Re: changing the classpath at runtime in code

From:

"Aryeh M. Friedman" <Aryeh.Friedman@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 25 Oct 2007 01:26:01 -0000

Message-ID:

<1193275561.652785.88340@e34g2000pro.googlegroups.com>

On Oct 24, 9:13 pm, Arne Vajh=F8j <a...@vajhoej.dk> wrote:

Aryeh M. Friedman wrote:

On Oct 24, 8:16 pm, Arne Vajh=F8j <a...@vajhoej.dk> wrote:

Aryeh M. Friedman wrote:

Is it possible for a java app to change it's classpath at runtime. I
tried:
System.setProperty("java.class.path","foo")
The reason for wanting to try is URLClassLoader will not physically
reread a class file if it is in the classpath.

Create a URLClassLoader with a url that are *not* in the parent
classloaders url's.

so just do:

URL[] url={new URL("file://foo")};
URLClassLoader laoder=new URLClassLoader(url);
?

I have a little demo example I often use to illustrate
(subdir test is not in classpath of program).

You posted this in the original thread but as noted in the linked to
thread almost all the classes I am dealing with *WILL* be in the
classpath.... so the question remains if I do the code in my previous
post will it now load from the class path or from "foo".

Arne

=========================

=======

import java.io.*;
import java.net.*;

public class DoubleDynmaic {
    private static void dynno(int n) {
       (new File("test")).mkdir();
       try {
          OutputStream os = new FileOutputStream("test/Test.java");
          PrintStream ps = new PrintStream(os);
          ps.println("public class Test {");
          ps.println(" public Test() {");
          ps.println(" System.out.println(" + n + ");");
          ps.println(" }");
          ps.println("}");
          ps.close();
          os.close();
          Runtime.getRuntime().exec("javac -d test
test/Test.java").waitFor();
          URL[] url = new URL[1];
          url[0] = new URL("file:test/");
          URLClassLoader cl = new URLClassLoader(url);
          Class.forName("Test", true, cl).newInstance();
       } catch (Exception e) {
          e.printStackTrace();
       }
    }
    public static void main(String[] args) {
       for(int i = 0; i < 10; i++) {
          dynno(i);
       }
    }

}