ClassNotFoundException: org/eclipse/jetty/alpn/ALPN, but I have access to this class

Question

I have such code:

public static void main(String[] args) throws Exception {
    System.out.println("ALPN class: " + ALPN.class);
    HelloWorldClient client = new HelloWorldClient("localhost", 10009);
}

This gives such output:

ALPN class: class org.eclipse.jetty.alpn.ALPN
Exception in thread "main" java.lang.IllegalArgumentException: ALPN is not configured properly. See https://github.com/grpc/grpc-java/blob/master/SECURITY.md#troubleshooting for more information.
    at io.grpc.netty.GrpcSslContexts.selectApplicationProtocolConfig(GrpcSslContexts.java:163)
    at io.grpc.netty.GrpcSslContexts.configure(GrpcSslContexts.java:136)
    at io.grpc.netty.GrpcSslContexts.configure(GrpcSslContexts.java:124)
    at io.grpc.netty.GrpcSslContexts.forClient(GrpcSslContexts.java:94)
    at btcduke.node.ln.HelloWorldClient.<init>(HelloWorldClient.java:35)
    at btcduke.node.ln.HelloWorldClient.main(HelloWorldClient.java:76)
Caused by: java.lang.ClassNotFoundException: org/eclipse/jetty/alpn/ALPN
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at io.grpc.netty.JettyTlsUtil.isJettyAlpnConfigured(JettyTlsUtil.java:34)
    at io.grpc.netty.GrpcSslContexts.selectApplicationProtocolConfig(GrpcSslContexts.java:153)
    ... 5 more

HelloWorldClient uses grpc, and it looks grpc is trying to load ALPN class dynamically. Am I right? This class can't be find, so I have error message. But please take a look,that I have access to this class (I print this class in first line). Do anyone knows why it happens this way? I have no idea :/

I toretically solved this issue by adding VM argument "-Xbootclasspath/p:" to run configuration option, but I don't understand why I needed to do this and also I don't think this is elegant method.

Answer 1

Documented at https://www.eclipse.org/jetty/documentation/jetty-9/index.php#alpn-chapter

For Java 8 up to 1.8.0_242 included.

You MUST use the alpn-boot provider for your specific JVM, as it modifies OpenJDK classes to enable support for ALPN.

See ALPN to OpenJDK version list:
https://www.eclipse.org/jetty/documentation/jetty-9/index.html#alpn-versions

This alpn-boot-<ver>.jar requires use of the -Xbootclasspath/p: option on the JVM command line.

You will also use the jetty-alpn-openjdk8-server-<ver>.jar on your normal Server classpath for your specific version of Jetty server.

For Java 8 from 1.8.0_252 and later (including Java 9+).

For Java 8 from 1.8.0_252 included and later, this provider uses the standard OpenJDK ALPN APIs introduced in Java 9 (see below) that have been backported to 1.8.0_252 and does not require the -Xbootclasspath/p: option on command line

For this operational mode, use the jetty-alpn-java-server-<ver>.jar artifact on your server classpath.

Answer 2

If you received an error message "ALPN is not configured properly" or "Jetty ALPN/NPN has not been properly configured", it most likely means that:

ALPN related dependencies are either not present in the classpath or that there is a classpath conflict or that a wrong version is used due to dependency management.

Looking closely at the provided stacktrace, it reveals that you need to configure "ALPN" properly

Caused by: java.lang.ClassNotFoundException: 
org/eclipse/jetty/alpn/ALPN
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at 
io.grpc.netty.JettyTlsUtil.isJettyAlpnConfigured(JettyTlsUtil.java:34)