class ClassLoaderFactory

class ClassLoaderFactory

package org.apache.catalina.startup 2003-03-24

---

package org.apache.catalina.startup;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

import org.apache.catalina.loader.StandardClassLoader;


/**
 * Utility class for building class loaders for Catalina.  The factory
 * method requires the following parameters in order to build a new class
 * loader (with suitable defaults in all cases):
 

 
A set of directories containing unpacked classes (and resources)
     that should be included in the class loader's
     repositories.
 
A set of directories containing classes and resources in JAR files.
     Each readable JAR file discovered in these directories will be
     added to the class loader's repositories.
 
ClassLoader instance that should become the parent of
     the new class loader.
 
 *
 * @author Craig R. McClanahan
 * @version $Revision: 1.8 $ $Date: 2002/02/17 08:26:02 $
 */


public final class ClassLoaderFactory {


 
   /**
     * Debugging detail level for processing the startup.
     */

    private static int debug = 0;



    /**
     * Return the debugging detail level.
     */

    public static int getDebug() {
        return (debug);
    }



    /**
     * 设置DEBUG级别
     */

    public static void setDebug(int newDebug) {
        debug = newDebug;
    }



    /**
     * 该类是一个静态类，用来创建和返回ClassLoader对象（实际上是StandardClassLoader对象）
     * 它将根据设置和参数返回apache定置的ClassLoader对象，以完成自己的类载入
     *
     * @param unpacked 类路径CLASSPATH的数组
     * @param packed 含有JAR文件的类路径
     * @param parent 父ClassLoader对象。当一个ClassLoader对象无法完成类载入时，它将请求父对象帮助
     *
     * @exception Exception if an error occurs constructing the class loader
     */

    public static ClassLoader createClassLoader(File unpacked[],
                                                File packed[],
                                                ClassLoader parent)
        throws Exception {

        if (debug >= 1)
            log("Creating new class loader");


        // list里将被填入所有需要附加到CLASSPATH上去的文件名

        ArrayList list = new ArrayList();


        // Add unpacked directories

        if (unpacked != null) {
            for (int i = 0; i < unpacked.length; i++)  {
                File file = unpacked[i];
                if (!file.isDirectory() || !file.exists() || !file.canRead())
                    continue;
                if (debug >= 1)
                    log("  Including directory " + file.getAbsolutePath());
                URL url = new URL("file", null,
                                  file.getCanonicalPath() + File.separator);
                list.add(url.toString());
            }
        }


        // Add packed directory JAR files

        if (packed != null) {
            for (int i = 0; i < packed.length; i++) {
                File directory = packed[i];
                if (!directory.isDirectory() || !directory.exists() ||
                    !directory.canRead())
                    continue;
                String filenames[] = directory.list();
                for (int j = 0; j < filenames.length; j++) {
                    String filename = filenames[j].toLowerCase();
                    if (!filename.endsWith(".jar"))
                        continue;
                    File file = new File(directory, filenames[j]);
                    if (debug >= 1)
                        log("  Including jar file " + file.getAbsolutePath());
                    URL url = new URL("file", null,
                                      file.getCanonicalPath());
                    list.add(url.toString());
                }
            }
        }
        

        // 填好了list



        // 创建StandardClassLoader对象，并返回

        String array[] = (String[]) list.toArray(new String[list.size()]);
        StandardClassLoader classLoader = null;
        if (parent == null)
            classLoader = new StandardClassLoader(array);
        else
            classLoader = new StandardClassLoader(array, parent);
        classLoader.setDelegate(true);
        return (classLoader);

    }



    /**
     * 输出日志
     */

    private static void log(String message) {
        System.out.print("ClassLoaderFactory:  ");
        System.out.println(message);
    }



    /**
     * 输出日志和异常信息
     */

    private static void log(String message, Throwable exception) {
        log(message);
        exception.printStackTrace(System.out);
    }

}