上下文数据传递与隔离Java ThreadLocal / Grpc Context

前言：

Java ThreadLocal使用示例：

1. 定义一个ThreadLocalUtil工具类来存储用户信息

   public class ThreadLocalUtil {
   
       private static final ThreadLocal<UserEntity> threadLocal = new ThreadLocal<>();
   
       public static void setThreadLocal(UserEntity userEntity) {
           threadLocal.set(userEntity);
       }
   
       public static UserEntity getThreadLocal() {
           return threadLocal.get();
       }
   
       public static void removeThreadLocal() {
           threadLocal.remove();
       }
   }

2. 赋值ThreadLocal的User用户信息

   @Slf4j
   @Configuration
   public class HelperInterceptor extends OncePerRequestFilter {
   
       @Override
       protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
           UserEntity userEntity = new UserEntity();
           try {
               String token = request.getHeader("TOKEN");
               if (token != null && !token.isEmpty()) {
                   String userName = JwtUtil.getUserName(token);
                   String userId = JwtUtil.getUserId(token);
                   userEntity.setUserName(userName);
                   userEntity.setUserId(userId);
               }
           } catch (Exception e) {
               log.error("HelperInterceptor: ", e);
           } finally {
               ThreadLocalUtil.setThreadLocal(userEntity);
               filterChain.doFilter(request, response);
           }
       }
   }
   

3. 其他位置从ThreadLocal获取User信息

   ThreadLocalUtil.getThreadLocal();

4. 注意点：Java Spring Boot中，当使用内置的Web服务器如tomcat，线程池通常会被配置为可复用的并不会立即销毁，ThreadLocal又是与线程绑定的，一旦遇到使用过的线程可能会从ThreadLocal获取到旧数据，所以我们每次用完ThreadLocal就需要clear，或者每次ThreadLocal进行初始化赋值。

Grpc Context使用示例：

1. 定义一个GrpcMetadataKey工具类来存储Context Key，保证存取引用地址一致

   public interface GrpcMetadataKey {
   
       Context.Key<String> CONTEXT_IP = Context.key("ip");
   
   }
   

2. 赋值Context CONTEXT_IP 的ip信息

   @GrpcGlobalServerInterceptor
   public class GlobalInterceptor implements ServerInterceptor {
   
       @Override
       public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(ServerCall<ReqT, RespT> call, Metadata headers, ServerCallHandler<ReqT, RespT> next) {
   
           Context context = Context.current().withValue(
                   GrpcMetadataKey.CONTEXT_IP
                   , headers.get(Metadata.Key.of("x-forwarded-for", Metadata.ASCII_STRING_MARSHALLER)));
   
           return Contexts.interceptCall(context, call, headers, next);
       }
   }
   

3. 其他位置从Context获取User信息

   GrpcMetadataKey.CONTEXT_IP.get();

4. 注意点：与Java ThreadLocal类似，Context一定要进行初始化赋值或清空。