Java调用Companies House API遇401错误：响应码200但openStream报错

核心问题分析 #

这种getResponseCode()返回200但openStream()触发401的情况，大概率和认证头传递、连接状态管理或重定向处理有关，结合Companies House API的认证规则，以下是常见错误点和修复方式：

1. 认证头设置错误 #

Companies House API要求使用Basic Auth，规则是：

• 用户名：你的API密钥
• 密码：空字符串
• 需将API_KEY:拼接后做Base64编码，再放入Authorization头

如果代码里没有正确生成这个头，或编码时遗漏冒号，就会导致认证失败。比如错误写法：

// 错误：未加冒号或编码字符集不正确
String auth = Base64.getEncoder().encodeToString(apiKey.getBytes());
conn.setRequestProperty("Authorization", "Basic " + auth);

正确写法：

String authCredentials = apiKey + ":";
String encodedAuth = Base64.getEncoder().encodeToString(authCredentials.getBytes(StandardCharsets.UTF_8));
String authHeader = "Basic " + encodedAuth;
conn.setRequestProperty("Authorization", authHeader);

2. 重定向时未携带认证头 #

HttpURLConnection默认自动跟随重定向，但不会将Authorization头传递到重定向后的请求中。如果API返回重定向，后续请求会因缺少认证头触发401。

解决方法：手动处理重定向，确保每个请求都带上认证头：

// 禁用自动重定向
conn.setInstanceFollowRedirects(false);

int responseCode = conn.getResponseCode();
if (responseCode >= 300 && responseCode < 400) {
    String redirectUrl = conn.getHeaderField("Location");
    URL newUrl = new URL(redirectUrl);
    HttpURLConnection newConn = (HttpURLConnection) newUrl.openConnection();
    // 重新设置认证头等必要头信息
    newConn.setRequestProperty("Authorization", authHeader);
    newConn.setRequestProperty("Accept", "application/json");
    InputStream in = newConn.getInputStream();
    // 后续响应处理逻辑
} else {
    InputStream in = conn.getInputStream();
    // 后续响应处理逻辑
}

3. 连接状态重复读取异常 #

如果先调用getResponseCode()再调用openStream()，可能因连接状态已被读取，导致后续获取流时异常。建议统一使用getInputStream()或getErrorStream()处理响应，避免混用：

try {
    InputStream in = conn.getInputStream();
    // 处理正常响应
} catch (IOException e) {
    InputStream errorIn = conn.getErrorStream();
    // 处理错误响应（如读取401错误信息）
}

4. 缺失Postman默认请求头 #

Postman会自动添加Accept、User-Agent等默认头，若Java代码未设置这些头，可能被API服务器拒绝。建议补充：

conn.setRequestProperty("Accept", "application/json");
conn.setRequestProperty("User-Agent", "Java HTTP Client");

完整示例代码 #

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.Base64;

public class CompaniesHouseApiClient {
    public static void main(String[] args) throws Exception {
        String apiKey = "YOUR_API_KEY";
        String companyNumber = "00000001";
        String apiUrl = "https://api.company-information.service.gov.uk/company/" + companyNumber;

        String authCredentials = apiKey + ":";
        String encodedAuth = Base64.getEncoder().encodeToString(authCredentials.getBytes(StandardCharsets.UTF_8));
        String authHeader = "Basic " + encodedAuth;

        URL url = new URL(apiUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setRequestProperty("Authorization", authHeader);
        conn.setRequestProperty("Accept", "application/json");
        conn.setInstanceFollowRedirects(false);

        int responseCode = conn.getResponseCode();
        InputStream inputStream;

        if (responseCode >= 300 && responseCode < 400) {
            String redirectUrl = conn.getHeaderField("Location");
            URL newUrl = new URL(redirectUrl);
            HttpURLConnection newConn = (HttpURLConnection) newUrl.openConnection();
            newConn.setRequestMethod("GET");
            newConn.setRequestProperty("Authorization", authHeader);
            newConn.setRequestProperty("Accept", "application/json");
            inputStream = newConn.getInputStream();
        } else if (responseCode == 200) {
            inputStream = conn.getInputStream();
        } else {
            inputStream = conn.getErrorStream();
        }

        // 读取响应内容
        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            System.out.print(new String(buffer, 0, bytesRead));
        }
        inputStream.close();
        conn.disconnect();
    }
}

内容的提问来源于stack exchange，提问作者Jagjit Bains