Adding files to java classpath at runtime [duplicate]

by

You can only add folders or jar files to a class loader. So if you have a single class file, you need to put it into the appropriate folder structure first.

Here is a rather ugly hack that adds to the SystemClassLoader at runtime:

import java.io.IOException;
import java.io.File;
import java.net.URLClassLoader;
import java.net.URL;
import java.lang.reflect.Method;

public class ClassPathHacker {

  private static final Class[] parameters = new Class[]{URL.class};

  public static void addFile(String s) throws IOException {
    File f = new File(s);
    addFile(f);
  }//end method

  public static void addFile(File f) throws IOException {
    addURL(f.toURL());
  }//end method


  public static void addURL(URL u) throws IOException {

    URLClassLoader sysloader = (URLClassLoader) ClassLoader.getSystemClassLoader();
    Class sysclass = URLClassLoader.class;

    try {
      Method method = sysclass.getDeclaredMethod("addURL", parameters);
      method.setAccessible(true);
      method.invoke(sysloader, new Object[]{u});
    } catch (Throwable t) {
      t.printStackTrace();
      throw new IOException("Error, could not add URL to system classloader");
    }//end try catch

   }//end method

}//end class

The reflection is necessary to access the protected method addURL. This could fail if there is a SecurityManager.

More Related Contents:

  1. Compile time vs Run time Dependency – Java
  2. What is a classpath and how do I set it?
  3. Capturing stdout when calling Runtime.exec
  4. Get a list of resources from classpath directory
  5. Find where java class is loaded from
  6. Call “java -jar MyFile.jar” with additional classpath option
  7. Execute external program
  8. How to add directory to classpath in an application run profile in IntelliJ IDEA?
  9. Printing Runtime exec() OutputStream to console
  10. How to get the x and y of a program window in Java?
  11. Classpath does not work under linux
  12. How to load/reference a file as a File instance from the classpath
  13. java.lang.NoClassDefFoundError: Could not initialize class XXX
  14. Execute jar file with multiple classpath libraries from command prompt
  15. Is it possible to mix –class-path and –module-path in javac (JDK 9)?
  16. IntelliJ IDEA: “cannot resolve symbol” for String, System and other Java classes
  17. Including jar files in class path
  18. How can I save a file to the class path [closed]
  19. Java: NullPointerException from class.getResource( … )
  20. Can I create a custom classpath on a per application basis in Tomcat
  21. Adding external resources to class-path in Tomcat 8
  22. Getting Ant to recognise a classpath
  23. How do I auto load a database jar in Groovy without using the -cp switch?
  24. Casting a class to an unrelated interface
  25. How to read text file from classpath in Java?
  26. On-the-fly, in-memory java code compilation for Java 5 and Java 6
  27. Adding to the classpath on OSX
  28. Run a jar File from java program
  29. Is WEB-INF in the CLASSPATH?
  30. URLClassLoader and accessibility of package-private methods

Leave a Comment