好玩Java之自定义类加载器

可以通过以下方式，进行自定义类加载器的使用。
这样会破坏双亲委派，优先自己加载。

public class TestClassLoader extends URLClassLoader {

    protected TestClassLoader(URL[] urls, ClassLoader parent) {
        super(urls, parent);
    }

    /**
     * 重写loadClass方法，部分类加载破坏双亲委派模型，（优先加载子类）。
     *
     * @param name
     * @param resolve
     * @return
     * @throws ClassNotFoundException
     */
    @Override
    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) {
                if (resolve) {
                    resolveClass(c);
                }
                return c;
            }
            try {
                c = findClass(name);
                if (c != null) {
                    System.out.println("loaded from child, name=" + name);
                    if (resolve) {
                        resolveClass(c);
                    }
                    return c;
                }
            } catch (ClassNotFoundException e) {
                // Ignore
            }


            try {
                if (getParent() != null) {
                    c = super.loadClass(name, resolve);
                    if (c != null) {
                        System.out.println("loaded from parent, name=" + name);
                        if (resolve) {
                            resolveClass(c);
                        }
                        return c;
                    }
                }
            } catch (ClassNotFoundException e) {
                // Ignore
            }
            try {
                c = findSystemClass(name);
                if (c != null) {
                    System.out.println("loaded from system, name=" + name);
                    if (resolve) {
                        resolveClass(c);
                    }
                    return c;
                }
            } catch (ClassNotFoundException e) {
                // Ignore
            }
            throw new ClassNotFoundException(name);
        }
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        return super.findClass(name);
    }
}