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Sentinel源码（一）SentinelResourceAspect
2022-08-02 14:01:00 【Ethan_199402】
本文版本：1.8.0
SentinelResourceAspect
Sentinel是做什么的就不详细介绍了，有需要的请点击注解支持
接下来就从SentinelResourceAspect开始探索Sentinel
我们知道，只要在方法上加上SentinelResource，就可以配置一些限流熔断策略，那么就要看这个注解被用在源码的什么地方
@Aspect
public class SentinelResourceAspect extends AbstractSentinelAspectSupport {
@Pointcut("@annotation(com.alibaba.csp.sentinel.annotation.SentinelResource)")
public void sentinelResourceAnnotationPointcut() {
}
@Around("sentinelResourceAnnotationPointcut()")
public Object invokeResourceWithSentinel(ProceedingJoinPoint pjp) throws Throwable {
Method originMethod = resolveMethod(pjp);
SentinelResource annotation = originMethod.getAnnotation(SentinelResource.class);
if (annotation == null) {
// Should not go through here.
throw new IllegalStateException("Wrong state for SentinelResource annotation");
}
String resourceName = getResourceName(annotation.value(), originMethod);
EntryType entryType = annotation.entryType();
int resourceType = annotation.resourceType();
Entry entry = null;
try {
entry = SphU.entry(resourceName, resourceType, entryType, pjp.getArgs());
Object result = pjp.proceed();
return result;
} catch (BlockException ex) {
return handleBlockException(pjp, annotation, ex);
} catch (Throwable ex) {
Class<? extends Throwable>[] exceptionsToIgnore = annotation.exceptionsToIgnore();
// The ignore list will be checked first.
if (exceptionsToIgnore.length > 0 && exceptionBelongsTo(ex, exceptionsToIgnore)) {
throw ex;
}
if (exceptionBelongsTo(ex, annotation.exceptionsToTrace())) {
traceException(ex);
return handleFallback(pjp, annotation, ex);
}
// No fallback function can handle the exception, so throw it out.
throw ex;
} finally {
if (entry != null) {
entry.exit(1, pjp.getArgs());
}
}
}
}
可以看到，SentinelResourceAspect继承于AbstractSentinelAspectSupport，定义如下切面
@Pointcut("@annotation(com.alibaba.csp.sentinel.annotation.SentinelResource)")
public void sentinelResourceAnnotationPointcut() {
}
也就是所有使用到@SentinelResource的地方，可以看到环绕通知中使用entry = SphU.entry(resourceName, resourceType, entryType, pjp.getArgs());进行代码增强，紧接着就执行真正的代码逻辑Object result = pjp.proceed();，所以可以知道所有的奥秘都在SphU.entry()这个方法中，关于他的详细介绍我们放在下一篇文中章中
异常
接下来看发生异常时，这个aop做了什么
阻塞异常
由于触发流控制、断路或系统保护而被 Sentinel 阻塞
catch (BlockException ex) {
return handleBlockException(pjp, annotation, ex);
那么就看handleBlockException方法
protected Object handleBlockException(ProceedingJoinPoint pjp, SentinelResource annotation, BlockException ex)
throws Throwable {
// Execute block handler if configured.
Method blockHandlerMethod = extractBlockHandlerMethod(pjp, annotation.blockHandler(),
annotation.blockHandlerClass());
if (blockHandlerMethod != null) {
Object[] originArgs = pjp.getArgs();
// Construct args.
Object[] args = Arrays.copyOf(originArgs, originArgs.length + 1);
args[args.length - 1] = ex;
try {
if (isStatic(blockHandlerMethod)) {
return blockHandlerMethod.invoke(null, args);
}
return blockHandlerMethod.invoke(pjp.getTarget(), args);
} catch (InvocationTargetException e) {
// throw the actual exception
throw e.getTargetException();
}
}
// If no block handler is present, then go to fallback.
return handleFallback(pjp, annotation, ex);
}
首先提取blockhandler方法extractBlockHandlerMethod
private Method extractBlockHandlerMethod(ProceedingJoinPoint pjp, String name, Class<?>[] locationClass) {
if (StringUtil.isBlank(name)) {
return null;
}
boolean mustStatic = locationClass != null && locationClass.length >= 1;
Class<?> clazz;
if (mustStatic) {
clazz = locationClass[0];
} else {
// By default current class.
clazz = pjp.getTarget().getClass();
}
MethodWrapper m = ResourceMetadataRegistry.lookupBlockHandler(clazz, name);
if (m == null) {
// First time, resolve the block handler.
Method method = resolveBlockHandlerInternal(pjp, name, clazz, mustStatic);
// Cache the method instance.
ResourceMetadataRegistry.updateBlockHandlerFor(clazz, name, method);
return method;
}
if (!m.isPresent()) {
return null;
}
return m.getMethod();
}
可以看到，根据传进来的locationClass作为寻找blockhandler的基类，如果没有传，那就是当前类。
如果提供的类中没有对应的blockhandler方法，也会resolveBlockHandlerInternal方法找到
当获得了blockHandlerMethod，接下来就调用这个方法，如果没有获得blockHandlerMethod，则调用fallback
//当获得了blockHandlerMethod，接下来就调用这个方法
if (blockHandlerMethod != null) {
Object[] originArgs = pjp.getArgs();
// Construct args.
Object[] args = Arrays.copyOf(originArgs, originArgs.length + 1);
args[args.length - 1] = ex;
try {
if (isStatic(blockHandlerMethod)) {
return blockHandlerMethod.invoke(null, args);
}
return blockHandlerMethod.invoke(pjp.getTarget(), args);
} catch (InvocationTargetException e) {
// throw the actual exception
throw e.getTargetException();
}
}
//如果没有获得blockHandlerMethod，则调用fallback
// If no block handler is present, then go to fallback.
return handleFallback(pjp, annotation, ex);
其他异常
catch (Throwable ex) {
Class<? extends Throwable>[] exceptionsToIgnore = annotation.exceptionsToIgnore();
// The ignore list will be checked first.
if (exceptionsToIgnore.length > 0 && exceptionBelongsTo(ex, exceptionsToIgnore)) {
throw ex;
}
if (exceptionBelongsTo(ex, annotation.exceptionsToTrace())) {
traceException(ex);
return handleFallback(pjp, annotation, ex);
}
// No fallback function can handle the exception, so throw it out.
throw ex;
首先如果是SentinelResource注解上配置的需要忽略的异常，则直接抛出该异常
// The ignore list will be checked first.
if (exceptionsToIgnore.length > 0 && exceptionBelongsTo(ex, exceptionsToIgnore)) {
throw ex;
}
如果是SentinelResource注解配置的需要跟踪的异常（默认是Throwable），则调用Fallback方法
if (exceptionBelongsTo(ex, annotation.exceptionsToTrace())) {
traceException(ex);
return handleFallback(pjp, annotation, ex);
}
那么再看一下handleFallback方法
protected Object handleFallback(ProceedingJoinPoint pjp, String fallback, String defaultFallback,
Class<?>[] fallbackClass, Throwable ex) throws Throwable {
Object[] originArgs = pjp.getArgs();
// Execute fallback function if configured.
Method fallbackMethod = extractFallbackMethod(pjp, fallback, fallbackClass);
if (fallbackMethod != null) {
// Construct args.
int paramCount = fallbackMethod.getParameterTypes().length;
Object[] args;
if (paramCount == originArgs.length) {
args = originArgs;
} else {
args = Arrays.copyOf(originArgs, originArgs.length + 1);
args[args.length - 1] = ex;
}
try {
if (isStatic(fallbackMethod)) {
return fallbackMethod.invoke(null, args);
}
return fallbackMethod.invoke(pjp.getTarget(), args);
} catch (InvocationTargetException e) {
// throw the actual exception
throw e.getTargetException();
}
}
// If fallback is absent, we'll try the defaultFallback if provided.
return handleDefaultFallback(pjp, defaultFallback, fallbackClass, ex);
}
可以看到，类似于handleBlockException方法首先使用extractFallbackMethod获得fallback方法，根据传进来的locationClass作为寻找fallbackMethod的基类，如果没有传，那就是当前类。
如果提供的类中没有对应的fallback方法，也会resolveFallbackInternal方法找到
当获得了fallbackMethod，接下来就调用这个方法，如果没有获得fallbackMethod，则调用defaultFallback，同样的如果没有配置defaultFallback，则会直接抛出异常
protected Object handleDefaultFallback(ProceedingJoinPoint pjp, String defaultFallback,
Class<?>[] fallbackClass, Throwable ex) throws Throwable {
// Execute the default fallback function if configured.
Method fallbackMethod = extractDefaultFallbackMethod(pjp, defaultFallback, fallbackClass);
if (fallbackMethod != null) {
// Construct args.
Object[] args = fallbackMethod.getParameterTypes().length == 0 ? new Object[0] : new Object[] {
ex};
try {
if (isStatic(fallbackMethod)) {
return fallbackMethod.invoke(null, args);
}
return fallbackMethod.invoke(pjp.getTarget(), args);
} catch (InvocationTargetException e) {
// throw the actual exception
throw e.getTargetException();
}
}
// If no any fallback is present, then directly throw the exception.
throw ex;
}
总结
- SentinelResource注解可以配置两个Handler，一个是由于触发流控制、断路或系统保护而被 Sentinel 阻塞时，需要调用的blockHandler，一个是可配置的异常发生时（默认为Throwable）需要调用的fallback
- 当抛出BlockException时，调用handleBlockException方法寻找配置的blockHandler并调用
- 当抛出Throwable时，如果配置了exceptionsToIgnore，配置的异常列表会被直接抛出，无论是否配置在exceptionsToTrace列表中；如果该异常也没有配置在exceptionsToTrace中，也会抛出；如果配置在exceptionsToTrace中，则根据handleFallback方法找到配置的fallback并调用
- 如果blockHandler没有配置，会调用fallback，如果fallback没有配置，则调用defaultFallback，如果defaultFallback也没有配置则直接抛出异常
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