apache/hadoop · error · NullPointerException

Source must not be null

Error message

Source must not be null

What it means

First guard clause of Storage.nativeCopyFileUnbuffered: it throws NullPointerException before any I/O happens when srcFile is null. The method copies a large file (typically a fsimage/edits segment) using OS-specific unbuffered IO, and its contract requires a non-null regular-file source.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/Storage.java:1327

   * <strong>Note:</strong> Setting <code>preserveFileDate</code> to
   * {@code true} tries to preserve the file's last modified
   * date/times using {@link File#setLastModified(long)}, however it is
   * not guaranteed that the operation will succeed.
   * If the modification operation fails, no indication is provided.
   *
   * @param srcFile  an existing file to copy, must not be {@code null}
   * @param destFile  the new file, must not be {@code null}
   * @param preserveFileDate  true if the file date of the copy
   *  should be the same as the original
   *
   * @throws NullPointerException if source or destination is {@code null}
   * @throws IOException if source or destination is invalid
   * @throws IOException if an IO error occurs during copying
   */
  public static void nativeCopyFileUnbuffered(File srcFile, File destFile,
      boolean preserveFileDate) throws IOException {
    if (srcFile == null) {
      throw new NullPointerException("Source must not be null");
    }
    if (destFile == null) {
      throw new NullPointerException("Destination must not be null");
    }
    if (srcFile.exists() == false) {
      throw new FileNotFoundException("Source '" + srcFile + "' does not exist");
    }
    if (srcFile.isDirectory()) {
      throw new IOException("Source '" + srcFile + "' exists but is a directory");
    }
    if (srcFile.getCanonicalPath().equals(destFile.getCanonicalPath())) {
      throw new IOException("Source '" + srcFile + "' and destination '" +
          destFile + "' are the same");
    }
    File parentFile = destFile.getParentFile();
    if (parentFile != null) {
      if (!parentFile.mkdirs() && !parentFile.isDirectory()) {
        throw new IOException("Destination '" + parentFile

View on GitHub (pinned to 2add963021)

Solutions

1. Pass a non-null srcFile
2. Fail fast at the call site with an actionable message: Objects.requireNonNull(srcFile, "srcFile")
3. Fix the upstream lookup that produced null (e.g. validate the config key exists before building the File)

Example fix

// before
Storage.nativeCopyFileUnbuffered(resolveSrc(cfg), dst, true); // resolveSrc returns null
// after
File src = Objects.requireNonNull(resolveSrc(cfg), "checkpoint src missing from config");
Storage.nativeCopyFileUnbuffered(src, dst, true);

Objects.requireNonNull(srcFile, "srcFile must be resolved before copy");
if (!srcFile.isFile()) throw new FileNotFoundException(srcFile.toString());

static boolean isCopyableSource(File f) {
  return f != null && f.isFile();
}

When it happens

Trigger: Calling nativeCopyFileUnbuffered with a null File, usually because the caller resolved the source path from a nullable lookup (missing config property, absent checkpoint file) and forwarded it unchecked.

Common situations: Unit tests invoking the helper directly; code that maps a configuration value to a File and skips the missing-property case; refactors where a field initialization was dropped.

Related errors

• Destination must not be null
• The filePath should not be null!
• Block cannot be null
• Provided block and location cannot be null
• Source '{srcFile}' does not exist

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/e522782da8f69ef7. Report an issue: GitHub.