Why do Word and PPT files become garbled TXT files when downloading files in Java?

Java file download: The root cause of garbled code of Word and PPT files becoming TXT

When downloading files using Java, sometimes you will encounter the situation where Word and PPT files become garbled TXT files after downloading. This article will analyze the causes behind this phenomenon and provide solutions.

Detailed explanation of the problem

Some Java file download code (such as Code Example 2, which does not provide specific code but describes its core problem) are prone to garbled code when dealing with files such as Word and PPT. This is closely related to the fixed buffer size in the code (e.g. 1024 bytes). When the file size is not an integer multiple of the buffer size, the last read buffer may contain incomplete data, resulting in garbled code at the end of the file, which is eventually interpreted as a TXT file. TXT files are usually smaller, so this problem may not be obvious in small TXT files, but may also occur in larger TXT files.

Root Cause Analysis

The core of the problem is that the code fails to properly handle the last read data length. Fixed-size buffers may read data that is insufficient in buffer size when reading the end of the file, and these remaining bytes are incorrectly written to the output stream, resulting in garbled code.

Solution: Dynamically adjust the buffer read length

To solve this problem, it is necessary to dynamically adjust the number of bytes read per time to ensure that only the actual read data is written. The correct code should look like this:

 int len;
byte[] bytes = new byte[1024]; // The buffer size can be adjusted as needed try (InputStream inStream = ...; OutputStream outStream = ...) {
    while ((len = inStream.read(bytes)) != -1) {
        outStream.write(bytes, 0, len);
    }
} catch (IOException e) {
    e.printStackTrace();
}

The key to this code is the return value len of inStream.read(bytes) method. It represents the actual number of bytes read this time. outStream.write(bytes, 0, len) only writes len bytes, avoiding writing of unnecessary garbled bytes. In this way, the integrity and correctness of the file can be guaranteed regardless of the file size.

By using this method of dynamically adjusting the buffer reading length, the problem of Word and PPT files being garbled as TXT files during Java file download can be effectively avoided. Remember that choosing the right buffer size (such as 1024 bytes or larger) can improve efficiency, but the key is to control the number of bytes written based on the return value of inStream.read() .

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