code4craft/webmagic · error · IllegalArgumentException

language and script must not be null!

Error message

language and script must not be null!

What it means

The ScriptProcessor constructor requires both a Language and a script string. If either is null it throws IllegalArgumentException "language and script must not be null!" before any engine is created. It is a fail-fast guard against unusable script processor configuration.

Solutions

1. Pass a valid Language enum value (check spelling of the config value used to resolve it).
2. Ensure the script string is non-null before constructing — load it via ScriptProcessorBuilder.script/scriptFromFile which validate IO errors.
3. Add a caller-side null check with a clear message identifying which argument was null.

Example fix

// before
new ScriptProcessor(languageConfig, scriptText, 1);
// after
Objects.requireNonNull(languageConfig, "language");
Objects.requireNonNull(scriptText, "script");
new ScriptProcessor(languageConfig, scriptText, 1);

if (language == null) throw new IllegalStateException("Language not resolved from config");
if (script == null || script.trim().isEmpty()) throw new IllegalStateException("Script is empty");

try {
    processor = new ScriptProcessor(language, script, threadNum);
} catch (IllegalArgumentException e) {
    if (e.getMessage().contains("must not be null")) {
        throw new IllegalStateException("language and script are required to build ScriptProcessor", e);
    }
    throw e;
}

When it happens

Trigger: Calling new ScriptProcessor(null, script, threadNum) or new ScriptProcessor(language, null, threadNum) — e.g. a Language enum value resolved to null from config, or a script string loaded from an empty/missing source and never defaulted.

Common situations: Language loaded from a config file with a typo that resolves to null; a file/classpath script read returning null (or the caller passing a null literal) and forwarded directly to the constructor.

Related errors

• task or site can not be null
• threadNum should be more than one!
• emptySleepTime should be more than zero!
• Illegal HTTP Method
• illegal encoding

AI-assisted analysis of code4craft/webmagic@67816a19d6 (2026-09-08). Data as JSON: /api/errors/e7630389705ad4af. Report an issue: GitHub.

Appendix: source

Thrown at webmagic-scripts/src/main/java/us/codecraft/webmagic/scripts/ScriptProcessor.java:34

/**
 * @author code4crafter@gmail.com
 * @since 0.4.1
 */
public class ScriptProcessor implements PageProcessor {

    private ScriptEnginePool enginePool;

    private String defines;

    private String script;

    private final Language language;

    private Site site = Site.me();

    public ScriptProcessor(Language language, String script, int threadNum) {
        if (language == null || script == null) {
            throw new IllegalArgumentException("language and script must not be null!");
        }
        this.language = language;
        enginePool = new ScriptEnginePool(language, threadNum);
        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(language.getDefineFile());
        try {
            defines = IOUtils.toString(resourceAsStream, Charset.defaultCharset());
        } catch (IOException e) {
            throw new IllegalArgumentException(e);
        }
        this.script = script;
    }

    @Override
    public void process(Page page) {
        ScriptEngine engine = enginePool.getEngine();
        try {
            ScriptContext context = engine.getContext();
            context.setAttribute("page", page, ScriptContext.ENGINE_SCOPE);

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