changing the classpath at runtime in code
13 Message(s) by 4 Author(s) originally posted in java programmer
| From: Aryeh M. Friedman |
Date: Wednesday, October 24, 2007
|
| From: =?ISO-8859-1?Q?Arne_Vajh=F8j?= |
Date: Wednesday, October 24, 2007
|
wrote in message:
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 won't physically
reread a class file if it is in the classpath.
Create a URLClassLoader with a url that are *not* in the
parent
class
load ers url's.
Arne
| From: Aryeh M. Friedman |
Date: Wednesday, October 24, 2007
|
wrote in message:
wrote in message:
> 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 won't 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=3D{new URL("file://foo")};
URLClassLoader laoder=3Dnew URLClassLoader(url);
?
| From: =?ISO-8859-1?Q?Arne_Vajh=F8j?= |
Date: Wednesday, October 24, 2007
|
wrote in message:
wrote in message:
wrote in message:
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 won't 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 isn't in classpath of program).
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);
}
}
}
| From: Aryeh M. Friedman |
Date: Wednesday, October 24, 2007
|
wrote in message:
wrote in message:
wrote in message:
wrote in message:
> 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 won't 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=3D{new URL("file://foo")};
> URLClassLoader laoder=3Dnew URLClassLoader(url);
> ?
I have a little demo example I often use to illustrate
(subdir test isn't 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
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D
import JAVA.io.*;
import JAVA.net.*;
public class DoubleDynmaic {
private static void dynno(int n) {
(new File("test")).mkdir();
try {
OutputStream os =3D new FileOutputStream("test/Test.JAVA");
PrintStream ps =3D 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 =3D new URL[1];
url[0] =3D new URL("file:test/");
URLClassLoader cl =3D new URLClassLoader(url);
Class.forName("Test", true, cl).newInstance();
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
for(int I =3D 0; i < 10; i++) {
dynno(i);
}
}
> }
| From: Aryeh M. Friedman |
Date: Wednesday, October 24, 2007
|
wrote in message:
wrote in message:
wrote in message:
wrote in message:
> 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 won't 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=3D{new URL("file://foo")};
> URLClassLoader laoder=3Dnew URLClassLoader(url);
> ?
I have a little demo example I often use to illustrate
(subdir test isn't in classpath of program).
Perhaps google ate my previous response.... but as I said several
places (including the linked to thread) almost all my classes *WILL*
be in the classpath... btw as mentioned in an other thread your demo
does not quite work once divorced from the code to rewrite the class
(see orginial thread)... so the question remains does the code above
load from "foo" or from the classpath when I do loader.loadClass(...)
| From: =?ISO-8859-1?Q?Arne_Vajh=F8j?= |
Date: Wednesday, October 24, 2007
|
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
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 won't 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 isn't 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".
If the class get loaded by the parent classloader because it is
in the apps general classpath, then you can (as far as I know)
neither get it unloaded or reloaded.
You need to get those classes of the classpath.
Arne
| From: Daniel Pitts |
Date: Wednesday, October 24, 2007
|
| From: Daniel Pitts |
Date: Wednesday, October 24, 2007
|
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
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 won't 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 isn't in classpath of program).
Perhaps google ate my previous response.... but as I said several
places (including the linked to thread) almost all my classes *WILL*
be in the classpath... btw as mentioned in an other thread your demo
does not quite work once divorced from the code to rewrite the class
(see orginial thread)... so the question remains does the code above
load from "foo" or from the classpath when I do loader.loadClass(...)
Here's the scoop.
If its ever on the class path, you can not reload it. What you're trying
to do isn't possible to do without restricting what's on the class
path. That isn't a bad restriction! Just make it happen.
Changing the class path after the fact is not going to help either.
--
Daniel Pitts' Tech Blog:
<http://virtualinfinity.net/wordpress/>
| From: Aryeh M. Friedman |
Date: Wednesday, October 24, 2007
|
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
> 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 won't 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=3D{new URL("file://foo")};
> URLClassLoader laoder=3Dnew URLClassLoader(url);
> ?
I have a little demo example I often use to illustrate
(subdir test isn't 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".
If the class get loaded by the parent classloader because it is
in the apps general classpath, then you can (as far as I know)
neither get it unloaded or reloaded.
You need to get those classes of the classpath.
Since this is for a commercial unit
testing product this isn't
possible in practice (it isn't
safe to make assumptions about where
people place things). Some one off
line suggested forking a process
to do it.... if I can not find a ClassLoader based
solution I'll have
to do that but it is
down right a) not
portable b)
evil
| From: Daniel Pitts |
Date: Thursday, October 25, 2007
|
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
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 won't 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 isn't 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".
If the class get loaded by the parent classloader because it is
in the apps general classpath, then you can (as far as I know)
neither get it unloaded or reloaded.
You need to get those classes of the classpath.
Since this is for a commercial unit testing product this isn't
possible in practice (it isn't safe to make assumptions about where
people place things). Some one off line suggested forking a process
to do it.... if I can not find a ClassLoader based solution I'll have
to do that but it is down right a) not portable b) evil
Hmm, I think as a publisher of said software, you can say how it should
work. If you can not make any assumptions whatsoever then you're lost.
You will end up writing this program for clients who want to be able to
bounce a
network signal off the moon for some reason.
It's all about making reasonable assumptions. It is reasonable to
assume that you can have a
degree of
control the environment/context in
which your application starts up. Document the fact that the code to be
tested can not be in the same path as your product.
Also, you seem to make a big deal about this code being "commercial".
This rule applies for any publicly distributed product, whether
commercial or otherwise.
Honestly, I think you're going down the wrong road with this. Have you
looked at other existing test frameworks? What is yours going to offer
that, say, JUnit does not?
--
Daniel Pitts' Tech Blog:
<http://virtualinfinity.net/wordpress/>
| From: Roedy Green |
Date: Thursday, October 25, 2007
|
On Wed, 24 Oct 2007 23:38:10 -0000, "Aryeh M. Friedman"
wrote in message, quoted or indirectly quoted someone
who said :
Is it possible for a JAVA app to change it's classpath at runtime
yes but it requires firing up a new classloader.
See
http://mindprod.com/jgloss/classloader.html
--
Roedy
Green Canadian Mind Products
The JAVA Glossary
http://mindprod.com
| From: =?ISO-8859-1?Q?Arne_Vajh=F8j?= |
Date: Friday, October 26, 2007
|
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
wrote in message:
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 won't 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 isn't 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".
If the class get loaded by the parent classloader because it is
in the apps general classpath, then you can (as far as I know)
neither get it unloaded or reloaded.
You need to get those classes of the classpath.
Since this is for a commercial unit testing product this isn't
possible in practice (it isn't safe to make assumptions about where
people place things). Some one off line suggested forking a process
to do it.... if I can not find a ClassLoader based solution I'll have
to do that but it is down right a) not portable b) evil
You don't have any control over where people put their stuff,
but you've control over your stuff.
If the only thing in classpath is your
jar file, then you can
create your own classloader for their stuff and unload and reload
as needed.
Arne
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