Android & Spring Boot: File Upload, List, Download, and Delete

Below is a basic example of how to create an Android application that interacts with a Spring Boot backend for file upload, listing, download, and deletion functionalities.

---

Spring Boot Backend

1. Setup Spring Boot Application

   • Add dependencies to pom.xml:

     <dependencies>
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-web</artifactId>
         </dependency>
     </dependencies>

2. Controller for File Operations

   import org.springframework.http.HttpHeaders;
   import org.springframework.http.HttpStatus;
   import org.springframework.http.ResponseEntity;
   import org.springframework.web.bind.annotation.*;
   import org.springframework.web.multipart.MultipartFile;
   
   import java.io.File;
   import java.io.IOException;
   import java.nio.file.Files;
   import java.nio.file.Path;
   import java.nio.file.Paths;
   import java.util.stream.Collectors;
   
   @RestController
   @RequestMapping("/files")
   public class FileController {
       private static final String UPLOAD_DIR = "uploads";
   
       public FileController() {
           File uploadDir = new File(UPLOAD_DIR);
           if (!uploadDir.exists()) uploadDir.mkdir();
       }
   
       @PostMapping("/upload")
       public ResponseEntity<String> uploadFile(@RequestParam("file") MultipartFile file) {
           try {
               Path filePath = Paths.get(UPLOAD_DIR, file.getOriginalFilename());
               Files.write(filePath, file.getBytes());
               return ResponseEntity.ok("File uploaded successfully");
           } catch (IOException e) {
               return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("File upload failed");
           }
       }
   
       @GetMapping
       public ResponseEntity<?> listFiles() {
           File folder = new File(UPLOAD_DIR);
           String[] files = folder.list();
           if (files != null) {
               return ResponseEntity.ok(files);
           } else {
               return ResponseEntity.ok(new String[]{});
           }
       }
   
       @GetMapping("/{filename}")
       public ResponseEntity<byte[]> downloadFile(@PathVariable String filename) {
           try {
               Path filePath = Paths.get(UPLOAD_DIR, filename);
               byte[] fileBytes = Files.readAllBytes(filePath);
               return ResponseEntity.ok()
                       .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + filename + "\"")
                       .body(fileBytes);
           } catch (IOException e) {
               return ResponseEntity.status(HttpStatus.NOT_FOUND).build();
           }
       }
   
       @DeleteMapping("/{filename}")
       public ResponseEntity<?> deleteFile(@PathVariable String filename) {
           File file = new File(UPLOAD_DIR, filename);
           if (file.exists() && file.delete()) {
               return ResponseEntity.ok("File deleted successfully");
           } else {
               return ResponseEntity.status(HttpStatus.NOT_FOUND).body("File not found");
           }
       }
   }
   

3. Run Spring Boot Application

   • Use @SpringBootApplication in the main class.
   • Run the application and ensure endpoints like http://localhost:8080/files work.

---

Android Application

1. Add Dependencies Add dependencies in build.gradle:

   implementation 'com.squareup.okhttp3:okhttp:4.9.3'
   implementation 'com.google.code.gson:gson:2.10'

2. HTTP Helper Class

   import okhttp3.*;
   import java.io.File;
   import java.io.IOException;
   
   public class HttpHelper {
       private static final OkHttpClient client = new OkHttpClient();
       private static final String BASE_URL = "http://localhost:8080/files"; // Use your server's IP
   
       public static void uploadFile(File file, Callback callback) {
           RequestBody requestBody = new MultipartBody.Builder()
                   .setType(MultipartBody.FORM)
                   .addFormDataPart("file", file.getName(),
                           RequestBody.create(file, MediaType.parse("application/octet-stream")))
                   .build();
           Request request = new Request.Builder()
                   .url(BASE_URL + "/upload")
                   .post(requestBody)
                   .build();
           client.newCall(request).enqueue(callback);
       }
   
       public static void listFiles(Callback callback) {
           Request request = new Request.Builder()
                   .url(BASE_URL)
                   .get()
                   .build();
           client.newCall(request).enqueue(callback);
       }
   
       public static void downloadFile(String filename, Callback callback) {
           Request request = new Request.Builder()
                   .url(BASE_URL + "/" + filename)
                   .get()
                   .build();
           client.newCall(request).enqueue(callback);
       }
   
       public static void deleteFile(String filename, Callback callback) {
           Request request = new Request.Builder()
                   .url(BASE_URL + "/" + filename)
                   .delete()
                   .build();
           client.newCall(request).enqueue(callback);
       }
   }
   

3. Activity Example

   import android.os.Bundle;
   import android.widget.Toast;
   import androidx.appcompat.app.AppCompatActivity;
   import okhttp3.Call;
   import okhttp3.Callback;
   import okhttp3.Response;
   
   import java.io.File;
   import java.io.IOException;
   
   public class MainActivity extends AppCompatActivity {
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
   
           // Example: Upload a file
           File file = new File(getFilesDir(), "example.txt");
           HttpHelper.uploadFile(file, new Callback() {
               @Override
               public void onFailure(Call call, IOException e) {
                   runOnUiThread(() -> Toast.makeText(MainActivity.this, "Upload failed", Toast.LENGTH_SHORT).show());
               }
   
               @Override
               public void onResponse(Call call, Response response) throws IOException {
                   runOnUiThread(() -> Toast.makeText(MainActivity.this, "Upload success", Toast.LENGTH_SHORT).show());
               }
           });
   
           // Example: List files
           HttpHelper.listFiles(new Callback() {
               @Override
               public void onFailure(Call call, IOException e) {
                   runOnUiThread(() -> Toast.makeText(MainActivity.this, "Failed to list files", Toast.LENGTH_SHORT).show());
               }
   
               @Override
               public void onResponse(Call call, Response response) throws IOException {
                   String responseData = response.body().string();
                   runOnUiThread(() -> Toast.makeText(MainActivity.this, "Files: " + responseData, Toast.LENGTH_LONG).show());
               }
           });
       }
   }
   

---

Testing

• Run the Spring Boot server on your computer.
• Start the Android emulator or connect a device.
• Replace localhost with your server's IP if testing on a real device.
• Test each feature (upload, list, download, delete).