mybatis源码阅读的第一个类，还是比较简单的，算是一个好的开始

package org.apache.ibatis.io;

import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.nio.charset.Charset;
import java.util.Properties;

/*相当于一个工具类，使用类加载器*/
public class Resources {

    //内部存放一个ClassLoaderWrapper，类加载包装类
    private static ClassLoaderWrapper classLoaderWrapper = new ClassLoaderWrapper();


    private static Charset charset;/*指定编码类型，null使用系统默认*/

    Resources() {/*构造方法*/
    }

    /*get set方法*/
    public static ClassLoader getDefaultClassLoader() {
        return classLoaderWrapper.defaultClassLoader;
    }

    public static void setDefaultClassLoader(ClassLoader defaultClassLoader) {
        classLoaderWrapper.defaultClassLoader = defaultClassLoader;
    }

    public static Charset getCharset() {
        return charset;
    }

    public static void setCharset(Charset charset) {
        Resources.charset = charset;
    }
    /*get set结束*/


    /*对于只读的通用资源，加载为 URL。*/
    public static URL getResourceURL(String resource) throws IOException {
        // issue #625
        return getResourceURL(null, resource);
    }

    public static URL getResourceURL(ClassLoader loader, String resource) throws IOException {
        URL url = classLoaderWrapper.getResourceAsURL(resource, loader);
        if (url == null) {
            throw new IOException("Could not find resource " + resource);
        }
        return url;
    }


    /*对于简单的只读二进制或文本数据，加载为 Stream。*/
    public static InputStream getResourceAsStream(String resource) throws IOException {
        return getResourceAsStream(null, resource);
    }

    public static InputStream getResourceAsStream(ClassLoader loader, String resource) throws IOException {
        InputStream in = classLoaderWrapper.getResourceAsStream(resource, loader);
        if (in == null) {
            throw new IOException("Could not find resource " + resource);
        }
        return in;
    }

    /*对于只读的配置属性文件，加载为 Properties。 */
    public static Properties getResourceAsProperties(String resource) throws IOException {
        Properties props = new Properties();
        InputStream in = getResourceAsStream(resource);
        props.load(in);
        in.close();
        return props;
    }

    public static Properties getResourceAsProperties(ClassLoader loader, String resource) throws IOException {
        Properties props = new Properties();
        InputStream in = getResourceAsStream(loader, resource);
        props.load(in);
        in.close();
        return props;
    }


    /*对于简单的只读文本数据，加载为 Reader。*/
    public static Reader getResourceAsReader(String resource) throws IOException {
        Reader reader;
        if (charset == null) {
            reader = new InputStreamReader(getResourceAsStream(resource));
        } else {
            reader = new InputStreamReader(getResourceAsStream(resource), charset);
        }
        return reader;
    }

    public static Reader getResourceAsReader(ClassLoader loader, String resource) throws IOException {
        Reader reader;
        if (charset == null) {
            reader = new InputStreamReader(getResourceAsStream(loader, resource));
        } else {
            reader = new InputStreamReader(getResourceAsStream(loader, resource), charset);
        }
        return reader;
    }


    /*对于可读写的二进制或文本文件，加载为 File。   */
    public static File getResourceAsFile(String resource) throws IOException {
        return new File(getResourceURL(resource).getFile());
    }

    public static File getResourceAsFile(ClassLoader loader, String resource) throws IOException {
        return new File(getResourceURL(loader, resource).getFile());
    }


    /*使用url路径， 对于简单的只读二进制或文本数据，加载为 Stream。 */
    public static InputStream getUrlAsStream(String urlString) throws IOException {
        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();
        return conn.getInputStream();
    }

    /*使用url路径，  对于简单的只读文本数据，加载为 Reader。 */
    public static Reader getUrlAsReader(String urlString) throws IOException {
        Reader reader;
        if (charset == null) {
            reader = new InputStreamReader(getUrlAsStream(urlString));
        } else {
            reader = new InputStreamReader(getUrlAsStream(urlString), charset);
        }
        return reader;
    }

    /*使用url路径，  对于只读的配置属性文件，加载为 Properties。 */
    public static Properties getUrlAsProperties(String urlString) throws IOException {
        Properties props = new Properties();
        InputStream in = getUrlAsStream(urlString);
        props.load(in);
        in.close();
        return props;
    }


    /*加载指定类的类类型*/
    public static Class<?> classForName(String className) throws ClassNotFoundException {
        return classLoaderWrapper.classForName(className);
    }

}