如何在Http拦截器中检索JSON有效负载？

import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
import org.springframework.http.MediaType;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonPayloadInterceptor extends HandlerInterceptorAdapter {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 获取请求主体
        String payload = request.getReader().lines().collect(Collectors.joining(System.lineSeparator()));
        
        // 检查Content-Type是否为JSON
        String contentType = request.getContentType();
        if (contentType != null && contentType.contains(MediaType.APPLICATION_JSON_VALUE)) {
            // 解析JSON数据
            ObjectMapper objectMapper = new ObjectMapper();
            JsonNode jsonPayload = objectMapper.readTree(payload);
            
            // 对JSON数据进行处理
            // 例如，提取特定字段
            String username = jsonPayload.get("username").asText();
            System.out.println("Username: " + username);
            
            // 或执行其他操作
            // ...
        }
        
        return true;
    }
}