apache/druid · error · UOE

HDFS CharSequence not supported

Error message

HDFS CharSequence not supported

What it means

Same pattern as openReader: the HDFS FileObject's getCharContent(ignoreEncodingErrors) throws UOE("HDFS CharSequence not supported") because returning the whole file content as a CharSequence is not implemented for HDFS-backed binary segment files. The method exists only to satisfy the javax.tools.FileObject interface and is intentionally unimplemented for this storage backend.

Solutions

1. Read via openInputStream() and materialize the CharSequence yourself from the bytes.
2. Use a different URIDataPuller/FileObject implementation for character-content access.
3. Guard call sites: for hdfs:// scheme URIs, never call getCharContent.

Example fix

// before
CharSequence cs = fileObject.getCharContent(false);
// after
try (InputStream in = fileObject.openInputStream()) {
  CharSequence cs = new String(ByteStreams.toByteArray(in), StandardCharsets.UTF_8);
}

if ("hdfs".equalsIgnoreCase(uri.getScheme())) { /* do not call getCharContent */ }

boolean supportsCharContent(FileObject fo) { return !isHdfsFileObject(fo); }

try { return fo.getCharContent(false); }
catch (UOE e) { return slurpInputStream(fo.openInputStream()); }

When it happens

Trigger: Calling getCharContent on the FileObject produced by HdfsDataSegmentPuller.buildFileObject — any consumer expecting in-memory character content of an hdfs:// URI.

Common situations: Generic FileObject-based tooling that buffers file content as CharSequence; code ported from local-filesystem FileObjects to HDFS URIs without changing the content-access API.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• HDFS Reader not supported
• HDFS Writer not supported
• CharSequence not supported
• Aggregator[ ] cannot vectorize
• AppenderatorsManager methods should only called by services…

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/e35e62a52cd7a0d1. Report an issue: GitHub.

Appendix: source

Thrown at extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPuller.java:146

      }

      @Override
      public OutputStream openOutputStream() throws IOException
      {
        final FileSystem fs = path.getFileSystem(config);
        return fs.create(path, overwrite);
      }

      @Override
      public Reader openReader(boolean ignoreEncodingErrors)
      {
        throw new UOE("HDFS Reader not supported");
      }

      @Override
      public CharSequence getCharContent(boolean ignoreEncodingErrors)
      {
        throw new UOE("HDFS CharSequence not supported");
      }

      @Override
      public Writer openWriter()
      {
        throw new UOE("HDFS Writer not supported");
      }

      @Override
      public long getLastModified()
      {
        try {
          final FileSystem fs = path.getFileSystem(config);
          return fs.getFileStatus(path).getModificationTime();
        }
        catch (IOException ex) {
          throw new HdfsIOException(ex);
        }

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