使用springboot的RestTemplate获取微信二维码

// 二维码地址(小程序码，永久有效，数量暂无限制)
public final String WECHAT_ACODE_UNLIMIT_URL = "https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=";

public void getWxAcodePic(Integer param) {

    RestTemplate restTemplate = new RestTemplate();
    /**
     * 组装地址
     * 访问需要在地址中加入access_token，这里不详细写获取过程
     */
    StringBuilder postUrl = new StringBuilder(WECHAT_ACODE_UNLIMIT_URL);
    postUrl.append(tokenService.getWechatAccessToken());

    try {
        // 组装接口参数，这里做测试只写一个简单的int参数，根据需要自行修改
        String reqParamJson = this.buildAcodeUnlimitParam(param);

        HttpHeaders headers = new HttpHeaders();
        //定义请求参数类型，这里用json所以是MediaType.APPLICATION_JSON
        headers.setContentType(MediaType.APPLICATION_JSON);
        //RestTemplate带参传的时候要用HttpEntity<?>对象传递
        HttpEntity<String> request = new HttpEntity<>(reqParamJson, headers);
        ResponseEntity<Resource> resp = restTemplate.postForEntity(postUrl.toString(), request, Resource.class);
        Resource RespBody = resp.getBody();
        // 这里需要判断，返回的是不是流，如果不是流，则会返回错误信息，这里省略
        // 返回成功
        if(HttpStatus.OK.equals(resp.getStatusCode()) && null != RespBody) {
            // 组装文件路径
            String filePath = ImageBean.IMAGE_ORDER_ACODE_PATH + order.getOpenId() + order.getEventId() + ImageBean.IMAGE_TYPE_JPG;
            File acodePic = new File(filePath);
            FileOutputStream fileOutStream = new FileOutputStream(acodePic);
            int i;
            while((i = in.read()) != -1 ){
                fileOutStream.write(i);
            }
            // 释放资源
            fileOutStream.flush();
            fileOutStream.close();
            in.close();
        }
    } catch (IOException e) {
        // 会有json解析等错误，需要处理，自行斟酌
        e.printStackTrace();
    }
}

/**
 * 二维码参数组装
 * 
 * @return
 * @throws JsonProcessingException
 */
public String buildAcodeUnlimitParam(Integer orderId) throws JsonProcessingException  {
    Map<String, String> reqParam = new HashMap<>();
    reqParam.put("page", "pages/info/info");
    reqParam.put("scene", orderId.toString());
    ObjectMapper mapper = new ObjectMapper();
    return mapper.writeValueAsString(reqParam);
}

tokenService中access_token的获取方法

// 微信登录请求参数
public static final String WECHAT_APP_ID = "ur app id";
public static final String WECHAT_SECRET = "ur secret";
// 微信accessToken获取地址
public static final String WECHAT_ACCESS_URL = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential";

/** 微信accessToken缓存 */
public static String WECHAT_ACCESS_TOKEN_CACHE = null;
public static Long WECHAT_ACCESS_TOKEN_CACHE_TIME = null;

@Override
public String getWechatAccessToken() {
    
    String accessToken = null;
    Long now = System.currentTimeMillis();
    if(null != WECHAT_ACCESS_TOKEN_CACHE
        && null != WECHAT_ACCESS_TOKEN_CACHE_TIME
        && 5000000 > now - WECHAT_ACCESS_TOKEN_CACHE_TIME) {

        return WECHAT_ACCESS_TOKEN_CACHE;
    } else {
        RestTemplate restTemplate = new RestTemplate();
        // 组装接口地址
        StringBuilder accessUrl = new StringBuilder(WECHAT_ACCESS_URL);
        accessUrl.append("&appid=").append(WECHAT_APP_ID);
        accessUrl.append("&secret=").append(WECHAT_SECRET);
      
        String resp = restTemplate.getForObject(accessUrl.toString(), String.class);
      
        ObjectMapper mapper = new ObjectMapper();
        try {
            @SuppressWarnings("unchecked")
            Map<String, String> jsonMap = mapper.readValue(resp, Map.class);
            accessToken = jsonMap.get("access_token");
        } catch (JsonParseException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
      	    e.printStackTrace();
        } catch (IOException e) {
   	    e.printStackTrace();
        }
        WECHAT_ACCESS_TOKEN_CACHE = accessToken;
        WECHAT_ACCESS_TOKEN_CACHE_TIME = now;
    }
    return accessToken;
}