Retrying unreliable logic in java using Retry4j Library

While implementing specific requirements in java, we often need to deal with unreliable codes, timeout, Unexpected exceptions, and need to retry-operations because of the asynchronous process and functionalities in the application. Like while working on one of the projects which were not very new and service-oriented application we figured out that multiple factors can make the automation test and framework unreliable resulting in the wrong results and values. So we must find a way to Retry the logic in java which can be light and highly configurable.

So we decided to use nice open source library Retry4j which is easy and simple to implement our retry logic. In this tutorial, I would like to show you how to handle those unexpected exceptions and conditions using the Retry4j library.

Retry4j

Retry4j is a simple Java library to assist with retrying transient failure situations or unreliable code. Retry4j aims to be readable, well documented, and streamlined.

Dependencies:

Can be added in both Gradle and Maven projects. Here is an example of Gradle.

Gradle:

compile group: 'com.evanlennick', name: 'retry4j', version: '0.15.0'

Example for handling the Exceptions

To demonstrate the example of handling the exception and extracting a return value from a method that throws a Run time exception every time until a specific limit is reached within the method. In the end, the method should be returning the String ‘Retry’ instead of throwing a Run time exception.

RetryConfig:

First Step is define retry Configuration using the RetryConfig.class like below:

RetryConfig retryConfig = new RetryConfigBuilder().withMaxNumberOfTries(5)
                                   .withFixedBackoff().withDelayBetweenTries(2, SECONDS)
                                   .retryOnSpecificExceptions(RuntimeException.class).build();

You can see I have used the Maximum Retries as 5 and included the delay of 2 seconds and in the end we have defined which exception we should be handling here like RuntimeException.class.

Callable:

After the Configuration is set we need to create a Callable statement

Callable<Object> callable = () -> {
    //code that you want to retry until success OR retries are exhausted OR an unexpected exception is thrown
};

CallExecutorBuilder

Now the final step is to execute the callable statement we have created using the Retry Configuration like the below Example:

Status<Object> result = new CallExecutorBuilder().config(config).build().execute(callable);

Remember the callable can have any of the return types So we can create a simple variable and define which return type result we want to store in the Status variable.

Example:

public class RetryLogicExample {
    private int counter = 0;

    public String getRetryString() {
        System.out.println("In method trying for : " + counter);
        counter++;
        if (counter < 4) {
            System.out.println("Throw the Exception");
            throw new RuntimeException();
        }
        return "Retry";
    }

    public static void main(String[] args) {
        RetryLogicExample retry = new RetryLogicExample();
        RetryConfig retryConfig = new RetryConfigBuilder().withMaxNumberOfTries(5)
                                         .withFixedBackoff().withDelayBetweenTries(2, SECONDS)
                                         .retryOnSpecificExceptions(RuntimeException.class).build();
        Callable<Object> callable = () -> {
            return retry.getRetryString();
        };
        Status<String> result = new CallExecutorBuilder().config(retryConfig).build().execute(callable);
        System.out.println("Retry string at the End: " + result.getResult());
    }
}

Output:

Running the above code produces the result like below where the method failing for 3 times(String with 0) but succeeding at last and We print the result from the method.

In method trying for : 0
Throw the Exception
In method trying for : 1
Throw the Exception
In method trying for : 2
Throw the Exception
In method trying for : 3
Retry string at the End: Retry

Retry4j provides lots of options and configurations you can set for the condition you need to handle like for example if we need to run the code again on a specific value it returns can be done through the simple config changes.

Value Handling Config

RetryConfig config = retryConfigBuilder
        .retryOnReturnValue("retry on this value!")
        .build();

Value and Exception Handling Config

RetryConfig config = retryConfigBuilder
        .retryOnSpecificExceptions(FileNotFoundException.class)
        .retryOnReturnValue("retry on this value!")
        .build();  

I would suggest you to check and read the documenation and try to implement the examples from the Retry4j Git Hub Page. You can also find the same Java example as well in the GitHub Location.