Upgrade to Servlet 3.1, Tomcat 8 and Jetty 9

Upgrade to latest versions of Tomcat and Jetty and to the latest Servlet
API whilst will remaining compatible with Tomcat 7 and Jetty 8.

Fixes gh-1832, gh-369

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/DefaultErrorAttributes.java

@@ -29,6 +29,7 @@ import javax.servlet.http.HttpServletResponse;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
 import org.springframework.http.HttpStatus;
+import org.springframework.util.StringUtils;
 import org.springframework.validation.BindingResult;
 import org.springframework.validation.ObjectError;
 import org.springframework.web.context.request.RequestAttributes;
@@ -121,10 +122,10 @@ public class DefaultErrorAttributes implements ErrorAttributes, HandlerException
 			}
 		}
 		Object message = getAttribute(requestAttributes, "javax.servlet.error.message");
-		if ((message != null || errorAttributes.get("message") == null)
+		if ((!StringUtils.isEmpty(message) || errorAttributes.get("message") == null)
 				&& !(error instanceof BindingResult)) {
-			errorAttributes.put("message", message == null ? "No message available"
-					: message);
+			errorAttributes.put("message",
+					StringUtils.isEmpty(message) ? "No message available" : message);
 		}
 	}
 

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/BasicErrorControllerIntegrationTests.java

@@ -73,10 +73,10 @@ public class BasicErrorControllerIntegrationTests {
 	public void testErrorForMachineClient() throws Exception {
 		ResponseEntity<Map> entity = new TestRestTemplate().getForEntity(
 				"http://localhost:" + this.port, Map.class);
-		assertThat(entity.getBody().toString(), endsWith("status=500, "
-				+ "error=Internal Server Error, "
-				+ "exception=java.lang.IllegalStateException, "
-				+ "message=Server Error, " + "path=/}"));
+		String body = entity.getBody().toString();
+		assertThat(body, endsWith("status=500, " + "error=Internal Server Error, "
+				+ "exception=java.lang.IllegalStateException, " + "message=Expected!, "
+				+ "path=/}"));
 	}
 
 	@Test

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/BasicErrorControllerMockMvcTests.java

@@ -128,7 +128,8 @@ public class BasicErrorControllerMockMvcTests {
 	@Target(ElementType.TYPE)
 	@Retention(RetentionPolicy.RUNTIME)
 	@Documented
-	@Import({ EmbeddedServletContainerAutoConfiguration.class,
+	@Import({ EmbeddedServletContainerAutoConfiguration.EmbeddedTomcat.class,
+			EmbeddedServletContainerAutoConfiguration.class,
 			ServerPropertiesAutoConfiguration.class,
 			DispatcherServletAutoConfiguration.class, WebMvcAutoConfiguration.class,
 			HttpMessageConvertersAutoConfiguration.class,