Provide a way to disable the Restarter

Allow the Restarter to be disabled via a System property.

Fixes gh-3173

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/RestartApplicationListener.java

@@ -35,10 +35,12 @@ public class RestartApplicationListener implements ApplicationListener<Applicati
 
 	private int order = HIGHEST_PRECEDENCE;
 
+	private static final String ENABLED_PROPERTY = "spring.devtools.restart.enabled";
+
 	@Override
 	public void onApplicationEvent(ApplicationEvent event) {
 		if (event instanceof ApplicationStartedEvent) {
-			Restarter.initialize(((ApplicationStartedEvent) event).getArgs());
+			onApplicationStartedEvent((ApplicationStartedEvent) event);
 		}
 		if (event instanceof ApplicationReadyEvent
 				|| event instanceof ApplicationFailedEvent) {
@@ -46,6 +48,18 @@ public class RestartApplicationListener implements ApplicationListener<Applicati
 		}
 	}
 
+	private void onApplicationStartedEvent(ApplicationStartedEvent event) {
+		// It's too early to use the Spring environment but we should still allow
+		// users to disable restart using a System property.
+		String enabled = System.getProperty(ENABLED_PROPERTY);
+		if (enabled == null || Boolean.parseBoolean(enabled)) {
+			Restarter.initialize(event.getArgs());
+		}
+		else {
+			Restarter.disable();
+		}
+	}
+
 	@Override
 	public int getOrder() {
 		return this.order;

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/Restarter.java

@@ -78,12 +78,16 @@ import org.springframework.util.ReflectionUtils;
  */
 public class Restarter {
 
+	private static final String[] NO_ARGS = {};
+
 	private static Restarter instance;
 
 	private Log logger = new DeferredLog();
 
 	private final boolean forceReferenceCleanup;
 
+	private boolean enabled = true;
+
 	private URL[] initialUrls;
 
 	private final String mainClassName;
@@ -185,6 +189,14 @@ public class Restarter {
 		}
 	}
 
+	/**
+	 * Set if restart support is enabled.
+	 * @param enabled if restart support is enabled
+	 */
+	private void setEnabled(boolean enabled) {
+		this.enabled = false;
+	}
+
 	/**
 	 * Add additional URLs to be includes in the next restart.
 	 * @param urls the urls to add
@@ -215,6 +227,10 @@ public class Restarter {
 	 * Restart the running application.
 	 */
 	public void restart() {
+		if (!this.enabled) {
+			this.logger.debug("Application restart is disabled");
+			return;
+		}
 		this.logger.debug("Restarting application");
 		getLeakSafeThread().call(new Callable<Void>() {
 
@@ -402,6 +418,14 @@ public class Restarter {
 		return this.initialUrls;
 	}
 
+	/**
+	 * Initialize and disable restart support.
+	 */
+	public static void disable() {
+		initialize(NO_ARGS, false, RestartInitializer.NONE);
+		getInstance().setEnabled(false);
+	}
+
 	/**
 	 * Initialize restart support. See
 	 * {@link #initialize(String[], boolean, RestartInitializer)} for details.