPointerException in AbstractRestClientHelper derived class [message #1840822 is a reply to message #1840798] Mon, 26 April 2021 07:43 Go to previous message
Paolo Bazzi is currently offline Paolo BazziFriend
Messages: 33
Registered: January 2017
Location: Switzerland
Member
Using "object" as Data Object Attribute definition is possible, but you afterwards need to check which type was deserialized. If the structure of the response is quite stable, I would recomment to use concrete data objects to model the structure:

For this kind of response:

{
    "result": [
        {
            "remoteip": "",
            "useragent": "Jersey/2.31 (HttpUrlConnection 11.0.10)",
            "header": "",
            "servergreeting": "Bienvenue! Le serveur est en marche!. Vous pouvez envoyez vos rêquetes."
        }
    ],
    "id": 11
}


I would use a structure like this:

@TypeName("YGBaseEntityDo")
public class YGBaseEntityDo extends DoEntity {

  public DoList<YGResultEntityDo > result() {
    return doList("result");
  }

  public DoValue<Integer> id() {
    return doValue("id");
  }
}


and

@TypeName("YGResultEntityDo")
public class YGResultEntityDo extends DoEntity {

  public DoValue<String> remoteip() {
    return doValue("remoteip");
  }

  public DoValue<String> useragent() {
    return doValue("useragent");
  }

  public DoValue<String> header() {
    return doValue("header");
  }

  public DoValue<String> servergreeting() {
    return doValue("servergreeting");
  }

}


Regards,
Paolo


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