How to Use OkHttp 4.x with Grails

OkHttp 4.x is a bit controversial evolution of the popular Java HTTP client. The version 4.x has been rewritten to Kotlin and it now…

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How to Use OkHttp 4.x with Grails

OkHttp 4.x is a bit controversial evolution of the popular Java HTTP client. The version 4.x has been rewritten to Kotlin and it now requires Kotlin Stdlib as a dependency.

If any library such as Segment Analytics Java Client or Recurly Java Client depends on OkHttp 4.x you may get an exception similar to the following one when running Grails or probably any other older Spring Boot application:

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APPLICATION FAILED TO START
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Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

okio.Segment.writeTo(Segment.kt:169)

The following method did not exist:

kotlin.collections.ArraysKt.copyInto([B[BIII)[B

The issue is caused by the old version of the Kotlin libraries on the classpath. Grails 4.x framework is still using Spring Dependency Management Plugin under the hood with a couple of Maven BOMs secretly added under the hood. One of them is an older version of Spring Boot Dependencies BOM which specifies the version of Kotlin libraries to 1.2.71 whereas OkHttp depends on 1.4.10 at the time of writing causing the binary incompatibility in the runtime.

Luckily, there is an easy solution to fix this. The Kotlin version is specified as kotlin.version property in the BOM and Spring Dependency Management Plugin supports overriding the properties in gradle.properties file so the only required change is to add the following line at the end of the file.

kotlin.version = 1.4.10

After this change the application should start as expected.