kezhenxu94 commented on a change in pull request #7069:
URL: https://github.com/apache/skywalking/pull/7069#discussion_r647925154



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File path: 
apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/jvm/JVMUtil.java
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@@ -0,0 +1,158 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package org.apache.skywalking.apm.agent.core.jvm;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import java.lang.management.ManagementFactory;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.text.SimpleDateFormat;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Date;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import org.apache.skywalking.apm.agent.core.logging.api.ILog;
+import org.apache.skywalking.apm.agent.core.logging.api.LogManager;
+import org.apache.skywalking.apm.agent.core.util.CollectionUtil;
+import org.apache.skywalking.apm.network.common.v3.KeyStringValuePair;
+
+public class JVMUtil {
+
+    private static final ILog LOGGER = LogManager.getLogger(JVMUtil.class);
+    private final static String PATH_SEPARATOR = "/";
+    private final static String JAR_SEPARATOR = "!";
+    private static List<String> LAST_LIB_JAR_NAMES = new ArrayList<>();
+    private static Set<ClassLoader> CURRENT_CLASSLOADER_LIST = new HashSet<>();
+
+    public static Set<ClassLoader> getCurrentClassloaderList() {
+        return CURRENT_CLASSLOADER_LIST;
+    }
+
+    /**
+     * Build the required JVM information to add to the instance properties
+     */
+    public static List<KeyStringValuePair> buildJVMInfo() {
+        List<KeyStringValuePair> jvmInfo = new ArrayList<>();
+        jvmInfo.add(KeyStringValuePair.newBuilder().setKey("Start 
Time").setValue(getVmStartTime()).build());
+        Gson gson = new GsonBuilder().disableHtmlEscaping().create();
+        jvmInfo.add(KeyStringValuePair.newBuilder().setKey("JVM 
Arguments").setValue(gson.toJson(getVmArgs())).build());
+        List<String> libJarNames = getLibJarNames();
+        if (isLibJarNamesUpdated(libJarNames)) {
+            jvmInfo.add(KeyStringValuePair.newBuilder().setKey("Jar 
Dependencies").setValue(gson.toJson(libJarNames)).build());
+            LAST_LIB_JAR_NAMES.clear();
+            LAST_LIB_JAR_NAMES.addAll(libJarNames);
+        }
+        return jvmInfo;
+    }
+
+    private static String getVmStartTime() {
+        long startTime = ManagementFactory.getRuntimeMXBean().getStartTime();
+        return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new 
Date(startTime));

Review comment:
       > cc @kezhenxu94 If you accept the start time, should we detect the 
changes base on the `start time` unchanged?
   
   We can detect from start time along with other properties, such as service 
instance name, this can be discussed in another issue or PR that focuses on 
event (changes detector).
   
   > And another 2 questions
   > 
   > 1. Should we have a document to list all property keys?
   > 2. Should we consider a value holder or some mechanism to indicate value 
no change? Refer https://github.com/apache/skywalking/pull/7069/files#r647909609
   
   This PR is related to events, but is not specifically only for events, 
right? Those unchanged properties are also to be displayed in UI and I feel 
like they must be reported no matter they changed or not. I don't think we want 
to do something in OAP like, "if this property (`libs`) is not changed, we 
query the previous one and copy its value to this record" (otherwise UI could 
get nothing for this property), no?




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