Remove folder from Java classpath at runtime -

is there way remove folder classpath similar adding folder @ runtime (can directory added class path @ runtime?)

please find below snippet technical example demonstrate adding / removing path.

create following source files in directory

import java.io.file; import java.lang.reflect.field; import java.lang.reflect.method; import java.net.url; import java.net.urlclassloader; import java.util.stack; import sun.misc.urlclasspath;  public class evilpathdemo {      public static void addpath(string path) throws exception {         url u = new file(path).touri().tourl();         urlclassloader urlclassloader = (urlclassloader)             classloader.getsystemclassloader();         class<?> urlclass = urlclassloader.class;         method method = urlclass.getdeclaredmethod("addurl",                 new class[]{url.class}         );         method.setaccessible(true);         method.invoke(urlclassloader, new object[]{u});     }      public static void removepath(string path) throws exception {         url url = new file(path).touri().tourl();         urlclassloader urlclassloader = (urlclassloader)              classloader.getsystemclassloader();         class<?> urlclass = urlclassloader.class;         field ucpfield = urlclass.getdeclaredfield("ucp");         ucpfield.setaccessible(true);         urlclasspath ucp = (urlclasspath) ucpfield.get(urlclassloader);         class<?> ucpclass = urlclasspath.class;         field urlsfield = ucpclass.getdeclaredfield("urls");         urlsfield.setaccessible(true);         stack urls = (stack) urlsfield.get(ucp);         urls.remove(url);     }      public static void main(string[] args) throws exception {         string parm = args.length == 1 ? args[0] : "";         string evilpath = "/tmp";          string classpath = system.getproperty("java.class.path");         boolean isevilpathset = false;         (string path : classpath.split(file.pathseparator)) {             if (path.equalsignorecase(evilpath)) {                 system.out.printf("evil path '%s' in classpath%n", evilpath);                 isevilpathset = true;                 break;             }         }         if (isevilpathset && parm.equalsignorecase("remove")) {             system.out.printf("evil path '%s' removed%n", evilpath);             removepath(evilpath);         }         trytoload("foo");         if (parm.equalsignorecase("add")) {             system.out.printf("evil path '%s' added%n", evilpath);             addpath(evilpath);         }         trytoload("bar");     }      private static void trytoload(string classname) {         try {             class<?> foo = class.forname(classname);             system.out.printf("class loaded: %s%n", foo.getname());         } catch (classnotfoundexception ex) {             system.out.println(ex);         }     } } 

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public class foo {     static {         system.out.println("i'm foo...");     } } 

.

public class bar {     static {         system.out.println("i'm bar...");     } } 

compile them follow

javac evilpathdemo.java javac -d /tmp foo.java bar.java 

during test try load classes foo , bar.

without /tmp in classpath

java -cp . evilpathdemo java.lang.classnotfoundexception: foo java.lang.classnotfoundexception: bar 

adding /tmp classpath

java -cp . evilpathdemo add java.lang.classnotfoundexception: foo evil path '/tmp' added i'm bar... class loaded: bar 

with /tmp in classpath

java -cp .:/tmp evilpathdemo evil path '/tmp' in classpath i'm foo... class loaded: foo i'm bar... class loaded: bar 

remove /tmp classpath

java -cp .:/tmp evilpathdemo remove evil path '/tmp' in classpath evil path '/tmp' removed java.lang.classnotfoundexception: foo java.lang.classnotfoundexception: bar 

during testing found out following cases not working.

• addpath(evilpath);
  trytoload("foo");
  removepath(evilpath); // had not effect
  trytoload("bar");
• removepath(evilpath);
  trytoload("foo");
  addpath(evilpath); // had no effect
  trytoload("bar");
• trytoload("foo");
  removepath(evilpath); // had no effect
  trytoload("bar");

i did not spent time find out why. because don't see practical use in it. if need/wish play classpaths have how classloaders working.