Jersey Exception : SEVERE: A message body reader for Java class

Question

I have a Jersey based Rest WS which outputs JSON. I am implementing a Jersey Client to invoke the WS and consume the JSON response. The client code I have is below

Answer 1

Q) Code was working fine in Intellj but failing in command line.

Sol) Add dependencies of jersey as a direct dependency rather than a transient one.

Reasoning: Since, it was working fine with IntelliJ, dependencies are correctly configured.

1. Get required dependencies by one of the following:

   1. check for the IntelliJ running command. Stackoverflow-link
   2. List dependencies from maven mvn dependency:tree

2. Now, add those problematic jersey dependencies explicitly.

Answer 2

If you are building an uberjar or "shaded jar", make sure your meta inf service files are merged. (This bit me multiple times on a dropwizard project.)

If you are using the gradle shadowJar plugin, you want to call mergeServiceFiles() in your shadowJar target: https://github.com/johnrengelman/shadow#merging-service-files

Not sure what the analogous commands are for maven or other build systems.

Answer 3

You need to implement your own MessageBodyReader and MessageBodyWriter for your class Lorg.shoppingsite.model.entity.jpa.User.

package javax.ws.rs.ext;

import java.io.IOException;
import java.io.InputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;

public interface MessageBodyReader<T extends Object> {

    public boolean isReadable(Class<?> type, 
        Type genericType, 
        Annotation[] annotations, 
        MediaType mediaType);

    public T readFrom(Class<T> type, 
        Type genericType, 
        Annotation[] annotations, 
        MediaType mediaType, 
        MultivaluedMap<String, String> httpHeaders, 
        InputStream entityStream) throws IOException, WebApplicationException;
}

package javax.ws.rs.ext;

import java.io.IOException;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;

public interface MessageBodyWriter<T extends Object> {

    public boolean isWriteable(Class<?> type, 
        Type genericType, 
        Annotation[] annotations, 
        MediaType mediaType);

    public long getSize(T t, 
        Class<?> type, 
        Type genericType, 
        Annotation[] annotations, 
        MediaType mediaType);

    public void writeTo(T t, 
        Class<?> type, 
        Type genericType, 
        Annotation[] annotations, 
        MediaType mediaType, 
        MultivaluedMap<String, Object> httpHeaders, 
        OutputStream entityStream) throws IOException, WebApplicationException;
}

Answer 4

Try adding:

<dependency>
    <groupId>com.owlike</groupId>
    <artifactId>genson</artifactId>
    <version>1.4</version>
</dependency>

Also this problem may occur if you're using HTTP GET with message body so in this case adding jersey-json lib, @XmlRootElement or modifying web.xml won't help. You should use URL QueryParam or HTTP POST.

Answer 5

Some may be confused why add jersey-json jar can't solve this problem. I found out that this jar has to newer than jersey-json-1.7.jar( 1.7.0 doesn't work, but 1.7.1 works fine.). hope this can help

Answer 6

Just check if you are running different instances in eclipse. I quit all my other sessions, clean build fixed the problem