Hopefully the most correct way to process a JAX-RS Response and convert it to a Throwable, without losing other Throwables that may happen along the way.

RFC7807ThrowableConverter.java

public static final <T extends Throwable> T toThrowable(final Class<T> throwableClass, final Throwable cause, Response response) {
    Objects.requireNonNull(throwableClass, "throwableClass == null");

    Constructor<T> c = null;
    try {
      c = throwableClass.getConstructor(String.class, Throwable.class);
    } catch (final NoSuchMethodException e) {
      throw new IllegalArgumentException("throwableClass", e);
    }
    assert c != null : throwableClass + ".getConstructor(String.class, Throwable.class) == null";
    
    T returnValue = null;

    String message = null;
    if (cause != null) {
      message = cause.getMessage();
    }
    
    if (response == null || !MediaType.APPLICATION_JSON_TYPE.isCompatible(response.getMediaType())) {
      try {
        returnValue = c.newInstance(message, cause);
      } catch (final IllegalAccessException | InstantiationException | InvocationTargetException e) {
        throw new IllegalArgumentException("throwableClass", e);
      }
    } else {
      try {
        if (response.bufferEntity()) {
          final JsonObject payload = response.readEntity(JsonObject.class);
          assert payload != null : "response.readEntity(JsonObject.class) == null";
          // See https://tools.ietf.org/html/rfc7807.
          final JsonValue detailValue = payload.get("detail");
          if (detailValue != null && detailValue instanceof JsonString) {
            message = ((JsonString)detailValue).getString();
          }
        }
        assert returnValue == null : "returnValue != null: " + returnValue;
        returnValue = c.newInstance(message, cause);
      } catch (final IllegalAccessException | InstantiationException | InvocationTargetException constructorInvocationFailed) {
        response = null;
        throw new IllegalArgumentException("throwableClass", constructorInvocationFailed);
      } catch (final IllegalStateException | ProcessingException responseReadEntityFailed) {
        assert returnValue == null : "returnValue != null: " + returnValue;
        try {
          returnValue = c.newInstance(message, cause);
        } catch (final IllegalAccessException | InstantiationException | InvocationTargetException constructorInvocationFailed) {
          response = null;
          final IllegalArgumentException e = new IllegalArgumentException("throwableClass", constructorInvocationFailed);
          e.addSuppressed(responseReadEntityFailed);
          throw e;
        }
        returnValue.addSuppressed(responseReadEntityFailed);
      } finally {
        if (response != null) {
          try {
            response.close();
          } catch (final ProcessingException responseClosingFailed) {
            if (returnValue == null) {
              try {
                returnValue = c.newInstance(message, cause);
              } catch (final IllegalAccessException | InstantiationException | InvocationTargetException constructorInvocationFailed) {
                final IllegalArgumentException e = new IllegalArgumentException("throwableClass", constructorInvocationFailed);
                e.addSuppressed(responseClosingFailed);
                throw e;
              }
            }
            returnValue.addSuppressed(responseClosingFailed);
          }
        }
      }
    }
    assert returnValue != null : "returnValue == null";
    return returnValue;
  }