package org.hotswap.agent.util.classloader;
import org.hotswap.agent.logging.AgentLogger;
import sun.misc.URLClassPath;
import java.lang.reflect.Field;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;
/**
* Helper methods to enhance URL ClassLoader.
*/
public class URLClassLoaderHelper {
private static AgentLogger LOGGER = AgentLogger.getLogger(URLClassLoaderHelper.class);
/**
* Insert classpath at the beginning of the classloader path.
* This implementation will replace ucp field (URLClassPath) with new definition. Any existing Loader
* is discarded and recreated.
*
* @param classLoader URL classloader
* @param extraClassPath path to prepend
*/
public static void prependClassPath(URLClassLoader classLoader, URL[] extraClassPath) {
synchronized (classLoader) {
// set new URLClassPath to the classloader via reflection
try {
Field ucpField = URLClassLoader.class.getDeclaredField("ucp");
ucpField.setAccessible(true);
URL[] origClassPath = getOrigClassPath(classLoader, ucpField);
URL[] modifiedClassPath = new URL[origClassPath.length + extraClassPath.length];
System.arraycopy(extraClassPath, 0, modifiedClassPath, 0, extraClassPath.length);
System.arraycopy(origClassPath, 0, modifiedClassPath, extraClassPath.length, origClassPath.length);
ucpField.set(classLoader, new ExtraURLClassPath(modifiedClassPath));
LOGGER.debug("Added extraClassPath URLs {} to classLoader {}", Arrays.toString(extraClassPath), classLoader);
} catch (Exception e) {
LOGGER.error("Unable to add extraClassPath URLs {} to classLoader {}", e, Arrays.toString(extraClassPath), classLoader);
}
}
}
public static void setWatchResourceLoader(URLClassLoader classLoader, final ClassLoader watchResourceLoader) {
synchronized (classLoader) {
// set new URLClassPath to the classloader via reflection
try {
Field ucpField = URLClassLoader.class.getDeclaredField("ucp");
ucpField.setAccessible(true);
URL[] origClassPath = getOrigClassPath(classLoader, ucpField);
ucpField.set(classLoader, new ExtraURLClassPath(origClassPath, watchResourceLoader));
LOGGER.debug("WatchResourceLoader registered to classLoader {}", classLoader);
} catch (Exception e) {
LOGGER.debug("Unable to register WatchResourceLoader to classLoader {}", e, classLoader);
}
}
}
private static URL[] getOrigClassPath(URLClassLoader classLoader, Field ucpField) throws IllegalAccessException {
URL[] origClassPath;
URLClassPath urlClassPath = (URLClassPath) ucpField.get(classLoader);
if (urlClassPath instanceof ExtraURLClassPath) {
origClassPath = ((ExtraURLClassPath)urlClassPath).getOrigClassPath();
} else {
origClassPath = classLoader.getURLs();
}
return origClassPath;
}
private static class ExtraURLClassPath extends sun.misc.URLClassPath {
private ClassLoader watchResourceLoader;
URL[] origClassPath;
public ExtraURLClassPath(URL[] origClassPath) {
super(origClassPath);
this.origClassPath = origClassPath;
}
public ExtraURLClassPath(URL[] origClassPath, ClassLoader watchResourceLoader) {
super(origClassPath);
this.origClassPath = origClassPath;
this.watchResourceLoader = watchResourceLoader;
}
@Override
public URL findResource(String name, boolean check) {
if (watchResourceLoader != null) {
URL resource = watchResourceLoader.getResource(name);
if (resource != null) {
return resource;
}
}
return super.findResource(name, check);
}
/**
* Return orig classpath as was set by hotswap agent.
* Note: cannot use classLoader.getURLs(), because Tomcat WebappClassLoader does not return modified classPath.
*/
public URL[] getOrigClassPath() {
return origClassPath;
}
}
}