Do not load the entire file into a byte[] or String , as this will cause OutOfMemoryError for large files.
Use a buffer (e.g., 8KB) to read from the S3ObjectInputStream and write directly to your destination. 3. Modern CRT-based S3 Client (SDK v2)
Returns immediately, allowing you to monitor progress via a Download object. Code Example: download large file from s3 bucket java
To download a large file from an S3 bucket in Java, the most efficient approach is using the S3 Transfer Manager from the AWS SDK for Java . This tool automatically parallelizes the download process into smaller chunks, significantly reducing transfer time for large objects. 1. Using AWS S3 Transfer Manager (Recommended)
TransferManager xferMgr = TransferManagerBuilder.standard().build(); File localFile = new File("downloaded_large_file.zip"); try { // Schedules the download; returns immediately Download download = xferMgr.download("your-bucket-name", "large-file-key", localFile); // Optional: Block and wait for completion download.waitForCompletion(); } catch (AmazonServiceException e) { System.err.println(e.getErrorMessage()); } finally { xferMgr.shutdownNow(); } Use code with caution. 2. Streaming via S3ObjectInputStream Do not load the entire file into a
Downloads parts of the object in parallel to maximize throughput.
For files larger than 100MB, the S3 Transfer Manager is the industry standard because it manages multi-threaded downloads without requiring custom code. Modern CRT-based S3 Client (SDK v2) Returns immediately,
Supports pausing and resuming downloads, which is critical for massive files.
If you need to process data as it arrives (e.g., streaming a CSV to a user's browser in a Spring Boot app) without saving it to disk first, use the getObjectContent method.