What causes "File format 'markdown' does not support writing." in apache/seatunnel?

Change the sink format to a writable format (text, csv, json, parquet, orc, canal_json, debezium_json, maxwell_json).

apache/seatunnel · error · UnsupportedOperationException

File format 'markdown' does not support writing.

Error message

File format 'markdown' does not support writing.

What it means

The MARKDOWN FileFormat enum member only supports reading (MarkdownReadStrategy). Calling getWriteStrategy() on it throws UnsupportedOperationException because writing markdown output files is not supported by the file sink.

Source

Thrown at seatunnel-connectors-v2/connector-file/connector-file-base/src/main/java/org/apache/seatunnel/connectors/seatunnel/file/config/FileFormat.java:179

                    "File format 'debezium_json' does not support reading.");
        }
    },
    MAXWELL_JSON("maxwell_json") {
        @Override
        public WriteStrategy getWriteStrategy(FileSinkConfig fileSinkConfig) {
            return new MaxWellJsonWriteStrategy(fileSinkConfig);
        }

        @Override
        public ReadStrategy getReadStrategy() {
            throw new UnsupportedOperationException(
                    "File format 'maxwell_json' does not support reading.");
        }
    },
    MARKDOWN("md", "markdown") {
        @Override
        public WriteStrategy getWriteStrategy(FileSinkConfig fileSinkConfig) {
            throw new UnsupportedOperationException(
                    "File format 'markdown' does not support writing.");
        }

        @Override
        public ReadStrategy getReadStrategy() {
            return new MarkdownReadStrategy();
        }
    },
    PDF("pdf") {
        @Override
        public WriteStrategy getWriteStrategy(FileSinkConfig fileSinkConfig) {
            throw new UnsupportedOperationException("File format 'pdf' does not support writing.");
        }

        @Override
        public ReadStrategy getReadStrategy() {
            return new PdfReadStrategy();
        }

View on GitHub (pinned to cf67b549a7)

Solutions

Change the sink format to a writable format (text, csv, json, parquet, orc, canal_json, debezium_json, maxwell_json).
If markdown output is needed, write as 'text' and format the content, or generate markdown downstream.
Check the FileFormat capability matrix (read vs write) before configuring a sink.
Keep 'md'/'markdown' only in source configurations.

Example fix

// before
sink {
  LocalFile {
    format = "markdown"
  }
}
// after
sink {
  LocalFile {
    format = "text"
  }
}

Defensive patterns

Strategy: validation

Validate before calling

FileFormat fmt = FileFormat.valueOf(config.get("format"));
try {
    fmt.getWriteStrategy(fileSinkConfig);
} catch (UnsupportedOperationException e) {
    throw new IllegalArgumentException("markdown is read-only; choose a writable format");
}

Type guard

boolean isWritable(FileFormat fmt, FileSinkConfig cfg) {
    try { fmt.getWriteStrategy(cfg); return true; }
    catch (UnsupportedOperationException e) { return false; }
}

Try / catch

try {
    fmt.getWriteStrategy(fileSinkConfig);
} catch (UnsupportedOperationException e) {
    log.error("markdown cannot be used as a file sink format; use text/csv/json/parquet", e);
    throw new IllegalArgumentException(e);
}

Prevention

Treat 'md'/'markdown' strictly as a source format.
Probe FileFormat.getWriteStrategy during sink config validation.
Use 'text' plus post-processing when markdown-like output is required.
Audit format fields when converting source configs into sink configs.

When it happens

Trigger: Configuring a file sink with format = "md" or "markdown"; write-strategy resolution invokes FileFormat.MARKDOWN.getWriteStrategy().

Common situations: Reusing a markdown source config for a sink; assuming all readable formats are also writable; exporting query results to markdown via the file sink.

Related errors

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/29774219b6d0eb2b. Report an issue: GitHub.