java.util.ServiceLoader.Provider Java Examples

@Test(dataProvider = "badproviders",
      expectedExceptions = ServiceConfigurationError.class)
public void testBadProvider(String testName, String ignore) throws Exception {
    Path mods = compileTest(TEST2_MODULE);

    // compile the bad provider
    Path source = BADPROVIDERS_DIR.resolve(testName);
    Path output = Files.createTempDirectory(USER_DIR, "tmp");
    boolean compiled = CompilerUtils.compile(source, output);
    assertTrue(compiled);

    // copy the compiled class into the module
    Path classFile = Paths.get("p", "Provider.class");
    Files.copy(output.resolve(classFile),
               mods.resolve(TEST2_MODULE).resolve(classFile),
               StandardCopyOption.REPLACE_EXISTING);

    // load providers and instantiate each one
    loadProviders(mods, TEST2_MODULE).forEach(Provider::get);
}
 

@Test(dataProvider = "badfactories",
      expectedExceptions = ServiceConfigurationError.class)
public void testBadFactory(String testName, String ignore) throws Exception {
    Path mods = compileTest(TEST1_MODULE);

    // compile the bad factory
    Path source = BADFACTORIES_DIR.resolve(testName);
    Path output = Files.createTempDirectory(USER_DIR, "tmp");
    boolean compiled = CompilerUtils.compile(source, output);
    assertTrue(compiled);

    // copy the compiled class into the module
    Path classFile = Paths.get("p", "ProviderFactory.class");
    Files.copy(output.resolve(classFile),
               mods.resolve(TEST1_MODULE).resolve(classFile),
               StandardCopyOption.REPLACE_EXISTING);

    // load providers and instantiate each one
    loadProviders(mods, TEST1_MODULE).forEach(Provider::get);
}
 

/**
 * Basic test ServiceLoader.load specifying the platform class loader.
 * The providers on the module path and class path should not be located.
 */
@Test
public void testWithPlatformClassLoader() {
    ClassLoader pcl = ClassLoader.getPlatformClassLoader();

    // iterator
    ServiceLoader<ScriptEngineFactory> loader
        = ServiceLoader.load(ScriptEngineFactory.class, pcl);
    Set<String> names = collectAll(loader)
            .stream()
            .map(ScriptEngineFactory::getEngineName)
            .collect(Collectors.toSet());
    assertFalse(names.contains("BananaScriptEngine"));
    assertFalse(names.contains("PearScriptEngine"));

    // stream
    names = ServiceLoader.load(ScriptEngineFactory.class, pcl)
            .stream()
            .map(Provider::get)
            .map(ScriptEngineFactory::getEngineName)
            .collect(Collectors.toSet());
    assertFalse(names.contains("BananaScriptEngine"));
    assertFalse(names.contains("PearScriptEngine"));
}
 

/**
 * Basic test of stream() to ensure that elements for providers in named
 * modules come before elements for providers in unnamed modules.
 */
@Test
public void testStreamOrder() {
    List<Class<?>> types = ServiceLoader.load(ScriptEngineFactory.class)
            .stream()
            .map(Provider::type)
            .collect(Collectors.toList());

    boolean foundUnnamed = false;
    for (Class<?> factoryClass : types) {
        if (factoryClass.getModule().isNamed()) {
            if (foundUnnamed) {
                assertTrue(false, "Named module element after unnamed");
            }
        } else {
            foundUnnamed = true;
        }
    }
}
 

/**
 * Basic test of the public static provider method. BananaScriptEngine
 * defines a provider method that returns the same instance.
 */
@Test
public void testSingleton() {
    Optional<Provider<ScriptEngineFactory>> oprovider
        = ServiceLoader.load(ScriptEngineFactory.class)
            .stream()
            .filter(p -> p.type().getName().equals("org.banana.BananaScriptEngineFactory"))
            .findFirst();
    assertTrue(oprovider.isPresent());
    Provider<ScriptEngineFactory> provider = oprovider.get();

    // invoke Provider::get twice
    ScriptEngineFactory factory1 = provider.get();
    ScriptEngineFactory factory2 = provider.get();
    assertTrue(factory1 == factory2);
}
 

public static List<Plugin> getAllPlugins(Path dynamicPluginDir) throws IOException {
  var pluginMap = new HashMap<Class<?>, Plugin>();
  Consumer<Provider<Plugin>> addToMap = provider -> pluginMap.computeIfAbsent(provider.type(), __ -> provider.get());
  
  // load core plugins
  ServiceLoader<Plugin> loader = ServiceLoader.load(Plugin.class, Plugin.class.getClassLoader());
  loader.stream().forEach(addToMap);
  
  // load dynamic plugins
  loadDynamicPlugins(dynamicPluginDir, addToMap);
  
  return pluginMap.values().stream()
      .sorted(Comparator.comparing(Plugin::name))   // have a stable order
      .collect(toUnmodifiableList());
}
 

/**
 * Uses SPI to find a {@link DataSourceFactory} with the requested name or
 * {@code null} if one is not found.
 *

 * @param name the name of the class that implements the factory
 * @return a {@link DataSourceFactory} for {@code name} or {@code null} if one
 * is not found
 */
public static DataSourceFactory newFactory(String name) {
  if (name == null) throw new IllegalArgumentException("DataSourceFactory name is null");
  return ServiceLoader
          .load(DataSourceFactory.class)
          .stream()
          .filter(p -> p.type().getName().equals(name))
          .findFirst()
          .map(Provider::get)
          .orElse(null);
}
 

private static void loadDynamicPlugins(Path dynamicPluginDir, Consumer<? super Provider<Plugin>> consumer) throws IOException {
  if (!Files.isDirectory(dynamicPluginDir)) {
    return; // silent return, maybe there is not dynamic plugins
  }
  
  try(var stream = Files.list(dynamicPluginDir)) {
    stream.flatMap(Plugins::findDynamicPlugins).forEach(consumer);
  }
}
 

private static Stream<Provider<Plugin>> findDynamicPlugins(Path path) {
  var finder = ModuleFinder.of(path);
  var moduleNames = finder.findAll().stream().map(ref -> ref.descriptor().name()).collect(toUnmodifiableSet());
  
  var boot = ModuleLayer.boot();
  var cf = boot.configuration().resolve(finder, ModuleFinder.of(), moduleNames);

  var classLoader = new ClassLoader(Plugins.class.getClassLoader()) { /* empty */ };
  var layer = boot.defineModulesWithOneLoader(cf, classLoader);

  var serviceLoader = ServiceLoader.load(layer, Plugin.class);
  return serviceLoader.stream();
}
 

@Test(expectedExceptions = { ConcurrentModificationException.class })
public void testSpliteratorTryAdvance() {
    ServiceLoader<ScriptEngineFactory> sl = load(ScriptEngineFactory.class);
    Stream<Provider<ScriptEngineFactory>> stream = sl.stream();
    Spliterator<Provider<ScriptEngineFactory>> spliterator = stream.spliterator();
    sl.reload();
    spliterator.tryAdvance(System.out::println);
}
 

@Test(expectedExceptions = { ConcurrentModificationException.class })
public void testStreamFindAny() {
    ServiceLoader<ScriptEngineFactory> sl = load(ScriptEngineFactory.class);
    Stream<Provider<ScriptEngineFactory>> stream = sl.stream();
    sl.reload();
    stream.findAny();
}
 

public void testReload() {
    ServiceLoader<ScriptEngineFactory> sl = load(ScriptEngineFactory.class);
    List<String> names1 = sl.stream()
            .map(Provider::get)
            .map(ScriptEngineFactory::getEngineName)
            .collect(Collectors.toList());
    assertFalse(names1.isEmpty());
    sl.reload();
    List<String> names2 = sl.stream()
            .map(Provider::get)
            .map(ScriptEngineFactory::getEngineName)
            .collect(Collectors.toList());
    assertEquals(names1, names2);
}
 

@Test
public void sanityTest2() throws Exception {
    Path mods = compileTest(TEST2_MODULE);
    List<Provider> list = loadProviders(mods, TEST2_MODULE);
    assertTrue(list.size() == 1);
    Object p = list.get(0).get();
    assertTrue(p != null);
}
 

@Test
public void sanityTest1() throws Exception {
    Path mods = compileTest(TEST1_MODULE);
    List<Provider> list = loadProviders(mods, TEST1_MODULE);
    assertTrue(list.size() == 1);

    // the provider is a singleton, enforced by the provider factory
    Object p1 = list.get(0).get();
    Object p2 = list.get(0).get();
    assertTrue(p1 != null);
    assertTrue(p1 == p2);
}
 

/**
 * Basic test of Provider::get
 */
@Test
public void testProviderGet() {
    Set<String> names = ServiceLoader.load(ScriptEngineFactory.class)
            .stream()
            .map(Provider::get)
            .map(ScriptEngineFactory::getEngineName)
            .collect(Collectors.toSet());
    assertTrue(names.contains("BananaScriptEngine"));
    assertTrue(names.contains("PearScriptEngine"));
}
 

/**
 * Basic test of Provider::type
 */
@Test
public void testProviderType() {
    Set<String> types = ServiceLoader.load(ScriptEngineFactory.class)
            .stream()
            .map(Provider::type)
            .map(Class::getName)
            .collect(Collectors.toSet());
    assertTrue(types.contains("org.banana.BananaScriptEngineFactory"));
    assertTrue(types.contains("org.pear.PearScriptEngineFactory"));
}
 

@Test
public void testFactoryMethodUsingStreamNoPermission() {
    ServiceLoader<S2> sl = doPrivileged(loadAction(S2.class), noPermissions());
    try {
        sl.stream().map(Provider::get).count();
        assertTrue(false);
    } catch (ServiceConfigurationError e) {
        assertTrue(e.getCause() instanceof AccessControlException);
    }
}
 

@Test
public void testConstructorUsingStreamNoPermission() {
    ServiceLoader<S1> sl = doPrivileged(loadAction(S1.class), noPermissions());
    try {
        sl.stream().map(Provider::get).count();
        assertTrue(false);
    } catch (ServiceConfigurationError e) {
        assertTrue(e.getCause() instanceof AccessControlException);
    }
}
 

private static JMXConnectorServer
    getConnectorServerAsService(ClassLoader loader, JMXServiceURL url,
                                Map<String, ?> map, MBeanServer mbs,
                                Predicate<Provider<?>> filter)
    throws IOException {
    final ConnectorFactory<JMXConnectorServerProvider,JMXConnectorServer>
          factory = (p) -> p.newJMXConnectorServer(url, map, mbs);
    return JMXConnectorFactory.getConnectorAsService(
                                 JMXConnectorServerProvider.class,
                                 loader, url, filter, factory);
}
 

/**
 * Resolves a test module and loads it into its own layer. ServiceLoader
 * is then used to load all providers.
 */
private List<Provider> loadProviders(Path mp, String moduleName) throws Exception {
    ModuleFinder finder = ModuleFinder.of(mp);

    ModuleLayer bootLayer = ModuleLayer.boot();

    Configuration cf = bootLayer.configuration()
            .resolveAndBind(finder, ModuleFinder.of(), Set.of(moduleName));

    ClassLoader scl = ClassLoader.getSystemClassLoader();

    ModuleLayer layer = ModuleLayer.boot().defineModulesWithOneLoader(cf, scl);

    Class<?> service = layer.findLoader(moduleName).loadClass(TEST_SERVICE);

    return ServiceLoader.load(layer, service)
            .stream()
            .collect(Collectors.toList());
}
 

@Test
public void testFactoryMethodUsingStreamWithPermission() {
    ServiceLoader<S2> sl = doPrivileged(loadAction(S2.class), withPermissions(PERM));
    assertTrue(sl.stream().map(Provider::get).count() == 1);
}
 

@Test
public void testConstructorUsingStreamWithPermission() {
    ServiceLoader<S1> sl = doPrivileged(loadAction(S1.class), withPermissions(PERM));
    assertTrue(sl.stream().map(Provider::get).count() == 1);
}
 

/**
 * Test a service provider that defines more than one no-args
 * public static "provider" method.
 */
@Test(expectedExceptions = ServiceConfigurationError.class)
public void testWithTwoFactoryMethods() throws Exception {
    Path mods = compileTest(TEST1_MODULE);

    ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS
                                     + ClassWriter.COMPUTE_FRAMES);
    cw.visit(V1_9,
            ACC_PUBLIC + ACC_SUPER,
            "p/ProviderFactory",
            null,
            "java/lang/Object",
            null);

    // public static p.Service provider()
    MethodVisitor mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC,
            "provider",
            "()Lp/Service;",
            null,
            null);
    mv.visitTypeInsn(NEW, "p/ProviderFactory$1");
    mv.visitInsn(DUP);
    mv.visitMethodInsn(INVOKESPECIAL,
            "p/ProviderFactory$1",
            "<init>", "()V",
            false);
    mv.visitInsn(ARETURN);
    mv.visitMaxs(0, 0);
    mv.visitEnd();

    // public static p.ProviderFactory$1 provider()
    mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC,
            "provider",
            "()Lp/ProviderFactory$1;",
            null,
            null);
    mv.visitTypeInsn(NEW, "p/ProviderFactory$1");
    mv.visitInsn(DUP);
    mv.visitMethodInsn(INVOKESPECIAL,
            "p/ProviderFactory$1",
            "<init>",
            "()V",
            false);
    mv.visitInsn(ARETURN);
    mv.visitMaxs(0, 0);
    mv.visitEnd();

    cw.visitEnd();

    // write the class bytes into the compiled module directory
    Path classFile = mods.resolve(TEST1_MODULE)
            .resolve("p")
            .resolve("ProviderFactory.class");
    Files.write(classFile, cw.toByteArray());

    // load providers and instantiate each one
    loadProviders(mods, TEST1_MODULE).forEach(Provider::get);
}
 

private ToolbarEntryService() {
    loader = ServiceLoader.load(ToolbarEntry.class);
    toolbarEntries = loader.stream().map(Provider::get).collect(Collectors.toList());
}
 

private ContextMenuService() {
    loader = ServiceLoader.load(ContextMenuEntry.class);
    contextMenuEntries = Collections
            .unmodifiableList(loader.stream().map(Provider::get).collect(Collectors.toList()));
}
 

private MenuEntryService() {
    loader = ServiceLoader.load(MenuEntry.class);
    menuEntries = loader.stream().map(Provider::get).collect(Collectors.toList());
    populateMenuTree(menuEntryTree, menuEntries);
}
 

/**
 * Creates a connector from a provider loaded from the ServiceLoader.
 * <p>
 * The pair (P,C) will be either one of: <br>
 * a. (JMXConnectorProvider, JMXConnector) or <br>
 * b. (JMXConnectorServerProvider, JMXConnectorServer)
 *
 * @param providerClass The service type for which an implementation
 *        should be looked up from the {@code ServiceLoader}. This will
 *        be either {@code JMXConnectorProvider.class} or
 *        {@code JMXConnectorServerProvider.class}
 *
 * @param loader The ClassLoader to use when looking up an implementation
 *        of the service. If null, then only installed services will be
 *        considered.
 *
 * @param url The JMXServiceURL of the connector for which a provider is
 *        requested.
 *
 * @param filter A filter used to exclude or return provider
 *        implementations. Typically the filter will either exclude
 *        system services (system default implementations) or only
 *        retain those.
 *        This can allow to first look for custom implementations (e.g.
 *        deployed on the CLASSPATH with META-INF/services) and
 *        then only default to system implementations.
 *
 * @param factory A functional factory that can attempt to create an
 *        instance of connector {@code C} from a provider {@code P}.
 *        Typically, this is a simple wrapper over {@code
 *        JMXConnectorProvider::newJMXConnector} or {@code
 *        JMXConnectorProviderServer::newJMXConnectorServer}.
 *
 * @throws IOException if {@code C} could not be instantiated, and
 *         at least one provider {@code P} threw an exception that wasn't a
 *         {@code MalformedURLException} or a {@code JMProviderException}.
 *
 * @throws JMXProviderException if a provider {@code P} for the protocol in
 *         <code>url</code> was found, but couldn't create the connector
 *         {@code C} for some reason.
 *
 * @return an instance of {@code C} if a provider {@code P} was found from
 *         which one could be instantiated, {@code null} otherwise.
 */
static <P,C> C getConnectorAsService(Class<P> providerClass,
                                     ClassLoader loader,
                                     JMXServiceURL url,
                                     Predicate<Provider<?>> filter,
                                     ConnectorFactory<P,C> factory)
    throws IOException {

    // sanity check
    if (JMXConnectorProvider.class != providerClass
        && JMXConnectorServerProvider.class != providerClass) {
        // should never happen
        throw new InternalError("Unsupported service interface: "
                                + providerClass.getName());
    }

    ServiceLoader<P> serviceLoader = loader == null
            ? ServiceLoader.loadInstalled(providerClass)
            : ServiceLoader.load(providerClass, loader);
    Stream<Provider<P>> stream = serviceLoader.stream().filter(filter);
    ProviderFinder<P,C> finder = new ProviderFinder<>(factory, url);

    try {
        stream.filter(finder).findFirst();
        return finder.get();
    } catch (UncheckedIOException e) {
        if (e.getCause() instanceof JMXProviderException) {
            throw (JMXProviderException) e.getCause();
        } else {
            throw e;
        }
    }
}
 

/**
 * Creates a JMXConnector from the first JMXConnectorProvider service
 * supporting the given url that can be loaded from the given loader.
 * <p>
 * Parses the list of JMXConnectorProvider services that can be loaded
 * from the given loader, only retaining those that satisfy the given filter.
 * Then for each provider, attempts to create a new JMXConnector.
 * The first JMXConnector successfully created is returned.
 * <p>
 * The filter predicate is usually used to either exclude system providers
 * or only retain system providers (see isSystemProvider(...) above).
 *
 * @param loader The ClassLoader to use when looking up an implementation
 *        of the service. If null, then only installed services will be
 *        considered.
 *
 * @param url The JMXServiceURL of the connector for which a provider is
 *        requested.
 *
 * @param filter A filter used to exclude or return provider
 *        implementations. Typically the filter will either exclude
 *        system services (system default implementations) or only
 *        retain those.
 *        This can allow to first look for custom implementations (e.g.
 *        deployed on the CLASSPATH with META-INF/services) and
 *        then only default to system implementations.
 *
 * @throws IOException if no connector could not be instantiated, and
 *         at least one provider threw an exception that wasn't a
 *         {@code MalformedURLException} or a {@code JMProviderException}.
 *
 * @throws JMXProviderException if a provider for the protocol in
 *         <code>url</code> was found, but couldn't create the connector
 *         some reason.
 *
 * @return an instance of JMXConnector if a provider was found from
 *         which one could be instantiated, {@code null} otherwise.
 */
private static JMXConnector getConnectorAsService(ClassLoader loader,
                                                  JMXServiceURL url,
                                                  Map<String, ?> map,
                                                  Predicate<Provider<?>> filter)
    throws IOException {

    final ConnectorFactory<JMXConnectorProvider, JMXConnector> factory =
            (p) -> p.newJMXConnector(url, map);
    return getConnectorAsService(JMXConnectorProvider.class, loader, url,
                                 filter, factory);
}
 

/**
 * Checks whether the given provider is our system provider for
 * the RMI connector.
 * If providers for additional protocols are added in the future
 * then the name of their modules may need to be added here.
 * System providers will be loaded only if no other provider is found.
 * @param provider the provider to test.
 * @return true if this provider is a default system provider.
 */
static boolean isSystemProvider(Provider<?> provider) {
    Module providerModule = provider.type().getModule();
    return providerModule.isNamed()
       && providerModule.getName().equals("java.management.rmi");
}