• An example of a Java-based REST Service/Client.
• Will be using for programmatic push of text files, so no UI will be needed.

source: https://javatutorial.net/java-file-upload-rest-service

REST Service

Repo: https://github.com/JavaTutorialNetwork/Tutorials/tree/master/FileUploaderRESTService

package net.javatutorial.tutorials.services;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.ws.rs.Consumes;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.UriInfo;

import com.sun.jersey.core.header.FormDataContentDisposition;
import com.sun.jersey.multipart.FormDataParam;

/**
 * This example shows how to build Java REST web-service to upload files
 * accepting POST requests with encryption type "multipart/form-data".
 * For more details please read the full tutorial
 * on https://javatutorial.net/java-file-upload-rest-service
 * @author javatutorial.net
 */
@Path("/upload")
public class FileUploadService {
    
    /** The path to the folder where we want to store the uploaded files */
    private static final String UPLOAD_FOLDER = "c:/uploadedFiles/";
    
    public FileUploadService() {}
    
    @Context
    private UriInfo context;

    /**
     * Returns text response to caller containing current time-stamp
     * @return error response in case of missing parameters an internal exception or
     * success response if file has been stored successfully
     */
    @POST
    @Consumes(MediaType.MULTIPART_FORM_DATA)
    public Response uploadFile(
        @FormDataParam("file") InputStream uploadedInputStream,
        @FormDataParam("file") FormDataContentDisposition fileDetail) {
        
        // check if all form parameters are provided
        if (uploadedInputStream == null || fileDetail == null)
            return Response.status(400).entity("Invalid form data").build();
        
        // create our destination folder, if it not exists
        try {
            createFolderIfNotExists(UPLOAD_FOLDER);
        } catch (SecurityException se) {
            return Response.status(500).entity("Can not create destination folder on server").build();
        }

        String uploadedFileLocation = UPLOAD_FOLDER + fileDetail.getFileName();
        try {
            saveToFile(uploadedInputStream, uploadedFileLocation);
        } catch (IOException e) {
            return Response.status(500).entity("Can not save file").build();
        }

        return Response.status(200).entity("File saved to " + uploadedFileLocation).build();
    }

    /**
     * Utility method to save InputStream data to target location/file
     * @param inStream - InputStream to be saved
     * @param target - full path to destination file
     */
    private void saveToFile(InputStream inStream, String target) throws IOException {
        OutputStream out = null;
        int read = 0;
        byte[] bytes = new byte[1024];

        out = new FileOutputStream(new File(target));
        while ((read = inStream.read(bytes)) != -1) {
            out.write(bytes, 0, read);
        }
        out.flush();
        out.close();
    }
    
    /**
     * Creates a folder to desired location if it not already exists
     * @param dirName - full path to the folder
     * @throws SecurityException - in case you don't have permission to create the folder
     */
    private void createFolderIfNotExists(String dirName) throws SecurityException {
        File theDir = new File(dirName);
        if (!theDir.exists()) {
            theDir.mkdir();
        }
    }

}

Client

Repo: https://github.com/JavaTutorialNetwork/Tutorials/tree/master/FileUploaderJavaClient

package net.javatutorial.tutorials.clienst;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.mime.MultipartEntity;
import org.apache.http.entity.mime.content.InputStreamBody;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.util.EntityUtils;

/**
 * This example shows how to upload files using POST requests
 * with encryption type "multipart/form-data".
 * For more details please read the full tutorial
 * on https://javatutorial.net/java-file-upload-rest-service
 * @author javatutorial.net
 */
public class FileUploaderClient {
    
    public static void main(String[] args) {
        
        // the file we want to upload
        File inFile = new File("C:\\Users\\admin\\Desktop\\Yana-make-up.jpg");
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(inFile);
            DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
            
            // server back-end URL
            HttpPost httppost = new HttpPost("http://localhost:8080/FileUploaderRESTService-1/rest/upload");
            MultipartEntity entity = new MultipartEntity();

            // set the file input stream and file name as arguments
            entity.addPart("file", new InputStreamBody(fis, inFile.getName()));
            httppost.setEntity(entity);

            // execute the request
            HttpResponse response = httpclient.execute(httppost);
            
            int statusCode = response.getStatusLine().getStatusCode();
            HttpEntity responseEntity = response.getEntity();
            String responseString = EntityUtils.toString(responseEntity, "UTF-8");
            
            System.out.println("[" + statusCode + "] " + responseString);
            
        } catch (ClientProtocolException e) {
            System.err.println("Unable to make connection");
            e.printStackTrace();
        } catch (IOException e) {
            System.err.println("Unable to read file");
            e.printStackTrace();
        } finally {
            try {
                if (fis != null) fis.close();
            } catch (IOException e) {}
        }
    }
    
}