使用java.net.*发送API请求无法获取400+响应体的解决办法咨询

问题根源在于HttpURLConnection在收到400及以上的错误状态码时，调用getInputStream()会直接抛出IOException，此时错误响应体需要通过getErrorStream()方法获取。

你需要调整代码逻辑，先获取响应状态码，根据状态码选择读取输入流或错误流，同时在异常捕获中也处理错误流的读取：

修改后的代码 #

public static String sendPostRequest(String requestUrl, String payload, Map<String, String> requestProperties) {
    StringBuffer jsonString = new StringBuffer();
    HttpURLConnection connection = null;
    BufferedReader br = null;
    try {
        URL url = new URL(requestUrl);
        connection = (HttpURLConnection) url.openConnection();

        connection.setDoInput(true);
        connection.setDoOutput(true);
        connection.setRequestMethod("POST");
        for (Map.Entry<String, String> entry : requestProperties.entrySet()) {
            connection.setRequestProperty(entry.getKey(), entry.getValue());
        }
        OutputStreamWriter writer = new OutputStreamWriter(connection.getOutputStream(), StandardCharsets.UTF_8);
        writer.write(payload);
        writer.close();

        // 获取响应状态码
        int responseCode = connection.getResponseCode();
        
        // 根据状态码选择对应的流
        InputStream inputStream;
        if (responseCode >= HttpURLConnection.HTTP_BAD_REQUEST) {
            inputStream = connection.getErrorStream();
        } else {
            inputStream = connection.getInputStream();
        }

        br = new BufferedReader(new InputStreamReader(inputStream));
        String line;
        while ((line = br.readLine()) != null) {
            jsonString.append(line);
        }

    } catch (Exception e) {
        log.error("Error for call " + requestUrl);
        log.error(e.getMessage());
        // 异常情况下尝试读取错误流
        if (connection != null) {
            try (BufferedReader errorBr = new BufferedReader(new InputStreamReader(connection.getErrorStream()))) {
                String line;
                while ((line = errorBr.readLine()) != null) {
                    jsonString.append(line);
                }
            } catch (Exception ex) {
                log.error("Failed to read error stream", ex);
            }
        }
    } finally {
        // 确保资源关闭
        try {
            if (br != null) br.close();
            if (connection != null) connection.disconnect();
        } catch (Exception e) {
            log.error("Failed to close resources", e);
        }
    }
    return jsonString.toString();
}

关键调整点 #

• 先调用getResponseCode()获取响应状态码，这一步会触发请求的实际发送，避免直接调用getInputStream()抛出异常
• 根据状态码判断使用getInputStream()还是getErrorStream()
• 在finally块中统一关闭流和连接，避免资源泄漏
• 异常捕获中额外处理错误流读取，确保即使抛出异常也能拿到错误响应体

内容的提问来源于stack exchange，提问作者Harish Algat