聊聊sentinel的SentinelResourceAspect-白红宇

聊聊sentinel的SentinelResourceAspect

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发布时间：2019-06-28

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本文主要研究一下sentinel的SentinelResourceAspect

SentinelResourceAspect

com/alibaba/csp/sentinel/annotation/aspectj/SentinelResourceAspect.java

@Aspectpublic class SentinelResourceAspect {    private final Logger logger = LoggerFactory.getLogger(SentinelResourceAspect.class);    @Pointcut("@annotation(com.alibaba.csp.sentinel.annotation.SentinelResource)")    public void sentinelResourceAnnotationPointcut() {    }    @Around("sentinelResourceAnnotationPointcut()")    public Object invokeResourceWithSentinel(ProceedingJoinPoint pjp) throws Throwable {        Method originMethod = getMethod(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 = annotation.value();        EntryType entryType = annotation.entryType();        Entry entry = null;        try {            ContextUtil.enter(resourceName);            entry = SphU.entry(resourceName, entryType);            Object result = pjp.proceed();            return result;        } catch (BlockException ex) {            return handleBlockException(pjp, annotation, ex);        } finally {            if (entry != null) {                entry.exit();            }            ContextUtil.exit();        }    }    //......}

使用aspect的around拦截，拦截标注有SentinelResource的注解

进入方法之前调用SphU.entry(resourceName, entryType)，结束之后调用entry.exit();

异常的时候调用handleBlockException方法

handleBlockException

private Object handleBlockException(ProceedingJoinPoint pjp, SentinelResource annotation, BlockException ex)        throws Exception {        // Execute fallback for degrading if configured.        Object[] originArgs = pjp.getArgs();        if (isDegradeFailure(ex)) {            Method method = extractFallbackMethod(pjp, annotation.fallback());            if (method != null) {                return method.invoke(pjp.getTarget(), originArgs);            }        }        // Execute block handler if configured.        Method blockHandler = extractBlockHandlerMethod(pjp, annotation.blockHandler(), annotation.blockHandlerClass());        if (blockHandler != null) {            // Construct args.            Object[] args = Arrays.copyOf(originArgs, originArgs.length + 1);            args[args.length - 1] = ex;            if (isStatic(blockHandler)) {                return blockHandler.invoke(null, args);            }            return blockHandler.invoke(pjp.getTarget(), args);        }        // If no block handler is present, then directly throw the exception.        throw ex;    }

这里会先判断是否是降级需要处理的异常，是的话，则调用fallback方法，否则调用block handler方法

SentinelResource

com/alibaba/csp/sentinel/annotation/SentinelResource.java

@Target(ElementType.METHOD)@Retention(RetentionPolicy.RUNTIME)@Inheritedpublic @interface SentinelResource {    /**     * @return name of the Sentinel resource     */    String value();    /**     * @return the entry type (inbound or outbound), outbound by default     */    EntryType entryType() default EntryType.OUT;    /**     * @return name of the block exception function, empty by default     */    String blockHandler() default "";    /**     * The {@code blockHandler} is located in the same class with the original method by default.     * However, if some methods share the same signature and intend to set the same block handler,     * then users can set the class where the block handler exists. Note that the block handler method     * must be static.     *     * @return the class where the block handler exists, should not provide more than one classes     */    Class
    [] blockHandlerClass() default {};    /**     * @return name of the fallback function, empty by default     */    String fallback() default "";}