Start java application from java program

Question

My problem is the following:
I start a java application A that allows you to select a couple of .java files.
After having choosen them, the application adds some additional information to these .java files (that means some more lines of code � we call it �infecting� the java files).
After the files have been infected, I want to start the application B implemented by these choosen and infected .java-files (without a new start of the Java Virtual Machine)
For doing so, we use the following method whichs works quite fine:
public static void ExecuteWithInvoke(String path, String classname)
     try
          new URLClassLoader(new URL[] {new File(path).toURL()})
               .loadClass(classname).getMethod("main",
               new Class[] { String[].class }).invoke(null,
               new Object[] { new String[] {} });
     catch (Exception e)
     {e.printStackTrace();}
The only problem that occurs:
When the application B is launched, the �old� version of the choosen .java files is used and not the current, already infected version of these files. (I guess because the �old� .class files are used.)
I solved this problem by finishing the program A after the infecting and restart my application B manually. In this case the infected .java files are used (I guess the new Start of the Java Virtual Machine solves my problem by reloading the �new� .class files)
How can I reach to start my application with the mentioned method but with the infected .java files and without having a new start of the JVM ??
Can anybody help me?
Thanks in advance
Sorry for my English, it�s a long time since I quit school

Answer 1

Hello,
my problem of reloading classes is still unsolved although you tried to help me!
Therefore I posted a little program to illustrate our difficulty.
It would be nice if somebody could have a look at this program.
We have a file Testdatei.java whose only method is the main method.
I get the class object of this file and with the help of Reflection the declared methods.
Evereything works fine so far.
Then I change the content of this file by adding an additional method a() (see change() for this).
Now I delete the old class file and I compile Testdatei.java again (see compileJava()) and once more I get the class object for this changed file. Afterwards I get the declared methods for this class via reflection.
But instead of showing now the methods main() and a() Reflection still only shows the method main().
I guess the changed class has not been reloaded!!
package testpackage;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import com.sun.tools.javac.Main;
public class LoadClass
     private File f;
     private Class c = null;
     private Object o;
     public LoadClass()
          f = new File("C:/AAJ/src/testpackage/Testdatei.java");
          try
               o = neuesExemplar(f.getPath(), "testpackage.Testdatei");
               c = o.getClass();
               System.out.println("Class " + c.getName() + " found.");
          catch (Exception e)
          {e.printStackTrace();}
          Method [] method = c.getDeclaredMethods();
          for (int i=0; i<method.length; i++)
               System.out.println(method.getName());
          change();          
          compileJava(f.getPath());
          File fileToDelete = new File("bin/testpackage/Testdatei.class");
          System.out.println(fileToDelete.delete());
          Class cla = null;
          try
               Object o = neuesExemplar(f.getPath(), "testpackage.Testdatei");
               cla = o.getClass();
               System.out.println("Class " + cla.getName() + " found.");
          catch (Exception e)
          {e.printStackTrace();}
          Method [] methods = cla.getDeclaredMethods();
          for (int i=0; i<methods.length; i++)
               System.out.println(methods[i].getName());
     private int compileJava(String javaFile)
     String[] args = {"-d", "C:/AAJ/bin/", "-classpath", System.getProperty("java.class.path"), javaFile};
     return Main.compile(args);
     public static void main(String[] args)
          new LoadClass();
     private Object neuesExemplar(String pfad, String klassename) throws Exception
     URL url = new File(pfad).toURL();
     URLClassLoader cl = new URLClassLoader( new URL[]{ url });
     Class c = cl.loadClass(klassename);
     return c.newInstance();
     private void change()
          FileWriter fw;
          BufferedWriter bw;
          try
               fw = new FileWriter(f);
               bw = new BufferedWriter(fw);               
               bw.write("package testpackage;");
               bw.newLine();
               bw.newLine();
               bw.write("public class Testdatei");
               bw.newLine();
               bw.write("{");
               bw.newLine();
               bw.write("public static void main (String [] args)");
               bw.newLine();
               bw.write("{");
               bw.write("System.out.println(4);");
               bw.newLine();
               bw.write("}");
               bw.newLine();
               bw.newLine();
               bw.write("private void a ()");
               bw.newLine();
               bw.write("{");
               bw.newLine();
               bw.write("System.out.println(55);");
               bw.newLine();
               bw.write("}");
               bw.newLine();
               bw.write("}");
               bw.close();
               fw.close();               
          catch (IOException e)
          {e.printStackTrace();}                                             
I�m using eclipse 3.1.0. Is it possible that it�s a bug in eclipse that eclipse holds the old class file in memory from the beginning and always refers to this one and not to the new compiled one?
Thanks a lot
Simon