skywalking07 - skywalking如何收集Controller的链路
对于我们在java中常用的注解@Controller、@RestController，在运行时，将会产生链路，在“链路追踪”中可以进行查看，那么来看看怎么收集的
Instrumentation 指明拦截的类
- 在org.apache.skywalking.apm.plugin.spring.mvc.v5.define.AbstractControllerInstrumentation抽象类的实现类ControllerInstrumentation、RestControllerInstrumentation中指定了ENHANCE_ANNOTATION分别为org.springframework.stereotype.Controller以及org.springframework.web.bind.annotation.RestController进行指定了增强的类。
public class RestControllerInstrumentation extends AbstractControllerInstrumentation { public static final String ENHANCE_ANNOTATION = "org.springframework.web.bind.annotation.RestController"; @Override protected String[] getEnhanceAnnotations() { return new String[] {ENHANCE_ANNOTATION}; } }
- 然后通过如下方法指定拦截增强的方法
@Override public InstanceMethodsInterceptPoint[] getInstanceMethodsInterceptPoints() { return new InstanceMethodsInterceptPoint[] { new DeclaredInstanceMethodsInterceptPoint() { @Override public ElementMatcher<MethodDescription> getMethodsMatcher() { return byMethodInheritanceAnnotationMatcher(named("org.springframework.web.bind.annotation.RequestMapping")); } }, new DeclaredInstanceMethodsInterceptPoint() { @Override public ElementMatcher<MethodDescription> getMethodsMatcher() { return byMethodInheritanceAnnotationMatcher(named("org.springframework.web.bind.annotation.GetMapping")) .or(byMethodInheritanceAnnotationMatcher(named("org.springframework.web.bind.annotation.PostMapping"))) .or(byMethodInheritanceAnnotationMatcher(named("org.springframework.web.bind.annotation.PutMapping"))) .or(byMethodInheritanceAnnotationMatcher(named("org.springframework.web.bind.annotation.DeleteMapping"))) .or(byMethodInheritanceAnnotationMatcher(named("org.springframework.web.bind.annotation.PatchMapping"))); } } }; }
- 同时定义了用来增强该类的增强类org.apache.skywalking.apm.plugin.spring.mvc.v5.ControllerConstructorInterceptor
InstanceConstructorInterceptor 进行类的增强
拦截构造实例的增强，直接对该Controller进行增强。该段代码中的注释比较重要！
/** * The <code>ControllerConstructorInterceptor</code> intercepts the Controller's constructor, in order to acquire the * mapping annotation, if exist. * <p> * But, you can see we only use the first mapping value, <B>Why?</B> * <p> * Right now, we intercept the controller by annotation as you known, so we CAN'T know which uri patten is actually * matched. Even we know, that costs a lot. * <p> * If we want to resolve that, we must intercept the Spring MVC core codes, that is not a good choice for now. * <p> * Comment by @wu-sheng */ public class ControllerConstructorInterceptor implements InstanceConstructorInterceptor { @Override public void onConstruct(EnhancedInstance objInst, Object[] allArguments) { String basePath = ""; RequestMapping basePathRequestMapping = objInst.getClass().getAnnotation(RequestMapping.class); if (basePathRequestMapping != null) { if (basePathRequestMapping.value().length > 0) { basePath = basePathRequestMapping.value()[0]; } else if (basePathRequestMapping.path().length > 0) { basePath = basePathRequestMapping.path()[0]; } } EnhanceRequireObjectCache enhanceRequireObjectCache = new EnhanceRequireObjectCache(); // PathMappingCache对象会存储方法中方法与URL映射的映射关系 enhanceRequireObjectCache.setPathMappingCache(new PathMappingCache(basePath)); objInst.setSkyWalkingDynamicField(enhanceRequireObjectCache); } }
- Right now, we intercept the controller by annotation as you known, so we CAN’T know which uri patten is actually matched. Even we know, that costs a lot.
截止目前，我们用注解的方式拦截controller，所以我们不知道匹配的具体的URI。即使我们能够知道，但是那个消耗太大。 - If we want to resolve that, we must intercept the Spring MVC core codes, that is not a good choice for now.
如果我们想要去解决这个问题，我们必须拦截Spring MVC 核心代码，但是目前那不是个好选择。
这段话，说明了一个问题，如果有如下代码：
@GetMapping("/test/{pageId}") public ApiResult<Boolean> test(@PathVariable("pageId") String pageId) { return ApiResult.ok(true); }
那么在链路追踪中，看到的链路就是：{GET} XXX/test/{pageId}，那么这个pageId并不会使用实际的值，例如“00001”等等，这么做主要考虑了性能的消耗。
不过这么做，对于进行性能分析会带来一定的困扰。尤其是我们工程中，每一个页面都是特殊编辑生成的，每个页面的性能相差巨大，如果仅仅是这样的展示，我们运用链路追踪中的Duration进行排序，则不会按照pageId进行归类了，很是头疼。所以你有解决方案吗？
AbstractMethodInterceptor 进行方法的增强
org.apache.skywalking.apm.plugin.spring.mvc.commons.interceptor.AbstractMethodInterceptor是RequestMappingMethodInterceptor以及RestMappingMethodInterceptor的父类。对方法进行增强，将上一步的映射关系在EnhanceRequireObjectCache中真正形成。并且生成对应的EntrySpan或者LocalSpan。
@Override public void beforeMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes, MethodInterceptResult result) throws Throwable { Boolean forwardRequestFlag = (Boolean) ContextManager.getRuntimeContext().get(FORWARD_REQUEST_FLAG); /** * Spring MVC plugin do nothing if current request is forward request. * Ref: https://github.com/apache/skywalking/pull/1325 */ if (forwardRequestFlag != null && forwardRequestFlag) { return; } String operationName; if (SpringMVCPluginConfig.Plugin.SpringMVC.USE_QUALIFIED_NAME_AS_ENDPOINT_NAME) { operationName = MethodUtil.generateOperationName(method); } else { EnhanceRequireObjectCache pathMappingCache = (EnhanceRequireObjectCache) objInst.getSkyWalkingDynamicField(); String requestURL = pathMappingCache.findPathMapping(method); if (requestURL == null) { requestURL = getRequestURL(method); // 添加方法与URL的映射关系 pathMappingCache.addPathMapping(method, requestURL); requestURL = pathMappingCache.findPathMapping(method); } operationName = getAcceptedMethodTypes(method) + requestURL; } RequestHolder request = (RequestHolder) ContextManager.getRuntimeContext() .get(REQUEST_KEY_IN_RUNTIME_CONTEXT); if (request != null) { StackDepth stackDepth = (StackDepth) ContextManager.getRuntimeContext().get(CONTROLLER_METHOD_STACK_DEPTH); if (stackDepth == null) { // 栈为空，为一个新的链路 ContextCarrier contextCarrier = new ContextCarrier(); CarrierItem next = contextCarrier.items(); while (next.hasNext()) { next = next.next(); next.setHeadValue(request.getHeader(next.getHeadKey())); } // 创建一个EntrySpan AbstractSpan span = ContextManager.createEntrySpan(operationName, contextCarrier); Tags.URL.set(span, request.requestURL()); Tags.HTTP.METHOD.set(span, request.requestMethod()); span.setComponent(ComponentsDefine.SPRING_MVC_ANNOTATION); SpanLayer.asHttp(span); if (SpringMVCPluginConfig.Plugin.SpringMVC.COLLECT_HTTP_PARAMS) { collectHttpParam(request, span); } if (!CollectionUtil.isEmpty(SpringMVCPluginConfig.Plugin.Http.INCLUDE_HTTP_HEADERS)) { collectHttpHeaders(request, span); } stackDepth = new StackDepth(); // 加入一个栈深度 ContextManager.getRuntimeContext().put(CONTROLLER_METHOD_STACK_DEPTH, stackDepth); } else { // 本地调用，创建一个LocalSpan AbstractSpan span = ContextManager.createLocalSpan(buildOperationName(objInst, method)); span.setComponent(ComponentsDefine.SPRING_MVC_ANNOTATION); } stackDepth.increment(); } }
总结
Controller的链路收集，主要分两步，一步是对类的增强，一步是对方法的增强。代码均位于apm-sniffer/apm-sdk-plugin/spring-plugins子工程中。
skywalking收集链路时，使用的URL都是通配符，在链路中，无法针对某个pageId，或者其他通配符的具体的值进行查找。或许skywalking出于性能考虑，但是对于这种不定的通用大接口，的确无法用于针对性的性能分析了。这个问题还需要深入思考寻找，能否在自己项目中，找到一个Balance，只针对自己需要分析性能的接口，按照具体值进行收集，而其他走默认呢？
PS:补充一下版本，SW 8.4版本，新版中已经将agent的部分抽到另一个git中了。
