Java 获取当前所有的线程
```java
ThreadGroup group = Thread.currentThread().getThreadGroup();
ThreadGroup topGroup = group;
// 遍历线程组树，获取根线程组
while (group != null) {
topGroup = group;
group = group.getParent();
}
// 激活的线程数加倍
int estimatedSize = topGroup.activeCount() * 2;
Thread[] slackList = new Thread[estimatedSize];
// 获取根线程组的所有线程
int actualSize = topGroup.enumerate(slackList);
// copy into a list that is the exact size
Thread[] list = new Thread[actualSize];
System.arraycopy(slackList, 0, list, 0, actualSize);
System.out.println("Thread list size == " + list.length);
for (Thread thread : list) {
System.out.println(thread.getName());
}
```