Make the configuration of the document root consistent across containers

Previously, if getValidDocumentRoot() returned null, only the embedded
Tomcat container would use a temporary directory. This left Jetty and
Undertow unable to provide a URL for the root of the servlet context,
i.e. servletContext.getResource("/") would return null.

This commit updates the embedded containers for Jetty and Undertow to
behave in the same way as Tomcat. A test has been added to verify that
all three containers can produce a non-null URL for the root of the
servlet context.

Closes gh-2878

spring-boot/src/main/java/org/springframework/boot/context/embedded/AbstractEmbeddedServletContainerFactory.java

@@ -164,4 +164,25 @@ public abstract class AbstractEmbeddedServletContainerFactory
 		return dir;
 	}
 
+	/**
+	 * Returns the absolute temp dir for given servlet container.
+	 * @param prefix servlet container name
+	 * @return The temp dir for given servlet container.
+	 */
+	protected File createTempDir(String prefix) {
+		try {
+			File tempFolder = File.createTempFile(prefix + ".", "." + getPort());
+			tempFolder.delete();
+			tempFolder.mkdir();
+			tempFolder.deleteOnExit();
+			return tempFolder;
+		}
+		catch (IOException ex) {
+			throw new EmbeddedServletContainerException(
+					"Unable to create tempdir. java.io.tmpdir is set to "
+							+ System.getProperty("java.io.tmpdir"),
+					ex);
+		}
+	}
+
 }

spring-boot/src/main/java/org/springframework/boot/context/embedded/jetty/JettyEmbeddedServletContainerFactory.java

@@ -319,7 +319,7 @@ public class JettyEmbeddedServletContainerFactory
 
 	private void configureDocumentRoot(WebAppContext handler) {
 		File root = getValidDocumentRoot();
-		if (root != null) {
+		root = (root != null ? root : createTempDir("jetty-docbase"));
 		try {
 			if (!root.isDirectory()) {
 				Resource resource = JarResource
@@ -327,15 +327,13 @@ public class JettyEmbeddedServletContainerFactory
 				handler.setBaseResource(resource);
 			}
 			else {
-					handler.setBaseResource(
+				handler.setBaseResource(Resource.newResource(root.getCanonicalFile()));
-							Resource.newResource(root.getCanonicalFile()));
 			}
 		}
 		catch (Exception ex) {
 			throw new IllegalStateException(ex);
 		}
 	}
-	}
 
 	/**
 	 * Add Jetty's {@code DefaultServlet} to the given {@link WebAppContext}.

spring-boot/src/main/java/org/springframework/boot/context/embedded/tomcat/TomcatEmbeddedServletContainerFactory.java

@@ -457,27 +457,6 @@ public class TomcatEmbeddedServletContainerFactory
 		this.resourceLoader = resourceLoader;
 	}
 
-	/**
-	 * Returns the absolute temp dir for given web server.
-	 * @param prefix webserver name
-	 * @return The temp dir for given web server.
-	 */
-	protected File createTempDir(String prefix) {
-		try {
-			File tempFolder = File.createTempFile(prefix + ".", "." + getPort());
-			tempFolder.delete();
-			tempFolder.mkdir();
-			tempFolder.deleteOnExit();
-			return tempFolder;
-		}
-		catch (IOException ex) {
-			throw new EmbeddedServletContainerException(
-					"Unable to create Tomcat tempdir. java.io.tmpdir is set to "
-							+ System.getProperty("java.io.tmpdir"),
-					ex);
-		}
-	}
-
 	/**
 	 * Set the Tomcat base directory. If not specified a temporary directory will be used.
 	 * @param baseDirectory the tomcat base directory

spring-boot/src/main/java/org/springframework/boot/context/embedded/undertow/UndertowEmbeddedServletContainerFactory.java

@@ -428,10 +428,11 @@ public class UndertowEmbeddedServletContainerFactory
 
 	private ResourceManager getDocumentRootResourceManager() {
 		File root = getValidDocumentRoot();
-		if (root != null && root.isDirectory()) {
+		root = (root != null ? root : createTempDir("undertow-docbase"));
+		if (root.isDirectory()) {
 			return new FileResourceManager(root, 0);
 		}
-		if (root != null && root.isFile()) {
+		if (root.isFile()) {
 			return new JarResourcemanager(root);
 		}
 		return ResourceManager.EMPTY_RESOURCE_MANAGER;

spring-boot/src/test/java/org/springframework/boot/context/embedded/AbstractEmbeddedServletContainerFactoryTests.java

@@ -23,8 +23,10 @@ import java.io.FilenameFilter;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.PrintWriter;
+import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.net.URL;
 import java.nio.charset.Charset;
 import java.security.KeyStore;
 import java.util.Arrays;
@@ -36,6 +38,7 @@ import java.util.Map.Entry;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.zip.GZIPInputStream;
 
 import javax.net.ssl.SSLException;
@@ -84,6 +87,7 @@ import static org.hamcrest.Matchers.hasEntry;
 import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.lessThan;
+import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
 import static org.junit.Assert.assertEquals;
@@ -673,6 +677,27 @@ public abstract class AbstractEmbeddedServletContainerFactoryTests {
 				is(equalTo(expectedMimeMappings.size())));
 	}
 
+	@Test
+	public void rootServletContextResource() throws Exception {
+		AbstractEmbeddedServletContainerFactory factory = getFactory();
+		AtomicReference<URL> rootResource = new AtomicReference<URL>();
+		this.container = factory
+				.getEmbeddedServletContainer(new ServletContextInitializer() {
+					@Override
+					public void onStartup(ServletContext servletContext)
+							throws ServletException {
+						try {
+							rootResource.set(servletContext.getResource("/"));
+						}
+						catch (MalformedURLException ex) {
+							throw new ServletException(ex);
+						}
+					}
+				});
+		this.container.start();
+		assertThat(rootResource.get(), is(not(nullValue())));
+	}
+
 	private boolean doTestCompression(int contentSize, String[] mimeTypes,
 			String[] excludedUserAgents) throws Exception {
 		String testContent = setUpFactoryForCompression(contentSize, mimeTypes,