Fix remote shell to support custom banners

Update the remote shell to use the `Banner` interface when possible.

Fixes gh-3988
Closes gh-5453

spring-boot-samples/spring-boot-sample-actuator-noweb/src/main/resources/banner.txt

+   ,--.   ,--.
+   \  /-~-\  /
+    )' a a `(
+   (  ,---.  )
+    `(_o_o_)'
+      )`-'(
+
+Spring Boot${spring-boot.formatted-version}

spring-boot-starters/spring-boot-starter-remote-shell/src/main/resources/commands/crash/login.groovy

 welcome = { ->
-	if (!crash.context.attributes['spring.environment'].getProperty("spring.main.show_banner", Boolean.class, Boolean.TRUE)) {
+
+	def environment = crash.context.attributes['spring.environment']
+	def propertyResolver = new org.springframework.boot.bind.RelaxedPropertyResolver(environment, "spring.main.");
+	def beanFactory = crash.context.attributes['spring.beanfactory']
+
+	if (!propertyResolver.getProperty("show-banner", Boolean.class, Boolean.TRUE)) {
 		return ""
 	}
 
+	// Try to print using the banner interface
+	if (beanFactory != null) {
+		try {
+			def banner = beanFactory.getBean("springBootBanner")
+			def out = new java.io.ByteArrayOutputStream()
+			banner.printBanner(environment, null, new java.io.PrintStream(out))
+			return out.toString()
+		} catch (Exception ex) {
+			// Ignore
+		}
+	}
+
 	// Resolve hostname
 	def hostName;
 	try {

spring-boot/src/main/java/org/springframework/boot/SpringApplicationBannerPrinter.java

@@ -63,13 +63,13 @@ class SpringApplicationBannerPrinter {
 		catch (UnsupportedEncodingException ex) {
 			logger.warn("Failed to create String for banner", ex);
 		}
-		return banner;
+		return new PrintedBanner(banner, sourceClass);
 	}
 
 	public Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
 		Banner banner = getBanner(environment, this.fallbackBanner);
 		banner.printBanner(environment, sourceClass, out);
-		return banner;
+		return new PrintedBanner(banner, sourceClass);
 	}
 
 	private Banner getBanner(Environment environment, Banner definedBanner) {
@@ -145,4 +145,28 @@ class SpringApplicationBannerPrinter {
 
 	}
 
+	/**
+	 * Decorator that allows a {@link Banner} to be printed again without needing to
+	 * specify the source class.
+	 */
+	private static class PrintedBanner implements Banner {
+
+		private final Banner banner;
+
+		private final Class<?> sourceClass;
+
+		PrintedBanner(Banner banner, Class<?> sourceClass) {
+			this.banner = banner;
+			this.sourceClass = sourceClass;
+		}
+
+		@Override
+		public void printBanner(Environment environment, Class<?> sourceClass,
+				PrintStream out) {
+			sourceClass = (sourceClass == null ? this.sourceClass : sourceClass);
+			this.banner.printBanner(environment, sourceClass, out);
+		}
+
+	}
+
 }

spring-boot/src/test/java/org/springframework/boot/BannerTests.java

@@ -21,14 +21,24 @@ import java.io.PrintStream;
 import org.junit.After;
 import org.junit.Rule;
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.runners.MockitoJUnitRunner;
 
 import org.springframework.boot.Banner.Mode;
 import org.springframework.boot.testutil.InternalOutputCapture;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.env.Environment;
+import org.springframework.test.util.ReflectionTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.reset;
+import static org.mockito.Mockito.verify;
 
 /**
  * Tests for {@link Banner} and its usage by {@link SpringApplication}.
@@ -37,6 +47,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Michael Stummvoll
  * @author Michael Simons
  */
+@RunWith(MockitoJUnitRunner.class)
 public class BannerTests {
 
 	private ConfigurableApplicationContext context;
@@ -51,6 +62,9 @@ public class BannerTests {
 	@Rule
 	public InternalOutputCapture out = new InternalOutputCapture();
 
+	@Captor
+	private ArgumentCaptor<Class<?>> sourceClassCaptor;
+
 	@Test
 	public void testDefaultBanner() throws Exception {
 		SpringApplication application = new SpringApplication(Config.class);
@@ -88,10 +102,18 @@ public class BannerTests {
 	public void testCustomBannerInContext() throws Exception {
 		SpringApplication application = new SpringApplication(Config.class);
 		application.setWebEnvironment(false);
-		final DummyBanner dummyBanner = new DummyBanner();
-		application.setBanner(dummyBanner);
+		Banner banner = mock(Banner.class);
+		application.setBanner(banner);
 		this.context = application.run();
-		assertThat(this.context.getBean("springBootBanner")).isEqualTo(dummyBanner);
+		Banner printedBanner = (Banner) this.context.getBean("springBootBanner");
+		assertThat(ReflectionTestUtils.getField(printedBanner, "banner"))
+				.isEqualTo(banner);
+		verify(banner).printBanner(any(Environment.class),
+				this.sourceClassCaptor.capture(), any(PrintStream.class));
+		reset(banner);
+		printedBanner.printBanner(this.context.getEnvironment(), null, System.out);
+		verify(banner).printBanner(any(Environment.class),
+				eq(this.sourceClassCaptor.getValue()), any(PrintStream.class));
 	}
 
 	@Test