Programmatically fill the JVM Permanent Generation

Question

I need to test some JMX monitoring scripts I have developed, In particular I would like to verify that my monitoring of the PermGen region is working. So in order to test this I would like to be able to run a bit of code that loads a significant number of classes in order to consume PermGen.

My current plan is to write a script to generate prefix(1..n).java compile them and then on cue run:

for( int i=1 ; i < n ; i ++){
    Class.forName("com.mypackage.prefix"+i);
}

Is there a more elegant solution to achieve this?

Answer 1

OK, so looks like String.intern() will do the trick. Here is one implementation I found. Credits goes to Gareth as well:

public static void main(String[] args) throws ClassNotFoundException {
    int i = 0;
    StringBuilder sb = new StringBuilder("a");
    for (i = 0; i < 20; i++) {
        sb.append(sb.toString());
    }
    System.err.println(sb.length());
    i = 0;
    Set<String> strings = new HashSet<String>();
    while (true) {
        strings.add(sb.append(i++).toString().intern());
        System.err.println(i);
    }
}