我有一个程序，用户选择一个目录来开始FileWalk; FileWalker访问目录结构中的每个文件，并使用.class加载CLassLoader文件，因此我可以使用Reflection在GUI中显示有关该类的信息。
如果用户选择具有此结构的文件夹FileReader：
D:\Users\Ste\Documents\Eclipse Workspace\Project Tests\File Reader
│
├───+bin
│ │ ReadFile.class
|
│
└───+src
│ ReadFile.java
ClassLoader加载ReadFile.class
但是，如果我在包测试中选择了添加了类的相同目录：
D:\Users\Ste\Documents\Eclipse Workspace\Project Tests\File Reader
│
├───+bin
│ │ ReadFile.class
│ │
│ └───+Test
│ TestClass.class
│
└───+src
│ ReadFile.java
│
└───+Test
TestClass.java
Eclipse抛出java.lang.ClassNotFoundException: Test.TestClass。
那我为什么要java.lang.ClassNotFoundException？下面是我的代码，其中包含一些System.out.println()来显示一些值。 （目录结构与上面的结构相同）
public class ReflectOnClasses extends SimpleFileVisitor<Path> {
//Starts the file walk from a starting directory
public static void startFileWalk(String directory){
//The startingDir is the directory the user selects on the Main UI Part
Path startingDir = FileSystems.getDefault().getPath(directory, "");
System.out.println("Staring Directory the user selected: " + startingDir);
System.out.println("--------------------------------------------------------------------------------------------------------");
//Create an instance of my FileVisitor
ReflectOnClasses reflectOnClasses = new ReflectOnClasses();
try {
//Walk the files from my startingDir using reflectOnClasses
Files.walkFileTree(startingDir, reflectOnClasses);
} catch (IOException e) {
// TODO Auto-generated catch block
System.out.println("An Error Occured");
e.printStackTrace();
}
}
//Visit files and do something with them
@Override
public FileVisitResult visitFile(Path filesPath, BasicFileAttributes attr) {
//If we find a .class file get it and reflect upon it
if(filesPath.toString().endsWith(".class")){
//Create a File object of the files directory
File parentDir = new File(filesPath.getParent().toString());
System.out.println("Parent Directory: " + filesPath.getParent().toString());
try{
//Convert parentDir to URL
URL url = parentDir.toURL();
URL[] urls = new URL[]{url};
//Create a new class loader with the directory
ClassLoader cl = new URLClassLoader(urls);
/*
* To load a class we need the class name and the package it belongs too in the format
* "example.package.name\FooBar". We can easily get the class name by getting the name
* of filesPath and removing the .class on the end
*/
String className = filesPath.getFileName().toString().replace(".class", "");
System.out.println("The className: " + className);
//classesPackage + className
String classToLoad = getPackageName(filesPath) + className;
System.out.println("The classToLoad: " + classToLoad);
//Load in the class
Class<?> cls = cl.loadClass(classToLoad);
System.out.println("--------------------------------------------------------");
//Pass the name of the class to addClassToVariableTree in CreatUI so it can be added as a TreeItem
CreateMainUI.addClassToVariableTree(classToLoad);
//Do the same for addClassToMethodTree
CreateMainUI.addClassToMethodTree(classToLoad);
//Array of the declared fields in the class
Field[] fieldsInClass = cls.getDeclaredFields();
//For each field in fieldsInClass we add it as a TreeItem using addVariableToClassTreeItem
for( Field field: fieldsInClass){
CreateMainUI.addVariableToClassNameTreeItem(field.getGenericType().toString(), field.getName());
}
//Array of all methods in the class
Method[] methodsInClass = cls.getDeclaredMethods();
//For each method we pass through the string representation of it, the class it belongs too and it's name. It will be formatted in CreateUI
for (Method method : methodsInClass) {
CreateMainUI.addMethodToClassNameTreeItem(method.toString(), classToLoad, method.getName());
}
} catch (MalformedURLException e) {
System.out.println("URL BAD");
}
catch (ClassNotFoundException e){
System.out.println("Class couldnt be found");
e.printStackTrace();
}
}
return CONTINUE;
}
private String getPackageName(Path filesPath){
/*
* To get the package name we will have to construct it manually. If the class
* was already loaded we could get the package info using built in Java methods, but we
* haven't loaded the class yet and can't without this package information hence we will
* build a package name up be traversing back up to the bin folder adding the folder titles
* to a String Builder as we go
*/
File currentFolder = filesPath.toFile().getParentFile();
String classesPackage = "";
while(true){
if(!(currentFolder.getName().equals("bin"))){
classesPackage = currentFolder.getName() + "." + classesPackage;
currentFolder = currentFolder.getParentFile();
}
else{
break;
}
}
return classesPackage;
}
}
控制台输出：
Staring Directory the user selected: D:\Users\Ste\Documents\Eclipse Workspace\Project Tests\File Reader
----------------------------------------------------
Parent Directory: D:\Users\Ste\Documents\Eclipse Workspace\Project Tests\File Reader\bin
The className: ReadFile
The classToLoad: ReadFile
--------------------------------------------------------
Parent Directory: D:\Users\Ste\Documents\Eclipse Workspace\Project Tests\File Reader\bin\Test
The className: TestClass
The classToLoad: Test.TestClass
Class couldnt be found
java.lang.ClassNotFoundException: Test.TestClass
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
at ste.wootten.honoursproject.mainpart.reflection.ReflectOnClasses.visitFile(ReflectOnClasses.java:146)
at ste.wootten.honoursproject.mainpart.reflection.ReflectOnClasses.visitFile(ReflectOnClasses.java:1)
at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:135)
at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:199)
at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:199)
at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:199)
at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:69)
at java.nio.file.Files.walkFileTree(Files.java:2591)
at java.nio.file.Files.walkFileTree(Files.java:2624)
at ste.wootten.honoursproject.mainpart.reflection.ReflectOnClasses.startFileWalk(ReflectOnClasses.java:41)
at ste.wootten.honoursproject.mainpart.CreateMainUI.selectDirectoryAndBeginFileWalk(CreateMainUI.java:258)
at ste.wootten.honoursproject.mainpart.CreateMainUI.createInterface(CreateMainUI.java:159)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:56)
at org.eclipse.e4.core.internal.di.InjectorImpl.processAnnotated(InjectorImpl.java:859)
at org.eclipse.e4.core.internal.di.InjectorImpl.inject(InjectorImpl.java:111)
at org.eclipse.e4.core.internal.di.InjectorImpl.internalMake(InjectorImpl.java:319)
at org.eclipse.e4.core.internal.di.InjectorImpl.make(InjectorImpl.java:240)
at org.eclipse.e4.core.contexts.ContextInjectionFactory.make(ContextInjectionFactory.java:161)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.createFromBundle(ReflectionContributionFactory.java:102)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.doCreate(ReflectionContributionFactory.java:71)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.create(ReflectionContributionFactory.java:53)
at org.eclipse.e4.ui.workbench.renderers.swt.ContributedPartRenderer.createWidget(ContributedPartRenderer.java:141)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createWidget(PartRenderingEngine.java:896)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:630)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:732)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$2(PartRenderingEngine.java:703)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$7.run(PartRenderingEngine.java:697)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createGui(PartRenderingEngine.java:682)
at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer.showTab(StackRenderer.java:1114)
at org.eclipse.e4.ui.workbench.renderers.swt.LazyStackRenderer$1.handleEvent(LazyStackRenderer.java:67)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler$1.run(UIEventHandler.java:41)
at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:180)
at org.eclipse.swt.widgets.Display.syncExec(Display.java:4687)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application$1.syncExec(E4Application.java:187)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler.handleEvent(UIEventHandler.java:38)
at org.eclipse.equinox.internal.event.EventHandlerWrapper.handleEvent(EventHandlerWrapper.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:1)
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148)
at org.eclipse.equinox.internal.event.EventAdminImpl.dispatchEvent(EventAdminImpl.java:135)
at org.eclipse.equinox.internal.event.EventAdminImpl.sendEvent(EventAdminImpl.java:78)
at org.eclipse.equinox.internal.event.EventComponent.sendEvent(EventComponent.java:39)
at org.eclipse.e4.ui.services.internal.events.EventBroker.send(EventBroker.java:81)
at org.eclipse.e4.ui.internal.workbench.UIEventPublisher.notifyChanged(UIEventPublisher.java:58)
at org.eclipse.emf.common.notify.impl.BasicNotifierImpl.eNotify(BasicNotifierImpl.java:374)
at org.eclipse.e4.ui.model.application.ui.impl.ElementContainerImpl.setSelectedElement(ElementContainerImpl.java:171)
at org.eclipse.e4.ui.workbench.renderers.swt.LazyStackRenderer.postProcess(LazyStackRenderer.java:103)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:646)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:732)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$2(PartRenderingEngine.java:703)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$7.run(PartRenderingEngine.java:697)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createGui(PartRenderingEngine.java:682)
at org.eclipse.e4.ui.workbench.renderers.swt.SWTPartRenderer.processContents(SWTPartRenderer.java:59)
at org.eclipse.e4.ui.workbench.renderers.swt.PerspectiveRenderer.processContents(PerspectiveRenderer.java:59)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:642)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:732)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$2(PartRenderingEngine.java:703)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$7.run(PartRenderingEngine.java:697)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createGui(PartRenderingEngine.java:682)
at org.eclipse.e4.ui.workbench.renderers.swt.PerspectiveStackRenderer.showTab(PerspectiveStackRenderer.java:103)
at org.eclipse.e4.ui.workbench.renderers.swt.LazyStackRenderer$1.handleEvent(LazyStackRenderer.java:67)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler$1.run(UIEventHandler.java:41)
at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:180)
at org.eclipse.swt.widgets.Display.syncExec(Display.java:4687)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application$1.syncExec(E4Application.java:187)
at org.eclipse.e4.ui.services.internal.events.UIEventHandler.handleEvent(UIEventHandler.java:38)
at org.eclipse.equinox.internal.event.EventHandlerWrapper.handleEvent(EventHandlerWrapper.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:197)
at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:1)
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148)
at org.eclipse.equinox.internal.event.EventAdminImpl.dispatchEvent(EventAdminImpl.java:135)
at org.eclipse.equinox.internal.event.EventAdminImpl.sendEvent(EventAdminImpl.java:78)
at org.eclipse.equinox.internal.event.EventComponent.sendEvent(EventComponent.java:39)
at org.eclipse.e4.ui.services.internal.events.EventBroker.send(EventBroker.java:81)
at org.eclipse.e4.ui.internal.workbench.UIEventPublisher.notifyChanged(UIEventPublisher.java:58)
at org.eclipse.emf.common.notify.impl.BasicNotifierImpl.eNotify(BasicNotifierImpl.java:374)
at org.eclipse.e4.ui.model.application.ui.advanced.impl.PerspectiveStackImpl.setSelectedElement(PerspectiveStackImpl.java:135)
at org.eclipse.e4.ui.model.application.ui.advanced.impl.PerspectiveStackImpl.setSelectedElement(PerspectiveStackImpl.java:1)
at org.eclipse.e4.ui.workbench.renderers.swt.LazyStackRenderer.postProcess(LazyStackRenderer.java:103)
at org.eclipse.e4.ui.workbench.renderers.swt.PerspectiveStackRenderer.postProcess(PerspectiveStackRenderer.java:77)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:646)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:732)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$2(PartRenderingEngine.java:703)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$7.run(PartRenderingEngine.java:697)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createGui(PartRenderingEngine.java:682)
at org.eclipse.e4.ui.workbench.renderers.swt.SWTPartRenderer.processContents(SWTPartRenderer.java:59)
at org.eclipse.e4.ui.workbench.renderers.swt.WBWRenderer.processContents(WBWRenderer.java:639)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:642)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:732)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$2(PartRenderingEngine.java:703)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$7.run(PartRenderingEngine.java:697)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createGui(PartRenderingEngine.java:682)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:964)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:923)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:86)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application.start(E4Application.java:150)
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:353)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
at org.eclipse.equinox.launcher.Main.run(Main.java:1438)
at org.eclipse.equinox.launcher.Main.main(Main.java:1414)
正如您所见，它找到ReadFile.class并加载正常，但当我想加载Test.TestClass时，它会显示ClassNotFoundException。任何想法??
答案 0 :(得分：1)
当你走TestFile.class
File parentDir = new File(filesPath.getParent().toString());
System.out.println("Parent Directory: " + filesPath.getParent().toString());
在此之后，您有parentDir = "D:\Users\Ste\Documents\Eclipse Workspace\Project Tests\File Reader\bin\Test"
URL url = parentDir.toURL();
URL[] urls = new URL[]{url};
//Create a new class loader with the directory
ClassLoader cl = new URLClassLoader(urls);
在此之后，您的类加载器搜索目录为file:///D:/Users/Ste.../bin/Test，这是不正确的（此处没有/Test/TestClass.class来匹配已编译的Test.TestClass）
在这种情况下，您应该从startingDir + "/bin"创建类加载器，而不是从parentDir创建。
如果您需要帮助来了解正在发生的事情，这是一个非常基本的Java Package Tutorial。