是否有可能找到给定包中的所有类或接口?(快速看了一下e.g. Package，似乎没有。)
当前回答
由于类装入器的动态特性，这是不可能的。类装入器不需要告诉VM它可以提供哪些类，相反，它们只是提交类请求，并且必须返回类或抛出异常。
但是，如果您编写自己的类装入器，或者检查类路径和它的jar，就有可能找到这些信息。不过，这将通过文件系统操作，而不是反射。甚至可能有一些库可以帮助你做到这一点。
如果有远程生成或交付的类，您将无法发现这些类。
通常的方法是在某个文件中注册需要访问的类，或者在不同的类中引用它们。或者在命名时使用惯例。
附录:反射库将允许您在当前类路径中查找类。它可以用来获取包中的所有类:
Reflections reflections = new Reflections("my.project.prefix");
Set<Class<? extends Object>> allClasses =
reflections.getSubTypesOf(Object.class);
其他回答
如果你在Spring-land，你可以使用PathMatchingResourcePatternResolver;
PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
Resource[] resources = resolver.getResources("classpath*:some/package/name/*.class");
Arrays.asList(resources).forEach(r->{
...
});
几乎所有的答案要么使用reflection，要么从文件系统读取类文件。如果尝试从文件系统读取类，则在将应用程序打包为JAR或其他格式时可能会出错。此外，您可能不想为此目的使用单独的库。
这里有另一种方法，它是纯java，不依赖于文件系统。
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;
import javax.tools.ToolProvider;
import java.io.File;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;
public class PackageUtil {
public static Collection<Class> getClasses(final String pack) throws Exception {
final StandardJavaFileManager fileManager = ToolProvider.getSystemJavaCompiler().getStandardFileManager(null, null, null);
return StreamSupport.stream(fileManager.list(StandardLocation.CLASS_PATH, pack, Collections.singleton(JavaFileObject.Kind.CLASS), false).spliterator(), false)
.map(javaFileObject -> {
try {
final String[] split = javaFileObject.getName()
.replace(".class", "")
.replace(")", "")
.split(Pattern.quote(File.separator));
final String fullClassName = pack + "." + split[split.length - 1];
return Class.forName(fullClassName);
} catch (ClassNotFoundException e) {
throw new RuntimeException(e);
}
})
.collect(Collectors.toCollection(ArrayList::new));
}
}
Java 8不是必须的。你可以使用for循环代替流。 你可以这样测试
public static void main(String[] args) throws Exception {
final String pack = "java.nio.file"; // Or any other package
PackageUtil.getClasses(pack).stream().forEach(System.out::println);
}
在包测试中定义要扫描的类
package test;
public class A {
private class B {}
enum C {}
record D() {}
}
对于org.reflections:reflections:0.10.2，它为我工作如下:
使用反射库扫描包测试中的类
@Test
void t() {
final String packagePath = "test";
final Reflections reflections =
new Reflections(packagePath, Scanners.SubTypes.filterResultsBy(v -> true));
reflections.getAll(Scanners.SubTypes).forEach(System.out::println);
}
输出
java.lang.constant.Constable
java.lang.Enum
java.lang.Comparable
java.lang.Record
java.lang.Object
java.io.Serializable
test.A$C
test.A$D
test.A$B
test.A
对于io.github.classgraph:classgraph:4.8.146，它为我工作如下:
@Test
void t() {
final String packagePath = "test";
try (ScanResult scanResult = new ClassGraph()
.enableClassInfo()
.ignoreClassVisibility()
.acceptPackages(packagePath)
.scan()) {
scanResult.getAllClasses()
.forEach(v -> {
System.out.println(v.getName());
});
}
}
输出
test.A
test.A$B
test.A$C
test.A$D
由于类装入器的动态特性，这是不可能的。类装入器不需要告诉VM它可以提供哪些类，相反，它们只是提交类请求，并且必须返回类或抛出异常。
但是，如果您编写自己的类装入器，或者检查类路径和它的jar，就有可能找到这些信息。不过，这将通过文件系统操作，而不是反射。甚至可能有一些库可以帮助你做到这一点。
如果有远程生成或交付的类，您将无法发现这些类。
通常的方法是在某个文件中注册需要访问的类，或者在不同的类中引用它们。或者在命名时使用惯例。
附录:反射库将允许您在当前类路径中查找类。它可以用来获取包中的所有类:
Reflections reflections = new Reflections("my.project.prefix");
Set<Class<? extends Object>> allClasses =
reflections.getSubTypesOf(Object.class);
这将扫描类加载器和所有父加载器，以查找jar文件和目录。 jar文件和由jar的类路径引用的目录也会被加载。
this code is testet with Java 8,11,18. on 8 everything works perfectly using the URLClassLoader and the getURLs() method. on 11 it works fine using reflections, but the JVM prints a warning on the stderr stream (not redirectible with System.setErr() with my JVM) on 18 the reflections are useless (throws NoSuchMethod/Field), and the only thing (where I know that it works) is to use the getResource() method. When the class loader loades the resources of the given package from the file system a simple path url is returned. When the class loader loades the resources from a jar a url like 'jar:file:[jar-path]!/[in-jar-path]' is returned.
我使用了答案https://stackoverflow.com/a/1157352/18252455(来自一个重复的问题)，并添加了读取类路径和搜索目录url的功能。
/**
* orig description:<br>
* Scans all classloaders for the current thread for loaded jars, and then scans
* each jar for the package name in question, listing all classes directly under
* the package name in question. Assumes directory structure in jar file and class
* package naming follow java conventions (i.e. com.example.test.MyTest would be in
* /com/example/test/MyTest.class)
* <p>
* in addition this method also scans for directories, where also is assumed, that the classes are
* placed followed by the java conventions. (i.e. <code>com.example.test.MyTest</code> would be in
* <code>directory/com/example/test/MyTest.class</code>)
* <p>
* this method also reads the jars Class-Path for other jars and directories. for the jars and
* directories referred in the jars are scanned with the same rules as defined here.<br>
* it is ensured that no jar/directory is scanned exactly one time.
* <p>
* if {@code bailError} is <code>true</code> all errors will be wrapped in a
* {@link RuntimeException}
* and then thrown.<br>
* a {@link RuntimeException} will also be thrown if something unexpected happens.<br>
*
* @param packageName
* the name of the package for which the classes should be searched
* @param allowSubPackages
* <code>true</code> is also classes in sub packages should be found
* @param loader
* the {@link ClassLoader} which should be used to find the URLs and to load classes
* @param bailError
* if all {@link Exception} should be re-thrown wrapped in {@link RuntimeException} and
* if a {@link RuntimeException} should be thrown, when something is not as expected.
* @see https://stackoverflow.com/questions/1156552/java-package-introspection
* @see https://stackoverflow.com/a/1157352/18252455
* @see https://creativecommons.org/licenses/by-sa/2.5/
* @see https://creativecommons.org/licenses/by-sa/2.5/legalcode
*/
public static Set <Class <?>> tryGetClassesForPackage(String packageName, boolean allowSubPackages, ClassLoader loader, boolean bailError) {
Set <URL> jarUrls = new HashSet <URL>();
Set <Path> directorys = new HashSet <Path>();
findClassPools(loader, jarUrls, directorys, bailError, packageName);
Set <Class <?>> jarClasses = findJarClasses(allowSubPackages, packageName, jarUrls, directorys, loader, bailError);
Set <Class <?>> dirClasses = findDirClasses(allowSubPackages, packageName, directorys, loader, bailError);
jarClasses.addAll(dirClasses);
return jarClasses;
}
private static Set <Class <?>> findDirClasses(boolean subPackages, String packageName, Set <Path> directorys, ClassLoader loader, boolean bailError) {
Filter <Path> filter;
Set <Class <?>> result = new HashSet <>();
for (Path startPath : directorys) {
String packagePath = packageName.replace(".", startPath.getFileSystem().getSeparator());
final Path searchPath = startPath.resolve(packagePath).toAbsolutePath();
if (subPackages) {
filter = p -> {
p = p.toAbsolutePath();
Path other;
if (p.getNameCount() >= searchPath.getNameCount()) {
other = searchPath;
} else {
other = searchPath.subpath(0, p.getNameCount());
}
if (p.startsWith(other)) {
return true;
} else {
return false;
}
};
} else {
filter = p -> {
p = p.toAbsolutePath();
if (p.getNameCount() > searchPath.getNameCount() + 1) {
return false;
} else if (p.toAbsolutePath().startsWith(searchPath)) {
return true;
} else {
return false;
}
};
}
if (Files.exists(searchPath)) {
findDirClassFilesRecursive(filter, searchPath, startPath, result, loader, bailError);
} // the package does not have to exist in every directory
}
return result;
}
private static void findDirClassFilesRecursive(Filter <Path> filter, Path path, Path start, Set <Class <?>> classes, ClassLoader loader, boolean bailError) {
try (DirectoryStream <Path> dirStream = Files.newDirectoryStream(path, filter)) {
for (Path p : dirStream) {
if (Files.isDirectory(p)) {
findDirClassFilesRecursive(filter, p, start, classes, loader, bailError);
} else {
Path subp = p.subpath(start.getNameCount(), p.getNameCount());
String str = subp.toString();
if (str.endsWith(".class")) {
str = str.substring(0, str.length() - 6);
String sep = p.getFileSystem().getSeparator();
if (str.startsWith(sep)) {
str = str.substring(sep.length());
}
if (str.endsWith(sep)) {
str = str.substring(0, str.length() - sep.length());
}
String fullClassName = str.replace(sep, ".");
try {
Class <?> cls = Class.forName(fullClassName, false, loader);
classes.add(cls);
} catch (ClassNotFoundException e) {
if (bailError) {
throw new RuntimeException(e);
}
}
}
}
}
} catch (IOException e) {
if (bailError) {
throw new RuntimeException(e);
}
}
}
private static Set <Class <?>> findJarClasses(boolean subPackages, String packageName, Set <URL> nextJarUrls, Set <Path> directories, ClassLoader loader, boolean bailError) {
String packagePath = packageName.replace('.', '/');
Set <Class <?>> result = new HashSet <>();
Set <URL> allJarUrls = new HashSet <>();
while (true) {
Set <URL> thisJarUrls = new HashSet <>(nextJarUrls);
thisJarUrls.removeAll(allJarUrls);
if (thisJarUrls.isEmpty()) {
break;
}
allJarUrls.addAll(thisJarUrls);
for (URL url : thisJarUrls) {
try (JarInputStream stream = new JarInputStream(url.openStream())) {
// may want better way to open url connections
readJarClassPath(stream, nextJarUrls, directories, bailError);
JarEntry entry = stream.getNextJarEntry();
while (entry != null) {
String name = entry.getName();
int i = name.lastIndexOf("/");
if (i > 0 && name.endsWith(".class")) {
try {
if (subPackages) {
if (name.substring(0, i).startsWith(packagePath)) {
Class <?> cls = Class.forName(name.substring(0, name.length() - 6).replace("/", "."), false, loader);
result.add(cls);
}
} else {
if (name.substring(0, i).equals(packagePath)) {
Class <?> cls = Class.forName(name.substring(0, name.length() - 6).replace("/", "."), false, loader);
result.add(cls);
}
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
entry = stream.getNextJarEntry();
}
stream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return result;
}
private static void readJarClassPath(JarInputStream stream, Set <URL> jarUrls, Set <Path> directories, boolean bailError) {
Object classPathObj = stream.getManifest().getMainAttributes().get(new Name("Class-Path"));
if (classPathObj == null) {
return;
}
if (classPathObj instanceof String) {
String[] entries = ((String) classPathObj).split("\\s+");// should also work with a single space (" ")
for (String entry : entries) {
try {
URL url = new URL(entry);
addFromUrl(jarUrls, directories, url, bailError);
} catch (MalformedURLException e) {
e.printStackTrace();
}
}
} else if (bailError) {
throw new RuntimeException("the Class-Path attribute is no String: " + classPathObj.getClass().getName() + " tos='" + classPathObj + "'");
}
}
private static void findClassPools(ClassLoader classLoader, Set <URL> jarUrls, Set <Path> directoryPaths, boolean bailError, String packageName) {
packageName = packageName.replace('.', '/');
while (classLoader != null) {
if (classLoader instanceof URLClassLoader) {
for (URL url : ((URLClassLoader) classLoader).getURLs()) {
addFromUrl(jarUrls, directoryPaths, url, bailError);
System.out.println("rurl-class-loade.url[n]r->'" + url + "'");
}
} else {
URL res = classLoader.getResource("");
if (res != null) {
addFromUrl(jarUrls, directoryPaths, res, bailError);
}
res = classLoader.getResource("/");
if (res != null) {
addFromUrl(jarUrls, directoryPaths, res, bailError);
}
res = classLoader.getResource("/" + packageName);
if (res != null) {
res = removePackageFromUrl(res, packageName, bailError);
if (res != null) {
addFromUrl(jarUrls, directoryPaths, res, bailError);
}
}
res = classLoader.getResource(packageName);
if (res != null) {
res = removePackageFromUrl(res, packageName, bailError);
if (res != null) {
addFromUrl(jarUrls, directoryPaths, res, bailError);
}
}
addFromUnknownClass(classLoader, jarUrls, directoryPaths, bailError, 8);
}
classLoader = classLoader.getParent();
}
}
private static URL removePackageFromUrl(URL res, String packagePath, boolean bailError) {
packagePath = "/" + packagePath;
String urlStr = res.toString();
if ( !urlStr.endsWith(packagePath)) {
if (bailError) {
throw new RuntimeException("the url string does not end with the packagepath! packagePath='" + packagePath + "' urlStr='" + urlStr + "'");
} else {
return null;
}
}
urlStr = urlStr.substring(0, urlStr.length() - packagePath.length());
if (urlStr.endsWith("!")) {
urlStr = urlStr.substring(0, urlStr.length() - 1);
}
if (urlStr.startsWith("jar:")) {
urlStr = urlStr.substring(4);
}
try {
return new URL(urlStr);
} catch (MalformedURLException e) {
if (bailError) {
throw new RuntimeException(e);
} else {
return null;
}
}
}
private static void addFromUnknownClass(Object instance, Set <URL> jarUrls, Set <Path> directoryPaths, boolean bailError, int maxDeep) {
Class <?> cls = instance.getClass();
while (cls != null) {
Field[] fields = cls.getDeclaredFields();
for (Field field : fields) {
Class <?> type = field.getType();
Object value;
try {
value = getValue(instance, field);
if (value != null) {
addFromUnknownValue(value, jarUrls, directoryPaths, bailError, type, field.getName(), maxDeep - 1);
}
} catch (IllegalArgumentException | IllegalAccessException | SecurityException e) {
if (bailError) {
final String version = System.getProperty("java.version");
String vers = version;
if (vers.startsWith("1.")) {
vers = vers.substring(2);
}
int dotindex = vers.indexOf('.');
if (dotindex != -1) {
vers = vers.substring(0, dotindex);
}
int versNum;
try {
versNum = Integer.parseInt(vers);
} catch (NumberFormatException e1) {
throw new RuntimeException("illegal version: '" + version + "' lastError: " + e.getMessage(), e);
}
if (versNum <= 11) {
throw new RuntimeException(e);
}
}
}
}
cls = cls.getSuperclass();
}
}
private static Object getValue(Object instance, Field field) throws IllegalArgumentException, IllegalAccessException, SecurityException {
try {
boolean flag = field.isAccessible();
boolean newflag = flag;
try {
field.setAccessible(true);
newflag = true;
} catch (Exception e) {}
try {
return field.get(instance);
} finally {
if (flag != newflag) {
field.setAccessible(flag);
}
}
} catch (IllegalArgumentException | IllegalAccessException | SecurityException e) {
try {
Field override = AccessibleObject.class.getDeclaredField("override");
boolean flag = override.isAccessible();
boolean newFlag = flag;
try {
override.setAccessible(true);
flag = true;
} catch (Exception s) {}
override.setBoolean(field, true);
if (flag != newFlag) {
override.setAccessible(flag);
}
return field.get(instance);
} catch (IllegalArgumentException | IllegalAccessException | NoSuchFieldException | SecurityException e1) {
e.addSuppressed(e1);
throw e;
}
}
}
private static void addFromUnknownValue(Object value, Set <URL> jarUrls, Set <Path> directoryPaths, boolean bailError, Class <?> type, String fieldName, int maxDeep) {
if (Collection.class.isAssignableFrom(type)) {
for (Object obj : (Collection <?>) value) {
URL url = null;
try {
if (obj instanceof URL) {
url = (URL) obj;
} else if (obj instanceof Path) {
url = ((Path) obj).toUri().toURL();
} else if (obj instanceof File) {
url = ((File) obj).toURI().toURL();
}
} catch (MalformedURLException e) {
if (bailError) {
throw new RuntimeException(e);
}
}
if (url != null) {
addFromUrl(jarUrls, directoryPaths, url, bailError);
}
}
} else if (URL[].class.isAssignableFrom(type)) {
for (URL url : (URL[]) value) {
addFromUrl(jarUrls, directoryPaths, url, bailError);
}
} else if (Path[].class.isAssignableFrom(type)) {
for (Path path : (Path[]) value) {
try {
addFromUrl(jarUrls, directoryPaths, path.toUri().toURL(), bailError);
} catch (MalformedURLException e) {
if (bailError) {
throw new RuntimeException(e);
}
}
}
} else if (File[].class.isAssignableFrom(type)) {
for (File file : (File[]) value) {
try {
addFromUrl(jarUrls, directoryPaths, file.toURI().toURL(), bailError);
} catch (MalformedURLException e) {
if (bailError) {
throw new RuntimeException(e);
}
}
}
} else if (maxDeep > 0) {
addFromUnknownClass(value, jarUrls, directoryPaths, bailError, maxDeep - 1);
}
}
private static void addFromUrl(Set <URL> jarUrls, Set <Path> directoryPaths, URL url, boolean bailError) {
if (url.getFile().endsWith(".jar") || url.getFile().endsWith(".zip")) {
// may want better way to detect jar files
jarUrls.add(url);
} else {
try {
Path path = Paths.get(url.toURI());
if (Files.isDirectory(path)) {
directoryPaths.add(path);
} else if (bailError) {
throw new RuntimeException("unknown url for class loading: " + url);
}
} catch (URISyntaxException e) {
if (bailError) {
throw new RuntimeException(e);
}
}
}
}
进口:
import java.io.File;
import java.io.IOException;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.net.MalformedURLException;
import java.net.URISyntaxException;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.DirectoryStream;
import java.nio.file.DirectoryStream.Filter;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.Attributes.Name;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;
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