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πŸ” Retry some code which failed due to an error or exception.
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retry is a library 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 ;-). This is a slightly enhanced version of the retry functionality with Java 8 compatibility.




Include the Retry library to your project with JitPack (Retry).



For Exceptions only. Use this in your "normal" application code.

// 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
// ...

With default number of retries (5):

Retry.onException(attempt -> {
    // code

Whitelisting a specific Exception class. If the specified Exception was raised, it won't retry and immediately rethrow the Exception.

Retry.onException(3, Arrays.asList(ClassNotFoundException.class), attempt -> {
    // code


For Throwables (Exceptions and Errors). You shouldn't use this in "normal" application code, only in tests. Otherwise, it's the same as Retry.onException(..).

// 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
// ...
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