path: root/nailgun_launcher/NailgunLauncher.java

package cbt;
import java.io.*;
import java.lang.reflect.*;
import java.net.*;
import java.nio.*;
import java.nio.file.*;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;

/** 
 * This launcher allows to use Nailgun without loading anything else permanenetly into its
 * classpath. The main method loads the given class from the given class math, calls it's main
 * methods passing in the additional arguments.
 */
public class NailgunLauncher{

  /** 
   * Persistent cache for caching classloaders for the JVM life time. Can be used as needed by user
   * code to improve startup time. 
   */
  public static ConcurrentHashMap<String,ClassLoader> classLoaderCache = 
    new ConcurrentHashMap<String,ClassLoader>();

  public static void main(String[] args) throws ClassNotFoundException, 
                                                NoSuchMethodException, 
                                                IllegalAccessException, 
                                                InvocationTargetException {
    if (args.length < 3) {

      System.out.println("usage: <main class> <class path> <... args>");
    
    } else {

      // TODO: cache this classloader, but invalidate on changes
      final URL[] urls = 
        Arrays.stream(
          args[1].split(File.pathSeparator)
        ).filter( cp -> !(cp == "") ).map( cp -> {
          try { return new URL("file:" + cp); }
          catch(MalformedURLException e) { throw new RuntimeException(e); }
        }).toArray(URL[]::new);

      URLClassLoader cl = new URLClassLoader(urls) {
        public String toString() {
          String suffix = "";
          if (getParent() != ClassLoader.getSystemClassLoader())
            suffix = ", "+getParent();
          return "URLClassLoader(" + Arrays.toString(getURLs()) + suffix +")";
        }
      };

      cl.loadClass(args[0])
        .getMethod("main", String[].class)
        .invoke(
          null/* _cls.newInstance()*/,
          (Object) Arrays.stream(args).skip(2).toArray(String[]::new)
        );

    }
  }
}