public class Launcher {
	// 成員 ClassLoader 類加載器，用來存儲 應(yīng)用程序類加載器，
	// 此加載器與線程綁定，用作線程的上下文類加載器。
	private ClassLoader loader;  
	// 兩個靜態(tài)內(nèi)部類
	static class AppClassLoader extends URLClassLoader {...}
	static class ExtClassLoader extends URLClassLoader {...}
	    // 構(gòu)造器
	    public Launcher() {
        Launcher.ExtClassLoader var1;
        try {
            var1 = Launcher.ExtClassLoader.getExtClassLoader();
        } catch (IOException var10) {
            throw new InternalError("Could not create extension class loader", var10);
        }
        try {
            this.loader = Launcher.AppClassLoader.getAppClassLoader(var1);
        } catch (IOException var9) {
            throw new InternalError("Could not create application class loader", var9);
        }
        Thread.currentThread().setContextClassLoader(this.loader);
        String var2 = System.getProperty("java.security.manager");
        if (var2 != null) {
            SecurityManager var3 = null;
            if (!"".equals(var2) && !"default".equals(var2)) {
                try {
                    var3 = (SecurityManager)this.loader.loadClass(var2).newInstance();
                } catch (IllegalAccessException var5) {
                } catch (InstantiationException var6) {
                } catch (ClassNotFoundException var7) {
                } catch (ClassCastException var8) {
                }
            } else {
                var3 = new SecurityManager();
            }
            if (var3 == null) {
                throw new InternalError("Could not create SecurityManager: " + var2);
            }
            System.setSecurityManager(var3);
        }
    }
}

 static class AppClassLoader extends URLClassLoader { 
        public Class<?> loadClass(String var1, boolean var2) throws ClassNotFoundException {
            // ...
            // 調(diào)用了一個 native 本地方法 knownToNotExist()，去查找該類的加載記錄
            if (this.ucp.knownToNotExist(var1)) {        // 如果有該類加載記錄
                Class var5 = this.findLoadedClass(var1); // 直接去已經(jīng)加載的類中找
                if (var5 != null) {
                    if (var2) {
                        this.resolveClass(var5);
                    }
                    return var5;
                } else {                                 // 如果沒找到報(bào)異常
                    throw new ClassNotFoundException(var1);
                }
            } else {                                     // 如果沒有該類的加載記錄
                return super.loadClass(var1, var2);      // 調(diào)用父類 ClassLoader 的 loadClass()
            }
        }
}

static class ExtClassLoader extends URLClassLoader {
	//...
}

 /** 允許直接調(diào)用的是這個根據(jù) 類名加載類 的方法， */
 public Class<?> loadClass(String name) throws ClassNotFoundException {
        return loadClass(name, false); // 內(nèi)部調(diào)用的是類加載方法默認(rèn)不對類進(jìn)行解析
    }

 	protected Class<?> loadClass(String name, boolean resolve)  throws ClassNotFoundException {
        synchronized (getClassLoadingLock(name)) { // 加載一個類的時候，鎖住對應(yīng)的類加載器對象
            // First, check if the class has already been loaded
            Class<?> c = findLoadedClass(name);    // 查詢已加載的類中是否有該類存在 
            if (c == null) {
                long t0 = System.nanoTime();       // 記錄開始時間
                try {
                    if (parent != null) {          // 非頂層類加載器
                        c = parent.loadClass(name, false);  // 調(diào)用父類加載器進(jìn)行加載
                    } else {
                        c = findBootstrapClassOrNull(name); // 調(diào)用啟動類加載器加載
                    }
                } catch (ClassNotFoundException e) {
                    // ClassNotFoundException thrown if class not found
                    // from the non-null parent class loader
                }
                if (c == null) { // 如果在 父類加載器 或 啟動類加載器 沒有找到需要加載的類
                    // If still not found, then invoke findClass in order
                    // to find the class.
                    long t1 = System.nanoTime();  // 記錄結(jié)束時間
                    c = findClass(name);          // 再由當(dāng)前加載器加載
                    // this is the defining class loader; record the stats
                    // 性能計(jì)數(shù)器
                    sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
                    sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                    sun.misc.PerfCounter.getFindClasses().increment();
                }
            }
            if (resolve) {
                resolveClass(c); // 對類進(jìn)行解析
            }
            return c;
        }
    }

    protected Class<?> findClass(String name) throws ClassNotFoundException {
        throw new ClassNotFoundException(name);
    }

    // Maps class name to the corresponding lock object when the current
    // class loader is parallel capable.
    // Note: VM also uses this field to decide if the current class loader
    // is parallel capable and the appropriate lock object for class loading.
    private final ConcurrentHashMap<String, Object> parallelLockMap;

    protected Object getClassLoadingLock(String className) {
        Object lock = this; // 這個鎖就是類加載器對象本身！
        if (parallelLockMap != null) {
            Object newLock = new Object(); 
            lock = parallelLockMap.putIfAbsent(className, newLock); // 放入集合里存儲
            if (lock == null) { // 如果沒有對應(yīng)的類加載器對象
                lock = newLock; // 創(chuàng)建一個新的類加載器
            }
        }
        return lock; // 返回類加載器對象
    }

	 /**
     * Returns a class loaded by the bootstrap class loader;
     * or return null if not found.
     */
    private Class<?> findBootstrapClassOrNull(String name)
    {
        if (!checkName(name)) return null;
        return findBootstrapClass(name);
    }
    // 返回 BootstrapClassLoader 啟動類加載器加載的類。
    private native Class<?> findBootstrapClass(String name);