Java 實現微信公眾號素材上傳介面：HTTPS POST 上傳圖片/多媒體檔案

核心代碼

public class WeChatMediaUploader {
    private static final String UPLOAD_URL = "https://api.weixin.qq.com/cgi-bin/media/upload?access_token=%s&type=%s";

    public static String upload(String accessToken, String type, File file) throws Exception {
        String url = String.format(UPLOAD_URL, accessToken, type); // type: image, voice, video, thumb
        HttpsURLConnection conn = createTrustAllConnection(url);
        conn.setRequestMethod("POST");
        conn.setDoOutput(true);
        conn.setRequestProperty("Connection", "Keep-Alive");
        conn.setRequestProperty("Charset", "UTF-8");

        String boundary = "----WebKitFormBoundary" + System.currentTimeMillis();
        conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

        try (OutputStream out = conn.getOutputStream();
             PrintWriter writer = new PrintWriter(new OutputStreamWriter(out, "UTF-8"), true)) {
            writer.append("--").append(boundary).append("\r\n");
            writer.append("Content-Disposition: form-data; name=\"media\"; filename=\"").append(file.getName()).append("\"\r\n");
            writer.append("Content-Type: ").append(Files.probeContentType(file.toPath())).append("\r\n\r\n");
            writer.flush();
            Files.copy(file.toPath(), out);
            out.flush();
            writer.append("\r\n").append("--").append(boundary).append("--\r\n");
            writer.flush();
        }

        try (BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream(), "UTF-8"))) {
            StringBuilder sb = new StringBuilder();
            String line;
            while ((line = br.readLine()) != null) sb.append(line);
            // 解析 JSON 回傳 media_id
            return parseMediaId(sb.toString());
        }
    }

    private static HttpsURLConnection createTrustAllConnection(String url) throws Exception {
        TrustManager[] tm = { new X509TrustManager() {
            public void checkClientTrusted(X509Certificate[] c, String a) {}
            public void checkServerTrusted(X509Certificate[] c, String a) {}
            public X509Certificate[] getAcceptedIssuers() { return new X509Certificate[0]; }
        }};
        SSLContext ssl = SSLContext.getInstance("TLS");
        ssl.init(null, tm, new SecureRandom());
        HttpsURLConnection conn = (HttpsURLConnection) new URL(url).openConnection();
        conn.setSSLSocketFactory(ssl.getSocketFactory());
        conn.setHostnameVerifier((h, s) -> true);
        return conn;
    }
}

注意

• 生產環境**不要**使用信任所有憑證，請正確載入微信 CA 憑證或使用預設信任庫。
• access_token 需定期刷新（有效期 2 小時）。
• 檔案大小限制：圖片 10MB、語音 2MB、視頻 10MB、縮略圖 64KB。