guava的retry工具类

逃离我推掉我的手 2023-01-10 01:20 170阅读 0赞

通常我们在访问第三方接口时，由于网络抖动或其他原因需要重试，spring和guava都提供了retry的工具。下面简单介绍一下guava的retry,相比较spring的retry，使用起来更加的简单便捷。

首先我们需要实例化一个重试器

eg:

/**
         * 创建一个重试器，重试器执行的方法
         */
        private static Retryer retryer = RetryerBuilder.newBuilder()
                // 出现异常时，会重试
                .retryIfException()
                // 失败后，隔2秒后重试
                .withWaitStrategy(WaitStrategies.fixedWait(2, TimeUnit.SECONDS))
                // 重试3次后，仍未成功，就不再重试
                .withStopStrategy(StopStrategies.stopAfterAttempt(3))
                .build();

通过构造方法即可看出各参数的含义。

/**
         * Constructor
         *
         * @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 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.
         */
        public Retryer(@Nonnull StopStrategy stopStrategy,
                       @Nonnull WaitStrategy waitStrategy,
                       @Nonnull Predicate<Attempt<V>> rejectionPredicate) {
    
            this(AttemptTimeLimiters.<V>noTimeLimit(), stopStrategy, waitStrategy, BlockStrategies.threadSleepStrategy(), rejectionPredicate);
        }

然后使用时，直接通过retryer.call(() -> //TODO业务逻辑)即可。

/**
         * 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);
                    }
                }
            }
        }

使用起来非常的简单，参照着就可以很容易实现一个重试的功能。