Custom MessageBodyReader is not called for String parameters

[tituslup]

Hi,

I have written a custom MessageBodyReader to handle a use case in my application where a POST method has multiple parameters that come from inside the message body. I know this is highly unusual in REST but its a legacy application. In this custom MessageBodyReader I'm parsing the incoming JSON and matching the parameter to the corresponding entry in the JSON using a custom annotation.

Here is some sample code from the method and from the reader:

@POST
@Path(/{id}/start-job)
public job startJob(@PathParam("id") ObjectID id, @JsonParam("targets") Target[] targets,
            @JsonParam("schedule") Schedule schedule, @JsonParam("tag") String tag ) throws ...

@Provider
@Consumes(MediaType.APPLICATION_JSON)
public class CustomMessageBodyReader implements MessageBodyReader<Object> {
    private final ObjectMapper objectMapper = new ObjectMapper() {{
        configure(JsonParser.Feature.AUTO_CLOSE_SOURCE, false);
    }};

    @Override
    public boolean isReadable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        for (Annotation annotation : annotations) {
            if (annotation instanceof JsonParam) {
                return true;
            }
        }
        return false;
    }

    @Override
    public Object readFrom(Class<Object> type, Type genericType, Annotation[] annotations, MediaType mediaType,
                           MultivaluedMap<String, String> httpHeaders, InputStream entityStream)
            throws IOException {

        for (Annotation annotation : annotations) {
            if (annotation instanceof JsonParam) {
                // the logic here does not even matter because does not reach this point for String parameters
            }
        }

        return objectMapper.readValue(entityStream, type);
    }
}

Observations:

1. This reader works fine for other methods with complex serializable objects. It is even called in this method for the parameters corresponding to Schedule and Target.
2. The reader is never called for String "tag". No calls to isReadable or readFrom.
3. If I remove from my method the first parameter ("@PathParam("id") ObjectID id, ") then my reader is not called at all, not even for the complex objects. The method now is exposed but everything passed inside the message body is sent to the first parameter which is ("targets") in this case.

What am I missing here?
How would you advise handling these situations where existing code needs to be exposed and methods have multiple objects that would need to be passed inside the body of a message?

I'm using Wildfly 34.0.1.

Thanks,
-Titus

[jamezp]

Have you tried adding a @Priority(10) annotation to your MessageBodyReader?

[tituslup]

I did play with @Priority before and had no success with it.
I have updated my code with @Priority again with these 3 values 1, 10 , 100, but it did not help me.

Reader change:

import jakarta.annotation.Priority;
import jakarta.ws.rs.Consumes;
import jakarta.ws.rs.ext.MessageBodyReader;
import jakarta.ws.rs.ext.Provider;


@Provider
@Consumes(MediaType.APPLICATION_JSON)
@Priority(10)
public class CustomMessageBodyReader implements MessageBodyReader<Object> {
...

Here are my examples:

@Path("/resources")
@Consumes(APPLICATION_JSON)
@Produces(APPLICATION_JSON)
public class Resource{

    @POST
    @Path("/test_payload1")
    public String test_payload1(
            @JsonPayloadParam("param1") String param1, @JsonPayloadParam("param2") String param2) {
        return "param1: " + param1 + " param2: " + param2;
    }

    @POST
    @Path("/test_payload2")
    public String test_payload2(
            @QueryParam("param0") String param0, @JsonPayloadParam("param1") String param1, @JsonPayloadParam("param2") String param2) {
        return "param0: " + param0 + " param1:" + param1 + " param2: " + param2;
    }

    // Resource here is just a Serializable class and has a string constructor
    @POST
    @Path("/test_payload3")
    public String test_payload3(
            @QueryParam("param0") String param0, @JsonPayloadParam("param1") Resource param1, @JsonPayloadParam("param2") Resource param2) {
        return "param0: " + param0 + " param1: " + param1 + " param2: " + param2;
    }

URL: .../resources/test_payload1?param0=p0
Payload: { "param1": "p1", "param2": "p2" }
-> CustomMessageBodyReader not called
Result: "param1: {\"param1\":\"p1\",\"param2\":\"p2\"} param2: "

URL:  .../resources/test_payload2?param0=p0
Payload: { "param1": "p1", "param2": "p2" }
-> CustomMessageBodyReader not called
Result: "param0: p0 param1:{\"param1\":\"p1\",\"param2\":\"p2\"} param2: "

URL:  .../resources/test_payload3?param0=p0
Payload: { "param1": "3010001",   "param2": "2850001" }
-> CustomMessageBodyReader is called
Result: "param0: p0 param1: (Resource: 3010001) param2: (Resource: 2850001)"

[tituslup]

I suspected this is related to "implements MessageBodyReader<Object> {" and then wrote another reader for String.
That reader is called. I still have to clarify if I can have two Readers accessing the same message body.

URL:  .../resources/test_payload2?param0=p0
Payload: { "param1": "p1", "param2": "p2" }
Result: "param1: \"p1\" param2: \"p2\""

Since String inherits from Object, shouldn't my generic MessageBodyReader<Object> + @Priority be enough to convince the system to choose it?