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
一般来说，类装入器不允许扫描类路径上的所有类。但通常唯一使用的类加载器是UrlClassLoader，我们可以从中检索目录和jar文件的列表(参见getURLs)，并逐个打开它们以列出可用的类。这种方法称为类路径扫描，在Scannotation和Reflections中实现。
Reflections reflections = new Reflections("my.package");
Set<Class<? extends Object>> classes = reflections.getSubTypesOf(Object.class);
另一种方法是使用Java可插入注释处理API编写注释处理器，该处理器将在编译时收集所有注释类，并构建索引文件供运行时使用。此机制在ClassIndex库中实现:
// package-info.java
@IndexSubclasses
package my.package;
// your code
Iterable<Class> classes = ClassIndex.getPackageClasses("my.package");
注意，由于Java编译器自动发现类路径上的任何处理器，因此扫描是完全自动化的，因此不需要额外的设置。
其他回答
基于@Staale的回答，为了不依赖第三方库，我将通过检查第一个包的物理位置来实现文件系统方法:
import java.io.File;
import java.io.FileFilter;
import java.util.ArrayList;
...
Class<?>[] foundClasses = new Class<?>[0];
final ArrayList<Class<?>> foundClassesDyn = new ArrayList<Class<?>>();
new java.io.File(
klass.getResource(
"/" + curPackage.replace( "." , "/")
).getFile()
).listFiles(
new java.io.FileFilter() {
public boolean accept(java.io.File file) {
final String classExtension = ".class";
if ( file.isFile()
&& file.getName().endsWith(classExtension)
// avoid inner classes
&& ! file.getName().contains("$") )
{
try {
String className = file.getName();
className = className.substring(0, className.length() - classExtension.length());
foundClassesDyn.add( Class.forName( curPackage + "." + className ) );
} catch (ClassNotFoundException e) {
e.printStackTrace(System.out);
}
}
return false;
}
}
);
foundClasses = foundClassesDyn.toArray(foundClasses);
那么这个呢:
public static List<Class<?>> getClassesForPackage(final String pkgName) throws IOException, URISyntaxException {
final String pkgPath = pkgName.replace('.', '/');
final URI pkg = Objects.requireNonNull(ClassLoader.getSystemClassLoader().getResource(pkgPath)).toURI();
final ArrayList<Class<?>> allClasses = new ArrayList<Class<?>>();
Path root;
if (pkg.toString().startsWith("jar:")) {
try {
root = FileSystems.getFileSystem(pkg).getPath(pkgPath);
} catch (final FileSystemNotFoundException e) {
root = FileSystems.newFileSystem(pkg, Collections.emptyMap()).getPath(pkgPath);
}
} else {
root = Paths.get(pkg);
}
final String extension = ".class";
try (final Stream<Path> allPaths = Files.walk(root)) {
allPaths.filter(Files::isRegularFile).forEach(file -> {
try {
final String path = file.toString().replace('/', '.');
final String name = path.substring(path.indexOf(pkgName), path.length() - extension.length());
allClasses.add(Class.forName(name));
} catch (final ClassNotFoundException | StringIndexOutOfBoundsException ignored) {
}
});
}
return allClasses;
}
然后你可以重载这个函数:
public static List<Class<?>> getClassesForPackage(final Package pkg) throws IOException, URISyntaxException {
return getClassesForPackage(pkg.getName());
}
如果你需要测试:
public static void main(final String[] argv) throws IOException, URISyntaxException {
for (final Class<?> cls : getClassesForPackage("my.package")) {
System.out.println(cls);
}
for (final Class<?> cls : getClassesForPackage(MyClass.class.getPackage())) {
System.out.println(cls);
}
}
如果你的IDE没有导入helper:
import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.file.FileSystemNotFoundException;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.stream.Stream;
工作原理:
从您的IDE JAR文件 没有外部依赖
我整理了一个简单的github项目来解决这个问题:
https://github.com/ddopson/java-class-enumerator
它既适用于基于文件的类路径，也适用于jar文件。
如果你在签出项目后运行'make'，它将打印出以下内容:
Cleaning...
rm -rf build/
Building...
javac -d build/classes src/pro/ddopson/ClassEnumerator.java src/test/ClassIShouldFindOne.java src/test/ClassIShouldFindTwo.java src/test/subpkg/ClassIShouldFindThree.java src/test/TestClassEnumeration.java
Making JAR Files...
jar cf build/ClassEnumerator_test.jar -C build/classes/ .
jar cf build/ClassEnumerator.jar -C build/classes/ pro
Running Filesystem Classpath Test...
java -classpath build/classes test.TestClassEnumeration
ClassDiscovery: Package: 'test' becomes Resource: 'file:/Users/Dopson/work/other/java-class-enumeration/build/classes/test'
ClassDiscovery: Reading Directory '/Users/Dopson/work/other/java-class-enumeration/build/classes/test'
ClassDiscovery: FileName 'ClassIShouldFindOne.class' => class 'test.ClassIShouldFindOne'
ClassDiscovery: FileName 'ClassIShouldFindTwo.class' => class 'test.ClassIShouldFindTwo'
ClassDiscovery: FileName 'subpkg' => class 'null'
ClassDiscovery: Reading Directory '/Users/Dopson/work/other/java-class-enumeration/build/classes/test/subpkg'
ClassDiscovery: FileName 'ClassIShouldFindThree.class' => class 'test.subpkg.ClassIShouldFindThree'
ClassDiscovery: FileName 'TestClassEnumeration.class' => class 'test.TestClassEnumeration'
Running JAR Classpath Test...
java -classpath build/ClassEnumerator_test.jar test.TestClassEnumeration
ClassDiscovery: Package: 'test' becomes Resource: 'jar:file:/Users/Dopson/work/other/java-class-enumeration/build/ClassEnumerator_test.jar!/test'
ClassDiscovery: Reading JAR file: '/Users/Dopson/work/other/java-class-enumeration/build/ClassEnumerator_test.jar'
ClassDiscovery: JarEntry 'META-INF/' => class 'null'
ClassDiscovery: JarEntry 'META-INF/MANIFEST.MF' => class 'null'
ClassDiscovery: JarEntry 'pro/' => class 'null'
ClassDiscovery: JarEntry 'pro/ddopson/' => class 'null'
ClassDiscovery: JarEntry 'pro/ddopson/ClassEnumerator.class' => class 'null'
ClassDiscovery: JarEntry 'test/' => class 'null'
ClassDiscovery: JarEntry 'test/ClassIShouldFindOne.class' => class 'test.ClassIShouldFindOne'
ClassDiscovery: JarEntry 'test/ClassIShouldFindTwo.class' => class 'test.ClassIShouldFindTwo'
ClassDiscovery: JarEntry 'test/subpkg/' => class 'null'
ClassDiscovery: JarEntry 'test/subpkg/ClassIShouldFindThree.class' => class 'test.subpkg.ClassIShouldFindThree'
ClassDiscovery: JarEntry 'test/TestClassEnumeration.class' => class 'test.TestClassEnumeration'
Tests Passed.
另见我的另一个答案
一般来说，类装入器不允许扫描类路径上的所有类。但通常唯一使用的类加载器是UrlClassLoader，我们可以从中检索目录和jar文件的列表(参见getURLs)，并逐个打开它们以列出可用的类。这种方法称为类路径扫描，在Scannotation和Reflections中实现。
Reflections reflections = new Reflections("my.package");
Set<Class<? extends Object>> classes = reflections.getSubTypesOf(Object.class);
另一种方法是使用Java可插入注释处理API编写注释处理器，该处理器将在编译时收集所有注释类，并构建索引文件供运行时使用。此机制在ClassIndex库中实现:
// package-info.java
@IndexSubclasses
package my.package;
// your code
Iterable<Class> classes = ClassIndex.getPackageClasses("my.package");
注意，由于Java编译器自动发现类路径上的任何处理器，因此扫描是完全自动化的，因此不需要额外的设置。
我刚写了一个util类，里面包含了测试方法，大家可以检查一下~
IteratePackageUtil.java:
package eric.j2se.reflect;
import java.util.Set;
import org.reflections.Reflections;
import org.reflections.scanners.ResourcesScanner;
import org.reflections.scanners.SubTypesScanner;
import org.reflections.util.ClasspathHelper;
import org.reflections.util.ConfigurationBuilder;
import org.reflections.util.FilterBuilder;
/**
* an util to iterate class in a package,
*
* @author eric
* @date Dec 10, 2013 12:36:46 AM
*/
public class IteratePackageUtil {
/**
* <p>
* Get set of all class in a specified package recursively. this only support lib
* </p>
* <p>
* class of sub package will be included, inner class will be included,
* </p>
* <p>
* could load class that use the same classloader of current class, can't load system packages,
* </p>
*
* @param pkg
* path of a package
* @return
*/
public static Set<Class<? extends Object>> getClazzSet(String pkg) {
// prepare reflection, include direct subclass of Object.class
Reflections reflections = new Reflections(new ConfigurationBuilder().setScanners(new SubTypesScanner(false), new ResourcesScanner())
.setUrls(ClasspathHelper.forClassLoader(ClasspathHelper.classLoaders(new ClassLoader[0])))
.filterInputsBy(new FilterBuilder().includePackage(pkg)));
return reflections.getSubTypesOf(Object.class);
}
public static void test() {
String pkg = "org.apache.tomcat.util";
Set<Class<? extends Object>> clazzSet = getClazzSet(pkg);
for (Class<? extends Object> clazz : clazzSet) {
System.out.println(clazz.getName());
}
}
public static void main(String[] args) {
test();
}
}
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