java - 动态链接 : Class not visible to ClassLoader, 但我已经尝试过每一个？

Question

抱歉，代码有点多，但到目前为止还相当简单。

因此，我尝试在类被修改和编译时即时执行动态类重新加载。我创建了一个与 WatchDir 示例类似的 JavaSystemCompiler 类，只不过每次保存 .java 文件时它只编译一次。我还创建了一个 JavaSystemClassLoader 应用程序，它执行加载项目目录中所有类的任务，无论包如何(它尚未处理 jar)，以及 ClassLoader 类 (JSCL_2.java)，以便实际执行加载和重新加载。一切正常，直到我尝试使用代理动态链接新类(在本例中为 RunContinually.java 和 RunContinuallyI.java)。我收到的错误是:

线程“main”中的异常 java.lang.IllegalArgumentException:类 RunContinuallyImpl 在类加载器中不可见

我已经尝试了以下四种组合:

JavaSystemClassLoader.class.getClassLoader().getParent();
JavaSystemClassLoader.class.getClassLoader();
JSCL_2.class.getClassLoader();
and 
JavaSystemClassLoader.class.getClassLoader().getSystemClassLoader();

它们都不起作用。下面列出了可编译的 .java 文件:

public interface RunContinuallyI {

    public abstract void printHobby();
}

public class RunContinuallyImpl extends Thread implements RunContinuallyI {
    public static int runNum = 0;

    public RunContinuallyImpl() {

    }

    public void run() {
        while(true) {
            printHobby();
            try { 
                sleep(5000);
            } catch (InterruptedException ie) {

            }
        }
    }

    public void printHobby() {
        System.out.println(++runNum + ": Compiling");
    }

    public static void main(String[] args) {
        new RunContinuallyImpl().start();
    }

}  

import ca.tecreations.Global;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
import java.util.Iterator;
import java.util.stream.Collectors;
import org.apache.commons.io.*;
/**
 *
 * @author Tim, with starter source from Advanced Java Class Tutorial: A Guide to Class Reloading
 * 
 * https://www.toptal.com/java/java-wizardry-101-a-guide-to-java-class-reloading
 * 
 */
public class JSCL_2 extends ClassLoader {
    private static final String className = JSCL_2.class.getName();
    ClassLoader parent;
    JSCL_2 loader;
    Class<?> _class;
    byte[] data;

    public JSCL_2(ClassLoader parent) {
        super(parent);
        this.parent = parent;
        loader = this;
//        System.out.println("Parent           : " + parent.getParent());
//        System.out.println("ParentClassLoader: " + parent.toString());
    }

    public Class<?> loadClass(String name) {
        if (name.startsWith("java.") | name.startsWith("javax.")) {
            try {
                return parent.loadClass(name);
            } catch (ClassNotFoundException cnfe) {
                System.out.println("Class Not Found: " + name);
            } 
        } else {
            String path = Global.getProjectPath() + name.replace(".",File.separator) + ".class";
            //System.out.println("" + className + ".loadClass : " + path + "," + name);
            data = loadClassData(path);
            if (data != null) {
                try {
                    _class = defineClass(name, data, 0, data.length);
                    resolveClass(_class);
                    return _class;
                } catch (Error e) {
                    System.out.println("Error while resolving: " + name);
                    e.printStackTrace();
                } 
            }
        }
        return null; 
    }

    public Class<?> reload(String path, String name) {
        try { 
            new Thread().sleep(2500); 
        } catch (InterruptedException ie) {
            System.out.println("Interrupted.");
        }       
        System.out.println("" + className + ".reload: " + name);
        data = loadClassData(path); 
        if (data != null) { 
            try {   
                _class = defineClass(name, data, 0, data.length);
                resolveClass(_class); 
                // is this where you use the proxy????
                // or is it better off in JavaSystemClassLoader.java?

                return _class;
            } catch (Error e) {
                System.out.println("Error: " + e.toString());
            } 
        }  
        return null;
    }  

    protected byte[] loadClassData(String path) {
        FileInputStream in = null;
        try {
            in = new FileInputStream(path);
        } catch (FileNotFoundException fnfe) {
            // So using this package, that shouldn't happend, but anyway
            System.out.println(className + ".loadClassData: File not found: " + path);
        }
        // okay, so load the class
        byte[] data = null;
        try { 
            data = IOUtils.toByteArray(in);
            in.close();
        } catch (IOException ioe) {
            System.err.println("IOException: reading class data.");
        }
        return data;
    }
}

import ca.tecreations.*;
import java.awt.BorderLayout;
import java.awt.event.*;
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.LinkOption.*;
import java.io.*;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import java.util.*;
import java.util.stream.Collectors;
import javax.swing.*;

public class JavaSystemClassLoader extends TFrame implements ActionListener {
    boolean _switch = true; // start with true, switch off, then on
    public static final String className = JavaSystemClassLoader.class.getName();
    public static final long buildNumber = 0L; 
    String classpath;
    DefaultListModel<String> model = new DefaultListModel<>();
    JList<String> list = new JList<String>(model);
    JButton clear = new JButton("Clear");
    private WatchService watcher = null;
    private Map<WatchKey,Path> keys = null;
    private boolean trace = false;
    boolean debugDirs = false; 
    List<String> loadedClasses = new ArrayList<String>();
    List<JSCL_2> loaders = new ArrayList<JSCL_2>();
    List<String> unavaiClasses = new ArrayList<String>();
    private ClassLoader parent = JavaSystemClassLoader.class.getClassLoader();


    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>)event;
    }

    /**
     * Register the given directory with the WatchService
     */
    private void register(Path dir) {
        WatchKey key = null;
        loadDir(dir.toAbsolutePath().toString());
        try {
            key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
        } catch (IOException ioe) {
            if (trace) System.err.println("Skipping: " + dir.toString());
        }
        if (key != null) {
            Path prev = keys.get(key);
            if (prev == null) {
                if (trace) System.out.format("register: %s\n", dir);
            } else {
                if (!dir.equals(prev)) {
                    if (trace) System.out.format("update: %s -> %s\n", prev, dir);
                    //model.addElement("dir.rename: " + prev + "," + dir);
                }
            }
            keys.put(key, dir);
        } 
    }

    /**
     * Register the given directory, and all its sub-directories, with the
     * WatchService.
     */
    private void registerAll(final Path start) {
        // register directory and sub-directories
        File[] roots = start.toFile().listFiles();
        if (roots != null) {
            for(int i = 0; i < roots.length;i++) {
                // exclude the one's giving errors

                // watch, this happens on windows 7 at least,
                if (roots[i].isDirectory()) { 
                    if (
                       !roots[i].getAbsolutePath().toLowerCase().endsWith("config.msi") &&
                    // now, i like comments in between, so
                       !roots[i].getAbsolutePath().equals("/System/Library/DirectoryServices/DefaultLocalDB/Default")  
                    ) {
                        //so we excluded those, now
                        register(Paths.get(roots[i].getAbsolutePath()));
                        registerAll(Paths.get(roots[i].getAbsolutePath()));
                        //model.addElement(roots[i].getAbsolutePath());
                    }
                }
            }
        }
    }

    /**
     * Creates a WatchService and registers the given directory
     */
    public JavaSystemClassLoader(String classpath) {
        super(className);
        this.classpath = classpath;
        setTitle("Java System Class Loader");
        try {
            watcher = FileSystems.getDefault().newWatchService();
            keys = new HashMap<WatchKey,Path>();
        } catch (IOException ioe) {
            System.out.println("IOE: " + ioe);
        }
        if (getStorage().wasCreated()) {
            setSize(640,480);
            setLocationRelativeTo(null);
        }
        add(new JScrollPane(list, 
                            JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
                            JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS),BorderLayout.CENTER);
        JPanel panel = new JPanel();
        panel.add(clear);
        add(panel,BorderLayout.SOUTH);
        clear.addActionListener(this);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource().equals(clear)) {
            model.removeAllElements();
        }        
    }

    public void windowClosing(WindowEvent e) {
        super.windowClosing(e);
        System.exit(0);
    }

    /**
     * Process all events for keys queued to the watcher
     */
    void processEvents() {
        for (;;) {

            // wait for key to be signalled
            WatchKey key;
            try {
                key = watcher.take();
            } catch (InterruptedException x) {
                return;
            }

            Path dir = keys.get(key);
            if (dir == null) {
                System.err.println("WatchKey not recognized!!: " + key.toString());
                continue;
            }

            for (WatchEvent<?> event: key.pollEvents()) {
                WatchEvent.Kind kind = event.kind();

                if (kind == OVERFLOW) {
                    System.out.println(className + ": KEY: OVERFLOW");
                    continue;
                }

                // Context for directory entry event is the file name of entry
                WatchEvent<Path> ev = cast(event);
                Path name = ev.context();
                Path child = dir.resolve(name);

                // print out event
                //if (child.toString().toLowerCase().endsWith(".class")) {
                //    System.out.format("%s: %s\n", event.kind().name(), child);
                //}

                // if directory is created, and watching recursively, then
                // register it and its sub-directories 
                if (kind == ENTRY_CREATE) {
                    if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                        registerAll(child);
                    }
                }
                // on create compile. if .java
                if (event.kind().name().equals("ENTRY_CREATE")) {
                    if (Files.isDirectory(child,NOFOLLOW_LINKS)) {
                        //if (debugDirs) model.addElement("dir.create: " + child + File.separator);
                    } else { 
                        if (_switch && child.toAbsolutePath().toString().toLowerCase().endsWith(".class")) {
                            //model.addElement("file.create: " + child);
                            //model.addElement("Load   : " + child.toString());
                            //System.out.println("Load  : " + child.toString());
                            String className = getClassNameFromClassFilename(Global.getProjectPath(),child.toAbsolutePath().toString());
                            //model.addElement("Class  : " + className);
                            load(child.toString(),className);
                        }    
                    }    
                } else if (event.kind().name().equals("ENTRY_DELETE")) {
                    if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                        //model.addElement("dir.delete: " + child + File.separator);
                    } else {
                        if (_switch && child.toString().endsWith(".class")) {
                            System.out.println("Deleted: " + child.toString());
                        }
                    }  
                } else if (event.kind().name().equals("ENTRY_MODIFY")) {
                    if (Files.isDirectory(child,NOFOLLOW_LINKS)) {
                        //model.addElement("dir.modify: " + child);
                    } else {
                        if (_switch && child.toString().toLowerCase().endsWith(".class")) {
                            //model.addElement("Reload: " + child.toString());
                            System.out.println("Reload: " + child.toString());
                            reload(child.toAbsolutePath().toString());       
                        } 
                    }
                } 
                int lastIndex = list.getModel().getSize() - 1;
                if (lastIndex >= 0) {
                    list.ensureIndexIsVisible(lastIndex);
                }

                // reset key and remove from set if directory no longer accessible
            }
            boolean valid = key.reset(); 
            if (!valid) {
                keys.remove(key);
                // all directories are inaccessible
                if (keys.isEmpty()) {
                    break;
                }
            }
            _switch = !_switch; 
        }
    } 

    public String getClassNameFromClassFilename(String classPath, String classFilename) {
        String target = "";
        if (classPath.endsWith(File.separator)) target = classFilename.substring(classPath.length());
        else target = classFilename.substring(classPath.length() + 1);
        target = target.substring(0,target.length() - 6); // remove .class
        target = target.replace(File.separatorChar,'.'); // form filename to class name
        return target;        
    }                                 

    public void printLoaded() {
        java.util.List<String> loaded = loadedClasses.stream().sorted().collect(Collectors.toList());
        for(int i = 0; i < loaded.size();i++) {
            System.out.println("Loaded     : " + loaded.get(i));
        }
    }

    public void printUnavailable() {
        java.util.List<String> unavailable = unavaiClasses.stream().sorted().collect(Collectors.toList());
        for(int i = 0; i < unavailable.size();i++) {
            System.out.println("Unavailable: " + unavailable.get(i));
        }
    }

    public static void main(String[] args) {
        // parse arguments
        //if (args.length == 0 || args.length > 2)
        //    usage();
        JavaSystemClassLoader loader = null;
        loader = new JavaSystemClassLoader(Global.getProjectPath());
        long start =  Runtime.getRuntime().freeMemory();
        loader.register(Paths.get(Global.getProjectPath()));
        loader.registerAll(Paths.get(Global.getProjectPath()));
        loader.printLoaded();
        loader.printUnavailable();
        long finished = Runtime.getRuntime().freeMemory();
        long total = start - finished;
        System.out.println("Memory Consumed: " + getMB(total));
        new RunContinuallyImpl().start();
        loader.processEvents();  
    }  

    public static String getMB(long total) {
        int megabytes = (int)(total / (1000 * 1000));
        return (megabytes + " MB");
    }

    public void loadDir(String path) {
        File[] f = new File(path).listFiles();
        for(int i = 0; i < f.length;i++) {
            if (f[i].isFile() && f[i].getAbsolutePath().toLowerCase().endsWith(".class")) {
                load(f[i].getAbsolutePath(),getClassNameFromClassFilename(Global.getProjectPath(),f[i].getAbsolutePath()));
            }
        }
    }  

    public void load(String fileName, String name) {
        //System.out.println(className + ".load  : " + fileName + " : " + name);
        //try {
        //    Class<?> cls = Class.forName(className);
        //} catch (ClassNotFoundException cnfe) {
        //    System.err.println("load  : Class not found: " + className);
        //}

        JSCL_2 loader = new JSCL_2(parent);
        Class<?> _class = null;
        _class = loader.loadClass(name);
        if (_class == null) {
            model.addElement("Load  : null: " + fileName + " , " + name);
            unavaiClasses.add(name);
        } else {
            loadedClasses.add(name);
            loaders.add(loader);
        }
    } 

    public void reload(String fileName) {
        String name = getClassNameFromClassFilename(Global.getProjectPath(),fileName);
        JSCL_2 loader = new JSCL_2(parent);
        Class<?> _class = loader.reload(fileName,name);
        if (_class == null) {
            model.addElement("Reload: null: " + fileName + " , " + name);
            // couldn't/wouldn't do it....


        } else {
            int found = unavaiClasses.indexOf(name);
            if (found == -1) {
                int index = loadedClasses.indexOf(name);
                loaders.set(index, loader);
                model.addElement("Reloaded: " + name); 

                // so is this where I need the proxy?
                InvocationHandler handler = new DynaCodeInvocationHandler(loader);
                Class<?> proxy = (Class<?>) Proxy.newProxyInstance(parent, new Class[] { _class}, handler);
            } else {
                System.err.println("This change necessitates an application restart.");
            }
        } 

    }   
} 

import ca.tecreations.Global;
//import ca.tecreations.apps.viewer.FileViewer;
import java.awt.*;
import java.awt.event.*;
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.LinkOption.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
/**
 * Example to watch a directory (or tree) for changes to files.
 * 
 */

public class JavaSystemCompiler extends TFrame implements ActionListener {
    private static boolean _switch = true; // start at true, switch off, then on.
    public static final String className = "JavaSystemCompiler";
    String classpath;
    DefaultListModel<String> model = new DefaultListModel<>();
    JList<String> list = new JList<String>(model);
    JButton view = new JButton("View");
    JButton clear = new JButton("Clear");
    private WatchService watcher = null;
    private Map<WatchKey,Path> keys = null;
    private boolean trace = true;
    boolean debugDirs = false; 

    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>)event;
    }

    /**
     * Register the given directory with the WatchService
     */
    private void register(Path dir) {
        WatchKey key = null;
        try {
            key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
        } catch (IOException ioe) {
            System.err.println("Skipping: " + dir.toString());
        }
        if (key != null) {
            Path prev = keys.get(key);
            if (prev == null) {
                System.out.format("register: %s\n", dir);
            } else {
                if (!dir.equals(prev)) {
                    System.out.format("update: %s -> %s\n", prev, dir);
                    //model.addElement("dir.rename: " + prev + "," + dir);
                }
            }
            keys.put(key, dir);
        } 
    }

    /**
     * Register the given directory, and all its sub-directories, with the
     * WatchService.
     */
    private void registerAll(final Path start) {
        // register directory and sub-directories
        File[] roots = start.toFile().listFiles();
        if (roots != null) {
            for(int i = 0; i < roots.length;i++) {
                // exclude the one's giving errors

                // watch, this happens on windows 7 at least,
                if (roots[i].isDirectory()) { 
                    if (
                       !roots[i].getAbsolutePath().toLowerCase().endsWith("config.msi") &&
                    // now, i like comments in between, so
                       !roots[i].getAbsolutePath().equals("/System/Library/DirectoryServices/DefaultLocalDB/Default")  
                    ) {
                    //so we excluded that one, now
                        register(Paths.get(roots[i].getAbsolutePath()));
                        registerAll(Paths.get(roots[i].getAbsolutePath()));
                        //model.addElement(roots[i].getAbsolutePath());
                    }
                }
            }
        }
    } 

    /**
     * Creates a WatchService and registers the given directory
     */
    public JavaSystemCompiler(String classpath) {
        super(className);
        this.classpath = classpath;
        setTitle("Java System Compiler");
        try { 
            watcher = FileSystems.getDefault().newWatchService();
            keys = new HashMap<WatchKey,Path>();
        } catch (IOException ioe) {
            System.out.println("IOE: " + ioe);
        }

        // enable trace after initial registration
        this.trace = true;
        if (getStorage().wasCreated()) {
            setSize(640,480);
            setLocationRelativeTo(null);
        }
        add(new JScrollPane(list, 
                            JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
                            JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS),BorderLayout.CENTER);
        JPanel panel = new JPanel();
        panel.add(clear);
        panel.add(view);
        add(panel,BorderLayout.SOUTH);
        clear.addActionListener(this);
        view.addActionListener(this);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource().equals(clear)) {
            model.removeAllElements();
        } else if (e.getSource().equals(view)) {
            String s = list.getSelectedValue();
            String filename = s.substring(s.indexOf(":") + 1).trim();
            if (s.startsWith("file")) {
//                if (new File(filename).exists()) new FileViewer(filename);
            }
        }        
    }

    public void windowClosing(WindowEvent e) {
        super.windowClosing(e);
        System.exit(0);
    }

    /**
     * Process all events for keys queued to the watcher
     */
    void processEvents() {
        WatchKey key;
        for (;;) {
            // wait for key to be signalled
            try {
                key = watcher.take();
            } catch (InterruptedException x) {
                return;
            }

            Path dir = keys.get(key);
            if (dir == null) {
                System.err.println("WatchKey not recognized!!: " + key.toString());
                continue;
            }

            for (WatchEvent<?> event: key.pollEvents()) {
                WatchEvent.Kind kind = event.kind();

                if (kind == OVERFLOW) {
                    System.out.println(className + ": KEY: OVERFLOW");
                    continue;
                }

                // Context for directory entry event is the file name of entry
                WatchEvent<Path> ev = cast(event);
                Path name = ev.context();
                Path child = dir.resolve(name);

                // print out event
                if (child.toString().toLowerCase().endsWith(".java")) {
                    if (_switch) {
                        System.out.format("%s: %s\n", event.kind().name(), child);
                    }
                }
                // if directory is created, and watching recursively, then
                // register it and its sub-directories
                if (kind == ENTRY_CREATE) {
                    if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                        registerAll(child);
                    }
                }
                // on create compile. if .java
                if (event.kind().name().equals("ENTRY_CREATE")) {

                    if (Files.isDirectory(child,NOFOLLOW_LINKS)) {
                        //if (debugDirs) model.addElement("dir.create: " + child + File.separator);
                        //register??
                    } else { 
                        if (child.toAbsolutePath().toString().toLowerCase().endsWith(".java")) {

                            //if (!buildUpdate) {
                                if (_switch) {
                                    //model.addElement("file.create: " + child);
                                    model.addElement("onCreate: " + SystemTool.compile(Global.getProjectPath(),child.toString()));
                                }
                            //}
                        }
                    }
                } else if (event.kind().name().equals("ENTRY_DELETE")) {

                    if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                        //model.addElement("dir.delete: " + child + File.separator);
                    } else {
                        if (child.toString().endsWith(".java")) {
                            if (_switch) {
                                model.addElement("onDelete: " + getDeleteClassFile(child.toString()));
                            }
                        }
                    } 
                } else if (event.kind().name().equals("ENTRY_MODIFY")) {
                    if (Files.isDirectory(child,NOFOLLOW_LINKS)) {
                        //model.addElement("dir.modify: " + child);
                    } else {
                        if (child.toString().toLowerCase().endsWith(".java")) {
                            //System.out.println("Child: " + child.toString());
                            if (new File(child.toString()).exists()) {
                                if (_switch) {
                                    model.addElement("compile: " + SystemTool.compile(Global.getProjectPath(), child.toString()));
                                }   
                            }  
                        }  
                    }
                } 
                int lastIndex = list.getModel().getSize() - 1;
                if (lastIndex >= 0) {
                    list.ensureIndexIsVisible(lastIndex);
                }
            }
            // reset key and remove from set if directory no longer accessible
            boolean valid = key.reset();  
            if (!valid) {
                keys.remove(key);
                // all directories are inaccessible
                if (keys.isEmpty()) {
                    break;
                }
            } 
            _switch = !_switch; 
        }
    }


    public static String getDeleteClassFile(String filename) {
        //so take the filename and modify to be .class file
        filename = filename.substring(0,filename.lastIndexOf(".")) + ".class";
        new File(filename).delete();
        // return the result of wether it exists or not.
        if (new File(filename).exists()) return filename + ": false";
        else return filename + ": true"; 
    }


    public static void main(String[] args) {
        // parse arguments
        //if (args.length == 0 || args.length > 2)
        //    usage();
        JavaSystemCompiler compiler = null;
        compiler = new JavaSystemCompiler(Global.getProjectPath());
        compiler.register(Paths.get(Global.getProjectPath()));
        compiler.registerAll(Paths.get(Global.getProjectPath()));
        compiler.processEvents();
    }
}

Global.getProjectPath 仅返回源文件和 .class 文件所在的路径。

我想您需要 org.apache.commons.io.jar，它可用 here .

Answer 1

要调试的代码太多了!

我认为您违反的限制来自 java.lang.reflect.Proxy API 文档。

All of the interface types must be visible by name through the specified class loader. In other words, for class loader cl and every interface i, the following expression must be true:

    Class.forName(i.getName(), false, cl) == i

在行

Class<?> proxy = (Class<?>) Proxy.newProxyInstance(parent, new Class[] { _class}, handler);

parent 应替换为 loader - 加载接口(interface)的 ClassLoader(假设 _class 是一个接口(interface)- 我没有遵循它)。