apache/flink · error · RuntimeException

Could not look up the main(String[]) method from the class %

Error message

Could not look up the main(String[]) method from the class %s: %s

What it means

Thrown by the private hasMainMethod(Class) helper when entryClass.getMethod("main", String[].class) raises something other than NoSuchMethodException (which would return false) — i.e. a SecurityException or other reflective-access Throwable. This is the lookup-time guard, distinct from the later invocation-time checks in callMainMethod.

Source

Thrown at flink-clients/src/main/java/org/apache/flink/client/program/PackagedProgram.java:315

        return getJobJarAndDependencies(
                jarFileUrl, extractedTempLibraries, isPython(entryPointClassName));
    }

    /** Deletes all temporary files created for contained packaged libraries. */
    private void deleteExtractedLibraries() {
        deleteExtractedLibraries(this.extractedTempLibraries);
        this.extractedTempLibraries.clear();
    }

    private static boolean hasMainMethod(Class<?> entryClass) {
        Method mainMethod;
        try {
            mainMethod = entryClass.getMethod("main", String[].class);
        } catch (NoSuchMethodException e) {
            return false;
        } catch (Throwable t) {
            throw new RuntimeException(
                    "Could not look up the main(String[]) method from the class "
                            + entryClass.getName()
                            + ": "
                            + t.getMessage(),
                    t);
        }

        return Modifier.isStatic(mainMethod.getModifiers())
                && Modifier.isPublic(mainMethod.getModifiers());
    }

    private static void callMainMethod(Class<?> entryClass, String[] args)
            throws ProgramInvocationException {
        Method mainMethod;
        if (!Modifier.isPublic(entryClass.getModifiers())) {
            throw new ProgramInvocationException(
                    "The class " + entryClass.getName() + " must be public.");
        }

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Check the appended ': <message>' for the underlying reflection error and address it (e.g. add the missing 'opens' / reflection permission).
2. If a SecurityManager is active, grant ReflectPermission / suppressAccessChecks as needed for the user-code classloader.
3. On Java 17+, add '--add-opens java.base/java.lang=ALL-UNNAMED' or open the user module to Flink if running modular code.
4. Ensure the entry class loads cleanly (no static-initializer failures that surface as LinkageError during getMethod).

// Verify reflective access works before submission
try {
    entryClass.getMethod("main", String[].class);
} catch (SecurityException se) {
    // adjust SecurityManager / --add-opens before proceeding
}

try {
    PackagedProgram.newBuilder().setJarFile(jar).setEntryPointClassName(cls).build();
} catch (ProgramInvocationException pie) {
    if (pie.getMessage().startsWith("Could not look up the main")) {
        // inspect pie.getCause() for SecurityException / LinkageError
    }
    throw pie;
}

When it happens

Trigger: A SecurityManager denies reflective access to the method, or the JVM throws an unexpected Throwable (e.g. a LinkageError surfacing through reflection) during getMethod on the entry class.

Common situations: Running Flink under a restrictive SecurityManager, or in a sandboxed/container environment that limits reflection. Module-system (JPMS) access denials on Java 17+ when the entry class is in a non-opened module.

Related errors

• The given program class does not have a main(String[]) metho
• The class %s must be public.
• The class %s has no main(String[]) method.
• The class %s declares a non-static main method.
• The class %s declares a non-public main method.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/27a9dbc27752fe82. Report an issue: GitHub.