解决Eclipse中HTTPS URL请求出现Connection Reset问题的方法

我在Eclipse中编写Java代码请求一个HTTP URL时，能正常收到301重定向响应，但当代码尝试重定向到对应的HTTPS URL时，触发了Connection Reset错误。原HTTP请求可以正常返回301状态码，问题只出在跳转后的HTTPS连接阶段。以下是我的代码：

try { 
    String url = "http://api.demo.globalgatewaye4.firstdata.com/transaction/search?start_date=2018-01-07&end_date=2018-01-09"; 
    URL obj = new URL(url); 
    HttpURLConnection conn = (HttpURLConnection) obj.openConnection(); 
    conn.setReadTimeout(5000); 
    conn.addRequestProperty("Authorization", "Basic *****************"); 
    System.out.println("Request URL ... " + url); 
    boolean redirect = false; 
    // normally, 3xx is redirect 
    int status = conn.getResponseCode(); 
    if (status != HttpURLConnection.HTTP_OK) { 
        if (status == HttpURLConnection.HTTP_MOVED_TEMP || status == HttpURLConnection.HTTP_MOVED_PERM || status == HttpURLConnection.HTTP_SEE_OTHER) 
            redirect = true; 
    } 
    System.out.println("Response Code ... " + status); 
    if (redirect) { 
        // get redirect url from "location" header field 
        String newUrl = conn.getHeaderField("Location"); 
        // get the cookie if need, for login 
        String cookies = conn.getHeaderField("Set-Cookie"); 
        // open the new connnection again 
        conn = (HttpURLConnection) new URL(newUrl).openConnection(); 
        conn.setRequestProperty("Cookie", cookies); 
        conn.addRequestProperty("Accept-Language", "en-US,en;q=0.8"); 
        conn.addRequestProperty("User-Agent", "Mozilla"); 
        conn.addRequestProperty("Referer", "google.com"); 
        System.out.println("Redirect to URL : " + newUrl); 
    } 
    BufferedReader in = new BufferedReader( 
            new InputStreamReader(conn.getInputStream())); 
    String inputLine; 
    StringBuffer html = new StringBuffer(); 
    while ((inputLine = in.readLine()) != null) { 
        html.append(inputLine); 
    } 
    in.close(); 
    System.out.println("URL Content... \n" + html.toString()); 
    System.out.println("Done"); 
} catch (Exception e) { 
    e.printStackTrace(); 
}

请问如何在Eclipse中解决这个问题，或者有没有通用的解决方法？

可能的解决方法 #

1. 处理HTTPS证书信任问题

Connection Reset很可能是因为Java默认不信任目标HTTPS站点的SSL证书。你可以创建一个信任所有证书的SSL上下文（仅用于测试环境，生产环境请谨慎使用），然后应用到HttpsURLConnection中：

// 先添加这个工具方法
private static void disableSSLCertificateChecking() throws NoSuchAlgorithmException, KeyManagementException {
    TrustManager[] trustAllCerts = new TrustManager[] {
        new X509TrustManager() {
            public X509Certificate[] getAcceptedIssuers() {
                return null;
            }
            public void checkClientTrusted(X509Certificate[] certs, String authType) {}
            public void checkServerTrusted(X509Certificate[] certs, String authType) {}
        }
    };

    SSLContext sc = SSLContext.getInstance("SSL");
    sc.init(null, trustAllCerts, new java.security.SecureRandom());
    HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());

    HostnameVerifier allHostsValid = new HostnameVerifier() {
        public boolean verify(String hostname, SSLSession session) {
            return true;
        }
    };
    HttpsURLConnection.setDefaultHostnameVerifier(allHostsValid);
}

在创建连接之前调用这个方法，比如在URL obj = new URL(url);之前添加disableSSLCertificateChecking();。

2. 完善重定向时的请求头传递

原代码在重定向时没有传递关键的Authorization头，而且添加了可能不必要的Referer（目标站点可能验证Referer合法性）。修改重定向部分的代码：

if (redirect) {
    String newUrl = conn.getHeaderField("Location");
    String cookies = conn.getHeaderField("Set-Cookie");
    
    // 打开新连接
    URL newUrlObj = new URL(newUrl);
    conn = (HttpURLConnection) newUrlObj.openConnection();
    
    // 传递原请求的Authorization头
    conn.addRequestProperty("Authorization", "Basic *****************");
    if (cookies != null) {
        conn.setRequestProperty("Cookie", cookies);
    }
    conn.addRequestProperty("Accept-Language", "en-US,en;q=0.8");
    conn.addRequestProperty("User-Agent", "Mozilla/5.0"); // 使用标准的User-Agent
    // 移除不必要的Referer，或者设置为原HTTP URL
    // conn.addRequestProperty("Referer", url);
    conn.setReadTimeout(5000);
    conn.setConnectTimeout(5000); // 添加连接超时
    System.out.println("Redirect to URL : " + newUrl);
}

3. 调整连接参数

原代码只设置了readTimeout，建议添加connectTimeout，同时设置followRedirects为false（因为我们手动处理重定向，避免自动跳转带来的问题）：

在第一次创建连接时添加：

conn.setConnectTimeout(5000);
conn.setInstanceFollowRedirects(false); // 禁用自动重定向，手动处理

4. 使用Apache HttpClient替代HttpURLConnection

HttpURLConnection对HTTPS和重定向的处理比较繁琐，Apache HttpClient会自动处理很多细节，包括证书（可配置）和重定向。示例代码（HttpClient 4.x）：

CloseableHttpClient httpClient = HttpClients.custom()
        .setSSLHostnameVerifier(NoopHostnameVerifier.INSTANCE)
        .setSSLContext(new SSLContextBuilder().loadTrustMaterial(null, (chain, authType) -> true).build())
        .build();

try {
    HttpGet request = new HttpGet("http://api.demo.globalgatewaye4.firstdata.com/transaction/search?start_date=2018-01-07&end_date=2018-01-09");
    request.addHeader("Authorization", "Basic *****************");
    request.addHeader("User-Agent", "Mozilla/5.0");

    CloseableHttpResponse response = httpClient.execute(request);
    try {
        System.out.println("Response Code: " + response.getStatusLine().getStatusCode());
        HttpEntity entity = response.getEntity();
        if (entity != null) {
            String result = EntityUtils.toString(entity);
            System.out.println("URL Content... \n" + result);
        }
    } finally {
        response.close();
    }
} catch (Exception e) {
    e.printStackTrace();
} finally {
    httpClient.close();
}

注意：生产环境中不要盲目信任所有证书，应该导入目标站点的合法证书到Java的信任库中。

内容的提问来源于stack exchange，提问作者Skadoosh