diff --git a/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java b/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java
index 92ddeb0453..617fea8710 100644
--- a/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java
+++ b/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java
@@ -187,6 +187,15 @@ final class JarURLConnection extends java.net.JarURLConnection {
 
 	@Override
 	public int getContentLength() {
+		long longContentLength = getContentLengthLong();
+		if (longContentLength > Integer.MAX_VALUE) {
+			return -1;
+		}
+		return (int) longContentLength;
+	}
+
+	@Override
+	public long getContentLengthLong() {
 		if (this.jarFile == null) {
 			return -1;
 		}
diff --git a/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarURLConnectionTests.java b/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarURLConnectionTests.java
index ef98792d9f..15c6df1a64 100644
--- a/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarURLConnectionTests.java
+++ b/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarURLConnectionTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -136,6 +136,20 @@ public class JarURLConnectionTests {
 				.hasSameContentAs(new ByteArrayInputStream(new byte[] { 3 }));
 	}
 
+	@Test
+	public void getContentLengthReturnsLengthOfUnderlyingEntry() throws Exception {
+		URL url = new URL(new URL("jar", null, -1,
+				"file:" + getAbsolutePath() + "!/nested.jar!/", new Handler()), "/3.dat");
+		assertThat(url.openConnection().getContentLength()).isEqualTo(1);
+	}
+
+	@Test
+	public void getContentLengthLongReturnsLengthOfUnderlyingEntry() throws Exception {
+		URL url = new URL(new URL("jar", null, -1,
+				"file:" + getAbsolutePath() + "!/nested.jar!/", new Handler()), "/3.dat");
+		assertThat(url.openConnection().getContentLengthLong()).isEqualTo(1);
+	}
+
 	private String getAbsolutePath() {
 		return this.rootJarFile.getAbsolutePath().replace('\\', '/');
 	}
diff --git a/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/JarResourceManager.java b/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/JarResourceManager.java
index aa0513fa20..9515aa6734 100644
--- a/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/JarResourceManager.java
+++ b/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/JarResourceManager.java
@@ -48,7 +48,7 @@ class JarResourceManager implements ResourceManager {
 	public Resource getResource(String path) throws IOException {
 		URL url = new URL("jar:file:" + this.jarPath + "!"
 				+ (path.startsWith("/") ? path : "/" + path));
-		URLResource resource = new URLResource(url, url.openConnection(), path);
+		URLResource resource = new URLResource(url, path);
 		if (resource.getContentLength() < 0) {
 			return null;
 		}
diff --git a/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowServletWebServerFactory.java b/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowServletWebServerFactory.java
index 660459345e..988a22645f 100644
--- a/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowServletWebServerFactory.java
+++ b/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowServletWebServerFactory.java
@@ -21,7 +21,6 @@ import java.io.IOException;
 import java.net.MalformedURLException;
 import java.net.Socket;
 import java.net.URL;
-import java.net.URLConnection;
 import java.nio.charset.Charset;
 import java.security.KeyManagementException;
 import java.security.KeyStore;
@@ -679,15 +678,9 @@ public class UndertowServletWebServerFactory extends AbstractServletWebServerFac
 		@Override
 		public Resource getResource(String path) {
 			for (URL url : this.metaInfResourceJarUrls) {
-				try {
-					URL resourceUrl = new URL(url + "META-INF/resources" + path);
-					URLConnection connection = resourceUrl.openConnection();
-					if (connection.getContentLength() >= 0) {
-						return new URLResource(resourceUrl, connection, path);
-					}
-				}
-				catch (IOException ex) {
-					// Continue
+				URLResource resource = getMetaInfResource(url, path);
+				if (resource != null) {
+					return resource;
 				}
 			}
 			return null;
@@ -704,6 +697,21 @@ public class UndertowServletWebServerFactory extends AbstractServletWebServerFac
 
 		@Override
 		public void removeResourceChangeListener(ResourceChangeListener listener) {
+
+		}
+
+		private URLResource getMetaInfResource(URL resourceJar, String path) {
+			try {
+				URL resourceUrl = new URL(resourceJar + "META-INF/resources" + path);
+				URLResource resource = new URLResource(resourceUrl, path);
+				if (resource.getContentLength() < 0) {
+					return null;
+				}
+				return resource;
+			}
+			catch (MalformedURLException ex) {
+				return null;
+			}
 		}
 	}