Created
February 6, 2018 08:24
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一个ThreadLocal 在不同ClassLoader下失效的问题
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import java.util.concurrent.atomic.AtomicInteger; | |
public class ThreadId { | |
// Atomic integer containing the next thread ID to be assigned | |
private static final AtomicInteger nextId = new AtomicInteger(0); | |
// Thread local variable containing each thread's ID | |
private static final ThreadLocal<Integer> threadId = new ThreadLocal<Integer>() { | |
@Override | |
protected Integer initialValue() { | |
return nextId.getAndIncrement(); | |
} | |
}; | |
// Returns the current thread's unique ID, assigning it if necessary | |
public static int get() { | |
return threadId.get(); | |
} | |
} |
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import java.lang.reflect.Method; | |
import java.net.URLClassLoader; | |
public class ThreadLocalTest { | |
static private URLClassLoader userClassLoader; | |
static { | |
URLClassLoader systemClassLoader = (URLClassLoader) ClassLoader.getSystemClassLoader(); | |
userClassLoader = new URLClassLoader(systemClassLoader.getURLs(), systemClassLoader.getParent()); | |
} | |
public static void main(String[] args) throws Exception { | |
System.err.println(ThreadId.get()); | |
Thread t1 = new Thread(new Runnable() { | |
@Override | |
public void run() { | |
System.err.println(ThreadId.get()); | |
} | |
}); | |
t1.start(); | |
t1.join(); | |
Thread t2 = new Thread(new Runnable() { | |
@Override | |
public void run() { | |
try { | |
Class<?> clazz = loadClassFromUserClassLoader(ThreadId.class.getName()); | |
Method getMethod = clazz.getMethod("get"); | |
System.err.println(getMethod.invoke(null)); | |
} catch (Exception e) { | |
e.printStackTrace(); | |
} | |
} | |
}); | |
t2.start(); | |
} | |
public static Class<?> loadClassFromUserClassLoader(String name) throws ClassNotFoundException { | |
return userClassLoader.loadClass(name); | |
} | |
} |
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