Adds garbage collection flags to improve server performance

src/main/java/net/knarcraft/minecraftserverlauncher/server/Server.java

@@ -370,17 +370,32 @@ public class Server {
     private String getJavaCommand() {
         ServerLauncherController controller = ServerLauncherController.getInstance();
 
-        if (serverVersion.toLowerCase().contains("latest")) {
+        if (versionAtLeast("1.17")) {
             return controller.getJavaCommand();
+        } else {
+            return controller.getOldJavaCommand();
+        }
+    }
+
+    /**
+     * Checks if the current server version is at least the given version
+     *
+     * @param version <p>The version to require</p>
+     * @return <p>True if the server version is at least the given version</p>
+     */
+    private boolean versionAtLeast(String version) {
+        if (serverVersion.toLowerCase().contains("latest")) {
+            return true;
         } else if (serverVersion.contains(".") && serverVersion.split("\\.").length >= 2) {
             try {
-                if (Integer.parseInt(serverVersion.split("\\.")[1]) >= 17) {
+                return Integer.parseInt(serverVersion.split("\\.")[0]) >=
-                    return controller.getJavaCommand();
+                        Integer.parseInt(version.split("\\.")[0]) &&
-                }
+                        Integer.parseInt(serverVersion.split("\\.")[1]) >=
+                                Integer.parseInt(version.split("\\.")[1]);
             } catch (NumberFormatException ignored) {
             }
         }
-        return controller.getOldJavaCommand();
+        return false;
     }
 
     /**
@@ -389,17 +404,7 @@ public class Server {
      * @throws IOException <p>If the process cannot be started</p>
      */
     private void startServerProcess() throws IOException {
-        ProcessBuilder builder;
+        ProcessBuilder builder = new ProcessBuilder(generateServerProcessArguments());
-        String serverPath;
-        //Decide the path of the .jar file to be executed
-        if (type.getName().equals("Custom")) {
-            serverPath = this.path + File.separator + serverVersion;
-        } else {
-            serverPath = jarDirectory + this.type.getName() + serverVersion + ".jar";
-        }
-        builder = new ProcessBuilder(getJavaCommand(), "-Xmx" + this.maxRam, "-Xms512M",
-                "-Djline.terminal=jline.UnsupportedTerminal", "-Dcom.mojang.eula.agree=true", "-jar", serverPath,
-                "nogui");
         builder.directory(new File(this.path));
         builder.redirectErrorStream(true);
         this.process = builder.start();
@@ -417,6 +422,64 @@ public class Server {
         }, 10, 500, TimeUnit.MILLISECONDS);
     }
 
+    /**
+     * Generates the process arguments required for starting this Minecraft server
+     *
+     * @return <p>The process arguments required for starting this Minecraft server</p>
+     */
+    private List<String> generateServerProcessArguments() {
+        //Decide the path of the .jar file to be executed
+        String serverPath;
+        if (type.getName().equalsIgnoreCase("Custom")) {
+            serverPath = this.path + File.separator + serverVersion;
+        } else {
+            serverPath = jarDirectory + this.type.getName() + serverVersion + ".jar";
+        }
+
+        List<String> processArguments = new ArrayList<>(20);
+        processArguments.add(getJavaCommand());
+        processArguments.add("-Xmx" + this.maxRam);
+        processArguments.add("-Xms512M");
+        if (versionAtLeast("1.8")) {
+            addGarbageCollectorFlags(processArguments);
+        }
+        processArguments.add("-Djline.terminal=jline.UnsupportedTerminal");
+        processArguments.add("-Dcom.mojang.eula.agree=true");
+        processArguments.add("-jar");
+        processArguments.add(serverPath);
+        processArguments.add("nogui");
+        return processArguments;
+    }
+
+    /**
+     * Adds garbage collector flags to the server process arguments to improve performance
+     *
+     * @param processArguments <p>The process arguments to add the flags to</p>
+     */
+    private void addGarbageCollectorFlags(List<String> processArguments) {
+        processArguments.add("-XX:+UseG1GC");
+        processArguments.add("-XX:+ParallelRefProcEnabled");
+        processArguments.add("-XX:MaxGCPauseMillis=200");
+        processArguments.add("-XX:+UnlockExperimentalVMOptions");
+        processArguments.add("-XX:+DisableExplicitGC");
+        processArguments.add("-XX:+AlwaysPreTouch");
+        boolean excessiveRam = Integer.parseInt(this.maxRam.substring(0, this.maxRam.length() - 1)) > 11;
+        processArguments.add("-XX:G1NewSizePercent=" + (excessiveRam ? 40 : 30));
+        processArguments.add("-XX:G1MaxNewSizePercent=" + (excessiveRam ? 50 : 40));
+        processArguments.add("-XX:G1HeapRegionSize=" + (excessiveRam ? "16M" : "8M"));
+        processArguments.add("-XX:G1ReservePercent=" + (excessiveRam ? 15 : 20));
+        processArguments.add("-XX:G1HeapWastePercent=5");
+        processArguments.add("-XX:G1MixedGCCountTarget=4");
+        processArguments.add("-XX:InitiatingHeapOccupancyPercent=" + (excessiveRam ? 20 : 15));
+        processArguments.add("-XX:G1MixedGCLiveThresholdPercent=90");
+        processArguments.add("-XX:G1RSetUpdatingPauseTimePercent=5");
+        processArguments.add("-XX:SurvivorRatio=32");
+        processArguments.add("-XX:+PerfDisableSharedMem");
+        processArguments.add("-XX:MaxTenuringThreshold=1");
+        processArguments.add("-Dusing.aikars.flags=https://mcflags.emc.gs");
+        processArguments.add("-Daikars.new.flags=true");
+    }
+
     /**
      * Updates a single console with process output
      *
@@ -580,4 +643,5 @@ public class Server {
                 this.getMaxRam()
         );
     }
+    
 }