Optimize plugin selector logic. (#651)

CHANGES.md

@@ -25,6 +25,7 @@ Release Notes.
 * Bump Lombok to 1.18.30 to adopt JDK21 compiling.
 * Fix PostgreSQL Jdbc URL parsing exception.
 * Bump up grpc version.
+* Optimize plugin selector logic.
 
 #### Documentation
 * Fix JDK requirement in the compiling docs.

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/plugin/PluginCfg.java

@@ -52,13 +52,13 @@ public enum PluginCfg {
                     LOGGER.error(e, "Failed to format plugin({}) define.", pluginDefine);
                 }
             }
-            pluginClassList = pluginSelector.select(pluginClassList);
         } finally {
             input.close();
         }
     }
 
     public List<PluginDefine> getPluginClassList() {
+        pluginClassList = pluginSelector.select(pluginClassList);
         return pluginClassList;
     }