通过File构造URL

背景：使用URLClassLoader自定义类加载器时需要用到File类和URL类。对比如下代码。

书中的源码：

String uri = request.getUri();
		String servletName = uri.substring(uri.lastIndexOf("/") + 1);
		URLClassLoader loader = null;

		try {
			// create a URLClassLoader
			URL[] urls = new URL[1];
			URLStreamHandler streamHandler = null;
			File classPath = new File(Constants.WEB_ROOT);
			// the forming of repository is taken from the createClassLoader
			// method in
			// org.apache.catalina.startup.ClassLoaderFactory
			String repository = (new URL("file", null,
					classPath.getCanonicalPath() + File.separator)).toString();
			// the code for forming the URL is taken from the addRepository
			// method in
			// org.apache.catalina.loader.StandardClassLoader class.
			urls[0] = new URL(null, repository, streamHandler);
			loader = new URLClassLoader(urls);
		} catch (IOException e) {
			System.out.println(e.toString());
		}
		Class myClass = null;
		try {
			myClass = loader.loadClass(servletName);
		} catch (ClassNotFoundException e) {
			System.out.println(e.toString());
		}

		Servlet servlet = null;

		try {
			servlet = (Servlet) myClass.newInstance();
			servlet.service((ServletRequest) request,
					(ServletResponse) response);
		} catch (Exception e) {
			System.out.println(e.toString());
		} catch (Throwable e) {
			System.out.println(e.toString());
		}

修改后的代码：

String uri = request.getUri();
		String servletName = uri.substring(uri.lastIndexOf("/") + 1);
		URLClassLoader loader = null;

		try {
			// create a URLClassLoader
			URL[] urls = new URL[1];
			URLStreamHandler streamHandler = null;
			File classPath = new File(Constants.WEB_ROOT);
			urls[0] = classPath.toURI().toURL();
			loader = new URLClassLoader(urls);
		} catch (IOException e) {
			System.out.println(e.toString());
		}
		Class myClass = null;
		try {
			myClass = loader.loadClass(servletName);
		} catch (ClassNotFoundException e) {
			System.out.println(e.toString());
		}

		Servlet servlet = null;

		try {
			servlet = (Servlet) myClass.newInstance();
			servlet.service((ServletRequest) request,
					(ServletResponse) response);
		} catch (Exception e) {
			System.out.println(e.toString());
		} catch (Throwable e) {
			System.out.println(e.toString());
		}

总结：用classPath.toURI().toURL();替换了书中的一堆代码，应用运行起来和书中没有什么区别。书可能是出的比较早，toURI是在jdk1.4以后引入的方法。还能是出于什么目的呢？我现在是没有考虑明白。