[
https://issues.apache.org/jira/browse/YARN-9813?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16923987#comment-16923987
]
Adam Antal commented on YARN-9813:
----------------------------------
Place of ClassCastException:
{code:java}
if (getConfig().getBoolean(YarnConfiguration.YARN_WEBAPP_UI2_ENABLE,
YarnConfiguration.DEFAULT_YARN_WEBAPP_UI2_ENABLE)) {
String onDiskPath = getConfig()
.get(YarnConfiguration.YARN_WEBAPP_UI2_WARFILE_PATH);
uiWebAppContext = new WebAppContext();
uiWebAppContext.setContextPath(UI2_WEBAPP_NAME);
if (null == onDiskPath) {
String war = "hadoop-yarn-ui-" + VersionInfo.getVersion() + ".war";
URLClassLoader cl = (URLClassLoader) ClassLoader.getSystemClassLoader();
URL url = cl.findResource(war);
if (null == url) {
onDiskPath = getWebAppsPath("ui2");
} else {
onDiskPath = url.getFile();
}
}
{code}
As for e.g.
[SO|https://stackoverflow.com/questions/54889465/urlclassloader-difference-between-getresource-and-findresource]
suggests, we can use the {{ClassLoader}} 's {{getResource()}} method instead
of casting it to URLClassLoader and calling {{findResource()}} on it. Will
upload a patch soon.
> RM does not start on JDK11 when UIv2 is enabled
> -----------------------------------------------
>
> Key: YARN-9813
> URL: https://issues.apache.org/jira/browse/YARN-9813
> Project: Hadoop YARN
> Issue Type: Bug
> Components: resourcemanager, yarn
> Affects Versions: 3.1.2
> Reporter: Adam Antal
> Assignee: Adam Antal
> Priority: Critical
>
> Starting a ResourceManager on JDK11 with UIv2 is enabled, RM startup fails
> with the following message:
> {noformat}
> Error starting ResourceManager
> java.lang.ClassCastException: class
> jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class
> java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and
> java.net.URLClassLoader are in module java.base of loader 'bootstrap')
> at
> org.apache.hadoop.yarn.server.resourcemanager.ResourceManager.startWepApp(ResourceManager.java:1190)
> at
> org.apache.hadoop.yarn.server.resourcemanager.ResourceManager.serviceStart(ResourceManager.java:1333)
> at
> org.apache.hadoop.service.AbstractService.start(AbstractService.java:194)
> at
> org.apache.hadoop.yarn.server.resourcemanager.ResourceManager.main(ResourceManager.java:1531)
> {noformat}
> It is a known issue that the systemClassLoader is not URLClassLoader anymore
> from JDK9 (see related UT failure: YARN-9512).
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