java发送消息到公众号代码

要使用 Java 发送消息到公众号，你需要先获取到对应公众号的 AppID 和 AppSecret，然后使用 Java 的 HTTP 客户端发送 POST 请求到微信公众平台提供的 API 地址。以下是一个简单的示例代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;

public class WeChatMessageSender {

    public static void main(String[] args) {

        String appId = "your_app_id";
        String appSecret = "your_app_secret";
        String openId = "user_open_id";
        String message = "Hello, world!";

        try {
            // 获取 access_token
            String accessTokenUrl = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=" + appId + "&secret=" + appSecret;
            URL url = new URL(accessTokenUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            StringBuilder response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();
            String accessToken = response.toString().split("\"access_token\":")[1].split(",")[0].replaceAll("\"", "");

            // 发送消息
            String messageUrl = "https://api.weixin.qq.com/cgi-bin/message/custom/send?access_token=" + accessToken;
            url = new URL(messageUrl);
            connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("POST");
            connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            connection.setDoOutput(true);
            String postData = "touser=" + openId + "&msgtype=text&text=" + URLEncoder.encode(message, "UTF-8");
            connection.getOutputStream().write(postData.getBytes());
            reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();
            System.out.println("消息发送成功！");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

在上面的代码中，我们首先获取了对应公众号的 access_token，然后使用 access_token 和用户的 open_id 发送了一条文本消息。注意：在实际使用中，你需要根据你的具体需求修改 AppID、AppSecret、open_id 和消息内容等信息。