上面要求添加 traceId，需求很简单。
唯一的难点是，jakarta.servlet.http.HttpServletRequest 不支持直接 put 请求头。
所以需要创建一个可修改的对象，包装请求。
另外，由于我们应用还使用了 openFeign ,需要将 traceId 传递进去。
PS: 老大非要把appName用做traceId前缀，无语~

过滤器

import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.http.HttpFilter;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.MDC;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

/**
 * 追踪id过滤器
 *
 */
@WebFilter(urlPatterns = "/*")
@Component
@Slf4j
public class TraceIdFilter extends HttpFilter {

    @Value("${spring.application.name:appName}")
    private String appName;

    @Override
    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) {
        try {
            // 添加 Header
            String traceId = request.getHeader(HConst.TRACE_ID);
            // 已存在则放行
            if (StringUtils.isNotBlank(traceId)) {
                // 放入日志
                MDC.put(HConst.TRACE_ID, traceId);
                response.setHeader(HConst.TRACE_ID,traceId);
                chain.doFilter(request, response);
            } else {
                // 不存在则自生成
                traceId = appName + "-" + UUIDGenerator.getUUID();
                log.info("appGenerator traceId : {}",traceId);
                // 推入请求
                MutableHttpServletRequest muRequest = new MutableHttpServletRequest(request);
                response.setHeader(HConst.TRACE_ID,traceId);
                muRequest.putHeader(HConst.TRACE_ID, traceId);
                // 放入日志
                MDC.put(HConst.TRACE_ID, traceId);
                chain.doFilter(muRequest, response);
            }
        } catch (Exception e) {
            log.error("TRACE_id异常：", e);
            throw new RuntimeException("TRACE_id异常");
        }
    }
}

可修改的请求适配器

import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletRequestWrapper;

import java.util.*;

/**
 * 可修改的请求对象
 *
 */
public final class MutableHttpServletRequest extends HttpServletRequestWrapper {
    /**
     * 保持自定义头、值
     */
    private final Map<String, String> customHeaders;

    public MutableHttpServletRequest(HttpServletRequest request){
        super(request);
        this.customHeaders = new HashMap<>();
    }

    public void putHeader(String name, String value){
        this.customHeaders.put(name, value);
    }

    @Override
    public String getHeader(String name) {
        // 检查
        String headerValue = customHeaders.get(name);
        if (headerValue != null){
            return headerValue;
        }
        // 返回原头
        return ((HttpServletRequest) getRequest()).getHeader(name);
    }

    @Override
    public Enumeration<String> getHeaderNames() {
        // 创建自定义头容器
        Set<String> set = new HashSet<String>(customHeaders.keySet());
        // 添加头
        @SuppressWarnings("unchecked")
        Enumeration<String> e = ((HttpServletRequest) getRequest()).getHeaderNames();
        while (e.hasMoreElements()) {
            // 复制到新容器
            String n = e.nextElement();
            set.add(n);
        }
        // 重新构建并返回
        return Collections.enumeration(set);
    }

}

调用了 openFeign，将 traceId 传入代码

@Slf4j
@Component
public class CipherInterceptor implements RequestInterceptor {

    @Override
    public void apply(RequestTemplate template) {
        try {
            // 添加traceId
            addTraceId(template);
            byte[] body = template.body();
            String bodyStr = new String(body, StandardCharsets.UTF_8);
            // 打印请求消息
            log.info("feign-request-path: {}", template.path());
            log.info("feign-request-bodyStr : {}", bodyStr);
        } catch (Exception e) {
            log.error("CipherInterceptor error :", e);
        }
    }

    /**
     * 添加请求头
     * @param template 请求对象
     */
    private static void addTraceId(RequestTemplate template) {
        Map<String, Collection<String>> headers = template.headers();
        String traceId = ServletUtil.getHeader(HConst.TRACE_ID);
        if (StringUtils.isBlank(traceId)) {
            traceId = "feign-" + UUIDGenerator.getUUID();
        }
        headers.put(HConst.TRACE_ID, Collections.singletonList(traceId));
        log.info("feign-request-headers: {}", headers);
    }

}

其它代码

从请求上下文中获取请求头方法，生成 UUID

    public static String getHeader(String name){
        // 获取请求头信息
        ServletRequestAttributes requestAttributes =
            (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = null;
        if (requestAttributes != null) {
            request = requestAttributes.getRequest();
            return request.getHeader(name);
    }
        return null;
    }

    public static String getUUID() {
        String s = UUID.randomUUID().toString();
        return s.replaceAll("-", "");
    }