apache/hadoop · error · FileNotFoundException

Mailformed URL while finding the web resource dir:{}

Error message

Mailformed URL while finding the web resource dir:{}

What it means

HttpServer2.getWebAppsPath() takes a development shortcut when src/main/webapps/<appName> exists on the working directory, converting its parent directory to a URL. If that File.toURI().toURL() throws MalformedURLException, it is rethrown as FileNotFoundException 'Mailformed URL...' (the typo is in the source). In practice this branch almost never fires because File URIs are well-formed; seeing it means the dev-mode path detection matched from an unusual location.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/http/HttpServer2.java:1353

  }

  /**
   * Get the pathname to the webapps files.
   * @param appName eg "secondary" or "datanode"
   * @return the pathname as a URL
   * @throws FileNotFoundException if 'webapps' directory cannot be found
   *   on CLASSPATH or in the development location.
   */
  protected String getWebAppsPath(String appName) throws FileNotFoundException {
    URL resourceUrl = null;
    File webResourceDevLocation = new File("src/main/webapps", appName);
    if (webResourceDevLocation.exists()) {
      LOG.info("Web server is in development mode. Resources "
          + "will be read from the source tree.");
      try {
        resourceUrl = webResourceDevLocation.getParentFile().toURI().toURL();
      } catch (MalformedURLException e) {
        throw new FileNotFoundException("Mailformed URL while finding the "
            + "web resource dir:" + e.getMessage());
      }
    } else {
      resourceUrl =
          getClass().getClassLoader().getResource("webapps/" + appName);

      if (resourceUrl == null) {
        throw new FileNotFoundException("webapps/" + appName +
            " not found in CLASSPATH");
      }
    }
    String urlString = resourceUrl.toString();
    return urlString.substring(0, urlString.lastIndexOf('/'));
  }

  /**
   * Get the port that the server is on
   * @return the port

View on GitHub (pinned to 2add963021)

Solutions

1. Change the working directory or move/rename the src/main/webapps dir so the classpath-based lookup is used instead
2. Run against a properly packaged jar where webapps/<app> is a classpath resource

File dev = new File("src/main/webapps", appName);
if (dev.exists()) {
  try { dev.getParentFile().toURI().toURL(); }
  catch (MalformedURLException e) { /* run from a normal directory or package instead */ }
}

try {
  path = server.getWebAppsPath(appName);
} catch (FileNotFoundException e) {
  // fall back to explicit classpath-based resource or an absolute webapps dir
}

When it happens

Trigger: Running a daemon or test from a directory that happens to contain src/main/webapps/<appName> while the path involves unusual characters or a broken filesystem view, making URL conversion fail.

Common situations: Development checkouts where the process working directory is odd (symlink farms, containers with strange mounts); extremely rare in packaged clusters.

Related errors

• Property %s not specified
• unknown scheme for endpoint:{}
• webapps/{} not found in CLASSPATH
• Problem in starting http server. Server handlers failed
• Unable to initialize WebAppContext

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/c669d4030ea7104a. Report an issue: GitHub.