Merge pull request #1690 from lilai23/fix_spi_2.1.x

fix_2.1.x: classloaders in Sermant should not load implementations of SPI interface from parent classloader

sermant-agentcore/sermant-agentcore-core/src/main/java/io/sermant/core/plugin/classloader/PluginClassLoader.java

@@ -20,8 +20,10 @@
 import io.sermant.core.config.ConfigManager;
 import io.sermant.core.plugin.agent.config.AgentConfig;
 
+import java.io.IOException;
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.logging.Level;
@@ -150,6 +152,17 @@ private Class<?> getClassFromLocalClassLoader(String name) {
         return clazz;
     }
 
+    @Override
+    public Enumeration<URL> getResources(String name) throws IOException {
+        // Due to class isolation, the service loader does not obtain the service provider from the parent
+        // classloader, but returns only the resources in current classloader
+        if (name.startsWith("META-INF/services/")) {
+            return findResources(name);
+        }
+
+        return super.getResources(name);
+    }
+
     /**
      * Load classes only through Sermant's own search path, not using localClassLoader, which would otherwise cause
      * stackoverflow