FtpURLConnection 图片下载编码问题

最新推荐文章于 2021-02-28 06:35:36 发布

渐渐遗忘

最新推荐文章于 2021-02-28 06:35:36 发布

阅读量807

点赞数

CC 4.0 BY-SA版权

分类专栏： Java 文章标签： FtpURLConnection ftp FileNotFoundException

本文链接：https://blog.youkuaiyun.com/yangyangmyself/article/details/84913087

Java 专栏收录该内容

43 篇文章

订阅专栏

本文探讨了Web项目中图片下载不全的问题，分析了直接运行Main方法与部署到Web项目时的不同表现，并深入讨论了文件编码对于下载过程的影响及解决方案。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

写道

问题：
1）Web项目中下载图片,存在下载不全，丢失部份图片
2）FTP路径存在中文图片名称或中文路径
3）直接运行Main方法可以下载图片，放在Web项目中下载失败，错误异常"FileNotFoundException"

写道

为什么直接运行Main方法可以成功下载？

Myeclipse/eclipse 右击类--->Run As-->Run Configuration，查看默认编码，直接运行Main方法，JVM启动时，将类文件默认编码设置-Dfile.encoding=UTF-8(Default VM Arguments)

什么时候设置GBK还是UTF-8，依据是什么？

默认情况FTP服务器所在服务有关，Windowns采用GBK，Linux采用UTF-8编码

写道

为什么Web项目中，在执行下载前通过System.setProperties("file.encoding","UTF-8")设置編码，仍然提示FileNotFoundException即编码问影响，设置不起作用？

JVM 参数存在缓存，JVM启动时已加载至缓存，FtpURLConnection从缓存获取，后续通过System改变不启作用，Myeclipse/eclipse：windows-->preferences-->installed JREs-->Edit

写道

Tomcat 启动时或运行Jar时设置-Dfile.encoding=UTF-8
FtpURLConnection用不好到处是坑，直接改JVM编码来适配FTP服务器，应用存在风险，建议下载图采用第三方工具如，Apache common net，附上FtpURLConnection getInputStream源码

public InputStream More ...getInputStream() throws IOException {
        if (!connected) {
            connect();
        }

        if (http != null)
            return http.getInputStream();

        if (os != null)
            throw new IOException("Already opened for output");

        if (is != null) {
            return is;
        }

        MessageHeader msgh = new MessageHeader();

        try {
            decodePath(url.getPath());
            if (filename == null || type == DIR) {
                ftp.ascii();
                cd(pathname);
                if (filename == null)
                    is = new FtpInputStream(ftp, ftp.list());
                else
                    is = new FtpInputStream(ftp, ftp.nameList(filename));
            } else {
                if (type == ASCII)
                    ftp.ascii();
                else
                    ftp.binary();
                cd(pathname);
                is = new FtpInputStream(ftp, ftp.get(filename));
            }

            /* Try to get the size of the file in bytes.  If that is
               successful, then create a MeteredStream. */
            try {
                String response = ftp.getResponseString();
                int offset;

                if ((offset = response.indexOf(" bytes)")) != -1) {
                    int i = offset;
                    int c;

                    while (--i >= 0 && ((c = response.charAt(i)) >= '0'
                                        && c <= '9'))
                        ;
                    i = Integer.parseInt(response.substring(i + 1, offset));
                    msgh.add("content-length", ""+i);
                    if (i > 0) {

                        // Wrap input stream with MeteredStream to ensure read() will always return -1
                        // at expected length.

                        // Check if URL should be metered
                        boolean meteredInput = ProgressMonitor.getDefault().shouldMeterInput(url, "GET");
                        ProgressSource pi = null;

                        if (meteredInput)   {
                            pi = new ProgressSource(url, "GET", i);
                            pi.beginTracking();
                        }

                        is = new MeteredStream(is, pi, i);
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
                /* do nothing, since all we were doing was trying to
                   get the size in bytes of the file */
            }

            String type = guessContentTypeFromName(fullpath);
            if (type == null && is.markSupported()) {
                type = guessContentTypeFromStream(is);
            }
            if (type != null) {
                msgh.add("content-type", type);
            }
        } catch (FileNotFoundException e) {
            try {
                cd(fullpath);
                /* if that worked, then make a directory listing
                   and build an html stream with all the files in
                   the directory */
                ftp.ascii();

                is = new FtpInputStream(ftp, ftp.list());
                msgh.add("content-type", "text/plain");
            } catch (IOException ex) {
                throw new FileNotFoundException(fullpath);
            }
        }
        setProperties(msgh);
        return is;
}