Implementing Retry Logic in Spring Framework

 In this post, we will learn about how retry can be implemented using Spring Retry Dependency.

What is retry and why do we need to implement it?

Retry is a technique used in software development to handle transient failures and improve the overall reliability of a system or application. When a service call or an operation fails temporarily due to reasons like network issues, high load, or temporary unavailability of resources, retrying the operation can be an effective strategy to ensure success.

What is Spring Retry?

Spring Retry is a module in the Spring Framework that provides support for adding retry functionality to methods in Spring-based applications. It helps in handling transient failures and retries failed operations to improve the stability and resilience of the application.

Spring Retry Components:

In Spring Retry, there are several components that you can use to implement the retry mechanism. Here are the key components:

RetryTemplate: RetryTemplate is the central class in Spring Retry that encapsulates the retry logic. It provides methods to execute the retryable operation, handle exceptions, and apply retry policies and back-off policies.

RetryPolicy: RetryPolicy defines the conditions under which a retry should be attempted. It determines whether a retry should happen based on the exception type or other custom conditions. Spring Retry provides various built-in implementations like SimpleRetryPolicy, AlwaysRetryPolicy, TimeoutRetryPolicy, etc. You can also create custom retry policies by implementing the RetryPolicy interface.

BackOffPolicy: BackOffPolicy defines the strategy for calculating the time to wait between retry attempts. It is responsible for applying a backoff delay between retries to avoid overloading the system in case of frequent failures. Spring Retry provides built-in implementations like FixedBackOffPolicy, ExponentialBackOffPolicy, etc., and you can create custom back-off policies as well.

RetryListener: RetryListener allows you to listen to events during the retry process. You can implement this interface to perform custom actions before and after each retry attempt.

RecoveryCallback: RecoveryCallback is used to define a fallback mechanism to be executed when all retry attempts fail. It allows you to gracefully recover from failures and take appropriate actions.

RetryContext: RetryContext represents the context information for the current retry attempt. It provides methods to get information about the current retry count, exception, and other details.

In order to implement the retry mechanism using Spring Retry, you typically need to:

1) Define a retry policy and a backoff policy based on your requirements.

2) Create a RetryTemplate and set the retry policy and backoff policy to it.

3) Implement the retryable operation, which can be a method annotated with @Retryable or a custom retry logic wrapped inside the RetryTemplate's execute method.

4) Optionally, you can use RetryListeners to listen to retry events and RecoveryCallback to handle failures.

Let's deep dive into each component and what is their role and responsibility in Retry logic.

1) RetryPolicy: In the Spring Retry framework, the RetryPolicy interface defines the contract for implementing retry policies. A retry policy determines when and how many times a retry should be attempted for a specific operation. Let's go through each field and method in the RetryPolicy interface:

canRetry(RetryContext context): This method checks whether a retry attempt can be made based on the provided retry context. The implementation of this method should consider factors like the number of previous retry attempts, the maximum number of allowed retries, and custom conditions for retries. It should return true if a retry attempt can be made, and false otherwise.

registerThrowable(RetryContext context, Throwable throwable): This method is called when a retry attempt fails with a Throwable. The retry policy implementation can use this method to perform any necessary updates or bookkeeping related to the retry attempt. For example, it can increment the retry count or update the retry context based on the specific throwable.

close(RetryContext context): This method is called when the retry operation is completed, either successfully or after exhausting all retries. It gives the retry policy a chance to clean up or perform any final actions related to the retry attempt.

getMaxAttempts(): This method returns the maximum number of retry attempts allowed by the retry policy. If the maximum number of attempts is not fixed (e.g., unlimited retries), this method should return a value less than 1.

setMaxAttempts(int maxAttempts): This method allows setting the maximum number of retry attempts. Some retry policies may have a fixed maximum number of retries, while others may allow this value to be configured.

2) BackOff Policy: 

BackOffPolicy is a strategy that determines the time interval between consecutive retry attempts. It defines how long to wait (back off) before retrying a failed operation, especially when dealing with transient failures. 

Backoff policies are used to prevent retrying a failed operation immediately, which can lead to excessive load on the system or cause a cascade of failures. By introducing a delay between retry attempts, backoff policies aim to give the system a chance to recover from the failure before trying again.

There are several types of backoff policies, each with different approaches to calculating the backoff delay:

FixedBackOffPolicy: This policy enforces a fixed delay between retry attempts. The same fixed delay is used for every retry, regardless of the number of previous attempts.

ExponentialBackOffPolicy: This policy increases the delay between retry attempts exponentially. It starts with a minimum interval and doubles the delay after each failed attempt until it reaches a maximum interval.

UniformRandomBackOffPolicy: This policy introduces a random delay between a specified minimum and maximum interval for each retry attempt.

ExponentialRandomBackOffPolicy: This policy is a combination of exponential backoff and random backoff. It multiplies the base delay by a random factor between 0 and a specified multiplier. This helps to add some variation to the backoff intervals.

NoBackOffPolicy: As the name suggests, this policy applies no delay between retry attempts. It retries the operation immediately.

The choice of the backoff policy depends on the specific use case and the characteristics of the system being retried. Some scenarios might benefit from a fixed delay, while others might require a more adaptive approach like exponential backoff or random backoff.

Spring Retry provides implementations for several of these back-off policies, making it easy to configure the desired behavior for retrying failed operations. By combining a RetryPolicy (to determine when to retry) with a BackOffPolicy (to determine how long to wait between retries), you can create robust retry mechanisms that improve the resilience of your applications when dealing with transient failures.

3) RetryListeners:

RetryListener is an interface provided by Spring Retry that allows you to receive callbacks and notifications about the progress of retry operations. By implementing this interface and registering it with the RetryTemplate, you can gain insight into when retries are attempted, whether they succeed or fail, and take appropriate actions based on those events.

The RetryListener interface consists of three methods:

open: This method is called before the first attempt of the retry operation. It provides you with the RetryContext object, which contains information about the retry operation, such as the number of retry attempts made so far and the last exception thrown (if any). The method has the following signature:

<T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback);

context: The RetryContext object that holds information about the retry operation.

callback: The RetryCallback object representing the operation that is being retried.

The open method returns a boolean value, indicating whether the RetryCallback should be executed (true) or skipped (false). If the method returns false, the retry operation is bypassed, and the callback is not executed.

onError: This method is called when a retry attempt fails with an exception. It provides you with the RetryContext object and the exception that caused the failure. The method has the following signature:

<T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable);

context: The RetryContext object holding information about the retry operation.

callback: The RetryCallback object representing the operation that was being retried.

throwable: The Throwable object representing the exception that caused the retry attempt to fail.

This method allows you to take any necessary actions, such as logging the error, performing cleanup, or deciding whether to continue retrying or aborting the retry operation based on the type of exception.

close: This method is called after the retry operation is completed, whether it was successful or not. It provides you with the RetryContext object and the RetryCallback used in the retry operation. The method has the following signature:

<T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable);

context: The RetryContext object holding information about the retry operation.

callback: The RetryCallback object representing the operation that was being retried.

throwable: The Throwable object representing the last exception thrown during the retry operation (null if no exception was thrown).

The close method allows you to perform any cleanup actions after the retry operation is finished, regardless of whether it succeeded or failed.

By implementing the RetryListener interface and registering it with the RetryTemplate using the registerListener method, you can customize the behavior of the retry operations, log the progress of retries, and take specific actions based on the results of retry attempts.

4) RetryContext: 

RetryContext is an interface provided by Spring Retry to encapsulate the context and state of a retry operation. It allows you to access information about the retry operation, such as the number of retry attempts made, the last exception thrown (if any), and control the flow of the retry process.

The RetryContext interface consists of the following fields and methods:

Fields:

getRetryCount(): Returns the number of retry attempts made so far, including the initial try. The count starts from zero and increments with each retry attempt.

getLastThrowable(): Returns the last exception thrown during the retry operation. It will be null if no exception occurred during the retries.

getExhaustedOnly(): Returns a boolean value indicating whether the context is exhausted and no more retries will be made. This flag is typically set when the maximum number of retries (if specified) is reached or when the RetryPolicy decides to stop the retry process.

Methods:

setAttribute(String name, Object value): Allows you to set a custom attribute in the RetryContext. You can use this method to store any additional information that you want to access during the retry operation.

getAttribute(String name): Returns the value of the custom attribute with the specified name that was previously set using setAttribute. If the attribute does not exist, it returns null.

hasAttribute(String name): Checks if the context contains an attribute with the given name.

removeAttribute(String name): Removes the custom attribute with the specified name from the RetryContext.

registerThrowable(Throwable throwable): Registers the given Throwable as the last exception thrown during the retry operation. This method is typically called when an error occurs, and you want to keep track of the last exception.

setExhaustedOnly(): Marks the context as exhausted, indicating that no more retries will be attempted. This method is typically called when the maximum number of retries is reached or when the RetryPolicy decides to stop the retry process.

registerListener(RetryListener listener): Registers a RetryListener with the context. This method allows you to receive callbacks and notifications about the progress of the retry operation.

The RetryContext provides a way to pass contextual information and control the behavior of the retry operation. By implementing RetryContext, you can customize the retry process, store additional information, and handle exceptions during the retries effectively.

5) RetryTemplate:

RetryTemplate is a class provided by Spring Retry, a subproject of Spring Framework, that simplifies the implementation of retry logic in Java applications. It is designed to handle retrying failed operations that might be transient in nature, such as network timeouts, temporary unavailability of resources, or other intermittent errors.

The RetryTemplate class encapsulates the retry logic and provides a set of methods and configurations to perform retries in a controlled manner. It is particularly useful for scenarios where you want to automatically retry an operation multiple times before giving up or throwing an exception.

Key features of RetryTemplate include:

Configurable Retry Policies: RetryTemplate allows you to define various retry policies, such as fixed number of retry attempts, exponential backoff, or custom strategies based on specific conditions.

Configurable Backoff Policies: You can configure different backoff policies to introduce a delay between retry attempts, allowing the system to recover from transient failures.

Recovery Callbacks: RetryTemplate allows you to specify a recovery callback, which is executed if all retry attempts fail. This callback can be used to provide fallback behavior or to perform alternative actions when the operation cannot be successfully executed.

RetryListeners: You can attach RetryListeners to the RetryTemplate to get notified about retry attempts, successful retries, and failed retries. This can be helpful for logging, monitoring, or custom handling of retries.

Stateless: RetryTemplate is designed to be stateless, meaning it does not hold any state related to the operations being retried. This allows it to be safely used in multi-threaded or concurrent environments.

Using RetryTemplate, you can wrap the code that needs to be retried in a RetryCallback, define the retry policy and backoff policy, and execute the operation using the RetryTemplate's execute method. The RetryTemplate will then automatically handle retrying the operation according to the defined policies.

Overall, RetryTemplate simplifies the implementation of retry logic and improves the resilience of applications, ensuring they can recover from transient failures and continue executing critical operations.

please find github link for sample piece of code for Spring retry based on 5xx Error and Token Expired Case.

GitHub Link: https://github.com/NithishReddy/SpringRetryCode