http (feature): Fallback to Java8 compatible URLConnectionChannel if …

…Java's HttpClient is unavailable (#3478)

airframe-http/.jvm/src/main/scala/wvlet/airframe/http/client/JavaHttpClientBackend.scala

@@ -15,7 +15,13 @@ package wvlet.airframe.http.client
 import wvlet.airframe.http.{ServerAddress}
 
 object JavaHttpClientBackend extends HttpClientBackend {
+  private val isJava8: Boolean = sys.props.get("java.version").exists(_.startsWith("1.8"))
+
   override def newHttpChannel(serverAddress: ServerAddress, config: HttpClientConfig): HttpChannel = {
-    new JavaHttpClientChannel(serverAddress, config)
+    // For JDK8, use URLConnectionChannel
+    if (isJava8)
+      new URLConnectionChannel(serverAddress, config)
+    else
+      new JavaHttpClientChannel(serverAddress, config)
   }
 }

airframe-http/.jvm/src/main/scala/wvlet/airframe/http/client/URLConnectionChannel.scala

@@ -24,6 +24,11 @@ import java.util.zip.{GZIPInputStream, InflaterInputStream}
 import scala.concurrent.duration.Duration
 import scala.jdk.CollectionConverters.*
 
+/**
+  * Java8-compatible HTTP channel implementation based on {{URL.openConnection}}
+  * @param serverAddress
+  * @param config
+  */
 class URLConnectionChannel(serverAddress: ServerAddress, config: HttpClientConfig) extends HttpChannel {
   override def send(request: Request, channelConfig: HttpChannelConfig): Response = {
     val url = s"${serverAddress.uri}${if (request.uri.startsWith("/")) request.uri

airframe-http/.jvm/src/main/scala/wvlet/airframe/http/client/URLConnectionClientBackend.scala

@@ -16,6 +16,7 @@ import wvlet.airframe.http.{ServerAddress}
 
 /**
   */
+@deprecated("This backend will be used automatically for Java8. No need to explicitly set this backend", "24.4.0")
 object URLConnectionClientBackend extends HttpClientBackend {
   override def newHttpChannel(serverAddress: ServerAddress, config: HttpClientConfig): HttpChannel = {
     new URLConnectionChannel(serverAddress, config)