ClassLoader双亲委派模式作用详解

    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);
    }

protected Class<?> loadClass(String name, boolean resolve)
        throws ClassNotFoundException
    {
        synchronized (getClassLoadingLock(name)) {
            // 首先, 检查这个类是否已经加载好了
            Class<?> c = findLoadedClass(name);
            // 如果没有加载过
            if (c == null) {
                long t0 = System.nanoTime();
                try {
                    // 如果父级ClassLoader不为空，那么就先尝试让父级ClassLoader加载
                    if (parent != null) {
                        c = parent.loadClass(name, false);
                    } else {
                        // 如果父级ClassLoader为空，有可能父级ClassLoader是BootstrapClassLoader，那么先尝试在BootstrapClassLoader加载
                        c = findBootstrapClassOrNull(name);
                    }
                } catch (ClassNotFoundException e) {
                    // ClassNotFoundException thrown if class not found
                    // from the non-null parent class loader
                }
                // 如果一直向上都没有加载目标class，那么最终回到当前ClassLoader加载
                if (c == null) {
                    // If still not found, then invoke findClass in order
                    // to find the class.
                    long t1 = System.nanoTime();
                    c = findClass(name);
                    // this is the defining class loader; record the stats
                    sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
                    sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                    sun.misc.PerfCounter.getFindClasses().increment();
                }
            }
            if (resolve) {
                resolveClass(c);
            }
            // 返回加载成功的类
            return c;
        }
    }