Logging Memory Usage in Java

Sometimes our system gets slow, and we want to investigate what’s going on. Checking the memory usage is one of the first steps in this process.

I wrote this command to help. It uses the following classes from java.lang.management: ManagementFactory, MemoryMXBean, and MemoryUsage.

@Command(path = CMD_PREFIX + "/memory")
public void mbeanMemory(CommandInvocation ci) {
  final MemoryMXBean memoryBean =
    ManagementFactory.getMemoryMXBean();

  final String date =
    new SimpleDateFormat("yyyy/MM/dd hh:mm:ss")
    .format(new Date());

  ci.out.println(String.format("[%s] heap:{%s}, non-heap:{%s}",
    date,
    describe(memoryBean.getHeapMemoryUsage()),
    describe(memoryBean.getNonHeapMemoryUsage())));
}

private static final String describe(MemoryUsage memory) {
  final long max = memory.getMax();
  final long used = memory.getUsed();
  final long free = max - used;

  return String.format("used:%sMB, free:%sMB, max:%sMB",
    bytesToMegs(used), bytesToMegs(free), bytesToMegs(max));
}

private static final long bytesToMegs(long bytes) {
  return bytes / (1024 * 1024);
}

The @Command annotation is a part of an OSGi Commands system created by one of my colleagues.