java - 我需要列出使用 java.lang.ApplicationShutdownHooks 注册的钩子(Hook)

Question

我有一个第 3 方应用程序有一个错误，导致它在只需要 1 个时注册多个关闭 Hook 。

我的问题是如何查看注册的关闭 Hook 是什么？我想迭代它们然后调用 remove 方法。持有 Hook 的集合是私有(private)静态的，不包含访问器。我们已经尝试过反射，但由于该类是包私有(private)的，我们必须让我们的 cracker 成为 java.lang 的一部分，这是一个被禁止的包。

有什么想法吗？

/*
 * %W% %E%
 *
 * Copyright (c) 2004, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
class ApplicationShutdownHooks {
static {
    Shutdown.add(1 /* shutdown hook invocation order */,
        new Runnable() {
            public void run() {
                runHooks();
            }
        });
}

/* The set of registered hooks */
private static IdentityHashMap<Thread, Thread> hooks = new IdentityHashMap<Thread, Thread>();

private void ApplicationShutdownHooks() {}

/* Add a new shutdown hook.  Checks the shutdown state and the hook itself,
 * but does not do any security checks.
 */
static synchronized void add(Thread hook) {
if(hooks == null)
    throw new IllegalStateException("Shutdown in progress");

if (hook.isAlive())
    throw new IllegalArgumentException("Hook already running");

if (hooks.containsKey(hook))
    throw new IllegalArgumentException("Hook previously registered");

    hooks.put(hook, hook);
}

/* Remove a previously-registered hook.  Like the add method, this method
 * does not do any security checks.
 */
static synchronized boolean remove(Thread hook) {
if(hooks == null)
    throw new IllegalStateException("Shutdown in progress");

if (hook == null) 
    throw new NullPointerException();

return hooks.remove(hook) != null;
}

/* Iterates over all application hooks creating a new thread for each
 * to run in. Hooks are run concurrently and this method waits for 
 * them to finish.
 */
static void runHooks() {
Collection<Thread> threads;
synchronized(ApplicationShutdownHooks.class) {
    threads = hooks.keySet();
    hooks = null;
}

for (Thread hook : threads) {
    hook.start();
}
for (Thread hook : threads) {
    try {
    hook.join();
    } catch (InterruptedException x) { }
}
}
}

Answer 1

私有(private)包不应该让你慢下来，这就是反射!允许使用各种巫毒魔法。

在这种情况下，您需要获取类，然后是字段，然后将其设置为可访问，然后读取其值。

    Class clazz = Class.forName("java.lang.ApplicationShutdownHooks");
    Field field = clazz.getDeclaredField("hooks");
    field.setAccessible(true);
    Object hooks = field.get(null);
    System.out.println(hooks); //hooks is a Map<Thread, Thread>

查看此类信息的更简单方法可能只是访问 take a heap dump应用程序并在内存分析器中分析它 MAT (对于 Eclipse)或 JProfiler .