code: @Override
  	protected Result check() throws Exception {
  		Runtime runtime = Runtime.getRuntime();
  		long freeMemory = runtime.freeMemory();
  		long totalMemory = runtime.totalMemory();
  		long maxMemory = runtime.maxMemory();
  		boolean ok = maxMemory - (totalMemory - freeMemory) > avalibleMemthreshold; // 剩余空间小于2M报警
  		if (ok) {
  			return Result.healthy();
  		} else {
  			String msg = "max:" + (maxMemory / 1024 / 1024) + "M,total:" + (totalMemory / 1024 / 1024) + "M,used:"
  							+ ((totalMemory / 1024 / 1024) - (freeMemory / 1024 / 1024)) + "M,free:" + (freeMemory / 1024 / 1024) + "M";
  			return Result.unhealthy(msg);
  		}
  	}
docs: 可用内存阈值=5M