在 org.apache.catalina.core.JreMemoryLeakPreventionListener 中急切调用 URLConnection 的 setDefaultUseCaches(false) 的原因是什么 [英] What is the reason that setDefaultUseCaches(false) of URLConnection is eagerly called in the org.apache.catalina.core.JreMemoryLeakPreventionListener
问题描述
这个问题可能有点难以找到答案.这是一个系列中的问题 考虑 Policy.getPolicy() 的原因是什么,因为它会保留对上下文的静态引用并可能导致内存泄漏.您可以阅读它,以便了解更多背景信息.
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.
从 org.apache.cxf.common.logging.JDKBugHacks
也来自 <代码>org.apache.catalina.core.JreMemoryLeakPreventionListener.
有一段代码.在这里.
URL url = new URL("jar:file://dummy.jar!/");
URLConnection uConn = new URLConnection(url) {
@Override
public void connect() throws IOException{
// NOOP
}
};
uConn.setDefaultUseCaches(false);
评论说
/*
* 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()
*/
但是我很难理解.为什么他们急切地调用 setDefaultUseCaches(false)
以及为什么在 Windows 上默认缓存为 true 是有害的?我在 java.net.JarURLConnection
.
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
.
推荐答案
我自己找到了答案.如果你认为我错了,任何人都可以纠正我.在 sun.net.www.protocol.jar.JarURLConnection
.我假设这是 java.net.JarURLConnection
的默认实现.下面有一段代码.
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.
如果缓存设置为true,则不会关闭JarFile 的连接.这意味着它被锁定了.
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;
}
}
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