安装两个Eclipse版本后Juno无法查看外部类方法

这是典型的类加载器约束冲突问题，根源在于你同时安装的Eclipse Juno和Mars版本，两者的插件依赖（尤其是Eclipse Recommenders与Guava库）版本不兼容，导致Juno的类加载器加载了冲突的类文件。下面是具体的解决方案：

一、快速修复步骤 #

1. 清理Juno插件缓存 #

关闭Juno，找到你的Juno安装目录下的configuration/org.eclipse.osgi文件夹，删除该文件夹内的所有文件和子文件夹（不要删除org.eclipse.osgi文件夹本身）。这个目录存储着Eclipse插件的缓存，清理后Juno会重新加载适配自身版本的插件。

2. 重置工作区元数据 #

先备份Juno工作区中的.metadata文件夹（它存储了工作区的配置和插件状态），然后删除整个.metadata文件夹。重启Juno时，它会自动重建干净的工作区元数据，避免Mars遗留的配置干扰。

3. 卸载Juno中冲突的插件 #

打开Juno，依次进入Help > About Eclipse > Installation Details，在「Installed Software」标签页中找到所有包含Eclipse Recommenders的插件，点击「Uninstall」按钮卸载它们，之后重启Juno。Mars版本的Recommenders插件依赖的Guava库版本和Juno不兼容，这是引发LinkageError的核心原因。

4. 使用独立的配置与工作区 #

为彻底避免两个Eclipse版本互相干扰，启动Juno时可通过命令行参数指定独立的工作区和配置目录：

# 指定独立工作区
eclipse.exe -data D:\Juno_Exclusive_Workspace
# 同时指定独立配置目录
eclipse.exe -data D:\Juno_Exclusive_Workspace -configuration D:\Juno_Exclusive_Config

二、问题根源解释 #

从你提供的日志能看到，错误发生在org.eclipse.recommenders相关类的调用中：

!ENTRY org.eclipse.core.jobs 4 2 2018-05-17 11:04:06.864
!MESSAGE An internal error occurred during: "".
!STACK 0
java.lang.LinkageError: loader constraint violation: when resolving method "org.eclipse.recommenders.utils.rcp.JdtUtils.getLocation(Lorg/eclipse/jdt/core/IPackageFragmentRoot;)Lcom/google/common/base/Optional;"
the class loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) of the current class, org/eclipse/recommenders/internal/rcp/providers/ClasspathEntryInfoProvider,
and the class loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) for resolved class, org/eclipse/recommenders/utils/rcp/JdtUtils,
have different Class objects for the type ipse/jdt/core/IPackageFragmentRoot;)Lcom/google/common/base/Optional; used in the signature
at org.eclipse.recommenders.internal.rcp.providers.ClasspathEntryInfoProvider.mapSourcePluginProjects(ClasspathEntryInfoProvider.java:220)
at org.eclipse.recommenders.internal.rcp.providers.ClasspathEntryInfoProvider.onEvent(ClasspathEntryInfoProvider.java:172)
at org.eclipse.recommenders.internal.rcp.providers.ClasspathEntryInfoProvider.scanOpenProjects(ClasspathEntryInfoProvider.java:132)
at org.eclipse.recommenders.internal.rcp.providers.ClasspathEntryInfoProvider.access$1(ClasspathEntryInfoProvider.java:128)
at org.eclipse.recommenders.internal.rcp.providers.ClasspathEntryInfoProvider$1.run(ClasspathEntryInfoProvider.java:105)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
!ENTRY org.eclipse.e4.ui.workbench 4 0 2018-05-17 11:04:07.488
!MESSAGE 
!STACK 0
org.eclipse.e4.core.di.InjectionException: java.lang.LinkageError: loader constraint violation: when resolving method "org.eclipse.recommenders.utils.rcp.JdtUtils.createUnresolvedType(Lorg/eclipse/jdt/internal/compiler/lookup/TypeBinding;)Lcom/google/common/base/Optional;"
the class loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) of the current class, org/eclipse/recommenders/internal/completion/rcp/BaseRecommendersCompletionContext,
and the class loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) for resolved class, org/eclipse/recommenders/utils/rcp/JdtUtils,
have different Class objects for the type (Lorg/eclipse/jdt/internal/compiler/lookup/TypeBinding;)Lcom/google/common/base/Optional; used in the signature
at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:63)
at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:231)
at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:212)
at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:131)
at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:171)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.executeCommand(KeyBindingDispatcher.java:277)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.press(KeyBindingDispatcher.java:496)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.processKeyEvent(KeyBindingDispatcher.java:547)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.filterKeySequenceBindings(KeyBindingDispatcher.java:368)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.access$0(KeyBindingDispatcher.java:314)
at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher$KeyDownFilter.handleEvent(KeyBindingDispatcher.java:83)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1262)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1052)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1077)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1062)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1104)
at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1100)
at org.eclipse.swt.widgets.Widget.wmChar(Widget.java:1521)
at org.eclipse.swt.widgets.Control.WM_CHAR(Control.java:4640)
at org.eclipse.swt.widgets.Canvas.WM_CHAR(Canvas.java:345)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4528)
at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:341)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:4976)
at org.eclipse.swt.internal.win32.OS.DispatchMessageW(Native Method)
at org.eclipse.swt.internal.win32.OS.DispatchMessage(OS.java:2546)
at org.eclip

核心冲突点是com.google.common.base.Optional类——Mars版本的Recommenders插件依赖的Guava库版本和Juno不匹配，当两个Eclipse版本共享配置或工作区时，Juno的类加载器会加载到Mars版本的Guava类，导致类型不匹配，最终触发LinkageError。

内容的提问来源于stack exchange，提问作者wmgeiger101x