如果用Spring那套RestTemplate不能獲取，或者獲取了生成的圖片檔案是無法開啟的，大小是150多k的（當寬度為430的時候，應該是55k左右），可以看看我的方法

package com.wx.scooter;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;

import org.apache.http.HttpResponse;
import org.apache.http
 
.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.protocol.HTTP;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders
 
;
import org.springframework.http.HttpMethod;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.wx.scooter.tool.CheckTool
 
;
import com.wx.scooter.tool.Constant;

public class TestQR {
    public static void main2(String[] args) throws Exception {
        //獲取token
        String result1 = get("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid="+Constant.NATIVE_APP_ID+"&secret="+Constant.NATIVE_APP_SECRET);
        String access_token = JSONObject.parseObject(result1).getString("access_token");
        if(CheckTool.isString(access_token)) {
            System.out.println("token為");
            System.out.println(access_token);
            Map<String, Object> params = new HashMap<>();
            params.put("scene", "test");
            params.put("page", "pages/index/index");
            params.put("width", 430);

            CloseableHttpClient  httpClient = HttpClientBuilder.create().build();

            HttpPost httpPost = new HttpPost("https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token="+access_token);
            httpPost.addHeader(HTTP.CONTENT_TYPE, "application/json");
            String body = JSON.toJSONString(params);
            StringEntity entity;
            entity = new StringEntity(body);
            entity.setContentType("image/png");

            httpPost.setEntity(entity);
            HttpResponse response;

            response = httpClient.execute(httpPost);
            InputStream inputStream = response.getEntity().getContent();

            File targetFile = new File("D:\\");  
            if(!targetFile.exists()){    
                targetFile.mkdirs();    
            }       
            FileOutputStream out = new FileOutputStream("D:\\upload\\5.png");

            byte[] buffer = new byte[8192];
            int bytesRead = 0;
            while((bytesRead = inputStream.read(buffer, 0, 8192)) != -1) {
                out.write(buffer, 0, bytesRead);
            }

            out.flush();
            out.close();
        } else {
            System.out.println("獲取access_token錯誤");
        }
    }

    /**
     * 傳送get請求
     * @param url
     * @return
     */
    public static String get(String url) {
        RestTemplate restTemplate = new RestTemplate();
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
        HttpEntity<String> entity = new HttpEntity<String>(url, headers);
        ResponseEntity<String> responseEntity = restTemplate.exchange(url, HttpMethod.GET, entity, String.class);
        return responseEntity.getBody();
    }
}