关于Guava-Retry重试工具的使用
关于Guava-Retry重试工具的使用
- 1 guava-retry的简介
- 2 guava-retry的使用
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- 1 导入maven依赖
- 2 添加一个重试方法
- 3 添加测试类
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- 3 总结
官网地址:
https://github.com/rholder/guava-retrying
https://codechina.csdn.net/mirrors/rholder/guava-retrying?utm_source=csdn_github_accelerator
1 guava-retry的简介
在日常的一些场景中, 很多需要进行重试的操作.查询资料Guava-Retry工具对于重试操作效果比较好.
Guava retryer是一个基于Guava，提供重试机制的库,是通过定义重试者角色来包装正常逻辑重试，支持重试次数和重试频度控制，能够兼容支持多个异常或者自定义实体对象的重试源定义，让重试功能有更多的灵活性, 而且也是线程安全的，入口调用逻辑采用的是java.util.concurrent.Callable的call方法.
2 guava-retry的使用
1 导入maven依赖
<dependency>
<groupId>com.github.rholdergroupId>
<artifactId>guava-retryingartifactId>
<version>2.0.0version>
dependency>
2 添加一个重试方法
@Slf4j
public class RetryDemo {
public static boolean retryMethod(Integer param) {
int i = new Random().nextInt(param);
log.info("随机生成的数:{}", i);
if (1 == i) {
log.info("为1,返回true.");
return true;
} else if (i < 1) {
log.info("小于1,抛出参数异常.");
throw new IllegalArgumentException("参数异常");
} else if (i > 1 && i < 10) {
log.info("大于1,小于10,抛出参数异常.");
return false;
} else {
//为其他
log.info("大于10,抛出自定义异常.");
throw new RemoteAccessException("大于10,抛出自定义异常");
}
}
}
3 添加测试类
@Slf4j
public class GuavaRetryTest {
public static void main(String[] args) {
Boolean result = false;
// RetryerBuilder 构建重试实例对象
// 1 可以设置重试源且可以支持多个重试源
// 2 可以设置根据结果重试
// 3 可以配置等待时间间隔
// 4 可以配置重试次数或重试超时时间
Retryer<Boolean> retryer = RetryerBuilder.<Boolean>newBuilder()
.retryIfExceptionOfType(RemoteAccessException.class)//设置异常重试源
.retryIfException()
.retryIfResult(res -> false) //设置根据结果重试
.withWaitStrategy(WaitStrategies.fixedWait(3, TimeUnit.SECONDS)) //设置等待间隔时间
.withStopStrategy(StopStrategies.stopAfterAttempt(3)) //设置最大重试次数
.withRetryListener(new RetryListener() {
@Override
public <V> void onRetry(Attempt<V> attempt) {
log.info("第【{}】次调用失败", attempt.getAttemptNumber());
}
})
.build();
try {
result = retryer.call(new Callable<Boolean>() {
@Override
public Boolean call() throws Exception {
return RetryDemo.retryMethod(110);
}
});
// 上述可以简化为
// result = retryer.call(() -> RetryDemo.retryMethod(110));
} catch (Exception e) {
e.printStackTrace();
log.info("超时三次错误,{}", e.getMessage());
}
System.out.println("方法调用返回状态= " + result);
}
}
说明:
RetryerBuilder类是一个工厂建造者,可以设置多个重试源,可以设置重试次数和重试超时时间等,创建重试者Retryer对象.
RetryerBuilder部分源码:
public class RetryerBuilder<V> {
// 单次任务执行时间限制
private AttemptTimeLimiter<V> attemptTimeLimiter;
// 停止策略
private StopStrategy stopStrategy;
// 等待策略
private WaitStrategy waitStrategy;
// 阻塞策略
private BlockStrategy blockStrategy;
// 重试源 支持Exception异常对象和自定义断言对象
private Predicate<Attempt<V>> rejectionPredicate = Predicates.alwaysFalse();
// 重试监听
private List<RetryListener> listeners = new ArrayList<RetryListener>();
private RetryerBuilder() {
}
// new一个RetryerBuilder对象
/**
* Constructs a new builder
*
* @param result of a {@link Retryer}'s call, the type of the call return value
* @return the new builder
*/
public static <V> RetryerBuilder<V> newBuilder() {
return new RetryerBuilder<V>();
}
// 创建一个Retryer对象
/**
* Builds the retryer.
*
* @return the built retryer.
*/
public Retryer<V> build() {
AttemptTimeLimiter<V> theAttemptTimeLimiter = attemptTimeLimiter == null ? AttemptTimeLimiters.<V>noTimeLimit() : attemptTimeLimiter;
StopStrategy theStopStrategy = stopStrategy == null ? StopStrategies.neverStop() : stopStrategy;
WaitStrategy theWaitStrategy = waitStrategy == null ? WaitStrategies.noWait() : waitStrategy;
BlockStrategy theBlockStrategy = blockStrategy == null ? BlockStrategies.threadSleepStrategy() : blockStrategy;
return new Retryer<V>(theAttemptTimeLimiter, theStopStrategy, theWaitStrategy, theBlockStrategy, rejectionPredicate, listeners);
}
// ...
}
Retryer部分源码:
public final class Retryer<V> {
// 停止策略
private final StopStrategy stopStrategy;
// 等待策略
private final WaitStrategy waitStrategy;
// 阻塞策略
private final BlockStrategy blockStrategy;
// 单次任务执行时间限制
private final AttemptTimeLimiter<V> attemptTimeLimiter;
// 重试源 支持Exception异常对象和自定义断言对象
private final Predicate<Attempt<V>> rejectionPredicate;
// 重试监听
private final Collection<RetryListener> listeners;
// RetryerBuilder建造者中build方法被使用
/**
* Constructor
*
* @param attemptTimeLimiter to prevent from any single attempt from spinning infinitely
* @param stopStrategy the strategy used to decide when the retryer must stop retrying
* @param waitStrategy the strategy used to decide how much time to sleep between attempts
* @param blockStrategy the strategy used to decide how to block between retry attempts; eg, Thread#sleep(), latches, etc.
* @param rejectionPredicate the predicate used to decide if the attempt must be rejected
* or not. If an attempt is rejected, the retryer will retry the call, unless the stop
* strategy indicates otherwise or the thread is interrupted.
* @param listeners collection of retry listeners
*/
@Beta
public Retryer(@Nonnull AttemptTimeLimiter<V> attemptTimeLimiter,
@Nonnull StopStrategy stopStrategy,
@Nonnull WaitStrategy waitStrategy,
@Nonnull BlockStrategy blockStrategy,
@Nonnull Predicate<Attempt<V>> rejectionPredicate,
@Nonnull Collection<RetryListener> listeners) {
Preconditions.checkNotNull(attemptTimeLimiter, "timeLimiter may not be null");
Preconditions.checkNotNull(stopStrategy, "stopStrategy may not be null");
Preconditions.checkNotNull(waitStrategy, "waitStrategy may not be null");
Preconditions.checkNotNull(blockStrategy, "blockStrategy may not be null");
Preconditions.checkNotNull(rejectionPredicate, "rejectionPredicate may not be null");
Preconditions.checkNotNull(listeners, "listeners may not null");
this.attemptTimeLimiter = attemptTimeLimiter;
this.stopStrategy = stopStrategy;
this.waitStrategy = waitStrategy;
this.blockStrategy = blockStrategy;
this.rejectionPredicate = rejectionPredicate;
this.listeners = listeners;
}
// 线程安全调用重试方法
/**
* Executes the given callable. If the rejection predicate
* accepts the attempt, the stop strategy is used to decide if a new attempt
* must be made. Then the wait strategy is used to decide how much time to sleep
* and a new attempt is made.
*
* @param callable the callable task to be executed
* @return the computed result of the given callable
* @throws ExecutionException if the given callable throws an exception, and the
* rejection predicate considers the attempt as successful. The original exception
* is wrapped into an ExecutionException.
* @throws RetryException if all the attempts failed before the stop strategy decided
* to abort, or the thread was interrupted. Note that if the thread is interrupted,
* this exception is thrown and the thread's interrupt status is set.
*/
public V call(Callable<V> callable) throws ExecutionException, RetryException {
long startTime = System.nanoTime();
for (int attemptNumber = 1; ; attemptNumber++) {
Attempt<V> attempt;
try {
V result = attemptTimeLimiter.call(callable);
attempt = new ResultAttempt<V>(result, attemptNumber, TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime));
} catch (Throwable t) {
attempt = new ExceptionAttempt<V>(t, attemptNumber, TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime));
}
for (RetryListener listener : listeners) {
listener.onRetry(attempt);
}
if (!rejectionPredicate.apply(attempt)) {
return attempt.get();
}
if (stopStrategy.shouldStop(attempt)) {
throw new RetryException(attemptNumber, attempt);
} else {
long sleepTime = waitStrategy.computeSleepTime(attempt);
try {
blockStrategy.block(sleepTime);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new RetryException(attemptNumber, attempt);
}
}
}
}
}
3 总结
Guava-Retry, 是一个非常灵活简单上手的工具. 可以完好的把重试功能和业务逻辑解耦, 不但支持多种设置, 如多异常判断,重试次数,重试时间,以及每次重试方法时的监听.并且是属于线程安全的, 在并发的场景下也能稳定支持.
参考资料:
https://blog.csdn.net/zzzgd_666/article/details/84377962