你好。我上面的解决方案（和其他站点）总是遇到一些问题。
作为开发人员，我正在为API编程附加程序。该API禁止使用任何外部库或第三方工具。该设置还包括jar或zip文件中的代码以及直接位于某些目录中的类文件的混合。因此，我的代码必须能够在每种设置下工作。经过大量研究，我提出了一种至少可用于所有可能设置的95％的方法。
以下代码基本上是永远可以使用的矫over过正的方法。
编码：
此代码在给定的程序包中扫描其中包含的所有类。它仅适用于当前版本中的所有类ClassLoader。
/**
* Private helper method
*
* @param directory
* The directory to start with
* @param pckgname
* The package name to search for. Will be needed for getting the
* Class object.
* @param classes
* if a file isn't loaded but still is in the directory
* @throws ClassNotFoundException
*/
private static void checkDirectory(File directory, String pckgname,
ArrayList<Class<?>> classes) throws ClassNotFoundException {
File tmpDirectory;
if (directory.exists() && directory.isDirectory()) {
final String[] files = directory.list();
for (final String file : files) {
if (file.endsWith(".class")) {
try {
classes.add(Class.forName(pckgname + '.'
+ file.substring(0, file.length() - 6)));
} catch (final NoClassDefFoundError e) {
// do nothing. this class hasn't been found by the
// loader, and we don't care.
}
} else if ((tmpDirectory = new File(directory, file))
.isDirectory()) {
checkDirectory(tmpDirectory, pckgname + "." + file, classes);
}
}
}
}
/**
* Private helper method.
*
* @param connection
* the connection to the jar
* @param pckgname
* the package name to search for
* @param classes
* the current ArrayList of all classes. This method will simply
* add new classes.
* @throws ClassNotFoundException
* if a file isn't loaded but still is in the jar file
* @throws IOException
* if it can't correctly read from the jar file.
*/
private static void checkJarFile(JarURLConnection connection,
String pckgname, ArrayList<Class<?>> classes)
throws ClassNotFoundException, IOException {
final JarFile jarFile = connection.getJarFile();
final Enumeration<JarEntry> entries = jarFile.entries();
String name;
for (JarEntry jarEntry = null; entries.hasMoreElements()
&& ((jarEntry = entries.nextElement()) != null);) {
name = jarEntry.getName();
if (name.contains(".class")) {
name = name.substring(0, name.length() - 6).replace('/', '.');
if (name.contains(pckgname)) {
classes.add(Class.forName(name));
}
}
}
}
/**
* Attempts to list all the classes in the specified package as determined
* by the context class loader
*
* @param pckgname
* the package name to search
* @return a list of classes that exist within that package
* @throws ClassNotFoundException
* if something went wrong
*/
public static ArrayList<Class<?>> getClassesForPackage(String pckgname)
throws ClassNotFoundException {
final ArrayList<Class<?>> classes = new ArrayList<Class<?>>();
try {
final ClassLoader cld = Thread.currentThread()
.getContextClassLoader();
if (cld == null)
throw new ClassNotFoundException("Can't get class loader.");
final Enumeration<URL> resources = cld.getResources(pckgname
.replace('.', '/'));
URLConnection connection;
for (URL url = null; resources.hasMoreElements()
&& ((url = resources.nextElement()) != null);) {
try {
connection = url.openConnection();
if (connection instanceof JarURLConnection) {
checkJarFile((JarURLConnection) connection, pckgname,
classes);
} else if (connection instanceof FileURLConnection) {
try {
checkDirectory(
new File(URLDecoder.decode(url.getPath(),
"UTF-8")), pckgname, classes);
} catch (final UnsupportedEncodingException ex) {
throw new ClassNotFoundException(
pckgname
+ " does not appear to be a valid package (Unsupported encoding)",
ex);
}
} else
throw new ClassNotFoundException(pckgname + " ("
+ url.getPath()
+ ") does not appear to be a valid package");
} catch (final IOException ioex) {
throw new ClassNotFoundException(
"IOException was thrown when trying to get all resources for "
+ pckgname, ioex);
}
}
} catch (final NullPointerException ex) {
throw new ClassNotFoundException(
pckgname
+ " does not appear to be a valid package (Null pointer exception)",
ex);
} catch (final IOException ioex) {
throw new ClassNotFoundException(
"IOException was thrown when trying to get all resources for "
+ pckgname, ioex);
}
return classes;
}
这三种方法使您能够查找给定程序包中的所有类。
您可以这样使用它：
getClassesForPackage("package.your.classes.are.in");
说明：
该方法首先获取电流ClassLoader。然后，它将获取包含所述程序包的所有资源并对其进行迭代URL。然后，它创建一个URLConnection并确定我们拥有哪种类型的UR1。它可以是目录（FileURLConnection），也可以是jar或zip文件中的目录（JarURLConnection）。根据连接的类型，我们将调用两种不同的方法。
首先让我们看看如果它是FileURLConnection。
它首先检查传递的文件是否存在并且是目录。如果是这样，它将检查它是否是一个类文件。如果是这样，Class将创建一个对象并将其放在中ArrayList。如果它不是类文件而是目录，我们只需对其进行迭代并执行相同的操作。其他所有案例/文件将被忽略。
如果URLConnection是JarURLConnection，则将调用另一个私有帮助器方法。此方法遍历zip / jar存档中的所有条目。如果一个条目是类文件，并且在包的内部，Class则将创建一个对象并将其存储在中ArrayList。
解析完所有资源后，它（main方法）将返回当前ArrayList包含的所有给定包中的类ClassLoader。
如果该过程在任何时候失败，ClassNotFoundException将抛出一个包含确切原因的详细信息。