参考来源：

以下代码一键运行：

package test;

import java.io.File;

import java.io.IOException;

import java.net.JarURLConnection;

import java.net.URL;

import java.net.URLClassLoader;

import java.util.Enumeration;

import java.util.HashSet;

import java.util.Set;

import java.util.jar.JarEntry;

import java.util.jar.JarFile;

public class ClassUtils {

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

String packageName = "org.objectweb.asm";

Set classNames = getClassName(packageName, false);

if (classNames != null) {

for (String className : classNames) {

System.out.println(className);

}

}

}

/**

* 获取某包下所有类

* @param packageName 包名

* @param isRecursion 是否遍历子包

* @return 类的完整名称

*/

public static Set getClassName(String packageName, boolean isRecursion) {

Set classNames = null;

ClassLoader loader = Thread.currentThread().getContextClassLoader();

String packagePath = packageName.replace(".", "/");

URL url = loader.getResource(packagePath);

if (url != null) {

String protocol = url.getProtocol();

if (protocol.equals("file")) {

classNames = getClassNameFromDir(url.getPath(), packageName, isRecursion);

} else if (protocol.equals("jar")) {

JarFile jarFile = null;

try{

jarFile = ((JarURLConnection) url.openConnection()).getJarFile();

} catch(Exception e){

e.printStackTrace();

}

if(jarFile != null){

getClassNameFromJar(jarFile.entries(), packageName, isRecursion);

}

}

} else {

/*从所有的jar包中查找包名*/

classNames = getClassNameFromJars(((URLClassLoader)loader).getURLs(), packageName, isRecursion);

}

return classNames;

}

/**

* 从项目文件获取某包下所有类

* @param filePath 文件路径

* @param className 类名集合

* @param isRecursion 是否遍历子包

* @return 类的完整名称

*/

private static Set getClassNameFromDir(String filePath, String packageName, boolean isRecursion) {

Set className = new HashSet();

File file = new File(filePath);

File[] files = file.listFiles();

for (File childFile : files) {

if (childFile.isDirectory()) {

if (isRecursion) {

className.addAll(getClassNameFromDir(childFile.getPath(), packageName+"."+childFile.getName(), isRecursion));

}

} else {

String fileName = childFile.getName();

if (fileName.endsWith(".class") && !fileName.contains("$")) {

className.add(packageName+ "." + fileName.replace(".class", ""));

}

}

}

return className;

}

/**

* @param jarEntries

* @param packageName

* @param isRecursion

* @return

*/

private static Set getClassNameFromJar(Enumeration jarEntries, String packageName, boolean isRecursion){

Set classNames = new HashSet();

while (jarEntries.hasMoreElements()) {

JarEntry jarEntry = jarEntries.nextElement();

if(!jarEntry.isDirectory()){

/*

* 这里是为了方便，先把"/" 转成 "." 再判断 ".class" 的做法可能会有bug

* (FIXME: 先把"/" 转成 "." 再判断 ".class" 的做法可能会有bug)

*/

String entryName = jarEntry.getName().replace("/", ".");

if (entryName.endsWith(".class") && !entryName.contains("$") && entryName.startsWith(packageName)) {

entryName = entryName.replace(".class", "");

if(isRecursion){

classNames.add(entryName);

} else if(!entryName.replace(packageName+".", "").contains(".")){

classNames.add(entryName);

}

}

}

}

return classNames;

}

/**

* 从所有jar中搜索该包，并获取该包下所有类

* @param urls URL集合

* @param packageName 包路径

* @param isRecursion 是否遍历子包

* @return 类的完整名称

*/

private static Set getClassNameFromJars(URL[] urls, String packageName, boolean isRecursion) {

Set classNames = new HashSet();

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

String classPath = urls[i].getPath();

//不必搜索classes文件夹

if (classPath.endsWith("classes/")) {continue;}

JarFile jarFile = null;

try {

jarFile = new JarFile(classPath.substring(classPath.indexOf("/")));

} catch (IOException e) {

e.printStackTrace();

}

if (jarFile != null) {

classNames.addAll(getClassNameFromJar(jarFile.entries(), packageName, isRecursion));

}

}

return classNames;

}

}