我观察到Hystrix将所有来自命令的异常视为断路故障.它包括从命令run()方法抛出并由Hystrix本身创建的异常,例如: HystrixTimeoutException.
但我有从run()方法抛出的业务异常,表示服务响应有效错误,必须进一步处理.
这种异常的一个例子是使用SpringWS的WebServiceTemplate时的WebServiceFaultException.
所以我不需要那些特定的例外来使电路跳闸.
如何实现这种行为?
有一种明显的方法可以将业务异常包装到holder对象中,从run()方法返回它,然后将它展开回Exception并重新抛出.但它想知道是否有更清洁的方式.
最佳答案 有以下解决方案.
返回异常而不是抛出
最直接和最脏的方法.这看起来有点时髦,因为你必须将命令擦除到Object并且有很多类型转换.
Observable<BusinessResponse> observable = new HystrixCommand<Object>() {
@Override
protected Object run() throws Exception {
try {
return doStuff(...);
} catch (BusinessException e) {
return e; // so Hystrix won't treat it as a failure
}
}
})
.observe()
.flatMap(new Func1<Object, Observable<BusinessResponse>>() {
@Override
public Observable<BusinessResponse> call(Object o) {
if (o instanceof BusinessException) {
return Observable.error((BusinessException)o);
} else {
return Observable.just((BusinessResponse)o);
}
}
});
使用holder对象来保存结果和异常
这个apporach需要引入额外的持有者类(也可以用于其他目的).
class ResultHolder<T, E extends Exception> {
private T result;
private E exception;
public ResultHolder(T result) {
this.result = result;
}
public ResultHolder(E exception) {
if (exception == null) {
throw new IllegalArgumentException("exception can not be null");
}
this.exception = exception;
}
public T get() throws E {
if (exception != null) {
throw exception;
} else {
return result;
}
}
public Observable<T> observe() {
if (exception != null) {
return Observable.error(exception);
} else {
return Observable.just(result);
}
}
@SuppressWarnings("unchecked")
public static <T, E extends Exception> ResultHolder<T, E> wrap(BusinessMethod<T, E> method) {
try {
return new ResultHolder<>(method.call());
} catch (Exception e) {
return new ResultHolder<>((E)e);
}
}
public static <T, E extends Exception> Observable<T> unwrap(ResultHolder<T, E> holder) {
return holder.observe();
}
interface BusinessMethod<T, E extends Exception> {
T call() throws E;
}
}
现在使用它的代码看起来更干净,唯一的缺点可能是相当多的泛型.此方法在Java 8中也是最好的,其中lambdas和方法引用可用,否则它看起来很笨重.
new HystrixCommand<ResultHolder<BusinessResponse, BusinessException>>() {
@Override
protected ResultHolder<BusinessResponse, BusinessException> run() throws Exception {
return ResultHolder.wrap(() -> doStuff(...));
}
}
.observe()
.flatMap(ResultHolder::unwrap);
使用HystrixBadRequestException
HystrixBadRequestException是一种特殊的异常,在断路器和指标方面不会算作失败.如documentation所示:
Unlike all other exceptions thrown by a HystrixCommand this will not
trigger fallback, not count against failure metrics and thus not
trigger the circuit breaker.
HystrixBadRequestException的实例不是由Hystrix本身创建的,因此将其用作业务异常的包装是安全的.但是,原始业务异常仍需要解包.
new HystrixCommand<BusinessResponse>() {
@Override
protected BusinessResponse run() throws Exception {
try {
return doStuff(...);
} catch (BusinessException e) {
throw new HystrixBadRequestException("Business exception occurred", e);
}
}
}
.observe()
.onErrorResumeNext(e -> {
if (e instanceof HystrixBadRequestException) {
e = e.getCause(); // Unwrap original BusinessException
}
return Observable.error(e);
})