eclipse rcp：类加载问题

Question

我有依赖于插件 B 的插件 A，我正在尝试从插件 A 加载插件 B 中定义的类。我确信该类在导出的包中。但是我得到了 ClassNotFoundException，我错过了什么吗？

page = (IPage) Class.forName(pageClass).newInstance();

错误信息：

java.lang.ClassNotFoundException: amarsoft.dbmp.credit.web.dataobject.DOListPage
    at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:513)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:429)
    at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:417)
    at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:169)
    at amarsoft.rcp.base.widgets.DefaultPageRegistry.findPage(DefaultPageRegistry.java:27)
    at amarsoft.rcp.base.widgets.AbstractPageControler.showPage(AbstractPageControler.java:27)
    at amarsoft.rcp.base.widgets.AbstractPageControler.showPage(AbstractPageControler.java:37)
    at amarsoft.dbmp.function.ui.FunctionListPage$3.linkActivated(FunctionListPage.java:261)
    at org.eclipse.ui.forms.widgets.AbstractHyperlink.handleActivate(AbstractHyperlink.java:233)
    at org.eclipse.ui.forms.widgets.AbstractHyperlink.handleMouseUp(AbstractHyperlink.java:327)
    at org.eclipse.ui.forms.widgets.AbstractHyperlink.access$2(AbstractHyperlink.java:311)
    at org.eclipse.ui.forms.widgets.AbstractHyperlink$4.handleEvent(AbstractHyperlink.java:125)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4165)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3754)
    at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2696)
    at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2660)
    at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2494)
    at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:674)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:667)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
    at amarsoft.adt.rcp.ADTApplication.start(ADTApplication.java:29)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:344)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:622)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:577)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1410)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1386)

Answer 1

如果您需要捆绑包；来自 pluginA 的 pluginB，然后一个 Class.forName(*) 应该可以工作。虽然我会指出使用PageClass class = new PageClass(); 也可以。当您可以直接依赖该类时，为什么还要尝试使用反射？

对于您提供其他插件应该通过提供实现来扩展的框架行为的常见模式，eclipse 提供了扩展点/扩展的概念。

插件 A 将提供一个扩展点。插件 B 将列出该扩展点的扩展，并提供一个实现类。在这种情况下，插件 B 需要插件 A，而不是相反。

然后插件 A 使用 org.eclipse.core.runtime.IExtensionRegistry.getConfigurationElementsFor(String) 读取所有贡献的扩展，并使用 org.eclipse.core.runtime.IConfigurationElement.createExecutableExtension(String) 实例化贡献的实现（注册表负责确保可以实例化类）。