Investigated JSP support

Summary: Tomcat works with WARs. Jetty doesn't work.

See spring-projectsgh-367

Author: Dave Syer

spring-boot/README.md

@@ -249,29 +249,22 @@ can also register items directly if your bean implements the `ServletContextInit
 interface.
 
 
-### JSP limitations
-When running a Spring Boot application that uses an embedded servlet container and is
-packaged as an executable JAR or WAR, there are some limitations in the JSP support.
-
-Due to the way that Jasper (Tomcat and Jetty's JSP engine) loads tag libraries, tag
-libraries packaged in JAR files nested within the JAR or WAR will not work correctly.
-When packaged and run as an executable JAR, you will see an error message produced during
-application startup that is similar to the following:
-
-> org.apache.jasper.JasperException: The absolute uri: http://www.springframework.org/tags
-> cannot be resolved in either web.xml or the jar files deployed with this application
-
-When packaged and run as an executable WAR, you will see an error message produced during
-application startup that is similar to the following:
-
-> java.io.FileNotFoundException: JAR entry
-> WEB-INF/lib-provided/tomcat-embed-jasper-7.0.47.jar!/javax/servlet/jsp/resources/web-jsptaglibrary_1_2.dtd
-> not found in my-app.war
-
-To avoid these limitations, rather than using the embedded servlet container support,
-package your application as a traditional (non-executable) WAR file and deploy it to a
-servlet container. Alternatively, you may want to consider using an alternative view
-technology.
+### JSP limitations When running a Spring Boot application that uses
+an embedded servlet container and is packaged as an executable
+archive, there are some limitations in the JSP support.
+
+* With Tomcat it should work if you use WAR packaging. I.e. an
+  executable WAR will work, and will also be deployable to a standard
+  container (Tomcat included). An executable JAR will not work because
+  of a hard coded file patter in Tomcat itself.
+  
+* Jetty does not currently work as an embedded container with
+  JSPs. There should be a way to make it work, so hopefully someone
+  can figure it out (pull requests always welcome).
+
+There is a
+[JSP sample](https://github.com/spring-projects/spring-boot/tree/master/spring-boot-samples/spring-boot-sample-web-jsp)
+so you can see how to set things up.
 
 ## Using YAML instead of Properties
 [YAML](http://yaml.org) is a superset of JSON, and as such is a very convenient format

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

@@ -304,7 +304,7 @@ protected final File getValidDocumentRoot() {
 		// Or maybe there is a document root in a well-known location
 		file = file != null ? file : getCommonDocumentRoot();
 		if (file == null && this.logger.isWarnEnabled()) {
-			this.logger.debug("None of the document roots "
+			this.logger.info("None of the document roots "
 					+ Arrays.asList(COMMON_DOC_ROOTS)
 					+ " point to a directory and will be ignored.");
 		}
@@ -340,7 +340,11 @@ private File getArchiveFileDocumentRoot(String extension) {
 	}
 
 	private File getWarFileDocumentRoot() {
-		return getArchiveFileDocumentRoot(".war");
+		File file = getArchiveFileDocumentRoot(".war");
+		if (file != null) {
+			return file;
+		}
+		return getArchiveFileDocumentRoot(".jar");
 	}
 
 	private File getCommonDocumentRoot() {

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

@@ -131,7 +131,12 @@ private void configureDocumentRoot(WebAppContext handler) {
 		File root = getValidDocumentRoot();
 		if (root != null) {
 			try {
-				handler.setBaseResource(Resource.newResource(root));
+				if (!root.isDirectory()) {
+					handler.setBaseResource(Resource.newClassPathResource(""));
+				}
+				else {
+					handler.setBaseResource(Resource.newResource(root));
+				}
 			}
 			catch (Exception ex) {
 				throw new IllegalStateException(ex);