System.getProperty("sun.boot.class.path");

System.getProperty("java.ext.dirs");

System.getProperty("java.class.path");

public class Launcher {
  static class AppClassLoader extends URLClassLoader {}
  static class ExtClassLoader extends URLClassLoader {}
  private static class BootClassPathHolder {}
}

public class Launcher {
  public Launcher() {
    ExtClassLoader var1;
    try {
     // 1. 創(chuàng)建ExtClassLoader
     var1 = Launcher.ExtClassLoader.getExtClassLoader();// 68
    } catch (IOException var10) {// 69
     throw new InternalError("Could not create extension class loader", var10);// 70
    }
    try {
     // 2. 創(chuàng)建AppClassLoader，并將ExtClassLoader作為ParentClassLoader
     this.loader = Launcher.AppClassLoader.getAppClassLoader(var1);// 76
    } catch (IOException var9) {// 77
     throw new InternalError("Could not create application class loader", var9);// 78
    }
    // 3. 將AppClassLoader掛載到當(dāng)前線(xiàn)程
    Thread.currentThread().setContextClassLoader(this.loader);// 83
    // ......
  }
}

package sun.misc;
public class URLClassPath {
  private static class Loader implements Closeable {}
  static class JarLoader extends Loader {}
  private static class FileLoader extends Loader {}
}

public static void main(String[] args) throws ClassNotFoundException {
    // 1. 重新設(shè)定ClassPath
    System.setProperty("java.class.path", "D:\\development\\idea\\workspace\\personal\\resources-operation\\target\\classes");
    // 2. 重新初始化Launcher
    Launcher launcher = new Launcher();
    // 3. 獲取AppClassLoader
    ClassLoader classLoader = launcher.getClassLoader();
    // 4. loadClass
    Class<?> aClass = classLoader.loadClass(ResourcesOperationApplication.class.getName());
    System.out.println(aClass.getName());
}

static class AppClassLoader extends URLClassLoader {
  final URLClassPath ucp = SharedSecrets.getJavaNetAccess().getURLClassPath(this);
  // 獲取AppClassLoader實(shí)例
  public static ClassLoader getAppClassLoader(final ClassLoader var0) throws IOException {
   // 1. 讀取classpath系統(tǒng)參數(shù)
   final String var1 = System.getProperty("java.class.path");
   // 2. 轉(zhuǎn)為File實(shí)例
   final File[] var2 = var1 == null ? new File[0] : Launcher.getClassPath(var1);
   return (ClassLoader) AccessController.doPrivileged(new PrivilegedAction<AppClassLoader>() {
    public AppClassLoader run() {
     // 3. File轉(zhuǎn)為URL
     URL[] var1x = var1 == null ? new URL[0] : Launcher.pathToURLs(var2);
     // 3. 創(chuàng)建實(shí)例
     return new AppClassLoader(var1x, var0);
    }
   });
  }
  AppClassLoader(URL[] var1, ClassLoader var2) {
   // 4. 初始化父類(lèi)，并傳遞了一組URL實(shí)例
   super(var1, var2, Launcher.factory);
   this.ucp.initLookupCache(this);
  }
 // ......
}
public class URLClassLoader extends SecureClassLoader implements Closeable {
  /* The search path for classes and resources */
  private final URLClassPath ucp;
  /* The context to be used when loading classes and resources */
  private final AccessControlContext acc;
  public URLClassLoader(URL[] urls, ClassLoader parent,
          URLStreamHandlerFactory factory) {
   super(parent);
   SecurityManager security = System.getSecurityManager();
   if (security != null) {
    security.checkCreateClassLoader();
   }
   acc = AccessController.getContext();
   // 5. 將URL實(shí)例封裝到URLClassPath中
   ucp = new URLClassPath(urls, factory, acc);
  }
}
public class URLClassPath {
  private ArrayList<URL> path;
  Stack<URL> urls;
  ArrayList<Loader> loaders;
  HashMap<String, Loader> lmap;
  private URLStreamHandler jarHandler;
  private boolean closed;
  public URLClassPath(URL[] var1, URLStreamHandlerFactory var2, AccessControlContext var3) {
    this.path = new ArrayList();// 101
    this.urls = new Stack();// 104
    this.loaders = new ArrayList();// 107
    this.lmap = new HashMap();// 110
    this.closed = false;// 116
    // 6. 將URL封裝到內(nèi)部的path中
    for(int var4 = 0; var4 < var1.length; ++var4) {// 138
     this.path.add(var1[var4]);// 139
    }
    this.push(var1);// 141
    if (var2 != null) {// 142
     this.jarHandler = var2.createURLStreamHandler("jar");// 143
    }
    if (DISABLE_ACC_CHECKING) {// 145
     this.acc = null;// 146
    } else {
     this.acc = var3;// 148
    }
  }
}

Class<?> aClass = classLoader.loadClass(ResourcesOperationApplication.class.getName());

public abstract class ClassLoader {
    protected Class<?> loadClass(String name, boolean resolve)
        throws ClassNotFoundException {
        synchronized (getClassLoadingLock(name)) {
            // First, check if the class has already been loaded
            Class<?> c = findLoadedClass(name);
            if (c == null) {
                long t0 = System.nanoTime();
                // 父系委托機(jī)制
                try {
                    if (parent != null) {
                        c = parent.loadClass(name, false);
                    } else {
                        c = findBootstrapClassOrNull(name);
                    }
                } catch (ClassNotFoundException e) {
                }
                if (c == null) {
                    // ...
                    // 查找類(lèi)資源
                    c = findClass(name);
                    // ...
                }
                // ...
            }
            return c;
        }
    }
    protected Class<?> findClass(final String name) throws ClassNotFoundException {
        final Class<?> result;
        try {
            result = AccessController.doPrivileged(
                new PrivilegedExceptionAction<Class<?>>() {
                    public Class<?> run() throws ClassNotFoundException {
                        // 1. 將類(lèi)的限定名轉(zhuǎn)為 '/' 分隔的形式，例：life.cqq.xxx.ClassName -> life/cqq/xxx/ClassName.class
                        String path = name.replace('.', '/').concat(".class");
                        // 2. 通過(guò)URLClassPath獲取類(lèi)資源
                        Resource res = ucp.getResource(path, false);
                        if (res != null) {
                            try {
                                // 最終根據(jù)類(lèi)名 & 已加載的類(lèi)資源創(chuàng)建Class對(duì)象
                                return defineClass(name, res);
                            } catch (IOException e) {
                                throw new ClassNotFoundException(name, e);
                            } catch (ClassFormatError e2) {
                                if (res.getDataError() != null) {
                                    e2.addSuppressed(res.getDataError());
                                }
                                throw e2;
                            }
                        } else {
                            return null;
                        }
                    }
                }, acc);
        } catch (java.security.PrivilegedActionException pae) {
            throw (ClassNotFoundException) pae.getException();
        }
        if (result == null) {
            throw new ClassNotFoundException(name);
        }
        return result;
    }
}
public class URLClassPath {
    public Resource getResource(String var1, boolean var2) {
        // ......
        Loader var3;
        // 3. getNextLoader：獲取可以處理類(lèi)資源的loader 
        for (int var5 = 0; (var3 = this.getNextLoader(var4, var5)) != null; ++var5) {// 249
            // 5. 通過(guò)獲取到的loader獲取類(lèi)資源
            Resource var6 = var3.getResource(var1, var2);// 250
            if (var6 != null) {// 251
                return var6;// 252
            }
        }
        return null;// 255
    }
    // getNextLoader最終會(huì)調(diào)用到該方法
    private Loader getLoader(final URL var1) throws IOException {
        try {
            return (Loader) AccessController.doPrivileged(new PrivilegedExceptionAction<Loader>() {// 565
                public Loader run() throws IOException {
                    String var1x = var1.getFile();// 568
                    // 4. 最終的判斷：根據(jù)URL創(chuàng)建不同的loader并返回
                    // url.endsWith("/") && "file".equals(var1.getProtocol() ? FileLoader : JarLoader
                    if (var1x != null && var1x.endsWith("/")) {// 569
                        return (Loader) ("file".equals(var1.getProtocol()) ? new FileLoader(var1) : new Loader(var1));// 570
                    } else {
                        return new JarLoader(var1, URLClassPath.this.jarHandler, URLClassPath.this.lmap,
                            URLClassPath.this.acc);// 576
                    }
                }
            }, this.acc);
        } catch (PrivilegedActionException var3) {// 580
            throw (IOException) var3.getException();// 581
        }
    }
}

public class URLClassPath {
    public Resource getResource(String var1, boolean var2) {
        // ......
        Loader var3;
        for (int var5 = 0; (var3 = this.getNextLoader(var4, var5)) != null; ++var5) {// 249
            // 0. 通過(guò)獲取到的loader獲取類(lèi)資源
            Resource var6 = var3.getResource(var1, var2);// 250
            if (var6 != null) {// 251
                return var6;// 252
            }
        }
        return null;// 255
    }
    // 1. 文件加載器
    private static class FileLoader extends Loader {
        private File dir;
        // ...
        Resource getResource(final String var1, boolean var2) {
            try {
                URL var4 = new URL(this.getBaseURL(), ".");// 1370
                final URL var3 = new URL(this.getBaseURL(), ParseUtil.encodePath(var1, false));// 1371=
                if (!var3.getFile().startsWith(var4.getFile())) {// 1373
                    return null;// 1375
                } else {
                    if (var2) {// 1378
                        URLClassPath.check(var3);// 1379
                    }
                    // 1) 根據(jù)loader對(duì)應(yīng)的文件目錄，拼接資源路徑參數(shù)構(gòu)建File實(shí)例
                    final File var5;
                    if (var1.indexOf("..") != -1) {// 1382
                        var5 = (new File(this.dir, var1.replace('/', File.separatorChar))).getCanonicalFile();// 1383 1384
                        if (!var5.getPath().startsWith(this.dir.getPath())) {// 1385
                            return null;// 1387
                        }
                    } else {
                        var5 = new File(this.dir, var1.replace('/', File.separatorChar));// 1390
                    }
                    // 2) 若File實(shí)例映射的文件存在，則返回Resource實(shí)例，否則返回空
                    return var5.exists() ? new Resource() {// 1393
                        // ...
                    } : null;// 1407
                }
            } catch (Exception var6) {// 1404
                return null;// 1405
            }
        }
    }
    // 2. Jar加載器
    static class JarLoader extends Loader {
        Resource getResource(String var1, boolean var2) {
            if (this.metaIndex != null && !this.metaIndex.mayContain(var1)) {// 1059 1060
                return null;// 1061
            } else {
                try {
                    this.ensureOpen();// 1066
                } catch (IOException var5) {// 1067
                    throw new InternalError(var5);// 1068
                }
                // 1) 若loader對(duì)應(yīng)Jar包中，存有資源名稱(chēng)的節(jié)點(diǎn)，則返回資源節(jié)點(diǎn)內(nèi)容
                JarEntry var3 = this.jar.getJarEntry(var1);// 1070
                if (var3 != null) {// 1071
                    return this.checkResource(var1, var2, var3);// 1072
                } else if (this.index == null) {// 1074
                    return null;// 1075
                } else {
                    HashSet var4 = new HashSet();// 1077
                    return this.getResource(var1, var2, var4);// 1078
                }
            }
        }
    }
}

public abstract class ClassLoader {
    // 1. 獲取資源也會(huì)遵循父系委托機(jī)制
    public URL getResource(String name) {
        URL url;
        if (parent != null) {
            url = parent.getResource(name);
        } else {
            url = getBootstrapResource(name);
        }
        if (url == null) {
            url = findResource(name);
        }
        return url;
    }
    protected URL findResource(String name) {
        return null;
    }
}
public class URLClassLoader extends SecureClassLoader implements Closeable {
    public URL findResource(final String name) {
        /*
         * The same restriction to finding classes applies to resources
         */
        URL url = AccessController.doPrivileged(
            new PrivilegedAction<URL>() {
                public URL run() {
                    // 2. 繼續(xù)通過(guò)類(lèi)加載器在父類(lèi)中維護(hù)的URLClassPath獲取資源
                    return ucp.findResource(name, true);
                }
            }, acc);
        return url != null ? ucp.checkURL(url) : null;
    }
}
public class URLClassPath {
    public URL findResource(String var1, boolean var2) {
        int[] var4 = this.getLookupCache(var1);// 224
        // 3. 本質(zhì)還是迭代loader集合進(jìn)行資源獲取
        Loader var3;
        for(int var5 = 0; (var3 = this.getNextLoader(var4, var5)) != null; ++var5) {// 225
            URL var6 = var3.findResource(var1, var2);// 226
            if (var6 != null) {// 227
                return var6;// 228
            }
        }
        return null;// 231
    }
}

public final class Class<T> implements java.io.Serializable,
    GenericDeclaration,
    Type,
    AnnotatedElement {
    // 本質(zhì)依舊是調(diào)用ClassLoader.getResource，唯一的不同在于對(duì)于資源名稱(chēng)進(jìn)行了一次特殊處理。
    // 做了哪些處理正如官方注釋所描述：
    // 1. 如果是絕對(duì)路徑(以 '/' 開(kāi)頭)，剔除 '/' 符號(hào)后返回
    // 2. 如果非絕對(duì)路徑，則拼接'.'號(hào)轉(zhuǎn)為'/'后的包名作為前綴后返回
    // 其實(shí)理解下來(lái)就是：以當(dāng)前類(lèi)文件所在的包為基準(zhǔn)，進(jìn)行相對(duì)、絕對(duì)路徑的拼接。絕對(duì)路徑則不采用包名作為前綴，相對(duì)路徑則以類(lèi)所在的包名作為前綴。
    public java.net.URL getResource(String name) {
        name = resolveName(name);
        ClassLoader cl = getClassLoader0();
        if (cl == null) {
            return ClassLoader.getSystemResource(name);
        }
        return cl.getResource(name);
    }
    /**
     * Add a package name prefix if the name is not absolute Remove leading "/"
     * if name is absolute
     */
    private String resolveName(String name) {
        if (name == null) {
            return name;
        }
        if (!name.startsWith("/")) {
            Class<?> c = this;
            while (c.isArray()) {
                c = c.getComponentType();
            }
            String baseName = c.getName();
            int index = baseName.lastIndexOf('.');
            if (index != -1) {
                name = baseName.substring(0, index).replace('.', '/')
                    +"/"+name;
            }
        } else {
            name = name.substring(1);
        }
        return name;
    }
}

Enumeration<URL> resources = classLoader.getResources("config.properties");
while (resources.hasMoreElements()) {
    URL url = resources.nextElement();
    // do something
}