apache/hadoop · error · IllegalArgumentException

Name cannot be have a '{}' char

Error message

Name cannot be have a '{}' char

What it means

checkTokenName() in MultipleOutputs accepts only the characters A-Z, a-z and 0-9 in a named output (and in a multi name); every other character triggers this IllegalArgumentException (the message grammar is original: "Name cannot be have a ..."). Notably underscore, dash and dot are NOT allowed in this mapred-era validator. The check runs for addNamedOutput/addMultiNamedOutput and for the multiName of getCollector on multi outputs.

Source

Thrown at hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/lib/MultipleOutputs.java:205

   * @param namedOutput named output Name
   * @throws IllegalArgumentException if the output name is not valid.
   */
  private static void checkTokenName(String namedOutput) {
    if (namedOutput == null || namedOutput.length() == 0) {
      throw new IllegalArgumentException(
        "Name cannot be NULL or emtpy");
    }
    for (char ch : namedOutput.toCharArray()) {
      if ((ch >= 'A') && (ch <= 'Z')) {
        continue;
      }
      if ((ch >= 'a') && (ch <= 'z')) {
        continue;
      }
      if ((ch >= '0') && (ch <= '9')) {
        continue;
      }
      throw new IllegalArgumentException(
        "Name cannot be have a '" + ch + "' char");
    }
  }

  /**
   * Checks if a named output name is valid.
   *
   * @param namedOutput named output Name
   * @throws IllegalArgumentException if the output name is not valid.
   */
  private static void checkNamedOutputName(String namedOutput) {
    checkTokenName(namedOutput);
    // name cannot be the name used for the default output
    if (namedOutput.equals("part")) {
      throw new IllegalArgumentException(
        "Named output name cannot be 'part'");
    }
  }

View on GitHub (pinned to 2add963021)

Solutions

1. Restrict names to letters and digits only: camelCase or simple concatenation ('clickstream', '202401')
2. Sanitize computed names before use: name.replaceAll("[^A-Za-z0-9]", "")
3. Centralize naming in one helper used by both driver and task so both sides apply the same sanitization

Example fix

// before: '-' is rejected by checkTokenName
MultipleOutputs.addNamedOutput(conf, "click-stream", TextOutputFormat.class, Text.class, Text.class);

// after: alphanumeric-only name
MultipleOutputs.addNamedOutput(conf, "clickstream", TextOutputFormat.class, Text.class, Text.class);

static String sanitizeToken(String s) {
  String t = (s == null) ? "" : s.replaceAll("[^A-Za-z0-9]", "");
  return t.isEmpty() ? "NA" : t;
}
// use everywhere a named output / multi name is built
MultipleOutputs.addNamedOutput(conf, sanitizeToken(channel), fmt, k, v);

static boolean isAlphanumericToken(String name) {
  return name != null && name.matches("[A-Za-z0-9]+");
}

When it happens

Trigger: addNamedOutput(conf, "click-stream", ...), "out_1", "cat.ext" or any name containing '-', '_', '.', '/' or whitespace. Also mos.getCollector("seq", "2024-01", reporter) — the dash in the date fails the check even though the named output itself was registered fine.

Common situations: Natural naming from file names, dates or categories ('click_stream', '2024-01') that includes separators; ports of the new-API org.apache.hadoop.mapreduce.lib.output.MultipleOutputs code where names with '_' and '-' were tolerated, then hitting the stricter old-API validator.

Related errors

• Name cannot be NULL or emtpy
• Name cannot be have a '{ch}' char
• Named output name cannot be 'part'
• Name cannot be NULL or emtpy
• output name cannot be 'part'

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/31bea43e7d71cde0. Report an issue: GitHub.