java - 在 Java 中计算可用内存的最佳方法是什么？

Question

我正在尝试计算我的 Java 程序可用的内存量。我有这个当前的实现:

long getAvailableMemory() {
  Runtime runtime = Runtime.getRuntime();
  long totalMemory = runtime.totalMemory();
  long freeMemory = runtime.freeMemory();
  long maxMemory = runtime.maxMemory();
  long usedMemory = totalMemory - freeMemory;
  long availableMemory = maxMemory - usedMemory;
  return availableMemory;
}

对吗？有没有更简单/更准确的方法来计算这些信息？看了别人的代码后，我看到这样的东西略有不同:

long getAvailableMemory() {
  long totalVmHeap = Runtime.getRuntime().totalMemory();
  long freeVmHeap = Runtime.getRuntime().freeMemory();
  long usedVmHeap = totalVmHeap - freeVmHeap;
  long maxVmHeap = Runtime.getRuntime().maxMemory();
  long availableVmHeap = maxVmHeap - usedVmHeap + freeVmHeap;
  return availableVmHeap;
}

无论如何，获取这些信息的正确方法是什么？

Answer 1

您的解决方案对我来说是正确的(在下面评论以解释您正在计算的内容):

long getAvailableMemory() {
  Runtime runtime = Runtime.getRuntime();
  long totalMemory = runtime.totalMemory(); // current heap allocated to the VM process
  long freeMemory = runtime.freeMemory(); // out of the current heap, how much is free
  long maxMemory = runtime.maxMemory(); // Max heap VM can use e.g. Xmx setting
  long usedMemory = totalMemory - freeMemory; // how much of the current heap the VM is using
  long availableMemory = maxMemory - usedMemory; // available memory i.e. Maximum heap size minus the current amount used
  return availableMemory;
}

我不确定您的用例是什么，但您可能希望查看的堆内也有一些限制，例如 PermGen 大小:How do I programmatically find out my PermGen space usage?