Can't Deserialize JSON in Java Servlet

Question

My endpoint can't make sense of incoming JSON.

Here's the endpoint:

import javax.ws.rs.Consumes;
import javax.ws.rs.DefaultValue;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import org.hibernate.Query;
import org.hibernate.Session;
import org.json.JSONObject;
...

@POST
@Path("/{department}/{team}")
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public Response handleJSON(JSONObject json , @PathParam("department") String department, @PathParam("team") String team){ 

    MyObj myObj = new MyObj();

    myObj.setDepartment(department);
    myObj.setTeam(team);
    myObj.setPlatform(json.optString("platform"));

    saveObj(myObj);

  return Response.ok(true).build();

}

I'm posting JSON containing the key/value for "platform" using Postman, with header: Content-Type as application/json

But I get this exception: com.owlike.genson.JsonBindingException: Could not deserialize to type class org.json.JSONObject

Looks like the problem has to do with: Illegal character at row 0 and column 1 expected { but read '-' !

But I'm pretty sure Postman should be sending valid JSON...

Here's more of the stacktrace:

09-Jul-2014 10:30:00.017 SEVERE [http-nio-8080-exec-4] com.sun.jersey.spi.container.ContainerResponse.logException Mapped exception to response: 500 (Internal Server Error)
 javax.ws.rs.WebApplicationException: com.owlike.genson.JsonBindingException: Could not deserialize to type class org.json.JSONObject
    at com.owlike.genson.ext.jaxrs.GensonJsonConverter.readFrom(GensonJsonConverter.java:127)
    at com.sun.jersey.spi.container.ContainerRequest.getEntity(ContainerRequest.java:474)
    at com.sun.jersey.server.impl.model.method.dispatch.EntityParamDispatchProvider$EntityInjectable.getValue(EntityParamDispatchProvider.java:123)
    at com.sun.jersey.server.impl.inject.InjectableValuesProvider.getInjectableValues(InjectableValuesProvider.java:46)
    at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$EntityParamInInvoker.getParams(AbstractResourceMethodDispatchProvider.java:153)
    at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:203)
    at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
    at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:288)
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1469)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1400)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339)
    at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:699)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:526)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:655)
    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:744)
Caused by: com.owlike.genson.JsonBindingException: Could not deserialize to type class org.json.JSONObject
    at com.owlike.genson.Genson.deserialize(Genson.java:391)
    at com.owlike.genson.ext.jaxrs.GensonJsonConverter.readFrom(GensonJsonConverter.java:125)
    ... 41 more
Caused by: com.owlike.genson.stream.JsonStreamException: Illegal character at row 0 and column 1 expected { but read '-' !
    at com.owlike.genson.stream.JsonReader.newWrongTokenException(JsonReader.java:949)
    at com.owlike.genson.stream.JsonReader.begin(JsonReader.java:425)
    at com.owlike.genson.stream.JsonReader.beginObject(JsonReader.java:157)
    at com.owlike.genson.reflect.BeanDescriptor.deserialize(BeanDescriptor.java:101)
    at com.owlike.genson.reflect.BeanDescriptor.deserialize(BeanDescriptor.java:90)
    at com.owlike.genson.convert.BeanViewConverter.deserialize(BeanViewConverter.java:102)
    at com.owlike.genson.convert.NullConverter$NullConverterWrapper.deserialize(NullConverter.java:56)
    at com.owlike.genson.Genson.deserialize(Genson.java:389)
    ... 42 more

Answer 1

You should first inspect how your request is being sent. It is probably being sent as an escaped String, instead of raw JSON.

In my case, that was what was happening when I was using a generic REST client to send requests as pure JSON Strings, as my client doesn't know the object definitions.

To prevent that, in your client, you could send a (org.codehaus.jettison.json) JSONObject instead of just a String (it has a constructor that accepts a JSON String), but that will depend on your dependencies. In my case I'm using Jersey 1.19.

Note that, depending on your classpath, (Jersey 1.19 with Genson in my case) you might also need to read the response input stream manually if you also want to read the response as a JSON String.

Answer 2

This might not be an ideal solution, but i do think it could work.

Hopefully you have the Jackson JSON dependency already...

you can find it here: http://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core

I would try the following code:

@POST
@Path("/{department}/{team}")
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public Response handleJSON(String json, @PathParam("department") String department,       @PathParam("team") String team){ 

    ObjectMapper mapper = new ObjectMapper();
    JsonNode node = mapper.readValue(json, JsonNode.class);

    MyObj myObj = new MyObj();

    myObj.setDepartment(department);
    myObj.setTeam(team);

    if (node.get("platform") != null) {
        myObj.setPlatform(node.get("platform").textValue());
    }

    saveObj(myObj);

    return Response.ok(true).build();

}

Notice that I am asking your WS Framework to just pass me the JSON as a String and just handling it myself. Maybe its not ideal, but should work.

Cheers!

Answer 3

I don't know which JSON Serializer you are using but most probably this will be Jettison or Jackson. As far as I know they don't support converting an instance of org.json.JSONObject directly. The more common way is to simply use custom Java Beans:

public class Foo implements Serializable {

    private String platform;

    // getters + setters

}

@POST
@Path("/{department}/{team}")
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public Response handleJson(Foo foo, @PathParam("department") String department, @PathParam("team") String team) {
    ...
    myObj.setPlatform(foo.getPlatform());
    ...
}

Foo should be annotated with @XmlRootElement if you are using Jettison.

If you don't want to create a custom Bean for every Entity you are expecting you can use Object, Map or String as parameter and serialize on your own:

@POST
@Path("/{department}/{team}")
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public Response handleJson(String json, @PathParam("department") String department, @PathParam("team") String team) {
    ...
    JSONObject jsonObject = new JSONObject(json);
    myObj.setPlatform(json.optString("platform"));
    ...
}

Last solution is implementing a MessageBodyReader which handles JSONObject. Simple example:

@Provider
public class JsonObjectReader implements MessageBodyReader<JSONObject> {

    @Override
    public boolean isReadable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        return type == JSONObject.class && MediaType.APPLICATION_JSON_TYPE.equals(mediaType);
    }

    @Override
    public JSONObject readFrom(Class<JSONObject> type, Type genericType,
            Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders, InputStream entityStream)
            throws IOException, WebApplicationException {
        return new JSONObject(IOUtils.toString(entityStream));
    }

}