ALPN is not compatible with both Java 8 and 9 about jetty-alpn HOT 8 CLOSED

You need to include the dependency for jetty-alpn-java-[client|server] only when using JDK 9.
This is easily done with a Maven profile.

The jar cannot be built with JDK 8 because it uses JDK 9 specific APIs.

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Typically we have used either the jetty start.jar modules or Maven profiles to assemble the correct jars.

Unfortunately we can't make this jar a Multi release jar because it users the service loader which cannot be version Ed. Perhaps we can put a dummy java 8 version in the jar that is a noop. I've reopened to consider this.

Also you can now use conscript for ssl which has the same alpn for Java 8 and java 9.

from jetty-alpn.

Right Maven profile can be used but only if you directly use Jetty library not if you are building a library that uses Jetty.

What about using a condition just like the NegotiatingServerConnectionFactory class (see https://github.com/eclipse/jetty.project/blob/jetty-9.4.x-1200/jetty-server/src/main/java/org/eclipse/jetty/server/NegotiatingServerConnectionFactory.java#L41) to determine the JVM version and use the service loader only when it is Java 9?

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I managed to find a workaround but I don't think it is a recommended way.

Using Jetty 9.4.8, with the following dependencies (in this order I suppose) and build with Java 9. I just have to add alpn-boot (-Xbootclasspath/p:/path/to/alpn-boot.jar) for running with Java 8 and the modules for Java 9 (--add-modules java.activation,java.xml.bind).

        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-alpn-java-server</artifactId>
            <version>${jetty.version}</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-alpn-java-client</artifactId>
            <version>${jetty.version}</version>
        </dependency>

        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-alpn-openjdk8-server</artifactId>
            <version>${jetty.version}</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-alpn-openjdk8-client</artifactId>
            <version>${jetty.version}</version>
        </dependency>

from jetty-alpn.

Yes this is the correct way.

Artifacts jetty-alpn-java-[client|server] are built by Jetty with target JDK 9, while artifacts jetty-alpn-openjdk8-[client|server] are built with target JDK 8.

A library may ship all artifacts, and Jetty will use the ServiceLoader to load the right implementation at runtime, preferring jetty-alpn-openjdk8-* when the runtime is JDK 8 and jetty-alpn-java-* when the runtime is JDK 9.

Unfortunately you still need the bootclasspath for JDK 8 only, so it's not a completely transparent solution, as you have to change the command line depending on the JDK version.

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Note that you may wish to consider using the conscrypt SSL provider with jetty. Not only is it much faster than native SSL, but it supports ALPN in both java8 and java9 without the need to modify the boot path.

https://www.eclipse.org/jetty/documentation/9.4.x/jetty-ssl-distribution.html

Documentation has also been updated for the next release: jetty/jetty.project@904acea

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no more warning, after I excluded JDK 9 version Alpn in Gradle

configurations.forEach {
  it.exclude("org.eclipse.jetty", "jetty-alpn-java-server")
  it.exclude("org.eclipse.jetty", "jetty-alpn-server")
}

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