我正在尝试创建一个Java工具，可以扫描Java应用程序的结构并提供一些有意义的信息。为此，我需要能够从项目位置（JAR / WAR或仅文件夹）扫描所有.class文件，并使用反射读取有关其方法的信息。但这似乎是不可能的。
我可以找到很多基于URLClassloader的解决方案，可以允许我从目录/归档中加载特定的类，但没有一个可以在没有任何有关类名或包结构的情况下加载类。
编辑： 我认为我表达得不好。我的问题不是我无法获取所有的class文件，我可以通过递归等方式做到并正确定位它们。我的问题是获得每个class文件的Class对象。
JarFile jarFile = new JarFile(pathToJar);
Enumeration<JarEntry> e = jarFile.entries();
URL[] urls = { new URL("jar:file:" + pathToJar+"!/") };
URLClassLoader cl = URLClassLoader.newInstance(urls);
while (e.hasMoreElements()) {
JarEntry je = e.nextElement();
if(je.isDirectory() || !je.getName().endsWith(".class")){
continue;
}
// -6 because of .class
String className = je.getName().substring(0,je.getName().length()-6);
className = className.replace('/', '.');
Class c = cl.loadClass(className);
}
编辑：
如上评论所建议的，Javassist也是一种可能性。在上面代码的while循环之前的某个地方初始化一个ClassPool，然后不要使用类加载器加载类，而是可以创建一个CtClass对象：
ClassPool cp = ClassPool.getDefault();
...
CtClass ctClass = cp.get(className);
new URL("jar:file:" + pathToJar+"!/") 导致了 ClassNotFoundException。对我有效的是：URL[] urls = { new URL("jar:" + pathToJar+"!/") }; 不确定为什么？希望能帮助其他人。 - taylorcressy列出jar文件中的所有类。
public static List getClasseNames(String jarName) {
ArrayList classes = new ArrayList();
if (debug)
System.out.println("Jar " + jarName );
try {
JarInputStream jarFile = new JarInputStream(new FileInputStream(
jarName));
JarEntry jarEntry;
while (true) {
jarEntry = jarFile.getNextJarEntry();
if (jarEntry == null) {
break;
}
if (jarEntry.getName().endsWith(".class")) {
if (debug)
System.out.println("Found "
+ jarEntry.getName().replaceAll("/", "\\."));
classes.add(jarEntry.getName().replaceAll("/", "\\."));
}
}
} catch (Exception e) {
e.printStackTrace();
}
return classes;
}
问题的一部分是找到特定包中的类，应用程序可能从jar文件或包/文件夹结构中加载。在某个包中有越来越多的服务类，它们实现了一个共同的接口，并希望在运行时检测到它们。
// Retrieve classes of a package and it's nested package from file based class repository
package esc;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;
public class GetClasses
{
private static boolean debug = false;
/**
* test function with assumed package esc.util
*/
public static void main(String... args)
{
try
{
final Class<?>[] list = getClasses("esc.util");
for (final Class<?> c : list)
{
System.out.println(c.getName());
}
}
catch (final IOException e)
{
e.printStackTrace();
}
}
/**
* Scans all classes accessible from the context class loader which belong to the given package and subpackages.
*
* @precondition Thread Class loader attracts class and jar files, exclusively
* @precondition Classes with static code sections are executed, when loaded and thus must not throw exceptions
*
* @param packageName
* [in] The base package path, dot-separated
*
* @return The classes of package /packageName/ and nested packages
*
* @throws IOException,
* ClassNotFoundException not applicable
*
* @author Sam Ginrich, http://www.java2s.com/example/java/reflection/recursive-method-used-to-find-all-classes-in-a-given-directory-and-sub.html
*
*/
public static Class<?>[] getClasses(String packageName) throws IOException
{
final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
assert classLoader != null;
if (debug)
{
System.out.println("Class Loader class is " + classLoader.getClass().getName());
}
final String packagePath = packageName.replace('.', '/');
final Enumeration<URL> resources = classLoader.getResources(packagePath);
final List<Class<?>> classes = new ArrayList<Class<?>>();
while (resources.hasMoreElements())
{
final URL resource = resources.nextElement();
final String proto = resource.getProtocol();
if ("file".equals(proto))
{
classes.addAll(findFileClasses(new File(resource.getFile()), packageName));
}
else if ("jar".equals(proto))
{
classes.addAll(findJarClasses(resource));
}
else
{
System.err.println("Protocol " + proto + " not supported");
continue;
}
}
return classes.toArray(new Class[classes.size()]);
}
/**
* Linear search for classes of a package from a jar file
*
* @param packageResource
* [in] Jar URL of the base package, i.e. file URL bested in jar URL
*
* @return The classes of package /packageResource/ and nested packages
*
* @throws -
*
* @author amicngh, Sam Ginrich@stackoverflow.com
*/
private static List<Class<?>> findJarClasses(URL packageResource)
{
final List<Class<?>> classes = new ArrayList<Class<?>>();
try
{
System.out.println("Jar URL Path is " + packageResource.getPath());
final URL fileUrl = new URL(packageResource.getPath());
final String proto = fileUrl.getProtocol();
if ("file".equals(proto))
{
final String filePath = fileUrl.getPath().substring(1); // skip leading /
final int jarTagPos = filePath.indexOf(".jar!/");
if (jarTagPos < 0)
{
System.err.println("Non-conformant jar file reference " + filePath + " !");
}
else
{
final String packagePath = filePath.substring(jarTagPos + 6);
final String jarFilename = filePath.substring(0, jarTagPos + 4);
if (debug)
{
System.out.println("Package " + packagePath);
System.out.println("Jar file " + jarFilename);
}
final String packagePrefix = packagePath + '/';
try
{
final JarInputStream jarFile = new JarInputStream(
new FileInputStream(jarFilename));
JarEntry jarEntry;
while (true)
{
jarEntry = jarFile.getNextJarEntry();
if (jarEntry == null)
{
break;
}
final String classPath = jarEntry.getName();
if (classPath.startsWith(packagePrefix) && classPath.endsWith(".class"))
{
final String className = classPath
.substring(0, classPath.length() - 6).replace('/', '.');
if (debug)
{
System.out.println("Found entry " + jarEntry.getName());
}
try
{
classes.add(Class.forName(className));
}
catch (final ClassNotFoundException x)
{
System.err.println("Cannot load class " + className);
}
}
}
jarFile.close();
}
catch (final Exception e)
{
e.printStackTrace();
}
}
}
else
{
System.err.println("Nested protocol " + proto + " not supprted!");
}
}
catch (final MalformedURLException e)
{
e.printStackTrace();
}
return classes;
}
/**
* Recursive method used to find all classes in a given directory and subdirs.
*
* @param directory
* The base directory
* @param packageName
* The package name for classes found inside the base directory
* @return The classes
* @author http://www.java2s.com/example/java/reflection/recursive-method-used-to-find-all-classes-in-a-given-directory-and-sub.html
* @throws -
*
*/
private static List<Class<?>> findFileClasses(File directory, String packageName)
{
final List<Class<?>> classes = new ArrayList<Class<?>>();
if (!directory.exists())
{
System.err.println("Directory " + directory.getAbsolutePath() + " does not exist.");
return classes;
}
final File[] files = directory.listFiles();
if (debug)
{
System.out.println("Directory "
+ directory.getAbsolutePath()
+ " has "
+ files.length
+ " elements.");
}
for (final File file : files)
{
if (file.isDirectory())
{
assert !file.getName().contains(".");
classes.addAll(findFileClasses(file, packageName + "." + file.getName()));
}
else if (file.getName().endsWith(".class"))
{
final String className = packageName
+ '.'
+ file.getName().substring(0, file.getName().length() - 6);
try
{
classes.add(Class.forName(className));
}
catch (final ClassNotFoundException cnf)
{
System.err.println("Cannot load class " + className);
}
}
}
return classes;
}
}