Java无第三方库获取网页文本返回空字符串问题求助

我是Java新手，尝试不依赖任何第三方库，通过Java代码获取网页文本，但当前代码返回空字符串。先后尝试了Scanner和BufferedReader两种方式，结果均一致，也试过其他代码但都无效，希望能解决该问题或提供其他原生实现方法。附上的代码使用HttpURLConnection请求GitHub上的version.txt文件：

public String checkUpdate(){

        String responseText;

        int responseCode;

        try{

            String urlString = "https://raw.githubusercontent.com/farhanaliofficial/Lite/main/version.txt";

            URL url = new URL(urlString);

            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            connection.setRequestMethod("GET");

            connection.setRequestProperty("accept","*/*");

            responseCode = connection.getResponseCode();
            
            Scanner scanner = new Scanner(connection.getInputStream());
            
//          BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            StringBuilder responseBuilder = new StringBuilder();
//          String line;
//
//          while ((line = reader.readLine()) != null) {
//              responseBuilder.append(line);
//          }
//          reader.close();
//          responseText = responseBuilder.toString();
            if(responseCode == 200){
            while (scanner.hasNextLine()) {
                responseBuilder.append(scanner.nextLine());
            }
            responseText = responseBuilder.toString();
            }else{
                responseText = responseCode+"";
            }
        }
        catch(Exception e){
            e.printStackTrace();
            responseText = e.toString();
        }
        return responseText;
    }

你的代码返回空字符串，核心原因是GitHub的raw服务器会拦截无User-Agent标识的请求，这类请求会被判定为非合法请求，返回空内容。另外代码未正确关闭资源，可能引发流读取异常。

以下是修正后的Scanner实现版本：

public String checkUpdate() {
    String responseText = "";
    int responseCode;

    try {
        String urlString = "https://raw.githubusercontent.com/farhanaliofficial/Lite/main/version.txt";
        URL url = new URL(urlString);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        
        // 添加User-Agent模拟浏览器请求，避免被服务器拦截
        connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36");
        connection.setRequestMethod("GET");
        connection.setRequestProperty("accept", "*/*");
        
        responseCode = connection.getResponseCode();

        if (responseCode == 200) {
            // 用try-with-resources自动关闭流，避免资源泄漏
            try (Scanner scanner = new Scanner(connection.getInputStream(), "UTF-8")) {
                StringBuilder responseBuilder = new StringBuilder();
                while (scanner.hasNextLine()) {
                    responseBuilder.append(scanner.nextLine());
                    // 如需保留原文本换行符，可取消下面注释
                    // responseBuilder.append(System.lineSeparator());
                }
                responseText = responseBuilder.toString();
            }
        } else {
            responseText = String.valueOf(responseCode);
        }
        // 显式关闭连接释放资源
        connection.disconnect();
    } catch (Exception e) {
        e.printStackTrace();
        responseText = e.toString();
    }
    return responseText;
}

如果偏好BufferedReader实现，同样可以用以下代码：

public String checkUpdateWithBufferedReader() {
    String responseText = "";
    int responseCode;

    try {
        String urlString = "https://raw.githubusercontent.com/farhanaliofficial/Lite/main/version.txt";
        URL url = new URL(urlString);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        
        connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36");
        connection.setRequestMethod("GET");
        connection.setRequestProperty("accept", "*/*");
        
        responseCode = connection.getResponseCode();

        if (responseCode == 200) {
            try (BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"))) {
                StringBuilder responseBuilder = new StringBuilder();
                String line;
                while ((line = reader.readLine()) != null) {
                    responseBuilder.append(line);
                    // 保留换行符可选
                    // responseBuilder.append(System.lineSeparator());
                }
                responseText = responseBuilder.toString();
            }
        } else {
            responseText = String.valueOf(responseCode);
        }
        connection.disconnect();
    } catch (Exception e) {
        e.printStackTrace();
        responseText = e.toString();
    }
    return responseText;
}

关键修改说明 #

• 添加User-Agent请求头：让服务器识别为合法浏览器请求，避免被拦截。
• 使用try-with-resources：自动关闭输入流，防止资源泄漏和读取异常。
• 指定UTF-8编码：确保文本读取不会出现乱码。
• 显式关闭连接：及时释放HttpURLConnection资源。

内容的提问来源于stack exchange，提问作者Farhan Ali