Reactor详解之:异常处理

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"简介"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"不管是在响应式编程还是普通的程序设计中，异常处理都是一个非常重要的方面。今天将会给大家介绍Reactor中异常的处理流程。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"Reactor的异常一般处理方法"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先举一个例子，我们创建一个Flux，在这个Flux中，我们产生一个异常，看看是什么情况："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Flux flux2= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i));\n flux2.subscribe(System.out::println);\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们会得到一个异常ErrorCallbackNotImplemented："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"100 / 1 = 100\n100 / 2 = 50\n\nreactor.core.Exceptions$ErrorCallbackNotImplemented: java.lang.ArithmeticException: / by zero\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那怎么处理这个异常呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有两种方式，第一种方式就是我们之前文章讲过的，在subscribe的时候指定onError方法："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Flux flux2= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i));\n\n flux2.subscribe(System.out::println,\n error -> System.err.println(\"Error: \" + error));\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"还是刚才的代码，但是这次我们在subscribe的时候，添加了onError处理器，看下运行结果："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Divided by zero :(\n100 / 1 = 100\n100 / 2 = 50\nError: java.lang.ArithmeticException: / by zero\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以看到异常已经被我们捕获了，并且进行了合适的处理。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除了在subscribe中进行处理，我们还可以在publish的时候，就指定异常的处理模式，这就是我们要介绍的第二种方法："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" Flux flux= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i))\n .onErrorReturn(\"Divided by zero :(\");\n flux.subscribe(System.out::println);\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中，在创建Flux的时候，手动指定了其onErrorReturn方法，我们看下输出结果："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"100 / 1 = 100\n100 / 2 = 50\nDivided by zero :(\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"注意，对于Flux或者Mono来说，所有的异常都是一个终止的操作，即使你使用了异常处理，原生成序列也不会继续。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"但是如果你对异常进行了处理，那么它会将oneError信号转换成为新的序列的开始，并将替换掉之前上游产生的序列。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"各种异常处理方式详解"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在一般的程序中，我们的异常应该怎么处理呢？大家很容易想到的是try catch。而Reactor中subscribe的onError方法，就是try catch的一个具体应用："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Flux flux2= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i));\n\n flux2.subscribe(System.out::println,\n error -> System.err.println(\"Error: \" + error));\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"还是上的例子，我们在onError方法中，对异常进行了处理。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果转换成为常规代码，应该是下面的样子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void normalErrorHandle(){\n try{\n Arrays.asList(1,2,0).stream().map(i -> \"100 / \" + i + \" = \" + (100 / i)).forEach(System.out::println);\n }catch (Exception e){\n System.err.println(\"Error: \" + e);\n }\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除了这种最基本的异常处理方法之外，Reactor还提供了很多种不同的异常处理方法，下面我们来一一介绍一下。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Static Fallback Value"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Static Fallback Value的意思是，在遇到异常的时候会fallback到一个静态的默认值。比如我们之前讲到的onErrorReturn。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Flux flux= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i))\n .onErrorReturn(\"Divided by zero :(\");\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当然onErrorReturn还支持一个Predicate参数，用来判断要falback的异常是否满足条件。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"public final Flux onErrorReturn(Predicate super Throwable> predicate, T fallbackValue) \n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Fallback Method"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除了fallback Value之外，还支持Fallback Method。也就是说如果你想在捕获异常之后调用其他的方法，就可以使用Fallback Method。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这里Fallback Method是用onErrorResume来表示的。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void useFallbackMethod(){\n Flux flux= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i))\n .onErrorResume(e -> System.out::println);\n flux.subscribe(System.out::println);\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Dynamic Fallback Value"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所谓的动态Fallback Value就是根据你抛出的异常进行判断，通过定位不同的Error从而fallback到不同的值："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void useDynamicFallback(){\n Flux flux= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i))\n .onErrorResume(error -> Mono.just(\n MyWrapper.fromError(error)));\n }\n\n public static class MyWrapper{\n public static String fromError(Throwable error){\n return \"That is a new Error\";\n }\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Catch and Rethrow"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"同样的，我们可以在捕获异常之后进行rethrow:"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Flux flux= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i))\n .onErrorResume(error -> Flux.error(\n new RuntimeException(\"oops, ArithmeticException!\", error)));\n\n Flux flux2= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i))\n .onErrorMap(error -> new RuntimeException(\"oops, ArithmeticException!\", error));\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有两种方式，第一种就是在onErrorResume中使用Flux.error构建一个新的Flux，另外一种就是直接在onErrorMap中进行处理。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Log or React on the Side"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有时候你只是想记录一下异常信息，并不想破坏原来的React结构，那么可以试着使用doOnError。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void useDoOnError(){\n Flux flux= Flux.just(1, 2, 0)\n .map(i -> \"100 / \" + i + \" = \" + (100 / i))\n .doOnError(error -> System.out.println(\"we got the error: \"+ error));\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Finally Block"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果我们在代码中使用了某些资源，一般情况下我们需要在finally中对其进行关闭，或者使用JDK7中引入的 try-with-resource 。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"举个例子，下面的是使用finally的方式："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Stats stats = new Stats();\nstats.startTimer();\ntry {\n doSomethingDangerous();\n}\nfinally {\n stats.stopTimerAndRecordTiming();\n}\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面是使用try-with-resource的方式："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"try (SomeAutoCloseable disposableInstance = new SomeAutoCloseable()) {\n return disposableInstance.toString();\n}\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那么在Reactor中，我们也有两种方式和其对应。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第一种就是doFinally方法："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Stats stats = new Stats();\nLongAdder statsCancel = new LongAdder();\n\nFlux flux =\nFlux.just(\"foo\", \"bar\")\n .doOnSubscribe(s -> stats.startTimer())\n .doFinally(type -> { \n stats.stopTimerAndRecordTiming();\n if (type == SignalType.CANCEL) \n statsCancel.increment();\n })\n .take(1); \n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中，doFinally实际上做的就是finally block做的事情。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第二种是使用using，我们先看一个using的定义："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public static Flux using(Callable extends D> resourceSupplier, Function super D, ? extends\n Publisher extends T>> sourceSupplier, Consumer super D> resourceCleanup)\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以看到using支持三个参数，resourceSupplier是一个生成器，用来在subscribe的时候生成要发送的resource对象。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"sourceSupplier是一个生成Publisher的工厂，接收resourceSupplier传过来的resource，然后生成Publisher对象。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"resourceCleanup用来对resource进行收尾操作。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那么我们怎么用呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"举个例子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void useUsing(){\n AtomicBoolean isDisposed = new AtomicBoolean();\n Disposable disposableInstance = new Disposable() {\n @Override\n public void dispose() {\n isDisposed.set(true);\n }\n\n @Override\n public String toString() {\n return \"DISPOSABLE\";\n }\n };\n\n Flux flux =\n Flux.using(\n () -> disposableInstance,\n disposable -> Flux.just(disposable.toString()),\n Disposable::dispose);\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中，我们创建了一个Disposable对象，作为resource，然后对这个resource进行加工，返回一个Flux对象，最后通过调用Disposable::dispose方法，对resource进行销毁。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Retrying"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有时候我们遇到了异常，可能需要重试几次，Reactor为我们提供了retry方法，先看一个例子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void testRetry(){\n Flux.interval(Duration.ofMillis(250))\n .map(input -> {\n if (input < 3){\n return \"tick \" + input;\n } \n throw new RuntimeException(\"boom\");\n })\n .retry(1)\n .elapsed()\n .subscribe(System.out::println, System.err::println);\n\n try {\n Thread.sleep(2100);\n } catch (InterruptedException e) {\n e.printStackTrace();\n }\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"看下输出结果："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"[264,tick 0]\n[255,tick 1]\n[241,tick 2]\n[506,tick 0]\n[252,tick 1]\n[253,tick 2]\njava.lang.RuntimeException: boom\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"retry的作用就是当遇到异常的时候，重启一个新的序列。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"elapsed是用来展示产生的value时间之间的duration。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"从结果我们可以看到，retry之前是不会产生异常信息的。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文的例子"},{"type":"link","attrs":{"href":"https://github.com/ddean2009/learn-reactive/tree/master/reactorIntroduction","title":null},"content":[{"type":"text","text":"learn-reactive"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"本文作者：flydean程序那些事"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"本文链接："},{"type":"link","attrs":{"href":"http://www.flydean.com/reactor-handle-errors/","title":null},"content":[{"type":"text","text":"http://www.flydean.com/reactor-handle-errors/"}],"marks":[{"type":"italic"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"本文来源：flydean的博客"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"欢迎关注我的公众号:「程序那些事」最通俗的解读，最深刻的干货，最简洁的教程，众多你不知道的小技巧等你来发现！"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}