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通过url获取文件资源,用于服务器文件上传form-data方式

/**
     * 通过url获取文件资源
     *
     * @param url 文件url
     * @param fileName 文件名称
     * @return
     * @throws IOException
     */
    public static ByteArrayResource getResourceByUrl(String url, String fileName) throws IOException {
        // 通过url获取输入流
        InputStream inputStream = getFileInputStream(url);
        if (inputStream == null) {
            return null;
        }
        // 读取输入流到字节数组
        byte[] bytes = readBytes(inputStream);
        // 将自己数组转为文件资源
        return new ByteArrayResource(bytes) {
            @Override
            public String getFilename() {
                // 指定文件名称
                return fileName;
            }
        };
    }

    /*读取网络文件*/
    private static InputStream getFileInputStream(String path) {
        URL url = null;
        try {
            url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            //设置超时间为3秒
            conn.setConnectTimeout(3 * 1000);
            //防止屏蔽程序抓取而返回403错误
            conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");
            //得到输入流
            return conn.getInputStream();
        } catch (Exception e) {
            logger.error("读取网络文件异常:" + path);
        }
        return null;
    }

    /**
     * 读取输入流到字节数组
     *
     * @param in
     * @return
     * @throws IOException
     */
    private static byte[] readBytes(InputStream in) throws IOException {
        //读取字节的缓冲
        byte[] buffer = new byte[1024];
        //最终的数据
        byte[] result = new byte[0];
        int size = 0;
        while ((size = in.read(buffer)) != -1) {
            int oldLen = result.length;
            byte[] tmp = new byte[oldLen + size];
            if (oldLen > 0) {//copy 旧字节
                System.arraycopy(result, 0, tmp, 0, oldLen);
            }
            //copy 新字节
            System.arraycopy(buffer, 0, tmp, oldLen, size);

            result = tmp;
        }
        return result;
    }