Java 在运行时实例化泛型的反射

Question

我正在尝试将我的应用程序与 Bukkit - A Minecraft Server API 集成。

基本上，我在想办法让这样的功能发挥作用：

Reflections reflections = new Reflections("com.mycompany");    
Set<Class<? extends BlockEvent>> classes = reflections.getSubTypesOf(BlockEvent.class);
for (Class<? extends BlockEvent> clazz : classes) {
    getServer().getPluginManager().registerEvents(new BlockListener<clazz>(), this);
}

我想为扩展 BlockEvent. Events are registered by passing an implemention of Listener into the registerEvents(Listener, Plugin) method exposed by the Bukkit API's PluginManager 的所有事件类型注册一个侦听器。显然 clazz 不是类型，不能这样使用。

这是通用的 class:

public class BlockListener<T extends BlockEvent> implements Listener {
  @EventHandler(priority = EventPriority.HIGHEST, ignoreCancelled = true)
  void onBlock(T event) {
    System.out.println("Block Event");
    Bukkit.getPluginManager().callEvent(new BlockChangeEvent(event.getBlock()));
  }
}

更新

    public Map<Class<? extends Event>, Set<RegisteredListener>> createRegisteredListeners(@NotNull Listener listener, @NotNull final Plugin plugin) {
        Validate.notNull(plugin, "Plugin can not be null");
        Validate.notNull(listener, "Listener can not be null");

        boolean useTimings = server.getPluginManager().useTimings();
        Map<Class<? extends Event>, Set<RegisteredListener>> ret = new HashMap<Class<? extends Event>, Set<RegisteredListener>>();
        Set<Method> methods;
        try {
            Method[] publicMethods = listener.getClass().getMethods();
            Method[] privateMethods = listener.getClass().getDeclaredMethods();
            methods = new HashSet<Method>(publicMethods.length + privateMethods.length, 1.0f);
            for (Method method : publicMethods) {
                methods.add(method);
            }
            for (Method method : privateMethods) {
                methods.add(method);
            }
        } catch (NoClassDefFoundError e) {
            plugin.getLogger().severe("Plugin " + plugin.getDescription().getFullName() + " has failed to register events for " + listener.getClass() + " because " + e.getMessage() + " does not exist.");
            return ret;
        }

        for (final Method method : methods) {
            final EventHandler eh = method.getAnnotation(EventHandler.class);
            if (eh == null) continue;
            // Do not register bridge or synthetic methods to avoid event duplication
            // Fixes SPIGOT-893
            if (method.isBridge() || method.isSynthetic()) {
                continue;
            }
            final Class<?> checkClass;
            if (method.getParameterTypes().length != 1 || !Event.class.isAssignableFrom(checkClass = method.getParameterTypes()[0])) {
                plugin.getLogger().severe(plugin.getDescription().getFullName() + " attempted to register an invalid EventHandler method signature \"" + method.toGenericString() + "\" in " + listener.getClass());
                continue;
            }
            final Class<? extends Event> eventClass = checkClass.asSubclass(Event.class);
            method.setAccessible(true);
            Set<RegisteredListener> eventSet = ret.get(eventClass);
            if (eventSet == null) {
                eventSet = new HashSet<RegisteredListener>();
                ret.put(eventClass, eventSet);
            }

            for (Class<?> clazz = eventClass; Event.class.isAssignableFrom(clazz); clazz = clazz.getSuperclass()) {
                // This loop checks for extending deprecated events
                if (clazz.getAnnotation(Deprecated.class) != null) {
                    Warning warning = clazz.getAnnotation(Warning.class);
                    WarningState warningState = server.getWarningState();
                    if (!warningState.printFor(warning)) {
                        break;
                    }
                    plugin.getLogger().log(
                            Level.WARNING,
                            String.format(
                                    "\"%s\" has registered a listener for %s on method \"%s\", but the event is Deprecated. \"%s\"; please notify the authors %s.",
                                    plugin.getDescription().getFullName(),
                                    clazz.getName(),
                                    method.toGenericString(),
                                    (warning != null && warning.reason().length() != 0) ? warning.reason() : "Server performance will be affected",
                                    Arrays.toString(plugin.getDescription().getAuthors().toArray())),
                            warningState == WarningState.ON ? new AuthorNagException(null) : null);
                    break;
                }
            }

            final CustomTimingsHandler timings = new CustomTimingsHandler("Plugin: " + plugin.getDescription().getFullName() + " Event: " + listener.getClass().getName() + "::" + method.getName() + "(" + eventClass.getSimpleName() + ")", pluginParentTimer); // Spigot
            EventExecutor executor = new EventExecutor() {
                @Override
                public void execute(@NotNull Listener listener, @NotNull Event event) throws EventException {
                    try {
                        if (!eventClass.isAssignableFrom(event.getClass())) {
                            return;
                        }
                        // Spigot start
                        boolean isAsync = event.isAsynchronous();
                        if (!isAsync) timings.startTiming();
                        method.invoke(listener, event);
                        if (!isAsync) timings.stopTiming();
                        // Spigot end
                    } catch (InvocationTargetException ex) {
                        throw new EventException(ex.getCause());
                    } catch (Throwable t) {
                        throw new EventException(t);
                    }
                }
            };
            if (false) { // Spigot - RL handles useTimings check now
                eventSet.add(new TimedRegisteredListener(listener, executor, eh.priority(), plugin, eh.ignoreCancelled()));
            } else {
                eventSet.add(new RegisteredListener(listener, executor, eh.priority(), plugin, eh.ignoreCancelled()));
            }
        }
        return ret;
    }

具体

method.getParameterTypes()[0]

不适用于泛型。

Answer 1

您可以创建一个通用方法，returns 您是 BlockEventListenerObject，如下所示：

private static <T extends BlockEvent> BlockEventListener<T> getBlockEventListener(Class<T> clazz) {
        return new BlockEventListener<T>();
}

然后你可以从你的循环中调用它，

getServer().getPluginManager().registerEvents(getBlockEventListener(clazz), this);

Answer 2

„…Basically how could I get functionality like this to work…“

Here is one way…

...
public void use( final Set< Class < ? extends BlockEvent > > classes, PluginManager pluginMgr ) throws ReflectiveOperationException { 
    
    for( Class < ? extends BlockEvent > clazz : ( classes ) ){ 
        
        pluginMgr.registerEvents( new BlockListener< >( clazz.newInstance( ) ), this );
    }        
}
...

我已经实施了一些 stand-in 类以使实验可测试。我用的是实验性的类这样的……

...    
final Set< Class < ? extends BlockEvent > > classes = new HashSet< >( );
    
classes.add( BlockParty.class );

final PluginManager pluginMgr = new PluginManager( );
    
final Deduper experimental = new DeduperAnswer( );
    
experimental.use( classes, pluginMgr );
...

单击绿色 Start 按钮 at the top of the page 并观察此输出...

BlockChangeEvent [ block: Block@404b9385 ]
                          Havana Block Party!
                     EXPERIMENT SUCCESSFUL

Java 在运行时实例化泛型的反射

Java Reflection to Instantiate Generics at Runtime

java

generics

reflection

minecraft