根据url获取文件demo

public String readFileByUrl(String urlStr) {
        String json = null;
        HttpURLConnection conn;
        try {
            conn = (HttpURLConnection) new URL(urlStr).openConnection();
            conn.setConnectTimeout(3 * 1000);
            conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");
            try (InputStream in = conn.getInputStream(); ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
                byte[] buffer = new byte[1024];
                int len = 0;
                while ((len = in.read(buffer)) != -1) {
                    bos.write(buffer, 0, len);
                }
                json = new String(bos.toByteArray());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return json;
    }