Why do heap memory usage and number of loaded classes keep increasing?
I am using JVM Explorer - link to JVM Explorer , to profile my Spring application. I have following questions about it.
Why 'Used Heap Memory' keeps increasing even after the application has started up and have not received any requests yet? (Image 1)
Why even after garbage collection and before receiving any requests 'Used Heap Memory' keeps increasing? (Image2)
Why after garbage collection, by sending some requests to the application number of loaded classes is increasing? Is not the application supposed to use previous classes? why is it just increasing almost everything (heap, number of loaded classes)? (Image3)
After application starts up - enlarge image 
After clicking on 'Run Garbage Collector' button. - enlarge image
After sending some requests to the application following completion of Garbage Collection Procedure - enlarge image
Why 'Used Heap Memory' keeps increasing even after the application has started up and have not received any requests yet? (Image 1)
Something in your JVM is creating objects. You would need a memory profiler to see what is doing this. It could be part of Swing, or yoru application or another library.
BTW Most profiling tools use JMX which processes a lot of garbage. eg when I run FlightRecorder or VisualVM on some of my applications it shows the JMX monitoring is creating most of the garbage.
Why even after garbage collection and before receiving any requests 'Used Heap Memory' keeps increasing? (Image2)
Whatever was creating objects is still creating objects.
Why after garbage collection, by sending some requests to the application number of loaded classes is increasing?
Classes are lazily loaded. Some classes are not needed until you do something.
Is not the application supposed to use previous classes?
Yes, but this doesn't mean it won't need more classes.
why is it just increasing almost everything (heap, number of loaded classes)? (Image3)
Your application is doing more work.
If you wan't to know what work the application is doing, I suggest using a memory profiler like VisualVM or Flight Recorder. I use YourKit for these sort of questions.
Note: it takes hard work to tune a Java program so that it doesn't produce garbage and I would say most libraries only try to reduce garbage if it causes a known performance problem.
I like @PeterLawrey's good answer, however this is missing there:
The memory is primarily meant to be used, not to be spared. It may easily be the case that your application is just well written: it can work with a small memory and it can re-create all it needs, but it can also efficiently exploit the fact that your system has a lot of memory and the application uses all the possible memory to work much more efficiently.
I can easily imagine that the thing which keeps taking up the memory is for instance a cache. If the cache contains a lot of data, the application works faster.
If you do not have issues like OutOfMemoryError you do not have to worry necessarily. You should still be vigilant and inspect it further, but your described situation does not automatically mean that something is wrong.
It is analogous to the constant lamentation of Windows users that "I have bought more memory but my Windows uses it all up" - it is good when the memory is being used! That's what we buy it for!
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