内容简介：PermGen Space是Oracle-Sun Hotspot才有的，同类产品Oralce JRockit, IBM J9, Taobao JVM 是没有的，在Java8中永久区(PermGen)已经变成元空间(Metaspace),这里怀旧一下。设置VM启动参数
PermGen Space是Oracle-Sun Hotspot才有的，同类产品Oralce JRockit, IBM J9, Taobao JVM 是没有的，在 Java 8中永久区(PermGen)已经变成元空间(Metaspace),这里怀旧一下。
案例：PermGen OOM
设置VM启动参数 -XX:PermSize=5m -XX:MaxPermSize=5m -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=d:\dump 运行下面代码(这里用的Maven仓库下的jar包，根据自己情况来)，通过不断的动态加载类（Spring经常干这样的事情），造成PermGen OOM. 一般JVM默认PermGen大约是80M左右(和环境也有点关系，不过八九不离十)，可以通过 jmap -heap pid 查看，为什么那么小可以看下 这个回答
import java.io.File;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.List;
public class PermGen {
private static List<Object> insList = new ArrayList<Object>();
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, MalformedURLException, InterruptedException {
permLeak();
}
private static void permLeak() throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, MalformedURLException, InterruptedException{
for (int i = 0; i < 1000 ; i++) {
URL[] urls = getURLS();
URLClassLoader loader = new URLClassLoader(urls,null);
Class<?> logfClass = Class.forName("org.apache.commons.logging.LogFactory",true,loader);
Method getLog = logfClass.getMethod("getLog", String.class);
Object result = getLog.invoke(logfClass, "TestPermGen");
insList.add(result);
System.out.println(i + " : " + result);
Thread.sleep(100);
}
}
private static URL[] getURLS() throws MalformedURLException{
File libDir = new File("D:\\HHSZXA\\.m2\\repository\\commons-logging\\commons-logging\\1.1.1");
File[] subFiles = libDir.listFiles();
int count = subFiles.length;
URL[] urls = new URL[count];
for (int i = 0; i < count ; i++) {
urls[i] = subFiles[i].toURI().toURL();
}
return urls;
}
}
输出：
0 : org.apache.commons.logging.impl.Jdk14Logger@2babbba1
1 : org.apache.commons.logging.impl.Jdk14Logger@5d08e435
2 : org.apache.commons.logging.impl.Jdk14Logger@30d46b95
3 : org.apache.commons.logging.impl.Jdk14Logger@4ec4f498
4 : org.apache.commons.logging.impl.Jdk14Logger@7dbc345a
5 : org.apache.commons.logging.impl.Jdk14Logger@7ee361ad
6 : org.apache.commons.logging.impl.Jdk14Logger@7d94a8eb
java.lang.OutOfMemoryError: PermGen space
Dumping heap to d:\dump\java_pid3276.hprof ...
Heap dump file created [2648239 bytes in 0.016 secs]
Exception in thread "Reference Handler" Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at PermGen.permLeak(PermGen.java:25)
at PermGen.main(PermGen.java:16)
Caused by: java.lang.OutOfMemoryError: PermGen space
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:792)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.apache.commons.logging.LogFactory.createFactory(LogFactory.java:1131)
at org.apache.commons.logging.LogFactory$2.run(LogFactory.java:1065)
at java.security.AccessController.doPrivileged(Native Method)
at org.apache.commons.logging.LogFactory.newFactory(LogFactory.java:1062)
at org.apache.commons.logging.LogFactory.getFactory(LogFactory.java:650)
at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:704)
... 6 more
java.lang.OutOfMemoryError: PermGen space
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:140)
通过控制台信息，可以初步判定是方法区OOM，原因是通过URLClassLoader类加载器加载某个动态类，这个动态类是由调用org.apache.commons.logging.LogFactory.getLog方法生成的，同时可以看到引起的错误的代码行数PermGen.java:25
首先看摘要
其中1131行代码,就是实例化某个类，这个类是什么，我们可以改变日志输出级别，或者直接打印。
一切真相大白，有兴趣更深入的童鞋，欢迎讨论。
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