What is the reason that setDefaultUseCaches(false) of URLConnection is eagerly called in the org.apache.catalina.core.JreMemoryLeakPreventionListener - api

Question

This question could be a bit difficult to find the answer. It's a questions in one series with What is the reason that Policy.getPolicy() is considered as it will retain a static reference to the context and can cause memory leak. You can read it so you may know more background.
Graped the source code from org.apache.cxf.common.logging.JDKBugHacks and also from org.apache.catalina.core.JreMemoryLeakPreventionListener.
There is a piece of code. Here it is.
URL url = new URL("jar:file://dummy.jar!/");
URLConnection uConn = new URLConnection(url) {
#Override
public void connect() throws IOException{
// NOOP
}
};
uConn.setDefaultUseCaches(false);
The comment said
/*
* Several components end up opening JarURLConnections without
* first disabling caching. This effectively locks the file.
* Whilst more noticeable and harder to ignore on Windows, it
* affects all operating systems.
*
* Those libraries/components known to trigger this issue
* include:
* - log4j versions 1.2.15 and earlier
* - javax.xml.bind.JAXBContext.newInstance()
*/
However I can hardly understand it. Why did they eagerly call setDefaultUseCaches(false) and why on Windows it's harmful that by default cache is true? I cannot find any clue in java.net.JarURLConnection.

Answer 1

I myself find an answer. Any one can correct me if you think I am wrong.
in sun.net.www.protocol.jar.JarURLConnection. I assume this is the default implementation of java.net.JarURLConnection. There is a piece of code below.
If cache is set to true, then it will not close the JarFile's connection. Which means it is locked.
class JarURLInputStream extends java.io.FilterInputStream {
JarURLInputStream (InputStream src) {
super (src);
}
public void close () throws IOException {
try {
super.close();
} finally {
if (!getUseCaches()) {
jarFile.close(); //will not close
}
}
}
}
public void connect() throws IOException {
if (!connected) {
/* the factory call will do the security checks */
jarFile = factory.get(getJarFileURL(), getUseCaches());
/* we also ask the factory the permission that was required
* to get the jarFile, and set it as our permission.
*/
if (getUseCaches()) {
jarFileURLConnection = factory.getConnection(jarFile);
}
if ((entryName != null)) {
jarEntry = (JarEntry)jarFile.getEntry(entryName);
if (jarEntry == null) {
try {
if (!getUseCaches()) {
jarFile.close(); //will not close
}
} catch (Exception e) {
}
throw new FileNotFoundException("JAR entry " + entryName +
" not found in " +
jarFile.getName());
}
}
connected = true;
}
}