Method findProvider

src/main/java/groovy/grape/Grape.java:162–219

(final String configuredImpl)

    }

    private static ServiceLoader.Provider<GrapeEngine> findProvider(final String configuredImpl) {
        List<ServiceLoader.Provider<GrapeEngine>> providers;
        try {
            ClassLoader grapeClassLoader = Grape.class.getClassLoader();
            ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();

            // Keep deterministic order while avoiding duplicate provider types when both
            // class loaders expose the same service entry.
            Map<String, ServiceLoader.Provider<GrapeEngine>> discovered = new LinkedHashMap<>();
            ServiceLoader.load(GrapeEngine.class, grapeClassLoader).stream()
                    .forEach(p -> discovered.putIfAbsent(p.type().getName(), p));
            if (contextClassLoader != null && contextClassLoader != grapeClassLoader) {
                ServiceLoader.load(GrapeEngine.class, contextClassLoader).stream()
                        .forEach(p -> discovered.putIfAbsent(p.type().getName(), p));
            }
            providers = discovered.values().stream().toList();
        } catch (ServiceConfigurationError sce) {
            LOGGER.log(ERROR, "Failed to discover service providers for {0}: {1}", GrapeEngine.class.getName(), sce.getMessage());
            return null;
        }

        if (configuredImpl != null) {
            for (ServiceLoader.Provider<GrapeEngine> provider : providers) {
                if (provider.type().getName().equals(configuredImpl)) {
                    providers.stream()
                            .filter(p -> !p.type().getName().equals(configuredImpl))
                            .forEach(p -> LOGGER.log(DEBUG, "Ignoring provider ''{0}'' (''{1}'' configured via -D{2})",
                                    p.type().getName(), configuredImpl, GRAPE_IMPL_SYSTEM_PROPERTY));
                    return provider;
                }
            }
            LOGGER.log(WARNING, "Configured implementation ''{0}'' not found via service loader", configuredImpl);
            return null;
        }

        if (providers.size() == 1) {
            return providers.get(0);
        }

        if (providers.size() > 1) {
            for (ServiceLoader.Provider<GrapeEngine> provider : providers) {
                if (provider.type().getName().equals(DEFAULT_GRAPE_ENGINE)) {
                    providers.stream()
                            .filter(p -> !p.type().getName().equals(DEFAULT_GRAPE_ENGINE))
                            .forEach(p -> LOGGER.log(DEBUG, "Ignoring provider ''{0}'' in favour of default ''{1}'' (set -D{2} to override)",
                                    p.type().getName(), DEFAULT_GRAPE_ENGINE, GRAPE_IMPL_SYSTEM_PROPERTY));
                    return provider;
                }
            }
            // Multiple providers discovered but the default is not among them.
            List<String> names = providers.stream().map(p -> p.type().getName()).toList();
            LOGGER.log(WARNING, "{0} providers discovered {1} but default ''{2}'' is not among them; set -D{3} to select one",
                    providers.size(), names, DEFAULT_GRAPE_ENGINE, GRAPE_IMPL_SYSTEM_PROPERTY);
        }

        // No system property set: empty list means security lockdown — return null silently.
        return null;
    }