Retries
You need to make a call that may fail. You need to wait for a value that meets your criteria. You write your own retry boilerplate. Why? Throw it away. You need not to support it anymore.
Motivation
Have you ever written a retry/wait code that looks like this?
private String computeWithRetries() {
int numberOfTries = 10;
int sleepTimeout = 1000; // one sec
for (int i = 0; i < numberOfTries; i++) {
try {
String value = computeValue();
} catch (Exception e) {
try {
Thread.sleep(sleepTimeout);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
continue;
}
if (value != null && !value.startsWith("B")) {
return value;
}
}
throw new RuntimeException("Could not compute anything");
}Ugh. That's terrible and you know it. It's hard to figure out what's going on, hard to extend, hard to reuse and easy to get it wrong. Luckily, there is an alternative.
Build tools
Add retries to your dependencies. Note that Guava is automatically added too.
Maven:
<dependency>
<groupId>me.alexpanov</groupId>
<artifactId>retries</artifactId>
<version>0.0.3</version>
</dependency>Gradle:
compile "me.alexpanov:retries:0.0.3"Getting started
Create a retryable:
//Nasty call that returns so much nulls
Retryable<String> retryable = new Retryable<String>() {
@Override
public String tryOnce() throws Exception {
return null;
}
};One call, one failure, RetryException is thrown
String resultAfterRetries = new Retries<String>(retryable).stopOnMaxFailures(1).perform();Code above will throw a subclass of RetryException:
me.alexpanov.retries.FailedToComputeAValueException
Same thing asynchronously, java.util.concurrent.ExecutionException is thrown
Future<String> resultAfterRetries = new Retries<String>(retryable).stopOnMaxFailures(1).performAsync();
String result = resultAfterRetries.get();Code above will throw an ExecutionException with a subclass of RetryException as a cause:
me.alexpanov.retries.FailedToComputeAValueException
One call, one failure, default value is returned
String resultAfterRetries = new Retries<String>(retryable).stopOnMaxFailures(1)
.orElse("default value")
.perform();
resultAfterRetries.equals("default value"); //trueSeveral calls, configured wait timeout
String resultAfterRetries = new Retries<String>(retryable).stopOnMaxFailures(10)
.waitAfterFailureAtLeast(10, TimeUnit.SECONDS)
.orElse("default value")
.perform();Ignoring results
Predicate<String> startsWithLetterB = new Predicate<String>() {
@Override
public boolean apply(String input) {
return input.startsWith("B");
}
};
String resultAfterRetries = new Retries<String>(retryable).stopOnMaxFailures(2)
.ignoreIfResult(startsWithLetterB)
.perform();Subscribing to failures for logging etc.
FailureSubscriber<String> logTheError = new FailureSubscriber<String>() {
@Override
public void onFailure(RetryFailure<String> details) {
LOG.info("Failure");
}
};
String resultAfterRetries = new Retries<String>(retryable).stopOnMaxFailures(10)
.onEachFailureDo(logTheError)
.perform();The code above will append a log message each time a call failed (exception, null or skipped result).
But what about my Callable(s)!?
I got you covered, man.
Retryable<String> retryable = new CallableToRetryable<String>(yourCallable);Licence
The Apache Software License, Version 2.0
Issues
Please feel free to add any issues regarding new functionality, improvements etc. in the Issues section