feat: 实现微信小程序码生成后端接口

- 新增 WxController 提供 /api/wx-mini/wxacode 接口
- 新增 WxService 实现 access_token 缓存和小程序码生成
- 新增 HttpUtil.postJsonBytes() 方法处理二进制响应
- 配置 application.yml 支持 env 环境参数

主要功能：
1. access_token 自动缓存，5分钟过期缓冲避免频繁调用
2. 支持生成任意页面小程序码，最大宽度 430px
3. 支持环境版本参数（release/trial/develop）
4. 返回 Base64 图片数据，避免服务器文件存储
5. 使用 Jackson ObjectMapper 处理 JSON 序列化

技术细节：
- HttpURLConnection 请求微信 API
- Base64 编码图片数据
- 场景参数限制 32 字符
- 错误处理和异常捕获

src/main/java/com/example/mini_program/controller/WxController.java

@@ -0,0 +1,61 @@
+package com.example.mini_program.controller;
+
+import com.example.mini_program.common.Result;
+import com.example.mini_program.service.WxService;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.Map;
+
+@Slf4j
+@RestController
+@RequestMapping("/api/wx-mini")
+@RequiredArgsConstructor
+public class WxController {
+
+    private final WxService wxService;
+
+    /**
+     * 生成小程序码
+     */
+    @PostMapping("/wxacode")
+    public Result<String> getWxacode(@RequestBody Map<String, String> request) {
+        String scene = request.get("scene");
+        String page = request.get("page");
+        String envVersion = request.get("envVersion");
+
+        if (scene == null || scene.trim().isEmpty()) {
+            return Result.error("scene不能为空");
+        }
+
+        page = (page != null && !page.trim().isEmpty()) ? page : "pages/scan/result/index";
+
+        Integer width = parseWidth(request.get("width"));
+
+        if (envVersion == null || envVersion.trim().isEmpty()) {
+            envVersion = wxService.getDefaultEnvVersion();
+        }
+
+        try {
+            String base64Image = wxService.getUnlimitedWxacode(scene, page, width, envVersion);
+            return Result.success(base64Image);
+        } catch (Exception e) {
+            log.error("生成小程序码失败", e);
+            return Result.error("生成小程序码失败: " + e.getMessage());
+        }
+    }
+
+    private Integer parseWidth(String widthStr) {
+        if (widthStr == null || widthStr.trim().isEmpty()) {
+            return 430;
+        }
+        try {
+            int width = Integer.parseInt(widthStr);
+            return width > 0 ? width : 430;
+        } catch (NumberFormatException e) {
+            log.warn("width参数格式错误: {}", widthStr);
+            return 430;
+        }
+    }
+}

src/main/java/com/example/mini_program/service/WxService.java

@@ -0,0 +1,128 @@
+package com.example.mini_program.service;
+
+import com.example.mini_program.config.WxMiniAppConfig;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import lombok.Data;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+
+import java.nio.charset.StandardCharsets;
+
+@Slf4j
+@Service
+public class WxService {
+
+    private static final String WXACODE_URL = "https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=%s";
+    private static final String TOKEN_URL = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=%s&secret=%s";
+    private static final int TOKEN_EXPIRE_BUFFER = 300; // access_token提前过期时间（秒）
+
+    private final WxMiniAppConfig wxMiniAppConfig;
+    private final RestTemplate restTemplate;
+    private final ObjectMapper objectMapper;
+
+    @Value("${wx.miniapp.env:release}")
+    private String defaultEnvVersion;
+
+    private String cachedAccessToken;
+    private long tokenExpireTime;
+
+    public WxService(WxMiniAppConfig wxMiniAppConfig, RestTemplate restTemplate) {
+        this.wxMiniAppConfig = wxMiniAppConfig;
+        this.restTemplate = restTemplate;
+        this.objectMapper = new ObjectMapper();
+    }
+
+    /**
+     * 生成小程序码
+     */
+    public String getUnlimitedWxacode(String scene, String page, int width, String envVersion) throws Exception {
+        // 参数校验
+        if (scene == null || scene.trim().isEmpty()) {
+            throw new IllegalArgumentException("scene不能为空");
+        }
+        if (scene.length() > 32) {
+            throw new IllegalArgumentException("scene长度不能超过32个字符");
+        }
+
+        // 使用传入的环境版本，若为空则使用默认值
+        if (envVersion == null || envVersion.trim().isEmpty()) {
+            envVersion = defaultEnvVersion;
+        }
+
+        String accessToken = getAccessToken();
+        String requestBody = objectMapper.writeValueAsString(new WxacodeRequest(scene, page, width, envVersion));
+
+        log.info("生成小程序码: scene={}, page={}, width={}, env={}", scene, page, width, envVersion);
+
+        byte[] response = com.example.mini_program.util.HttpUtil.postJsonBytes(
+            String.format(WXACODE_URL, accessToken),
+            requestBody
+        );
+
+        if (response.length > 0 && response[0] == '{') {
+            String errorMsg = new String(response, StandardCharsets.UTF_8);
+            log.error("微信API返回错误: {}", errorMsg);
+            throw new RuntimeException("微信小程序码生成失败: " + errorMsg);
+        }
+
+        log.info("小程序码生成成功，大小: {} bytes", response.length);
+        return java.util.Base64.getEncoder().encodeToString(response);
+    }
+
+    public String getDefaultEnvVersion() {
+        return defaultEnvVersion;
+    }
+
+    /**
+     * 获取微信access_token（带缓存）
+     */
+    private String getAccessToken() throws Exception {
+        if (cachedAccessToken != null && System.currentTimeMillis() < tokenExpireTime) {
+            return cachedAccessToken;
+        }
+
+        String url = String.format(TOKEN_URL, wxMiniAppConfig.getAppid(), wxMiniAppConfig.getSecret());
+        log.info("刷新access_token");
+
+        String response = restTemplate.getForObject(url, String.class);
+        JsonNode json = objectMapper.readTree(response);
+
+        String accessToken = json.get("access_token").asText();
+        int expiresIn = json.get("expires_in").asInt();
+
+        cachedAccessToken = accessToken;
+        tokenExpireTime = System.currentTimeMillis() + (expiresIn - TOKEN_EXPIRE_BUFFER) * 1000L;
+
+        log.info("access_token已更新，有效期: {} 秒", expiresIn);
+        return accessToken;
+    }
+
+    /**
+     * 小程序码请求参数
+     */
+    @Data
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    private static class WxacodeRequest {
+        private String scene;
+        private String page;
+        private Integer width;
+        private Boolean check_path;
+        private String env_version;
+        private Boolean auto_color;
+        private Boolean is_hyaline;
+
+        WxacodeRequest(String scene, String page, int width, String envVersion) {
+            this.scene = scene;
+            this.page = page;
+            this.width = width;
+            this.check_path = false;
+            this.env_version = envVersion;
+            this.auto_color = false;
+            this.is_hyaline = false;
+        }
+    }
+}

src/main/java/com/example/mini_program/util/HttpUtil.java

@@ -3,6 +3,7 @@ package com.example.mini_program.util;
 import lombok.extern.slf4j.Slf4j;
 
 import java.io.BufferedReader;
+import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.OutputStream;
 import java.net.HttpURLConnection;
@@ -55,6 +56,46 @@ public class HttpUtil {
         }
     }
 
+    public static byte[] postJsonBytes(String urlStr, String jsonBody) throws Exception {
+        HttpURLConnection conn = null;
+        try {
+            URL url = new URL(urlStr);
+            conn = (HttpURLConnection) url.openConnection();
+            conn.setRequestMethod("POST");
+            conn.setDoOutput(true);
+            conn.setConnectTimeout(CONNECT_TIMEOUT);
+            conn.setReadTimeout(READ_TIMEOUT);
+            conn.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
+            conn.setRequestProperty("Expect", ""); // 禁用 100-continue
+            try (OutputStream os = conn.getOutputStream()) {
+                os.write(jsonBody.getBytes(StandardCharsets.UTF_8));
+                os.flush();
+            }
+            int code = conn.getResponseCode();
+            if (code >= 300) {
+                String errorBody = readStringFromStream(conn.getErrorStream());
+                throw new RuntimeException("HTTP error " + code + ": " + errorBody);
+            }
+            try (InputStream is = conn.getInputStream()) {
+                return is.readAllBytes();
+            }
+        } finally {
+            if (conn != null) conn.disconnect();
+        }
+    }
+
+    private static String readStringFromStream(InputStream is) throws Exception {
+        if (is == null) return "";
+        try (BufferedReader reader = new BufferedReader(new InputStreamReader(is, StandardCharsets.UTF_8))) {
+            StringBuilder sb = new StringBuilder();
+            String line;
+            while ((line = reader.readLine()) != null) {
+                sb.append(line);
+            }
+            return sb.toString();
+        }
+    }
+
     private static String readResponse(HttpURLConnection conn) throws Exception {
         int code = conn.getResponseCode();
         try (BufferedReader reader = new BufferedReader(new InputStreamReader(

src/main/resources/application.yml

@@ -16,6 +16,7 @@ wx:
     appid: wx50fe0c5c28dd3060
     secret: e82fa407fad13a9df35503f2d176e5a4
     subscribe-template-id: Csf_dJU7DhvVFt_03sphPPBCGlnmcWQSPhgqfxHZ5RQ
+    env: develop  # 环境版本: release(正式版), trial(体验版), develop(开发版)
   corp: # 企业ID
       corpid: ww257614cff8a1b61b
       #  应用Secret