Retrying specific code on an Exception/Error in Java

Updated 2019-08-08: Using new version with lambda expressions.

» Introduction

This is already the second Java post within a few days. This time, I want to demonstrate, how to retry some specific code when an Exception or an Error is thrown. This might be helpful when dealing with distributed systems and a first call didn’t bring success. My first attempts in researching a solution for this were not very satisfying. Most times you only could retry the whole method or just use a simple loop. But I wanted something more granular and more extensible without copying the same loops over and over again. The closest solution I found was the “enterprisy” Stackoverflow answer by ach - which lost against the simple loop as the correct answer ;-). In this post, I want to present a slightly enhanced version of the retry functionality with Java 8 compatibility.

» Example

For Throwables (Exceptions and Errors). You shouldn’t use this in “normal” application code, only in tests.

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      // some code
      // ...
      Retry.onThrowable(5, attempt -> {
            // Code which will be retried.
            // A test with Assert.assertNull(new Object()) will retry
            // the code inside here until no Exception or Error is thrown
            // or the maximum attempts of 5 are exceeded.
      });
      // some more code
      // ...

For Exceptions only. Use this in your “normal” application code.

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      // some code
      // ...
      Retry.onException(5, attempt -> {
            // Code which will be retried.
            // A test with Assert.assertNull(new Object()) will immediately fail
            // as the assertion throws an Error and not an Exception,
            // but we are calling 'onException' instead of 'onThrowable'.
      });
      // some more code
      // ...

The implementation could be further enhanced, e.g. it should be possible to only retry on some specific Throwables (blacklist) or not retry on specific Throwables (whitelist).

» Source Code

The latest version of the code can be found in the git repository.