doc: 阅读circuit-breaker文档

spring/Spring Cloud/CircuitBreaker/CircuitBreaker.md

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+# CircuitBreaker
+resilience4j是一个轻量级的fault tolerance library，其针对函数式编程进行设计。resilence4j提供了更高阶的函数（`decorator`）来对`function interface, lambda expression, method reference`等内容进行增强。
+
+decorators包含如下分类：
+- CircuitBreaker
+- Rate Limiter
+- Retry
+- Bulkhead
+
+对于任何`function interface, lambda expression, method reference`，都可以使用多个decorators进行装饰。
+
+## Introduction
+在如下示例中，会展示如何通过CircuitBreaker和Retry来对lambda expression进行装饰，令lambda在发生异常时最多重试3次。
+
+可以针对多次retry之间的interval进行配置，也支持自定义的backoff algorithm。
+
+```java
+// Create a CircuitBreaker with default configuration
+CircuitBreaker circuitBreaker = CircuitBreaker
+  .ofDefaults("backendService");
+
+// Create a Retry with default configuration
+// 3 retry attempts and a fixed time interval between retries of 500ms
+Retry retry = Retry
+  .ofDefaults("backendService");
+
+// Create a Bulkhead with default configuration
+Bulkhead bulkhead = Bulkhead
+  .ofDefaults("backendService");
+
+Supplier<String> supplier = () -> backendService
+  .doSomething(param1, param2)
+
+// Decorate your call to backendService.doSomething() 
+// with a Bulkhead, CircuitBreaker and Retry
+// **note: you will need the resilience4j-all dependency for this
+Supplier<String> decoratedSupplier = Decorators.ofSupplier(supplier)
+  .withCircuitBreaker(circuitBreaker)
+  .withBulkhead(bulkhead)
+  .withRetry(retry)  
+  .decorate();
+
+// When you don't want to decorate your lambda expression,
+// but just execute it and protect the call by a CircuitBreaker.
+String result = circuitBreaker
+  .executeSupplier(backendService::doSomething);
+
+// You can also run the supplier asynchronously in a ThreadPoolBulkhead
+ ThreadPoolBulkhead threadPoolBulkhead = ThreadPoolBulkhead
+  .ofDefaults("backendService");
+
+// The Scheduler is needed to schedule a timeout 
+// on a non-blocking CompletableFuture
+ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(3);
+TimeLimiter timeLimiter = TimeLimiter.of(Duration.ofSeconds(1));
+
+CompletableFuture<String> future = Decorators.ofSupplier(supplier)
+    .withThreadPoolBulkhead(threadPoolBulkhead)
+    .withTimeLimiter(timeLimiter, scheduledExecutorService)
+    .withCircuitBreaker(circuitBreaker)
+    .withFallback(asList(TimeoutException.class, 
+                         CallNotPermittedException.class, 
+                         BulkheadFullException.class),  
+                  throwable -> "Hello from Recovery")
+    .get().toCompletableFuture();
+```
+## maven
+resilence4j需要jdk17及以上，如果使用maven，可以按照如下方式来引入
+
+引入所有包的方式如下
+```xml
+<dependency>
+    <groupId>io.github.resilience4j</groupId>
+    <artifactId>resilience4j-all</artifactId>
+    <version>${resilience4jVersion}</version>
+</dependency>
+```
+
+按需引入方式如下
+```xml
+<dependency>
+    <groupId>io.github.resilience4j</groupId>
+    <artifactId>resilience4j-circuitbreaker</artifactId>
+    <version>${resilience4jVersion}</version>
+</dependency>
+<dependency>
+    <groupId>io.github.resilience4j</groupId>
+    <artifactId>resilience4j-ratelimiter</artifactId>
+    <version>${resilience4jVersion}</version>
+</dependency>
+<dependency>
+    <groupId>io.github.resilience4j</groupId>
+    <artifactId>resilience4j-retry</artifactId>
+    <version>${resilience4jVersion}</version>
+</dependency>
+<dependency>
+    <groupId>io.github.resilience4j</groupId>
+    <artifactId>resilience4j-bulkhead</artifactId>
+    <version>${resilience4jVersion}</version>
+</dependency>
+<dependency>
+    <groupId>io.github.resilience4j</groupId>
+    <artifactId>resilience4j-cache</artifactId>
+    <version>${resilience4jVersion}</version>
+</dependency>
+<dependency>
+    <groupId>io.github.resilience4j</groupId>
+    <artifactId>resilience4j-timelimiter</artifactId>
+    <version>${resilience4jVersion}</version>
+</dependency>
+```