Don't quit application on restart failures

Update `Restarter` to support a `FailureHandler` strategy that can be
used to determine how to deal with errors. The
`LocalDevToolsAutoConfiguration` now uses a strategy that doesn't quit
the application, but instead continues to wait for further file changes.

This helps make restart much more usable in situations where you
accidentally break code.

Fixes gh-3210

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/autoconfigure/LocalDevToolsAutoConfigurationTests.java

@@ -30,8 +30,8 @@ import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfigurati
 import org.springframework.boot.devtools.classpath.ClassPathChangedEvent;
 import org.springframework.boot.devtools.classpath.ClassPathFileSystemWatcher;
 import org.springframework.boot.devtools.filewatch.ChangedFiles;
-import org.springframework.boot.devtools.filewatch.FileSystemWatcher;
 import org.springframework.boot.devtools.livereload.LiveReloadServer;
+import org.springframework.boot.devtools.restart.FailureHandler;
 import org.springframework.boot.devtools.restart.MockRestartInitializer;
 import org.springframework.boot.devtools.restart.MockRestarter;
 import org.springframework.boot.devtools.restart.Restarter;
@@ -48,6 +48,7 @@ import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.junit.Assert.assertThat;
+import static org.mockito.Matchers.any;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.reset;
@@ -138,7 +139,7 @@ public class LocalDevToolsAutoConfigurationTests {
 		ClassPathChangedEvent event = new ClassPathChangedEvent(this.context,
 				Collections.<ChangedFiles> emptySet(), true);
 		this.context.publishEvent(event);
-		verify(this.mockRestarter.getMock()).restart();
+		verify(this.mockRestarter.getMock()).restart(any(FailureHandler.class));
 	}
 
 	@Test
@@ -172,7 +173,10 @@ public class LocalDevToolsAutoConfigurationTests {
 		Map<String, Object> properties = new HashMap<String, Object>();
 		properties.put("spring.devtools.restart.trigger-file", "somefile.txt");
 		this.context = initializeAndRun(Config.class, properties);
-		FileSystemWatcher watcher = this.context.getBean(FileSystemWatcher.class);
+		ClassPathFileSystemWatcher classPathWatcher = this.context
+				.getBean(ClassPathFileSystemWatcher.class);
+		Object watcher = ReflectionTestUtils.getField(classPathWatcher,
+				"fileSystemWatcher");
 		Object filter = ReflectionTestUtils.getField(watcher, "triggerFilter");
 		assertThat(filter, instanceOf(TriggerFileFilter.class));
 	}

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/classpath/ClassPathFileChangeListenerTests.java

@@ -27,19 +27,18 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Captor;
+import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
-import org.springframework.boot.devtools.classpath.ClassPathChangedEvent;
-import org.springframework.boot.devtools.classpath.ClassPathFileChangeListener;
-import org.springframework.boot.devtools.classpath.ClassPathRestartStrategy;
 import org.springframework.boot.devtools.filewatch.ChangedFile;
 import org.springframework.boot.devtools.filewatch.ChangedFiles;
+import org.springframework.boot.devtools.filewatch.FileSystemWatcher;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationEventPublisher;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.junit.Assert.assertThat;
 import static org.mockito.BDDMockito.given;
-import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 
 /**
@@ -52,6 +51,15 @@ public class ClassPathFileChangeListenerTests {
 	@Rule
 	public ExpectedException thrown = ExpectedException.none();
 
+	@Mock
+	private ApplicationEventPublisher eventPublisher;
+
+	@Mock
+	private ClassPathRestartStrategy restartStrategy;
+
+	@Mock
+	private FileSystemWatcher fileSystemWatcher;
+
 	@Captor
 	private ArgumentCaptor<ApplicationEvent> eventCaptor;
 
@@ -64,31 +72,32 @@ public class ClassPathFileChangeListenerTests {
 	public void eventPublisherMustNotBeNull() throws Exception {
 		this.thrown.expect(IllegalArgumentException.class);
 		this.thrown.expectMessage("EventPublisher must not be null");
-		new ClassPathFileChangeListener(null, mock(ClassPathRestartStrategy.class));
+		new ClassPathFileChangeListener(null, this.restartStrategy,
+				this.fileSystemWatcher);
 	}
 
 	@Test
 	public void restartStrategyMustNotBeNull() throws Exception {
 		this.thrown.expect(IllegalArgumentException.class);
 		this.thrown.expectMessage("RestartStrategy must not be null");
-		new ClassPathFileChangeListener(mock(ApplicationEventPublisher.class), null);
+		new ClassPathFileChangeListener(this.eventPublisher, null, this.fileSystemWatcher);
 	}
 
 	@Test
 	public void sendsEventWithoutRestart() throws Exception {
 		testSendsEvent(false);
+		verify(this.fileSystemWatcher, never()).stop();
 	}
 
 	@Test
 	public void sendsEventWithRestart() throws Exception {
 		testSendsEvent(true);
+		verify(this.fileSystemWatcher).stop();
 	}
 
 	private void testSendsEvent(boolean restart) {
-		ApplicationEventPublisher eventPublisher = mock(ApplicationEventPublisher.class);
-		ClassPathRestartStrategy restartStrategy = mock(ClassPathRestartStrategy.class);
 		ClassPathFileChangeListener listener = new ClassPathFileChangeListener(
-				eventPublisher, restartStrategy);
+				this.eventPublisher, this.restartStrategy, this.fileSystemWatcher);
 		File folder = new File("s1");
 		File file = new File("f1");
 		ChangedFile file1 = new ChangedFile(folder, file, ChangedFile.Type.ADD);
@@ -99,10 +108,10 @@ public class ClassPathFileChangeListenerTests {
 		ChangedFiles changedFiles = new ChangedFiles(new File("source"), files);
 		Set<ChangedFiles> changeSet = Collections.singleton(changedFiles);
 		if (restart) {
-			given(restartStrategy.isRestartRequired(file2)).willReturn(true);
+			given(this.restartStrategy.isRestartRequired(file2)).willReturn(true);
 		}
 		listener.onChange(changeSet);
-		verify(eventPublisher).publishEvent(this.eventCaptor.capture());
+		verify(this.eventPublisher).publishEvent(this.eventCaptor.capture());
 		ClassPathChangedEvent actualEvent = (ClassPathChangedEvent) this.eventCaptor
 				.getValue();
 		assertThat(actualEvent.getChangeSet(), equalTo(changeSet));

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/classpath/ClassPathFileSystemWatcherTests.java

@@ -28,11 +28,9 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.junit.rules.TemporaryFolder;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.boot.devtools.classpath.ClassPathChangedEvent;
-import org.springframework.boot.devtools.classpath.ClassPathFileSystemWatcher;
-import org.springframework.boot.devtools.classpath.ClassPathRestartStrategy;
 import org.springframework.boot.devtools.filewatch.ChangedFile;
 import org.springframework.boot.devtools.filewatch.FileSystemWatcher;
+import org.springframework.boot.devtools.filewatch.FileSystemWatcherFactory;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
@@ -43,6 +41,7 @@ import org.springframework.util.FileCopyUtils;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.junit.Assert.assertThat;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link ClassPathFileSystemWatcher}.
@@ -62,7 +61,8 @@ public class ClassPathFileSystemWatcherTests {
 		this.thrown.expect(IllegalArgumentException.class);
 		this.thrown.expectMessage("Urls must not be null");
 		URL[] urls = null;
-		new ClassPathFileSystemWatcher(urls);
+		new ClassPathFileSystemWatcher(mock(FileSystemWatcherFactory.class),
+				mock(ClassPathRestartStrategy.class), urls);
 	}
 
 	@Test
@@ -99,7 +99,8 @@ public class ClassPathFileSystemWatcherTests {
 		public ClassPathFileSystemWatcher watcher() {
 			FileSystemWatcher watcher = new FileSystemWatcher(false, 100, 10);
 			URL[] urls = this.environemnt.getProperty("urls", URL[].class);
-			return new ClassPathFileSystemWatcher(watcher, restartStrategy(), urls);
+			return new ClassPathFileSystemWatcher(new MockFileSystemWatcherFactory(
+					watcher), restartStrategy(), urls);
 		}
 
 		@Bean
@@ -136,4 +137,19 @@ public class ClassPathFileSystemWatcherTests {
 
 	}
 
+	private static class MockFileSystemWatcherFactory implements FileSystemWatcherFactory {
+
+		private final FileSystemWatcher watcher;
+
+		public MockFileSystemWatcherFactory(FileSystemWatcher watcher) {
+			this.watcher = watcher;
+		}
+
+		@Override
+		public FileSystemWatcher getFileSystemWatcher() {
+			return this.watcher;
+		}
+
+	}
+
 }

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/RestarterTests.java

@@ -29,11 +29,9 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.ObjectFactory;
-import org.springframework.boot.devtools.restart.RestartInitializer;
-import org.springframework.boot.devtools.restart.Restarter;
 import org.springframework.boot.devtools.restart.classloader.ClassLoaderFile;
-import org.springframework.boot.devtools.restart.classloader.ClassLoaderFiles;
 import org.springframework.boot.devtools.restart.classloader.ClassLoaderFile.Kind;
+import org.springframework.boot.devtools.restart.classloader.ClassLoaderFiles;
 import org.springframework.boot.test.OutputCapture;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.scheduling.annotation.EnableScheduling;
@@ -250,10 +248,10 @@ public class RestarterTests {
 		}
 
 		@Override
-		public void restart() {
+		public void restart(FailureHandler failureHandler) {
 			try {
 				stop();
-				start();
+				start(failureHandler);
 			}
 			catch (Exception ex) {
 				throw new IllegalStateException(ex);
@@ -261,8 +259,9 @@ public class RestarterTests {
 		}
 
 		@Override
-		protected void relaunch(ClassLoader classLoader) throws Exception {
+		protected Throwable relaunch(ClassLoader classLoader) throws Exception {
 			this.relaunchClassLoader = classLoader;
+			return null;
 		}
 
 		@Override