Why Are My Images Coming Out Garbled?

If you are a Java developer using servlets and file uploads, you might have encountered a frustrating issue: uploaded images that appear garbled or corrupted when opened. This can be perplexing, especially if text files upload without any problems. In this blog post, we’ll explore why this happens and provide clear solutions to fix the problem.

Understanding the Issue

When working with file uploads, particularly image files, it’s essential to handle binary data correctly. The garbled output usually indicates that the binary stream is either not read properly or not written to the file correctly. The code segment below shows a typical file upload method using Apache Commons FileUpload:

protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    ...
    BufferedInputStream stream = new BufferedInputStream(item.openStream());
    ...
}

In this method, images and other binary files are processed, but the way the data is read can lead to issues that corrupt the image files.

Analyzing the Code

A key part of the code that contributes to the problem is found within the method for reading bytes from the input stream. Here is the relevant code snippet:

public static byte[] getBytes(InputStream src, int buffsize) throws IOException {
    ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
    byte[] buff = new byte[buffsize];

    while (true) {
        int nBytesRead = src.read(buff);
        if (nBytesRead < 0) {
            break;
        }
        byteStream.write(buff);
    }
    ...
}

Identifying the Problem

• Entire Buffer Write: The line byteStream.write(buff); writes the entire buffer regardless of how many bytes were actually read. This is problematic because, in many cases, nBytesRead will be less than the buffer size, meaning leftover bytes from previous reads may be written into the output, resulting in corruption.

Suggested Solution

To fix this issue, we need to adjust how bytes are written to the ByteArrayOutputStream. The revised code should look something like this:

public static byte[] getBytes(InputStream src, int buffsize) throws IOException {
    ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
    byte[] buff = new byte[buffsize];

    while (true) {
        int nBytesRead = src.read(buff);
        if (nBytesRead < 0) {
            break;
        } else {
            byteStream.write(buff, 0, nBytesRead); // Only write the bytes read
        }
    }
    ...
}

Key Changes

1. Conditional Write: The else clause ensures we only write the bytes that were actually read.
2. Specified Length: When writing, we now specify the number of bytes to write, using byteStream.write(buff, 0, nBytesRead);.

These changes prevent old, unneeded data from being written and ensure the image files are preserved without corruption.

Conclusion

If you’re facing issues with image uploads in your Java application, the culprit often lies in how you’re handling the input stream. By refining your byte-stream reading and writing logic, you can eliminate problems that lead to garbled images.

By following the above guidelines and correcting how you read and write byte streams, you can prevent future headaches with file uploads in your Java applications. Happy coding!