javax.faces.el.E​​valuationException：java.io.FileNotFoundException（是一个目录）

Question

我目前正在尝试上传多个文件，并且这些文件正在正确上传到目标目录中。但是在日志中它给了我这个错误：

javax.faces.el.EvaluationException: java.io.FileNotFoundException: /u01/app/Middleware/user_projects/domains/base_domain/servers/ServerProcessing1/logs/owsm/msglogging (Is a directory)

这是我上传文件的代码：

private String rFolder = null;
private File rootFolder = null;
rFolder = "/u01/app/Middleware/user_projects/domains/base_domain/servers/ServerProcessing1/logs";
rootFolder = new File(rFolder);
archivatingProcess();

private void archivatingProcess() throws FileNotFoundException, IOException { 
    File file = new File(rFolder);
    ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(file.getAbsoluteFile() + ".zip"));
    addDir(file, zos);
    zos.close();
}

private void addDir(File rootFolder, ZipOutputStream zos) throws FileNotFoundException, IOException {
    File[] files = rootFolder.listFiles();                                                     
    int fLength = files.length;
    byte[] buff = new byte[1024];
    for (int i = 0; i < fLength; i++) {
        if (files[i].isDirectory()) {
            zos.putNextEntry(new ZipEntry(files[i].getName() + "/"));
            zos.closeEntry();
            File[] fileIn = files[i].listFiles();
            for (File f : fileIn) {
                FileInputStream fis =
                new FileInputStream(f.getAbsolutePath());                        
                zos.putNextEntry(new ZipEntry(files[i].getName() + "/" + f.getName()));
                int len;
                while ((len = fis.read(buff)) > 0) {
                    zos.write(buff, 0, len);
                }
                zos.closeEntry();
                fis.close();
            }
        } else {                                                              
            FileInputStream fis = new FileInputStream(files[i].getAbsolutePath());
            zos.putNextEntry(new ZipEntry(files[i].getName()));
            int len;
            while ((len = fis.read(buff)) > 0) {
                zos.write(buff, 0, len);
            }
            zos.closeEntry();
            fis.close();                                                              
        }
    }
}

由于我是java的新手，我不确定为什么它会给我这个错误。我该如何调试呢？