前言：

       在写代码的时候，经常会遇到一些配置包路径的代码，然后框架根据提供的包路径进行扫描，比如Spring。所以这里自己去实现一下扫描包路径下类的代码。

       在看资料的过程中，总结出了两个不同的扫描方式，第一种是在扫描src下的包，这时候使用文件系统就可以获取到包下面的类文件；第二种是扫描jar包中的包路径，这时候需要使用JarURLConnection类了，这个可以将Jar包中目标包路径下的文件生成一个个JarEntity，遍历生成的JarEntitys就可以获取目标类文件。

代码实现：

public class Utils {

    //从包路径下扫描

    public static Set<Class> getClasses(String packagePath) {

        Set<Class> res = new HashSet<>();

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

        URL url = Thread.currentThread().getContextClassLoader().getResource(path);

        if (url == null) {

            System.out.println(packagePath + " is not exit");

            return res;

        }

        String protocol = url.getProtocol();

        if ("jar".equalsIgnoreCase(protocol)) {

            try {

                res.addAll(getJarClasses(url, packagePath));

            } catch (IOException e) {

                e.printStackTrace();

                return res;

            }

        } else if ("file".equalsIgnoreCase(protocol)) {

            res.addAll(getFileClasses(url, packagePath));

        }

        return res;

    }

    //获取file路径下的class文件

    private static Set<Class> getFileClasses(URL url, String packagePath) {

        Set<Class> res = new HashSet<>();

        String filePath = url.getFile();

        File dir = new File(filePath);

        String[] list = dir.list();

        if (list == null) return res;

        for (String classPath : list) {

            if (classPath.endsWith(".class")) {

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

                try {

                    Class<?> aClass = Class.forName(packagePath + "." + classPath);

                    res.add(aClass);

                } catch (ClassNotFoundException e) {

                    e.printStackTrace();

                }

            } else {

                res.addAll(getClasses(packagePath + "." + classPath));

            }

        }

        return res;

    }

    //使用JarURLConnection类获取路径下的所有类

    private static Set<Class> getJarClasses(URL url, String packagePath) throws IOException {

        Set<Class> res = new HashSet<>();

        JarURLConnection conn = (JarURLConnection) url.openConnection();

        if (conn != null) {

            JarFile jarFile = conn.getJarFile();

            Enumeration<JarEntry> entries = jarFile.entries();

            while (entries.hasMoreElements()) {

                JarEntry jarEntry = entries.nextElement();

                String name = jarEntry.getName();

                if (name.contains(".class") && name.replaceAll("/", ".").startsWith(packagePath)) {

                    String className = name.substring(0, name.lastIndexOf(".")).replace("/", ".");

                    try {

                        Class clazz = Class.forName(className);

                        res.add(clazz);

                    } catch (ClassNotFoundException e) {

                        e.printStackTrace();

                    }

                }

            }

        }

        return res;

    }

    public static void main(String[] args) {

        Set<Class> classes = Utils.getClasses("com.ioc");

        classes.addAll(Utils.getClasses("net.sf"));

        for (Class clazz : classes) {

            System.out.println(clazz.getName());

        }

    }

}

这里扫描的src结构是

 

扫描的Jar文件是 cglib.jar