Develop Reference

Find the memory allocated by the JVM

I am looking for an easy way to find out how much memory the JVM on my computer has allocated to a specific process, i have tried using VisualVM, but it cannot find the process.
I should mention that this it's running a Windows Service, not a regular process.
Any suggestions ?
Thank in advance.

there is a command that comes with the JRE called jps which you can use to see all the running java processes. using jps with -v gives you the launch parameters of each process.
You can see here the launch parameters which will tell you the memory usage of each process.
This command should run also on Windows, just replace the terminal with a command prompt.

I use in android (if you want to know a programatic way):
// get the total memory for my app
long total = Runtime.getRuntime().totalMemory();
// get the free memory available
long free = Runtime.getRuntime().freeMemory();
// some simple arithmetic to see how much i use
long used = total - free;
System.out.println("Used memory in bytes: " + used);
Works for the PC too(just tested)!

JVisualVM should work for you. There are specific cases where the process is not shown in visualVM.
See some known issues
Local Applications Cannot Be Monitored (Error Dialog On Startup) Description: An error dialog saying that local applications cannot be monitored is shown immediately after VisualVM startup. Locally running Java applications are displayed as (pid ###). Resolution: This can happen on Windows systems if the username contains capitalized letters. In this case, username is UserName but the jvmstat directory created by JDK is %TMP%\hsperfdata_username. To workaround the problem, exit all Java applications, delete the %TMP%\hsperfdata_username directory and create new%TMP%\hsperfdata_UserName directory.

JPS only displays JPS

I am trying to analyze the memory usage of my Java application using the Eclipse Memory Analyzer. It's acquire heap tool uses a combination of JPS and JMAP. For some reason, my application is not listed by JPS.
At first nothing was listed so then I thought it might be an permissions issue. I ran it in an administrator command prompt and it started to list itself, but it still not my application.
If I'm not mistaken, it should list both my application and Eclipse as it is a Java application.
This is in a Windows 7 64-bit environment.

The documentation for jps states the following:
The jps tool lists the instrumented HotSpot Java Virtual Machines (JVMs) on the target system. The tool is limited to reporting information on JVMs for which it has the access permissions.
The list of JVMs produced by the jps command may be limited by the permissions granted to the principal running the command. The command will only list the JVMs for which the principle has access rights as determined by operating system specific access control mechanisms.
So access problems will certainly prevent processes that the user running the command does not have access to, or does not own, from being listed in the output.

How to get profiling output of java programs running on Tomcat using java -prof option?

in java programs, running the programs with java profiler will generate profiling output
Ex- java -prof classfile_name
How to get same profiling output of java programs running on Tomcat?
I want to get an profiling output like this
count callee caller time , like this in profiling output
1 java.util.LinkedHashMap.init()V java.util.HashMap.(IF)V 0
Can you tell me how to get an output like this for programs running on Tomcat?

Tomcat is also just a Java application, so you can add the same VM parameters by defining the JAVA_OPTS environment variable in startup.bat/startup.sh of your Tomcat distribution.
However, I would really recommend to use a real profiler, there are several free and commercial alternatives. The major free one is visualvm and as a commercial solution I recommend JProfiler (disclaimer: my company develops that tool).
In those profilers, look for the "Hot spot" views which will show you the kind of information that you are looking for.

How to debug Java memory errors?

There is a Java Struts application running on Tomcat, that have some memory errors. Sometimes it becomes slowly and hoard all of the memory of Tomcat, until it crashes.
I know how to find and repair "normal code errors", using tests, debugging, etc, but I don't know how to deal with memory errors (How can I reproduce? How can I test? What are the places of code where is more common create a memory error? ).
In one question: Where can I start? Thanks
EDIT:
A snapshot sended by the IT Department (I haven't direct access to the production application)

Use one of the many "profilers". They hook into the JVM and can tell you things like how many new objects are being created per second, and what type they are etc.
Here's just one of many: http://www.ej-technologies.com/products/jprofiler/overview.html
I've used this one and it's OK.

http://kohlerm.blogspot.com/
It is quite good intro how to find memory leaks using eclipse memory analyzer.
If you prefer video tutorials, try youtube, although it is android specific it is very informative.

If your application becomes slowly you could create a heap dump and compare it to another heap dump create when the system is in a healthy condition. Look for differences in larger data structures.

You should run it under profiler (jprofile or yourkit, for example) for some time and see for memory/resource usage. Also try to make thread dumps.

There are couple of options profiler is one of them, another is to dump java heap to a file and analyze it with a special tool (i.e. IBM jvm provides a very cool tool called Memory Analizer that presents very detailed report of allocated memory in the time of jvm crash - http://www.ibm.com/developerworks/java/jdk/tools/memoryanalyzer/).
3rd option is to start your server with jmx server enabled and connect to it via JConsole with this approach you would be able to monitor memory ussage/allocation in the runtime. JConsole is provided with standard sun jdk under bin directory (here u may find how to connect to tomcat via jconsole - Connecting remote tomcat JMX instance using jConsole)

Running Java remotely using PowerShell

When I run PowerShell in a remote session (etsn {servername}), I sometimes can't seem to run Java processes, even the most simple:
[chi-queuing]: PS C:\temp> java -cp .\hello.jar Hello
Error occurred during initialization of VM
Could not reserve enough space for object heap
Hello.jar is an "Hello, world!" application that should just print "Hello" to standard output.
So, the question is, is there something special about running processes on the other side of a PowerShell session? Is there something special about how the Java VM works that might not allow treatment like this? The memory is allocated on the remote computer, right? Here is a readout on the physical memory available:
[chi-queuing]: PS C:\temp> $mem = Get-wmiobject -class Win32_OperatingSystem
[chi-queuing]: PS C:\temp> $mem.FreePhysicalMemory
1013000
But, when I remote desktop to the server and ask the OS how much free memory there is, it says 270 MB physical memory free. Let me know what you think!

According to this:
http://msdn.microsoft.com/en-us/library/aa384372(VS.85).aspx
MaxMemoryPerShellMB
Specifies the maximum amount of memory allocated per shell, including the shell's child processes. The default is 150 MB.
Increase Max Memory Per Shell MB
winrm set winrm/config/winrs '#{MaxMemoryPerShellMB="1000"}'

I have a different answer to share with you guys. I found myself in the same situation and increasing memory min/max for Java.exe or using winrm did NOT solve my issue.
I compared two servers: one working and one not working.
I used this link https://technet.microsoft.com/en-us/library/ff520073%28v=ws.10%29.aspx to check my Windows Management Foundation wich is needed to run WINRS and also remote powershell.
the result: Both servers running Windows Server 2008 R2. One server running WMF 2.0, one running WMF 3.0.
To my surprise, the server running 2.0 was working and the one running 3.0 was NOT!
My solution: I upgraded the 3.0 WMF to 4.0!

Just a fyi: we suffered the same symptoms, and had an endless investigation based on the other two answers.
The actual solution for us was changing jdk1.8.0_31 to jdk1.8.0_51.