03、resilience4j源码分析：CircuitBreaker模块之配置

2，CircuitBreakerConfig（熔断器配置）

CircuitBreakerConfig类中封装了与熔断器相关的配置属性，属性包括：请求调用失败的阈值、熔断器在打开状态时的持续时间、熔断器在半开状态下的Ring Buffer大小、熔断器在关闭状态下的Ring Buffer大小、是否记录请求调用失败的断言。Ring Buffer的原理在后面研究CircuitBreakerMetrics部分时再详细讲解，现在只需要了解，它是一个存储每次请求调用成功与否的环形缓存区。

另外CircuitBreakerConfig类通过Builder模式构造CircuitBreakerConfig实例及流式的设置配置属性值。

需主要关注的源码如下：

public class CircuitBreakerConfig {

//请求调用失败的阈值，百分比。默认是50%

public static final int DEFAULT_MAX_FAILURE_THRESHOLD = 50; // Percentage

//熔断器在打开状态时的持续时间。默认是60秒

public static final int DEFAULT_WAIT_DURATION_IN_OPEN_STATE = 60; // Seconds

//熔断器在半开状态下的ring buffer大小。默认10

public static final int DEFAULT_RING_BUFFER_SIZE_IN_HALF_OPEN_STATE = 10;

//熔断器在关闭状态下的ring buffer大小。默认100

public static final int DEFAULT_RING_BUFFER_SIZE_IN_CLOSED_STATE = 100;

//是否记录请求调用失败的断言，默认所有异常都记录。

public static final Predicate DEFAULT_RECORD_FAILURE_PREDICATE = (throwable) -> true;

......

/** 构造者模式 */

public static class Builder {

private Predicate recordFailurePredicate;

private Predicate errorRecordingPredicate;

//请求调用失败，存储异常记录的集合

private Class<? extends Throwable>[] recordExceptions = new Class[0];

//请求调用失败，忽略异常记录的集合

private Class<? extends Throwable>[] ignoreExceptions = new Class[0];

private float failureRateThreshold = DEFAULT_MAX_FAILURE_THRESHOLD;

private int ringBufferSizeInHalfOpenState = DEFAULT_RING_BUFFER_SIZE_IN_HALF_OPEN_STATE;

private int ringBufferSizeInClosedState = DEFAULT_RING_BUFFER_SIZE_IN_CLOSED_STATE;

private Duration waitDurationInOpenState = Duration.ofSeconds(DEFAULT_WAIT_DURATION_IN_OPEN_STATE);

private boolean automaticTransitionFromOpenToHalfOpenEnabled = false;

/** 构造CircuitBreakerConfig实例 */

public CircuitBreakerConfig build() {

buildErrorRecordingPredicate();

CircuitBreakerConfig config = new CircuitBreakerConfig();

config.waitDurationInOpenState = waitDurationInOpenState;

config.failureRateThreshold = failureRateThreshold;

config.ringBufferSizeInClosedState = ringBufferSizeInClosedState;

config.ringBufferSizeInHalfOpenState = ringBufferSizeInHalfOpenState;

config.recordFailurePredicate = errorRecordingPredicate;

config.automaticTransitionFromOpenToHalfOpenEnabled = automaticTransitionFromOpenToHalfOpenEnabled;

return config;

}

/** 异常记录集合与异常忽略集合取交集，如果有值则为false，否则为true。*/

private void buildErrorRecordingPredicate() {

this.errorRecordingPredicate =

getRecordingPredicate()

.and(buildIgnoreExceptionsPredicate()

.orElse(DEFAULT_RECORD_FAILURE_PREDICATE));

}

......

}

......

}

下一篇文章《Resilience4j源码解析-2.3 CircuitBreaker模块之有限状态机》讲解熔断器的核心理念-有限状态机，及状态转换部分。

源码的中文注释地址：

https://github.com/Justin02180218/resilience4j

==大家可以关注我的微信公众号，后续文章将在公众号中同步更新==