Eclipse 4.x中Command是如何映射到Handler的

1. Eclipse中的Command模式，使得具体的实现和Command定义分离，便于维护。

但是在Debug的时候，或者没有souce code的时候，我们想知道每一个commandId对应的Handler是什么，怎么办？

2. 在Eclipse 4.x中，其实当Eclipse启动完成后，它已经创建了commandId和对应Handler的Map，保存在EclipseContext中，

然后通过反射调用到对应的Handler。 见下图：

Eclipse是在上图中我框出来的地方，通过commandId在EclipseContext中查找到。

3. 如何将EclipseContext中的Handler都dump出来呢？

一句话，反射。

注意，以下代码我只在Eclipse 4.3.0上测试通过。

//try to print all handler in eclipse 4.xresult = ReflectionUtils.getField("e4Context", site);if(!isSuccess(result)) {return;}if(result instanceof IEclipseContext) {IEclipseContext context = (IEclipseContext)result;printHandlerForEclipseContext(context, 0);}

@SuppressWarnings("unchecked")private void printHandlerForEclipseContext(IEclipseContext context, int step) {Assert.isNotNull(context);Object result = null;if(step != 0) {result = ReflectionUtils.getField("localValueComputations", context);} else {result = ReflectionUtils.getField("localValues", context);}if(!isSuccess(result)) {return;}if(result instanceof Map) {String stepString = makeStep(step);Map<String, Object> localValueComputations = (Map<String, Object>)result;for (String string : localValueComputations.keySet()) {Object object = localValueComputations.get(string);String last = object.toString();if(string.startsWith("legacy::handler::")) {if(object instanceof ArrayList) {ArrayList list = (ArrayList)object;//TODO may be more than one item in listobject = list.get(0);if(object instanceof IHandlerActivation) {IHandlerActivation activation = (IHandlerActivation)object;last = activation.getHandler().toString();}}}System.out.println(stepString + string + ", " + last);}}result = null;result = ReflectionUtils.invokeMethod(context, "getChildren");if(!isSuccess(result)) {return;}if(result instanceof Set) {Set<IEclipseContext> children = (Set<IEclipseContext>)result;Iterator<IEclipseContext> iterator = children.iterator();IEclipseContext child = null;int moreStep = step + 1;while(iterator.hasNext()) {child = iterator.next();printHandlerForEclipseContext(child, moreStep);}step ++;}}

以下是我的屏幕输出的一部分,输出格式为：commandId, Handler

...

legacy::handler::org.eclipse.ui.edit.text.recenter, ActionHandler(org.eclipse.ui.texteditor.RecenterAction@7efaa9e2)
legacy::handler::org.eclipse.jdt.ui.edit.text.java.search.declarations.in.hierarchy, ActionHandler(org.eclipse.jdt.ui.actions.FindDeclarationsInHierarchyAction@14c26e4a)
legacy::handler::org.eclipse.jdt.ui.edit.text.java.search.declarations.in.project, ActionHandler(org.eclipse.jdt.ui.actions.FindDeclarationsInProjectAction@174043f5)
legacy::handler::org.eclipse.jdt.ui.edit.text.java.surround.with.try.multicatch, ActionHandler(org.eclipse.jdt.ui.actions.SurroundWithTryMultiCatchAction@49e3c996)
legacy::handler::org.eclipse.jdt.ui.edit.text.java.override.methods, ActionHandler(org.eclipse.jdt.ui.actions.OverrideMethodsAction@11e18e8c)
legacy::handler::org.eclipse.ui.edit.findPrevious, ActionHandler(org.eclipse.ui.texteditor.FindNextAction@69d5ee81)
handler::org.eclipse.jdt.ui.edit.text.java.remove.block.comment, org.eclipse.ui.internal.handlers.LegacyHandlerService$HandlerSelectionFunction@207462c0

...