File API - Java SDK Documentation

Overview

The File API provides endpoints for downloading and accessing files stored in collection records. It supports thumbnail generation for images, protected file access with tokens, and force download options.

Key Features:

Download files from collection records
Generate thumbnails for images (crop, fit, resize)
Protected file access with short-lived tokens
Force download option for any file type
Automatic content-type detection
Support for Range requests and caching

Backend Endpoints:

GET /api/files/{collection}/{recordId}/{filename} - Download/fetch file
POST /api/files/token - Generate protected file token

Download / Fetch File

Downloads a single file resource from a record.

Basic Usage

import com.bosbase.sdk.BosBase;
import java.util.*;

BosBase pb = new BosBase("http://127.0.0.1:8090");

// Get a record with a file field
ObjectNode record = pb.collection("posts").getOne("RECORD_ID", null, null, null, null);

// Get the file URL
String fileUrl = pb.files.getURL(record, record.get("image").asText());

// Use in your application
System.out.println("File URL: " + fileUrl);

File URL Structure

The file URL follows this pattern:

/api/files/{collectionIdOrName}/{recordId}/{filename}

Example:

http://127.0.0.1:8090/api/files/posts/abc123/photo_xyz789.jpg

Thumbnails

Generate thumbnails for image files on-the-fly.

Thumbnail Formats

The following thumbnail formats are supported:

Format	Example	Description
`WxH`	`100x300`	Crop to WxH viewbox (from center)
`WxHt`	`100x300t`	Crop to WxH viewbox (from top)
`WxHb`	`100x300b`	Crop to WxH viewbox (from bottom)
`WxHf`	`100x300f`	Fit inside WxH viewbox (without cropping)
`0xH`	`0x300`	Resize to H height preserving aspect ratio
`Wx0`	`100x0`	Resize to W width preserving aspect ratio

Using Thumbnails

// Get thumbnail URL
Map<String, String> options = new HashMap<>();
options.put("thumb", "100x100");
String thumbUrl = pb.files.getURL(record, record.get("image").asText(), options);

// Different thumbnail sizes
Map<String, String> smallOptions = new HashMap<>();
smallOptions.put("thumb", "50x50");
String smallThumb = pb.files.getURL(record, record.get("image").asText(), smallOptions);

Map<String, String> mediumOptions = new HashMap<>();
mediumOptions.put("thumb", "200x200");
String mediumThumb = pb.files.getURL(record, record.get("image").asText(), mediumOptions);

Map<String, String> largeOptions = new HashMap<>();
largeOptions.put("thumb", "500x500");
String largeThumb = pb.files.getURL(record, record.get("image").asText(), largeOptions);

// Fit thumbnail (no cropping)
Map<String, String> fitOptions = new HashMap<>();
fitOptions.put("thumb", "200x200f");
String fitThumb = pb.files.getURL(record, record.get("image").asText(), fitOptions);

// Resize to specific width
Map<String, String> widthOptions = new HashMap<>();
widthOptions.put("thumb", "300x0");
String widthThumb = pb.files.getURL(record, record.get("image").asText(), widthOptions);

// Resize to specific height
Map<String, String> heightOptions = new HashMap<>();
heightOptions.put("thumb", "0x200");
String heightThumb = pb.files.getURL(record, record.get("image").asText(), heightOptions);

Thumbnail Behavior

Image Files Only: Thumbnails are only generated for image files (PNG, JPG, JPEG, GIF, WEBP)
Non-Image Files: For non-image files, the thumb parameter is ignored and the original file is returned
Caching: Thumbnails are cached and reused if already generated
Fallback: If thumbnail generation fails, the original file is returned
Field Configuration: Thumb sizes must be defined in the file field’s thumbs option or use default 100x100

Protected Files

Protected files require a special token for access, even if you’re authenticated.

Getting a File Token

// Must be authenticated first
pb.collection("users").authWithPassword("user@example.com", "password", null, null, null, null, null, null, null, null);

// Get file token
String token = pb.files.getToken();

System.out.println("Token: " + token); // Short-lived JWT token

Using Protected File Token

// Get protected file URL with token
Map<String, String> options = new HashMap<>();
options.put("token", token);
String protectedFileUrl = pb.files.getURL(record, record.get("document").asText(), options);

// Access the file (e.g., download or display)
System.out.println("Protected file URL: " + protectedFileUrl);

Protected File Example

public String displayProtectedImage(String recordId) throws Exception {
    // Authenticate
    pb.collection("users").authWithPassword("user@example.com", "password", null, null, null, null, null, null, null, null);
    
    // Get record
    ObjectNode record = pb.collection("documents").getOne(recordId, null, null, null, null);
    
    // Get file token
    String token = pb.files.getToken();
    
    // Get protected file URL
    Map<String, String> options = new HashMap<>();
    options.put("token", token);
    options.put("thumb", "300x300");
    String imageUrl = pb.files.getURL(record, record.get("thumbnail").asText(), options);
    
    return imageUrl;
}

Token Lifetime

File tokens are short-lived (typically expires after a few minutes)
Tokens are associated with the authenticated user/superuser
Generate a new token if the previous one expires

Force Download

Force files to download instead of being displayed in the browser.

// Force download
Map<String, String> options = new HashMap<>();
options.put("download", "1");
String downloadUrl = pb.files.getURL(record, record.get("document").asText(), options);

System.out.println("Download URL: " + downloadUrl);

Download Parameter Values

// These all force download:
Map<String, String> options1 = new HashMap<>();
options1.put("download", "1");
String url1 = pb.files.getURL(record, filename, options1);

// These allow inline display (default):
Map<String, String> options2 = new HashMap<>();
options2.put("download", "0");
String url2 = pb.files.getURL(record, filename, options2);

// Or no download parameter
String url3 = pb.files.getURL(record, filename);

Complete Examples

Example 1: Image Gallery

public void displayImageGallery(String recordId) throws Exception {
    ObjectNode record = pb.collection("posts").getOne(recordId, null, null, null, null);
    
    List<String> images = new ArrayList<>();
    JsonNode imagesNode = record.get("images");
    if (imagesNode.isArray()) {
        for (JsonNode img : imagesNode) {
            images.add(img.asText());
        }
    } else if (imagesNode != null) {
        images.add(imagesNode.asText());
    }
    
    for (String filename : images) {
        // Thumbnail for gallery
        Map<String, String> thumbOptions = new HashMap<>();
        thumbOptions.put("thumb", "200x200");
        String thumbUrl = pb.files.getURL(record, filename, thumbOptions);
        
        // Full image URL
        String fullUrl = pb.files.getURL(record, filename);
        
        System.out.println("Thumbnail: " + thumbUrl);
        System.out.println("Full: " + fullUrl);
    }
}

Example 2: File Download Handler

public String downloadFile(String recordId, String filename) throws Exception {
    ObjectNode record = pb.collection("documents").getOne(recordId, null, null, null, null);
    
    // Get download URL
    Map<String, String> options = new HashMap<>();
    options.put("download", "1");
    String downloadUrl = pb.files.getURL(record, filename, options);
    
    return downloadUrl;
}

Example 3: Protected File Viewer

public String viewProtectedFile(String recordId) throws Exception {
    // Authenticate
    if (!pb.authStore.isValid()) {
        pb.collection("users").authWithPassword("user@example.com", "password", null, null, null, null, null, null, null, null);
    }
    
    // Get record
    ObjectNode record = pb.collection("private_docs").getOne(recordId, null, null, null, null);
    
    // Get token
    String token;
    try {
        token = pb.files.getToken();
    } catch (Exception e) {
        System.err.println("Failed to get file token: " + e.getMessage());
        return null;
    }
    
    // Get file URL
    Map<String, String> options = new HashMap<>();
    options.put("token", token);
    String fileUrl = pb.files.getURL(record, record.get("file").asText(), options);
    
    return fileUrl;
}

Example 4: Multiple Files with Thumbnails

public void displayFileList(String recordId) throws Exception {
    ObjectNode record = pb.collection("attachments").getOne(recordId, null, null, null, null);
    
    List<String> files = new ArrayList<>();
    JsonNode filesNode = record.get("files");
    if (filesNode.isArray()) {
        for (JsonNode file : filesNode) {
            files.add(file.asText());
        }
    }
    
    for (String filename : files) {
        // Check if it's an image
        String ext = filename.substring(filename.lastIndexOf('.') + 1).toLowerCase();
        boolean isImage = List.of("jpg", "jpeg", "png", "gif", "webp").contains(ext);
        
        if (isImage) {
            // Show thumbnail
            Map<String, String> thumbOptions = new HashMap<>();
            thumbOptions.put("thumb", "100x100");
            String thumbUrl = pb.files.getURL(record, filename, thumbOptions);
            System.out.println("Thumbnail: " + thumbUrl);
        }
        
        // File download link
        Map<String, String> downloadOptions = new HashMap<>();
        downloadOptions.put("download", "1");
        String downloadUrl = pb.files.getURL(record, filename, downloadOptions);
        System.out.println("Download: " + downloadUrl);
    }
}

Example 5: Image Upload Preview with Thumbnail

public String previewUploadedImage(ObjectNode record, String filename) {
    // Get thumbnail for preview
    Map<String, String> options = new HashMap<>();
    options.put("thumb", "200x200f");  // Fit to 200x200 without cropping
    String previewUrl = pb.files.getURL(record, filename, options);
    
    return previewUrl;
}

Error Handling

try {
    String fileUrl = pb.files.getURL(record, record.get("image").asText());
    
    // Verify URL is valid
    if (fileUrl == null || fileUrl.isEmpty()) {
        throw new RuntimeException("Invalid file URL");
    }
    
    System.out.println("File URL: " + fileUrl);
    
} catch (Exception e) {
    System.err.println("File access error: " + e.getMessage());
}

Protected File Token Error Handling

public String getProtectedFileUrl(ObjectNode record, String filename) {
    try {
        // Get token
        String token = pb.files.getToken();
        
        // Get file URL
        Map<String, String> options = new HashMap<>();
        options.put("token", token);
        return pb.files.getURL(record, filename, options);
        
    } catch (Exception e) {
        if (e.getMessage() != null && e.getMessage().contains("401")) {
            System.err.println("Not authenticated");
            // Redirect to login
        } else if (e.getMessage() != null && e.getMessage().contains("403")) {
            System.err.println("No permission to access file");
        } else {
            System.err.println("Failed to get file token: " + e.getMessage());
        }
        return null;
    }
}

Best Practices

Use Thumbnails for Lists: Use thumbnails when displaying images in lists/grids to reduce bandwidth
Lazy Loading: Consider lazy loading for images below the fold
Cache Tokens: Store file tokens and reuse them until they expire
Error Handling: Always handle file loading errors gracefully
Content-Type: Let the server handle content-type detection automatically
Range Requests: The API supports Range requests for efficient video/audio streaming
Caching: Files are cached with a 30-day cache-control header
Security: Always use tokens for protected files, never expose them in client-side code

Thumbnail Size Guidelines

Use Case	Recommended Size
Profile picture	`100x100` or `150x150`
List thumbnails	`200x200` or `300x300`
Card images	`400x400` or `500x500`
Gallery previews	`300x300f` (fit) or `400x400f`
Hero images	Use original or `800x800f`
Avatar	`50x50` or `75x75`

Limitations

Thumbnails: Only work for image files (PNG, JPG, JPEG, GIF, WEBP)
Protected Files: Require authentication to get tokens
Token Expiry: File tokens expire after a short period (typically minutes)
File Size: Large files may take time to generate thumbnails on first request
Thumb Sizes: Must match sizes defined in field configuration or use default 100x100

Files Upload and Handling - Uploading and managing files
API Records - Working with records
Collections - Collection configuration