get heap memory used by a method in a java class

i m writing a java code and i want run some performance tests . 开发者_开发百科I want to get the heap memory used by only one of the methods in my class.

 public AccessControl {

     public boolean Allowed () {
        code
        }
     public  void print () {
    code }
}

i want to get the heap memory used in java everytime the method Allowed is called at runtime. i read i can do it through HPROf but i noticed that HPROf doesnt provide memory calculations for methods but only for classes is there a code i can write inside the method to get the available memory and then the used memory? thanks

There is no such thing as "heap memory used by a method". Methods don't take up heap memory, objects do.

If you're interested in the objects created within a specific method (and, of course, the methods it calls directly and indirectly), you could compare heap snapshots created before and after the method call (doable by running in a debugger and setting breakpoints).

But what actual problem are you trying to solve? Memory leaks are usually diagnosed by first finding the GC roots for apparently-unnecessary objects and the using a debugger to find out where and why these references are set.

InMemProfiler can be used to profile memory allocations. In trace mode this tool can be used to identify the source of memory allocations.

You could use the option #tracetarget-org.yourcode.YourClass to get the "Allocating Classes" output to show the per method memory allocation within YourClass.

However, you will only be able to profile memory allocations for each allocated class separately. There is currently no summary given across all the allocated classes. If you were really keen you could git fork InMemProfiler and try and add this functionality.

I would recommend that when profiling you do not bias your results by introducing new code. If HPROF does not solve your problem, then you could use a debugger and apply breakpoints around where you want to analyze. You may also want to try JProfiler. I would recommend that instead of focusing on one specific place in your code, to look at the big picture first. Otherwise you risk premature optimization.

If you use oracle jvm, you can do it!

ThreadMXBean threadmx = ManagementFactory.getThreadMXBean();
long startbyte = ((com.sun.management.ThreadMXBean)threadmx)
    .getThreadAllocatedBytes(Thread.currentThread().getId());
//call method
int usedbyte = ((com.sun.management.ThreadMXBean)threadmx)
    .getThreadAllocatedBytes(Thread.currentThread().getId())-startbyte;

One way is to use a memory profiler like jprofiler, but if you just want to see the memory used by a set of statements use below code

Runtime runtime = Runtime.getRuntime();
long memoryUsedBefore = runtime.totalMemory() - runtime.freeMemory();
System.out.println("Memory used before: " + memoryUsedBefore );
    // set of memory consumption statements here
long memoryUsedAfter = runtime.totalMemory() - runtime.freeMemory();
System.out.println("Total Memory increased:" + (memoryUsedAfter - memoryUsedBefore ));