import sun.misc.FileURLMapper; //导入依赖的package包/类
private JarFile getJarFile(URL url) throws IOException {
    // Optimize case where url refers to a local jar file
    if (isOptimizable(url)) {
        FileURLMapper p = new FileURLMapper (url);
        if (!p.exists()) {
            throw new FileNotFoundException(p.getPath());
        }
        return checkJar(new JarFile(p.getPath()));
    }
    URLConnection uc = getBaseURL().openConnection();
    uc.setRequestProperty(USER_AGENT_JAVA_VERSION, JAVA_VERSION);
    JarFile jarFile = ((JarURLConnection)uc).getJarFile();
    return checkJar(jarFile);
}
 

import sun.misc.FileURLMapper; //导入依赖的package包/类
private JarFile getJarFile(URL url) throws IOException {
    // Optimize case where url refers to a local jar file
    if (isOptimizable(url)) {
        FileURLMapper p = new FileURLMapper (url);
        if (!p.exists()) {
            throw new FileNotFoundException(p.getPath());
        }
        return new JarFile (p.getPath());
    }
    URLConnection uc = getBaseURL().openConnection();
    uc.setRequestProperty(USER_AGENT_JAVA_VERSION, JAVA_VERSION);
    return ((JarURLConnection)uc).getJarFile();
}