关于struts2的上传问题

问题：我上次成功的文件要么打不开，要么是0字节

uploadAction:

for (int i = 0; i < file.size(); i++) {
InputStream is = new FileInputStream(file.get(i));

        String root = ServletActionContext.getRequest().getRealPath(
                "/upload");

System.out.println(root);

        File destFile = new File(root, this.getFileFileName().get(i));

        OutputStream os = new FileOutputStream(destFile);

        byte[] buffer = new byte[1024];
        int length = 0;

        while ((length = is.read()) > 0) {

            os.write(buffer, 0, length);
        }
        os.close();
        is.close();
    }

    return SUCCESS;

上传是上传成功了，也没有抛异常，但就是上传成功不对劲，上传的图片打开没有信息，上传的txt文件没有任何内容，用uedit打开是二进制的文件，但是我用servlet的FileItem 的write();方法上传就没有任何问题了，不知道怎么回事？

uploadAction:
InputStream is = new FileInputStream(file.get(i));

String root = ServletActionContext.getRequest().getRealPath(
"/upload");

System.out.println(root);

File destFile = new File(root, this.getFileFileName());

OutputStream os = new FileOutputStream(destFile);

byte[] buffer = new byte[1024];
int length = 0;

while ((length = is.read(buffer)) > 0) {
os.write(buffer, 0, length);
}
os.close();
is.close();

return SUCCESS;