[WICKET-6971] NullPointerException in ModificationWatcher

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 10.0.0-M1, 8.14.0, 9.10.0
• Environment: * Eclipse Version: 2021-12 (4.22.0) Build id: 20211202-1639 ; * Tomcat 9.0.44 ; * Java11(amazon-corretto-11.0.10.9.1-windows-x64-jdk)

Language

java

• Assignee: Martin Tzvetanov Grigorov
• Reporter: Ryo Tsunoda
• Created: 11/Apr/22 09:13
• Updated: 15/Apr/22 13:11
• Resolved: 15/Apr/22 13:11

Description

Sometimes this exception occurs after I edit the CSS.
 
```
2022-04-09 19:28:48.252 | ERROR | [ModificationWatcher Task] | org.apache.wicket.util.thread.Task | Unhandled exception thrown by user code in task ModificationWatcher
java.lang.NullPointerException: null
at org.apache.wicket.util.io.Connections.close(Connections.java:133) ~[wicket-util-8.14.0.jar:8.14.0]
at org.apache.wicket.core.util.resource.UrlResourceStream.updateContentLength(UrlResourceStream.java:247) ~[wicket-core-8.14.0.jar:8.14.0]
at org.apache.wicket.core.util.resource.UrlResourceStream.lastModifiedTime(UrlResourceStream.java:224) ~[wicket-core-8.14.0.jar:8.14.0]
at org.apache.wicket.markup.MarkupResourceStream.lastModifiedTime(MarkupResourceStream.java:148) ~[wicket-core-8.14.0.jar:8.14.0]
at org.apache.wicket.util.watch.ModificationWatcher.checkModified(ModificationWatcher.java:157) ~[wicket-util-8.14.0.jar:8.14.0]
at org.apache.wicket.util.watch.ModificationWatcher$1.run(ModificationWatcher.java:143) ~[wicket-util-8.14.0.jar:8.14.0]
at org.apache.wicket.util.thread.Task$1.run(Task.java:116) [wicket-util-8.14.0.jar:8.14.0]
at java.lang.Thread.run(Thread.java:829) [?:?]
```
 
connection.getInputStream() returns null.
Wicket can check null here.
https://github.com/apache/wicket/blob/wicket-8.x/wicket-util/src/main/java/org/apache/wicket/util/io/Connections.java#L133
 
Tomcat's CachedResourceURLConnection#getInputStream() sometimes returns a WebResource instance with no stream.
https://github.com/apache/tomcat/blob/9.0.x/java/org/apache/catalina/webresources/CachedResource.java#L516
 
I don't know the conditions under which it can be reproduced.
 

Issue Links

• links to: GitHub Pull Request #510