Resources:

• Java API: https://googlecloudplatform.github.io/google-cloud-java/0.26.0/index.html
• Support for Java and other languages - client libraries info https://cloud.google.com/vision/docs/reference/libraries

// Imports the Google Cloud client library
import com.google.cloud.vision.v1.AnnotateImageRequest;
import com.google.cloud.vision.v1.AnnotateImageResponse;
import com.google.cloud.vision.v1.BatchAnnotateImagesResponse;
import com.google.cloud.vision.v1.EntityAnnotation;
import com.google.cloud.vision.v1.Feature;
import com.google.cloud.vision.v1.Feature.Type;
import com.google.cloud.vision.v1.Image;
import com.google.cloud.vision.v1.ImageAnnotatorClient;
import com.google.protobuf.ByteString;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

public class QuickstartSample {
  public static void main(String... args) throws Exception {
    // Instantiates a client
    try (ImageAnnotatorClient vision = ImageAnnotatorClient.create()) {

      // The path to the image file to annotate
      String fileName = "./resources/wakeupcat.jpg";

      // Reads the image file into memory
      Path path = Paths.get(fileName);
      byte[] data = Files.readAllBytes(path);
      ByteString imgBytes = ByteString.copyFrom(data);

      // Builds the image annotation request
      List<AnnotateImageRequest> requests = new ArrayList<>();
      Image img = Image.newBuilder().setContent(imgBytes).build();
      Feature feat = Feature.newBuilder().setType(Type.LABEL_DETECTION).build();
      AnnotateImageRequest request = AnnotateImageRequest.newBuilder()
          .addFeatures(feat)
          .setImage(img)
          .build();
      requests.add(request);

      // Performs label detection on the image file
      BatchAnnotateImagesResponse response = vision.batchAnnotateImages(requests);
      List<AnnotateImageResponse> responses = response.getResponsesList();

      for (AnnotateImageResponse res : responses) {
        if (res.hasError()) {
          System.out.printf("Error: %s\n", res.getError().getMessage());
          return;
        }

        for (EntityAnnotation annotation : res.getLabelAnnotationsList()) {
          annotation.getAllFields().forEach((k, v)->
              System.out.printf("%s : %s\n", k, v.toString()));
        }
      }
    }
  }
}

STEP 1: Download Client Library
STEP 2: create project and code
STEP 3: add library as dependency to your project
NOTE: this code assume image is in a file can load --you would have to modify this to be a servlet to receive the image data in the request and then the reset would be similar.

compile 'com.google.cloud:google-cloud-vision:0.25.0-beta'

EXAMPLE JAVA CODE (from github from google)-

• import cloud libraries 

• istantiate the vision client

• load the image stored in a file

• set up the request to run label detection

• cycle through the results

// Imports the Google Cloud client library
import com.google.cloud.vision.v1.AnnotateImageRequest;
import com.google.cloud.vision.v1.AnnotateImageResponse;
import com.google.cloud.vision.v1.BatchAnnotateImagesResponse;
import com.google.cloud.vision.v1.EntityAnnotation;
import com.google.cloud.vision.v1.Feature;
import com.google.cloud.vision.v1.Feature.Type;
import com.google.cloud.vision.v1.Image;
import com.google.cloud.vision.v1.ImageAnnotatorClient;
import com.google.protobuf.ByteString;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

public class QuickstartSample {
  public static void main(String... args) throws Exception {
        // Instantiates a client
        try (ImageAnnotatorClient vision = ImageAnnotatorClient.create()) {

            // The path to the image file to annotate
 	          String fileName = "./resources/wakeupcat.jpg";

            // Reads the image file into memory
 	          Path path = Paths.get(fileName);
 	          byte[] data = Files.readAllBytes(path);
 	          ByteString imgBytes = ByteString.copyFrom(data);

            // Builds the image annotation request
 	          List<AnnotateImageRequest> requests = new ArrayList<>();
 	          Image img = Image.newBuilder().setContent(imgBytes).build();
 	          Feature feat = Feature.newBuilder().setType
 	          

            (Type.LABEL_DETECTION).build();
 	          AnnotateImageRequest request = AnnotateImageRequest.newBuilder()
 	          .addFeatures(feat)
 	          .setImage(img)
 	          .build();
 	          requests.add(request);

            // Performs label detection on the image file
 	          BatchAnnotateImagesResponese response = vision.batchAnnotateImages(requests);
 	          List<AnnotateImageResponse> responses = response.getResponsesList();

            for (AnnotateImageResponse res : responses) {
   	          if (res.hasError()) {
  	            System.out.printf("Error: %s\n", res.getError().getMessage());
  	            return;
 	              }

                for (EntityAnnotation annotation : res.getLabelAnnotationsList()){
  	             annotation.getAllFields().forEach((k, v)->
  	              System.out.printf("%s : %s\n", k, v.toString()));
 	              }
	           }


     }//end try
 	 }//end main
 }