How to view the current heap size that an applicat

问题:

I think I increased my heap size to 1 GB in NetBeans since I changed the config to look like this:

netbeans_default_options="-J-Xmx1g ......

After I restarted NetBeans, can I be sure that my app is given 1 GB now?

Is there a way to verify this?

回答1:

Use this code:

// Get current size of heap in bytes
long heapSize = Runtime.getRuntime().totalMemory(); 

// Get maximum size of heap in bytes. The heap cannot grow beyond this size.// Any attempt will result in an OutOfMemoryException.
long heapMaxSize = Runtime.getRuntime().maxMemory();

 // Get amount of free memory within the heap in bytes. This size will increase // after garbage collection and decrease as new objects are created.
long heapFreeSize = Runtime.getRuntime().freeMemory(); 

It was useful to me to know it.

回答2:

You can use jconsole (standard with most JDKs) to check heap sizes of any java process.

回答3:

public class CheckHeapSize {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        long heapSize = Runtime.getRuntime().totalMemory(); 

        // Get maximum size of heap in bytes. The heap cannot grow beyond this size.// Any attempt will result in an OutOfMemoryException.
        long heapMaxSize = Runtime.getRuntime().maxMemory();

         // Get amount of free memory within the heap in bytes. This size will increase // after garbage collection and decrease as new objects are created.
        long heapFreeSize = Runtime.getRuntime().freeMemory(); 

        System.out.println("heapsize"+formatSize(heapSize));
        System.out.println("heapmaxsize"+formatSize(heapMaxSize));
        System.out.println("heapFreesize"+formatSize(heapFreeSize));

    }
    public static String formatSize(long v) {
        if (v < 1024) return v + " B";
        int z = (63 - Long.numberOfLeadingZeros(v)) / 10;
        return String.format("%.1f %sB", (double)v / (1L << (z*10)), " KMGTPE".charAt(z));
    }
}

回答4:

Attach with jvisualvm from Sun Java 6 JDK. Startup flags are listed.

回答5:

You can Use the tool : Eclipse Memory Analyzer Tool http://www.eclipse.org/mat/ .

It is very useful.

回答6:

Personal favourite for when jvisualvm is overkill or you need cli-only: jvmtop

JvmTop 0.8.0 alpha   amd64  8 cpus, Linux 2.6.32-27, load avg 0.12
https://github.com/patric-r/jvmtop

PID MAIN-CLASS      HPCUR HPMAX NHCUR NHMAX    CPU     GC    VM USERNAME   #T DL
3370 rapperSimpleApp  165m  455m  109m  176m  0.12%  0.00% S6U37 web        21
11272 ver.resin.Resin [ERROR: Could not attach to VM]
27338 WatchdogManager   11m   28m   23m  130m  0.00%  0.00% S6U37 web        31
19187 m.jvmtop.JvmTop   20m 3544m   13m  130m  0.93%  0.47% S6U37 web        20
16733 artup.Bootstrap  159m  455m  166m  304m  0.12%  0.00% S6U37 web        46

回答7:

For check your java application heap size and CPU time use JProfiler tools that will access your JVM and display all heap and CPU time allocation

plug in available for eclipse and intellej Idea IDE

Link for Download Jprofiler

http://www.ej-technologies.com/download/jprofiler/files