LaunchedURLClassLoader#findResource(s) is startup bottleneck

[tsachev]

Our app is using spring boot and is starting usually in around a minute on my laptop, when launched with spring-boot:run, However after repackage things get ugly the startup time increases to 3 mins!!!.
I have investigated where the slow down came from and here is what I found:
trace profiler shows that 40 percent of the startup time goes in Throwable#fillStackTrace()
We have lots of jars as dependencies (400+) and I noticed that LauncedURLClassLoder already does some optimization in this area Handler.setUseFastConnectionExceptions(true) the thing is that this is not called for findResource, and this method is heavily used.
For example aspectj is loading classes bytecode (and not caching) (we use cache and custom aspects).

After the patch below the application started in reasonable time (only around 10 seconds slower then mvn spring-boot:run)

--- a/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/LaunchedURLClassLoader.java
+++ b/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/LaunchedURLClassLoader.java
@@ -82,7 +82,13 @@ public class LaunchedURLClassLoader extends URLClassLoader {
                        if (name.equals("") && hasURLs()) {
                                return getURLs()[0];
                        }
-                       return super.findResource(name);
+                       Handler.setUseFastConnectionExceptions(true);
+                       try {
+                               return super.findResource(name);
+                       }
+                       finally {
+                               Handler.setUseFastConnectionExceptions(false);
+                       }
                }
                catch (IllegalArgumentException ex) {
                        return null;
@@ -94,7 +100,13 @@ public class LaunchedURLClassLoader extends URLClassLoader {
                if (name.equals("") && hasURLs()) {
                        return Collections.enumeration(Arrays.asList(getURLs()));
                }
-               return super.findResources(name);
+               Handler.setUseFastConnectionExceptions(true);
+               try {
+                       return super.findResources(name);
+               }
+               finally {
+                       Handler.setUseFastConnectionExceptions(false);
+               }
        }

        private boolean hasURLs() {

I can create a pull request if this seems reasonable fix.

[wilkinsona]

This looks reasonable to me. It's a similar change to the one made in d241171. The contract for findResource is to return null if the resource cannot be found so the stack of any FileNotFoundException that may be thrown is of no interest to the caller.

@tsachev A pull request would be most welcome

[philwebb]

Reopening to backport. I'm an idiot that assigned it to the 1.3 milestone and I think it would be good in 1.2