code: public JsonResultSet getSimilarImages(String imageId, double threshold) {
  
      	JsonResultSet similar = new JsonResultSet();
          PostMethod queryMethod = null;
          String response = null;
          try {
  
              Part[] parts = {
                  new StringPart("id", imageId),
                  new StringPart("threshold", String.valueOf(threshold))
              };
  
              queryMethod = new PostMethod(webServiceHost + "/rest/visual/query_id/" + collectionName);
              queryMethod.setRequestEntity(new MultipartRequestEntity(parts, queryMethod.getParams()));
              int code = httpClient.executeMethod(queryMethod);
              if (code == 200) {
                  InputStream inputStream = queryMethod.getResponseBodyAsStream();
                  StringWriter writer = new StringWriter();
                  IOUtils.copy(inputStream, writer);
                  response = writer.toString();
  
                  queryMethod.releaseConnection();
  
                  similar = parseResponse(response);
              }
              else {
              	_logger.error("Http returned code: " + code);
              }
          } catch (Exception e) {
          	_logger.error("Exception for ID: " + imageId, e);
              response = null;
          } finally {
              if (queryMethod != null) {
                  queryMethod.releaseConnection();
              }
          }
          return similar;
      }
docs: Get similar images for a specific media item
  
  @param imageId
  @param threshold
  @return