此函数从类路径中找到Java类文件的第一个匹配文件名，如果找不到则返回null。

/**

 * Distribution License:

 * JSword is free software; you can redistribute it and/or modify it under

 * the terms of the GNU Lesser General Public License, version 2.1 as published by

 * the Free Software Foundation. This program is distributed in the hope

 * that it will be useful, but WITHOUT ANY WARRANTY; without even the

 * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 * See the GNU Lesser General Public License for more details.

 *

 * The License is available on the internet at:

 *       http://www.gnu.org/copyleft/lgpl.html

 * or by writing to:

 *      Free Software Foundation, Inc.

 *      59 Temple Place - Suite 330

 *      Boston, MA 02111-1307, USA

 *

 * Copyright: 2005

 *     The copyright to this program is held by it's authors.

 *

 * ID: $Id: ClassUtil.java 2230 2012-02-08 00:00:10Z dmsmith $

 */

import java.io.File;
/** 
 来自 n o w j a v a . c o m - 时  代  Java**/

import java.io.IOException;

import java.util.zip.ZipEntry;

import java.util.zip.ZipFile;


public class Main{

    public static void main(String[] argv) throws Exception{

        String classname = "nowjava.com";

        System.out.println(findClasspathEntry(classname));

    }

    private static final String EXTENSION_CLASS = ".class";

    private static final String EXTENSION_JAR = ".jar";

    private static final String EXTENSION_ZIP = ".zip";

    /**

     * The log stream

     */

    private static final Logger log = Logger.getLogger(ClassUtil.class);

    /**

     * This function finds the first matching filename for a Java class file

     * from the classpath, if none is found it returns null.

     */

    public static String findClasspathEntry(String classname,

            String classpath) {
            /* 
             来自 
            *nowjava.com - 时  代  Java*/

        String full = null;


        String[] paths = StringUtil.split(classpath, File.pathSeparator);

        for (int i = 0; i < paths.length; i++) {

            // Search the jar

            if (paths[i].endsWith(EXTENSION_ZIP)

                    || paths[i].endsWith(EXTENSION_JAR)) {

                ZipFile zip = null;

                try {

                    String fileName = classname.replace(',', '/')

                            + EXTENSION_CLASS;

                    zip = new ZipFile(paths[i]);

                    ZipEntry entry = zip.getEntry(fileName);


                    if (entry != null && !entry.isDirectory()) {

                        if (full != null && !full.equals(fileName)) {

                            log.warn("Warning duplicate " + classname

                                    + " found: " + full + " and "

                                    + paths[i]);

                        } else {

                            full = paths[i];

                        }

                    }

                } catch (IOException ex) {

                    // If that zip file failed, then ignore it and move on.

                    log.warn("Missing zip file for " + classname + " and "

                            + paths[i]);

                } finally {

                    IOUtil.close(zip);

                }

            } else {

                StringBuilder path = new StringBuilder(256);


                // Search for the file

                String extra = classname.replace('.', File.separatorChar);


                path.append(paths[i]);

                if (paths[i].charAt(paths[i].length() - 1) != File.separatorChar) {

                    path.append(File.separatorChar);

                }


                path.append(extra);

                path.append(EXTENSION_CLASS);

                String fileName = path.toString();


                if (new File(fileName).isFile()) {

                    if (full != null && !full.eq