automatically enable last GC if higher or equal to 1.7.0 u4

src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java

@@ -123,6 +123,68 @@ public class JvmInfo implements Streamable, Serializable, ToXContent {
         return this.version;
     }
 
+    public int versionAsInteger() {
+        try {
+            int i = 0;
+            String sVersion = "";
+            for (; i < version.length(); i++) {
+                if (!Character.isDigit(version.charAt(i)) && version.charAt(i) != '.') {
+                    break;
+                }
+                if (version.charAt(i) != '.') {
+                    sVersion += version.charAt(i);
+                }
+            }
+            if (i == 0) {
+                return -1;
+            }
+            return Integer.parseInt(sVersion);
+        } catch (Exception e) {
+            return -1;
+        }
+    }
+
+    public int versionUpdatePack() {
+        try {
+            int i = 0;
+            String sVersion = "";
+            for (; i < version.length(); i++) {
+                if (!Character.isDigit(version.charAt(i)) && version.charAt(i) != '.') {
+                    break;
+                }
+                if (version.charAt(i) != '.') {
+                    sVersion += version.charAt(i);
+                }
+            }
+            if (i == 0) {
+                return -1;
+            }
+            Integer.parseInt(sVersion);
+            int from;
+            if (version.charAt(i) == '_') {
+                // 1.7.0_4
+                from = ++i;
+            } else if (version.charAt(i) == '-' && version.charAt(i + 1) == 'u') {
+                // 1.7.0-u2-b21
+                i = i + 2;
+                from = i;
+            } else {
+                return -1;
+            }
+            for (; i < version.length(); i++) {
+                if (!Character.isDigit(version.charAt(i)) && version.charAt(i) != '.') {
+                    break;
+                }
+            }
+            if (from == i) {
+                return -1;
+            }
+            return Integer.parseInt(version.substring(from, i));
+        } catch (Exception e) {
+            return -1;
+        }
+    }
+
     public String vmName() {
         return vmName;
     }

src/main/java/org/elasticsearch/monitor/jvm/JvmStats.java

@@ -66,7 +66,15 @@ public class JvmStats implements Streamable, Serializable, ToXContent {
         memoryMXBean = ManagementFactory.getMemoryMXBean();
         threadMXBean = ManagementFactory.getThreadMXBean();
 
-        boolean enableLastGc = Booleans.parseBoolean(System.getProperty("monitor.jvm.enable_last_gc"), false);
+        JvmInfo info = JvmInfo.jvmInfo();
+        boolean defaultEnableLastGc = false;
+        if (info.versionAsInteger() == 170) {
+            defaultEnableLastGc = info.versionUpdatePack() >= 4;
+        } else if (info.versionAsInteger() > 170) {
+            defaultEnableLastGc = true;
+        }
+
+        boolean enableLastGc = Booleans.parseBoolean(System.getProperty("monitor.jvm.enable_last_gc"), defaultEnableLastGc);
         if (enableLastGc) {
             try {
                 Class sunGcClass = Class.forName("com.sun.management.GarbageCollectorMXBean");