# Class conflicts when writing Kotlin plugin with recent JDK

**URL:** <https://discuss.gradle.org/t/class-conflicts-when-writing-kotlin-plugin-with-recent-jdk/43252>\
**Category:** Help/Discuss\
**Created:** [July 1, 2022, 9:12pm UTC](https://discuss.gradle.org/t/class-conflicts-when-writing-kotlin-plugin-with-recent-jdk/43252 "2022-07-01T21:12:19Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![liblit](https://sea1.discourse-cdn.com/gradle/user_avatar/discuss.gradle.org/liblit/32/6697_2.png) [@liblit](https://discuss.gradle.org/u/liblit)\
**Post date:** [July 1, 2022, 9:12pm UTC](https://discuss.gradle.org/t/class-conflicts-when-writing-kotlin-plugin-with-recent-jdk/43252/1 "2022-07-01T21:12:19Z")

</div>

I am using Kotlin to write a Gradle plugin for personal use. I would like to use some features only found in recent versions of the Java standard library, such as [`javax.xml.parsers.SAXParserFactory.newDefaultNSInstance()`](https://docs.oracle.com/en/java/javase/17/docs/api/java.xml/javax/xml/parsers/SAXParserFactory.html#newDefaultNSInstance%28%29), which was added in Java 13.

I have configured Gradle for Kotlin plugin creation, and set it to use a Java 17 JDK for both Java and Kotlin:

```nohighlight
plugins {
    `java-gradle-plugin`
    kotlin("jvm") version "1.7.0"
    kotlin("plugin.serialization") version "1.7.0"
}

repositories(RepositoryHandler::mavenCentral)

java.toolchain.languageVersion.set(JavaLanguageVersion.of(17))

kotlin.jvmToolchain {
    languageVersion.set(JavaLanguageVersion.of(17))
}

```

Unfortunately, this leaves me with two `SAXParserFactory` implementations in my compilation classpath:

- `/home/liblit/.gradle/caches/7.4.2/generated-gradle-jars/gradle-api-7.4.2.jar!/javax/xml/parsers/SAXParserFactory.class`
- `/usr/lib/jvm/java-17!/java.xml/javax/xml/parsers/SAXParserFactory.class`

Kotlin compilation via the `compileKotlin` task seems to pick up the `grade-api-7.4.2.jar` implementation first, and unfortunately that’s a rather old version. It’s too old to include the `newDefaultNSInstance()` method I wish to use, so `compileKotlin` fails. I could work around this specific example by using other `SAXParserFactory` methods, but there’s a bigger general issue here.

**How can a Kotlin-based Gradle plugin use newer classes than the ones that are bundled into the Gradle API jar?** Is it possible to reorder dependencies such that my plugin uses the JDK-provided implementations instead? Or is it a terrible idea to build a plugin using a newer JDK than that used by Gradle’s APIs? If the latter, then what specific JDK is Gradle 7.4.2 built against, so that I can build my plugin using the same toolchain version?

I tried creating an analogous situation with a Java-based plugin, but in that case `compileJava` succeeds! I am not sure why. I think that the same two `SAXParserFactory` implementations are present in my compilation classpath. Perhaps the classpath is just ordered differently when compiling Java instead of Kotlin? Perhaps the order is non-deterministic and `compileJava` is getting lucky but `compileKotlin` is not?

---

<div class="post-metadata">

**Author:** ![Vampire](https://sea1.discourse-cdn.com/gradle/user_avatar/discuss.gradle.org/vampire/32/9082_2.png) [@Vampire](https://discuss.gradle.org/u/Vampire)\
**Post date:** [July 3, 2022, 11:16pm UTC](https://discuss.gradle.org/t/class-conflicts-when-writing-kotlin-plugin-with-recent-jdk/43252/2 "2022-07-03T23:16:07Z")

</div>

What you see is this: [Generated gradle-api jar contains JRE classes and in old version which confuses Kotlin compiler · Issue #16147 · gradle/gradle · GitHub](https://github.com/gradle/gradle/issues/16147)

---

<div class="post-metadata">

**Author:** ![liblit](https://sea1.discourse-cdn.com/gradle/user_avatar/discuss.gradle.org/liblit/32/6697_2.png) [@liblit](https://discuss.gradle.org/u/liblit)\
**Post date:** [July 4, 2022, 12:00am UTC](https://discuss.gradle.org/t/class-conflicts-when-writing-kotlin-plugin-with-recent-jdk/43252/3 "2022-07-04T00:00:27Z")

</div>

> [@Vampire](#):
>
> What you see is this: [Generated gradle-api jar contains JRE classes and in old version which confuses Kotlin compiler · Issue #16147 · gradle/gradle · GitHub](https://github.com/gradle/gradle/issues/16147)

Yes, that’s it exactly. I see no workarounds other than porting to Java, but at least now I have several items to thumbs-up, star, subscribe to, and/or watch. Thank you, @Vampire!