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https://github.com/rholder/guava-retrying

This is a small extension to Google's Guava library to allow for the creation of configurable retrying strategies for an arbitrary function call, such as something that talks to a remote service with flaky uptime.
https://github.com/rholder/guava-retrying

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This is a small extension to Google's Guava library to allow for the creation of configurable retrying strategies for an arbitrary function call, such as something that talks to a remote service with flaky uptime.

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[![Build Status](http://img.shields.io/travis/rholder/guava-retrying.svg)](https://travis-ci.org/rholder/guava-retrying) [![Latest Version](http://img.shields.io/badge/latest-2.0.0-brightgreen.svg)](https://github.com/rholder/guava-retrying/releases/tag/v2.0.0) [![License](http://img.shields.io/badge/license-apache%202-brightgreen.svg)](https://github.com/rholder/guava-retrying/blob/master/LICENSE)



##What is this?

The guava-retrying module provides a general purpose method for retrying arbitrary Java code with specific stop, retry,

and exception handling capabilities that are enhanced by Guava's predicate matching.



This is a fork of the excellent RetryerBuilder code posted [here](http://code.google.com/p/guava-libraries/issues/detail?id=490)

by Jean-Baptiste Nizet (JB).  I've added a Gradle build for pushing it up to my little corner of Maven Central so that

others can easily pull it into their existing projects with minimal effort.  It also includes

exponential and Fibonacci backoff [WaitStrategies](http://rholder.github.io/guava-retrying/javadoc/2.0.0/com/github/rholder/retry/WaitStrategies.html)

that might be useful for situations where more well-behaved service polling is preferred.



##Maven

```xml

    

      com.github.rholder

      guava-retrying

      2.0.0

    

```



##Gradle

```groovy

    compile "com.github.rholder:guava-retrying:2.0.0"

```



##Quickstart

A minimal sample of some of the functionality would look like:



```java

Callable callable = new Callable() {

    public Boolean call() throws Exception {

        return true; // do something useful here

    }

};



Retryer retryer = RetryerBuilder.newBuilder()

        .retryIfResult(Predicates.isNull())

        .retryIfExceptionOfType(IOException.class)

        .retryIfRuntimeException()

        .withStopStrategy(StopStrategies.stopAfterAttempt(3))

        .build();

try {

    retryer.call(callable);

} catch (RetryException e) {

    e.printStackTrace();

} catch (ExecutionException e) {

    e.printStackTrace();

}

```



This will retry whenever the result of the `Callable` is null, if an `IOException` is thrown, or if any other

`RuntimeException` is thrown from the `call()` method. It will stop after attempting to retry 3 times and throw a

`RetryException` that contains information about the last failed attempt. If any other `Exception` pops out of the

`call()` method it's wrapped and rethrown in an `ExecutionException`.



##Exponential Backoff



Create a `Retryer` that retries forever, waiting after every failed retry in increasing exponential backoff intervals

until at most 5 minutes. After 5 minutes, retry from then on in 5 minute intervals.



```java

Retryer retryer = RetryerBuilder.newBuilder()

        .retryIfExceptionOfType(IOException.class)

        .retryIfRuntimeException()

        .withWaitStrategy(WaitStrategies.exponentialWait(100, 5, TimeUnit.MINUTES))

        .withStopStrategy(StopStrategies.neverStop())

        .build();

```

You can read more about [exponential backoff](http://en.wikipedia.org/wiki/Exponential_backoff) and the historic role

it played in the development of TCP/IP in [Congestion Avoidance and Control](http://ee.lbl.gov/papers/congavoid.pdf).



##Fibonacci Backoff



Create a `Retryer` that retries forever, waiting after every failed retry in increasing Fibonacci backoff intervals

until at most 2 minutes. After 2 minutes, retry from then on in 2 minute intervals.



```java

Retryer retryer = RetryerBuilder.newBuilder()

        .retryIfExceptionOfType(IOException.class)

        .retryIfRuntimeException()

        .withWaitStrategy(WaitStrategies.fibonacciWait(100, 2, TimeUnit.MINUTES))

        .withStopStrategy(StopStrategies.neverStop())

        .build();

```



Similar to the `ExponentialWaitStrategy`, the `FibonacciWaitStrategy` follows a pattern of waiting an increasing amount

of time after each failed attempt.



Instead of an exponential function it's (obviously) using a

[Fibonacci sequence](https://en.wikipedia.org/wiki/Fibonacci_numbers) to calculate the wait time.



Depending on the problem at hand, the `FibonacciWaitStrategy` might perform better and lead to better throughput than

the `ExponentialWaitStrategy` - at least according to

[A Performance Comparison of Different Backoff Algorithms under Different Rebroadcast Probabilities for MANETs](http://www.comp.leeds.ac.uk/ukpew09/papers/12.pdf).



The implementation of `FibonacciWaitStrategy` is using an iterative version of the Fibonacci because a (naive) recursive

version will lead to a [StackOverflowError](http://docs.oracle.com/javase/7/docs/api/java/lang/StackOverflowError.html)

at a certain point (although very unlikely with useful parameters for retrying).



Inspiration for this implementation came from [Efficient retry/backoff mechanisms](https://paperairoplane.net/?p=640).



##Documentation

Javadoc can be found [here](http://rholder.github.io/guava-retrying/javadoc/2.0.0).



##Building from source

The guava-retrying module uses a [Gradle](http://gradle.org)-based build system. In the instructions

below, [`./gradlew`](http://vimeo.com/34436402) is invoked from the root of the source tree and serves as

a cross-platform, self-contained bootstrap mechanism for the build. The only

prerequisites are [Git](https://help.github.com/articles/set-up-git) and JDK 1.6+.



### check out sources

`git clone git://github.com/rholder/guava-retrying.git`



### compile and test, build all jars

`./gradlew build`



### install all jars into your local Maven cache

`./gradlew install`



##License

The guava-retrying module is released under version 2.0 of the

[Apache License](http://www.apache.org/licenses/LICENSE-2.0).



##Contributors

* Jean-Baptiste Nizet (JB)

* Jason Dunkelberger (dirkraft)

* Diwaker Gupta (diwakergupta)

* Jochen Schalanda (joschi)

* Shajahan Palayil (shasts)

* Olivier Grégoire (fror)

* Andrei Savu (andreisavu)

* (tchdp)

* (squalloser)

* Yaroslav Matveychuk (yaroslavm)

* Stephan Schroevers (Stephan202)

* Chad (voiceinsideyou)

* Kevin Conaway (kevinconaway)

* Alberto Scotto (alb-i986)