In this article, we are going to show how to start using the Failsafe library for handling failures in Java applications. Failsafe is a lightweight, zero-dependency library created by Jonathan Halterman and other great developers for handling everyday use cases. Need to mention that it is released under Apache 2.0 license so you can use it commercial projects.
To start using Failsafe library simply add dependecy to your project:
Check available versions here: net.jodah : failsafe
3. Getting started
The Failsafe library supports four policies, that determine which execution results or failures to handle and how to handle them:
In this tutorial, we are going to use a simple
Retry policy will handle
ConnectionException. We configured the maximum number of retries to 5 and delay between attempts to 2 seconds. When the
ConnectionException occurs, the system waits for 2s and tries to reconnect again until we reach the maximum number of retries.
connect() that we use in this example will be responsible for connection to the some kind of external system (like Database or FTP):
Failsafe library allows us to execute
Supplier with retries. The following code shows how to use the
The example with
Supplier is as follows:
Both examples using
Failsafe to handle
ConnectionException that might occur in the
connect() method. According to the defined policy, the program will be trying to connect at most 5 times, and it will wait 2 seconds after each try.
We could also execute a
Supplier asynchronously with a policy we choose as follows:
4. JUnit Test
The mockito test for our use case could look as follows:
DatabaseConnection represents the object that holds the connection to external system.
The mockito test that make a use of
RetryPolicy has the following structure:
In this test, we use mockito to simulate connection problems. The first attempt will throw the
ConnectionException and the second one will return the actual
This is set up in the following code:
Test verify if system calls
connect() method only two times (because the second call didn't throw an exception):
In this article, we presented a simple example of using the
Failsafe library to handle failures in the Java program. Setting up this library is easy, and we don't need extra dependencies to make use of it. The library could be used to reconnect to the external system that is not stable and needs several attempts.