以下是run方法的完整代码。

Question

我已运行应用程序在netbeans项目中加载名为ChocolateMilk.java的类名，我想使用JFileChooser调用此类，然后使用ClassLoader加载它。

这里是获取主类内部文件名的方法的代码。

public static String getTheFileName() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception ex) {
            System.err.println("Error " + ex.getMessage());
        }
        JFileChooser jfc = new  JFileChooser();
        jfc.setFileSelectionMode(fc.FILES_ONLY);
        jfc.setCurrentDirectory(new File(System.getProperty("user.dir") + File.separator + "build"+ File.separator + "classes"));
        jfc.showOpenDialog(null);
        File myfile ;

String fileNameWithOutExt = jfc.getName((myfile = jfc.getSelectedFile()));
        int pos = fileNameWithOutExt.lastIndexOf(".");
        if (pos > 0) {
            fileNameWithOutExt = fileNameWithOutExt.substring(0, pos);
        }
FilenameUtils.removeExtension(jfc.getName((myfile = jfc.getSelectedFile())));

        System.out.println("the program name is " +fileNameWithOutExt);
        return fileNameWithOutExt;
 }

我将getTheFileName方法作为foodProcessorEnvironmentA Class中运行方法的参数调用。

foodProcessorEnvironmentA.run(getTheFileName());

以下是run方法的完整代码。

public void run(String programName) {
                URLClassLoader classLoader ;
    // the class path is a string that inside foodProcessorEnvironmentA class as URL instance variable 


  classLoader = new URLClassLoader(classPath);
            Class prgramClass = null;

            try {
                prgramClass = classLoader.loadClass(programName);
            } catch (ClassNotFoundException ex) {
                Logger.getLogger(FoodProcessorEnvironmentA.class.getName()).log(Level.SEVERE, null, ex);
            }
            AbstractFoodProcessorProgram program = null;
            try {
                program = (AbstractFoodProcessorProgram) prgramClass.newInstance();
            } catch (InstantiationException ex) {
                Logger.getLogger(FoodProcessorEnvironmentA.class.getName()).log(Level.SEVERE, null, ex);
            } catch (IllegalAccessException ex) {
                Logger.getLogger(FoodProcessorEnvironmentA.class.getName()).log(Level.SEVERE, null, ex);
            }

            program.setEnvironment(this);

            program.start();

    //        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
        }

==========================

这是运行项目后的输出。

=============================

The fileName is: file:/Users/****/Desktop/FoodProcessor/build/classes/foodprocessor/
the program name is ChocolateMilk
Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: ChocolateMilk (wrong name: foodprocessor/ChocolateMilk)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:455)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:367)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at foodprocessor.FoodProcessorEnvironmentA.run(FoodProcessorEnvironmentA.java:31)
    at foodprocessor.FoodProcessor$1.run(FoodProcessor.java:191)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:744)
    at java.awt.EventQueue.access$400(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:697)
    at java.awt.EventQueue$3.run(EventQueue.java:691)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:714)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

===========

我希望我的问题很明确。谢谢。

Answer 1

您必须以与包括包的完全限定类名相对应的形式向Class.forName()提供文件名。在这种情况下，foodprocessor.ChocolateMilk.您需要知道包结构的头部在文件系统中的位置;将其用作提供给URLClassLoader;的网址，然后调用loadClass("foodprocessor.ChocolateMilk")。

Answer 2

我通过将包名称的字符串与dot和programName变量串联来解决问题。

这里

prgramClass = classLoader.loadClass("foodprocessor."+programName);

就是这样！

java.lang.NoClassDefFoundError :(错误的名字）

以下是run方法的完整代码。

2 个答案: