如何解决Java反射可在运行时实例化泛型
我正在尝试将我的应用程序与Bukkit - A Minecraft Server API集成。
基本上，我试图弄清楚如何使这种功能起作用：
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的所有事件类型注册一个侦听器。通过将实现Listener传递到Bukkit API的registerEvents(Listener,Plugin)公开的PluginManager方法中来注册事件。显然clazz不是一种类型，因此不能如此使用。
这是通用类：
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,eh.ignoreCancelled()));
}
}
return ret;
}
特别是
method.getParameterTypes()[0]
不适用于泛型。
解决方法
您可以创建一个通用方法来返回BlockEventListenerObject，如下所示：
private static <T extends BlockEvent> BlockEventListener<T> getBlockEventListener(Class<T> clazz) {
return new BlockEventListener<T>();
}
然后您可以从循环中调用它，
getServer().getPluginManager().registerEvents(getBlockEventListener(clazz),this);
„ ...基本上，我如何才能获得像这样的功能……”
...
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 );
}
}
...
我已经实现了一些替身类，以使实验可测试。我使用了像这样的实验课……
...
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 );
...
点击绿色的 开始 按钮at the top of the page并观察此输出…
BlockChangeEvent [ block: Block@404b9385 ]
Havana Block Party!
EXPERIMENT SUCCESSFUL
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