小程序登录，通过code获取openId

小程序的登录，通过前端传过来code，在服务端（java）获取openId.

首先你得有appid以及secret(秘钥).

下面是业务逻辑代码（这里为了方便展示直接写在了controller）

@GetMapping("getCode")
public AjaxResult getCode(String code){
    // 授权（必填）
    String wxspAppid = "填写小程序appid";
    String wxspSecret = "填写小程序密钥";
    //默认是authorization_code
    String grant_type = "authorization_code";
    // 请求参数
    String params = "appid=" + wxspAppid + "&secret=" + wxspSecret + "&js_code=" + code + "&grant_type=" + grant_type;
    // 发送请求
    String sr = HttpRequest.sendPost("https://api.weixin.qq.com/sns/jscode2session", params);
    // 解析相应内容（转换成json对象）
    JSONObject json = JSONObject.parseObject(sr);
    logger.info("解析code请求结果:"+json.toString());
    // 获取会话密钥（session_key）
    //String session_key = json.getString("session_key");
    //获取openId
    String openid = json.getString("openid");
    return AjaxResult.success(openid);
}

JSONObject 引入的是alibaba的jar

import com.alibaba.fastjson.JSONObject;

       <!--      alibaba json 工具  -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
        </dependency>

HttpRequest工具类类

package com.ckf.common.core.utils;

/**
 * @author serence
 * @date 2020/12/21 11:47
 */

import com.alibaba.fastjson.JSONObject;
import lombok.extern.slf4j.Slf4j;

import java.io.*;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;


@Slf4j
public class HttpRequest {
    /**
     * 向指定URL发送GET方法的请求
     *
     * @param url
     *            发送请求的URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return URL 所代表远程资源的响应结果
     */
    public static String sendGet(String url, String param) {
        String result = "";
        BufferedReader in = null;
        try {
            String urlNameString = url + "?" + param;
            URL realUrl = new URL(urlNameString);
            // 打开和URL之间的连接
            URLConnection connection = realUrl.openConnection();
            // 设置通用的请求属性
            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 建立实际的连接
            connection.connect();
            // 获取所有响应头字段
            Map<String, List<String>> map = connection.getHeaderFields();
            // 遍历所有的响应头字段
            /*
             * for (String key : map.keySet()) { System.out.println(key + "--->"
             * + map.get(key)); }
             */
            // 定义 BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"));

            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            log.error("发送GET请求出现异常:"+e);
        }
        // 使用finally块来关闭输入流
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (Exception e2) {
                e2.printStackTrace();
            }
        }
        return result;
    }

    /**
     * 单参数数据访问
     *
     */
    public static String sendGet(String url) {
        String result = "";
        BufferedReader in = null;
        try {
            String urlNameString = url;
            URL realUrl = new URL(urlNameString);
            // 打开和URL之间的连接
            URLConnection connection = realUrl.openConnection();
            // 设置通用的请求属性
            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 建立实际的连接
            connection.connect();
            // 获取所有响应头字段
            Map<String, List<String>> map = connection.getHeaderFields();
            // 遍历所有的响应头字段
            /*
             * for (String key : map.keySet()) { System.out.println(key + "--->"
             * + map.get(key)); }
             */
            // 定义 BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            //System.out.println("发送GET请求出现异常！" + e);
            e.printStackTrace();
        }
        // 使用finally块来关闭输入流
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (Exception e2) {
                e2.printStackTrace();
            }
        }
        return result;
    }

    /**
     * 向指定 URL 发送POST方法的请求
     *
     * @param url
     *            发送请求的 URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return 所代表远程资源的响应结果
     */
    public static String sendPost(String url, String param) {
        PrintWriter out = null;
        BufferedReader in = null;
        String result = "";
        try {
            URL realUrl = new URL(url);
            // 打开和URL之间的连接
            URLConnection conn = realUrl.openConnection();
            // 设置通用的请求属性
            conn.setRequestProperty("accept", "*/*");
            conn.setRequestProperty("connection", "Keep-Alive");
            conn.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 发送POST请求必须设置如下两行
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 获取URLConnection对象对应的输出流
            out = new PrintWriter(conn.getOutputStream());
            // 发送请求参数
            out.print(param);
            // flush输出流的缓冲
            out.flush();
            // 定义BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("发送 POST 请求出现异常！" + e);
            e.printStackTrace();
        }
        // 使用finally块来关闭输出流、输入流
        finally {
            try {
                if (out != null) {
                    out.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
        return result;
    }

    public static String doPost(String postUrl, JSONObject obj) {
        String lines = "";
        StringBuffer sb = new StringBuffer("");
        try {
            // 创建连接
            URL url = new URL(postUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setDoOutput(true);
            connection.setDoInput(true);
            connection.setRequestMethod("POST");
            connection.setUseCaches(false);
            connection.setInstanceFollowRedirects(true);
            connection.setRequestProperty("Content-Type", "application/json");
            connection.connect();
            // POST请求
            DataOutputStream out = new DataOutputStream(connection.getOutputStream());
            // out.writeChars(obj.toString());
            // out.write(obj.toString().getBytes("UTF-8"));
            out.write(obj.toString().getBytes());
            out.flush();
            out.close();
            // 读取响应
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"));

            while ((lines = reader.readLine()) != null) {
                lines = new String(lines.getBytes());
                sb.append(lines);
            }
            System.out.println(sb);

            reader.close();
            // 断开连接
            connection.disconnect();
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return sb.toString();
    }
    

}

好了，有问题的小伙伴请留言哦！