Sttp client failing with Java 8

[Andrapyre]

Description

When the sttp client runs with Java 8, it produces the following error in Github Actions on all Scala versions:

java.lang.UnsupportedClassVersionError: sttp/client4/httpurlconnection/HttpURLConnectionBackend$ has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

First raised in xerial/sbt-sonatype#548

[Andrapyre]

Refactoring to change to an OkHttp backend produces the following:

com.lumidion.sonatype.central.client.integration.test.SyncSttpItSpec *** ABORTED ***
[info]   java.lang.NoClassDefFoundError: java/net/http/HttpTimeoutException
[info]   at sttp.client4.okhttp.OkHttpBackend.adjustExceptions(OkHttpBackend.scala:49)
[info]   at sttp.client4.okhttp.OkHttpBackend.send(OkHttpBackend.scala:38)
[info]   at sttp.client4.wrappers.FollowRedirectsBackend.sendWithCounter(FollowRedirectsBackend.scala:19)
[info]   at sttp.client4.wrappers.FollowRedirectsBackend.send(FollowRedirectsBackend.scala:15)
[info]   at sttp.client4.Request.send(request.scala:159)
[info]   at com.lumidion.sonatype.central.client.sttp.core.SyncSonatypeClient.uploadBundle(SyncSonatypeClient.scala:27)
[info]   at com.lumidion.sonatype.central.client.integration.test.SyncSttpItSpec.$anonfun$new$7(SyncSttpItSpec.scala:42)
[info]   at org.scalatest.OutcomeOf.outcomeOf(OutcomeOf.scala:85)
[info]   at org.scalatest.OutcomeOf.outcomeOf$(OutcomeOf.scala:83)
[info]   at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104)
[info]   ...
[info]   Cause: java.lang.ClassNotFoundException: java.net.http.HttpTimeoutException
[info]   at java.net.URLClassLoader.findClass(URLClassLoader.java:387)
[info]   at sbt.internal.ManagedClassLoader.findClass(ManagedClassLoader.java:103)
[info]   at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
[info]   at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
[info]   at sttp.client4.okhttp.OkHttpBackend.adjustExceptions(OkHttpBackend.scala:49)
[info]   at sttp.client4.okhttp.OkHttpBackend.send(OkHttpBackend.scala:38)
[info]   at sttp.client4.wrappers.FollowRedirectsBackend.sendWithCounter(FollowRedirectsBackend.scala:19)
[info]   at sttp.client4.wrappers.FollowRedirectsBackend.send(FollowRedirectsBackend.scala:15)
[info]   at sttp.client4.Request.send(request.scala:159)
[info]   at com.lumidion.sonatype.central.client.sttp.core.SyncSonatypeClient.uploadBundle(SyncSonatypeClient.scala:27)

[Andrapyre]

@adamw, replying to your comment, this actions run produces the following results for Java 8:

• Scala 2.12 - java.lang.NoClassDefFoundError: java/net/http/HttpTimeoutException
• Scala 2.13 and 3.3.3 - java.lang.UnsupportedClassVersionError: sttp/client4/SyncBackend has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

This is after I refactored the HttpURLConnectionBackend to remove any direct or downstream calls (like this) to classes that are Java 11+ (see branch).

It must be that the httpclient package in the sttp core module is forcing Java 11+ for the whole package. The httpclient package would probably need to be removed from core and put in its own module and the build machine reverted to Java 8 for when non-httpclient libs are published, if you want to support Java 8 at all, that is.

From your responses, it seems like you haven't worked with Java 8 in a while and you don't get this complaint very often (it's been years since I worked with Java 8 myself), so there is probably not enough demand to justify these breaking changes. But maybe worth putting a note in the readme that users need Java 11+ to work with sttp.

[adamw]

@Andrapyre the main documentation page (https://sttp.softwaremill.com/en/latest/) specifies that: upported Java versions include 11+.