Java 中如何获取 classpath 下资源文件?

String name1 = "/prop/system.properties";
URL url1 = App.class.getResource(name1);

String name1 = "/prop/system.properties";
InputStream inputStream1 = App.class.getResourceAsStream(name1);

String name2 = "prop/system.properties";
 URL url2 = App.class.getClassLoader().getResource(name2);

String name2 = "prop/system.properties";
InputStream inputStream2 = App.class.getClassLoader().getResourceAsStream(name2);

String name3 = "prop/system";
ResourceBundle resourceBundle = ResourceBundle.getBundle(name3);

public final class Class<T> implements java.io.Serializable,GenericDeclaration,Type,AnnotatedElement {
    public java.net.URL getResource(String name) {
        name = resolveName(name);
        ClassLoader cl = getClassLoader0();
        if (cl==null) {
            // A system class.
            return ClassLoader.getSystemResource(name);
        }
        return cl.getResource(name);
    }
    public InputStream getResourceAsStream(String name) {
        name = resolveName(name);
        ClassLoader cl = getClassLoader0();
        if (cl==null) {
            // A system class.
            return ClassLoader.getSystemResourceAsStream(name);
        }
        return cl.getResourceAsStream(name);
    }
    private String resolveName(String name) {
        if (name == null) {
            return name;
        }
        if (!name.startsWith("/")) {
            Class<?> c = this;
            while (c.isArray()) {
                c = c.getComponentType();
            }
            String baseName = c.getName();
            int index = baseName.lastIndexOf('.');
            if (index != -1) {
                name = baseName.substring(0, index).replace('.', '/')
                    +"/"+name;
            }
        } else {
            name = name.substring(1);
        }
        return name;
    }
    ClassLoader getClassLoader0() { return classLoader; }
}

public abstract class ClassLoader {
    public URL getResource(String name) {
        URL url;
        if (parent != null) {
            url = parent.getResource(name);
        } else {
            url = getBootstrapResource(name);
        }
        if (url == null) {
            url = findResource(name);
        }
        return url;
    }
    public InputStream getResourceAsStream(String name) {
        URL url = getResource(name);
        try {
            return url != null ? url.openStream() : null;
        } catch (IOException e) {
            return null;
        }
    }
}