FindAllClassesUsingPlainJavaReflectionTest.java

@Slf4j
class FindAllClassesUsingPlainJavaReflectionTest {

  private static final Function<Throwable, RuntimeException> asRuntimeException = throwable -> {
    log.error(throwable.getLocalizedMessage());
    return new RuntimeException(throwable);
  };

  private static final Function<String, Collection<Class<?>>> findAllPackageClasses = basePackageName -> {

    Locale locale = Locale.getDefault();
    Charset charset = StandardCharsets.UTF_8;
    val fileManager = ToolProvider.getSystemJavaCompiler()
                                  .getStandardFileManager(/* diagnosticListener */ null, locale, charset);

    StandardLocation location = StandardLocation.CLASS_PATH;
    JavaFileObject.Kind kind = JavaFileObject.Kind.CLASS;
    Set<JavaFileObject.Kind> kinds = Collections.singleton(kind);
    val javaFileObjects = Try.of(() -> fileManager.list(location, basePackageName, kinds, /* recurse */ true))
                             .getOrElseThrow(asRuntimeException);

    String pathToPackageAndClass = basePackageName.replace(".", File.separator);
    Function<String, String> mapToClassName = s -> {
      String prefix = Arrays.stream(s.split(pathToPackageAndClass))
                            .findFirst()
                            .orElse("");
      return s.replaceFirst(prefix, "")
              .replaceAll(File.separator, ".");
    };

    return StreamSupport.stream(javaFileObjects.spliterator(), /* parallel */ true)
                        .filter(javaFileObject -> javaFileObject.getKind().equals(kind))
                        .map(FileObject::getName)
                        .map(fileObjectName -> fileObjectName.replace(".class", ""))
                        .map(mapToClassName)
                        .map(className -> Try.of(() -> Class.forName(className))
                                             .getOrElseThrow(asRuntimeException))
                        .collect(Collectors.toList());
  };

  @Test
  @DisplayName("should get classes recursively in given package")
  void test() {
    Collection<Class<?>> classes = findAllPackageClasses.apply(getClass().getPackage().getName());
    assertThat(classes).hasSizeGreaterThan(4);
    classes.stream().map(String::valueOf).forEach(log::info);
  }
}

PS:为了简化处理错误的样板文件等，我在这里使用了vavr和lombok库

其他实现可以在我的GitHub daggerok/java-reflection-find- annotation -classes-or-methods repo中找到

FindAllClassesUsingPlainJavaReflectionTest.java

@Slf4j
class FindAllClassesUsingPlainJavaReflectionTest {

  private static final Function<Throwable, RuntimeException> asRuntimeException = throwable -> {
    log.error(throwable.getLocalizedMessage());
    return new RuntimeException(throwable);
  };

  private static final Function<String, Collection<Class<?>>> findAllPackageClasses = basePackageName -> {

    Locale locale = Locale.getDefault();
    Charset charset = StandardCharsets.UTF_8;
    val fileManager = ToolProvider.getSystemJavaCompiler()
                                  .getStandardFileManager(/* diagnosticListener */ null, locale, charset);

    StandardLocation location = StandardLocation.CLASS_PATH;
    JavaFileObject.Kind kind = JavaFileObject.Kind.CLASS;
    Set<JavaFileObject.Kind> kinds = Collections.singleton(kind);
    val javaFileObjects = Try.of(() -> fileManager.list(location, basePackageName, kinds, /* recurse */ true))
                             .getOrElseThrow(asRuntimeException);

    String pathToPackageAndClass = basePackageName.replace(".", File.separator);
    Function<String, String> mapToClassName = s -> {
      String prefix = Arrays.stream(s.split(pathToPackageAndClass))
                            .findFirst()
                            .orElse("");
      return s.replaceFirst(prefix, "")
              .replaceAll(File.separator, ".");
    };

    return StreamSupport.stream(javaFileObjects.spliterator(), /* parallel */ true)
                        .filter(javaFileObject -> javaFileObject.getKind().equals(kind))
                        .map(FileObject::getName)
                        .map(fileObjectName -> fileObjectName.replace(".class", ""))
                        .map(mapToClassName)
                        .map(className -> Try.of(() -> Class.forName(className))
                                             .getOrElseThrow(asRuntimeException))
                        .collect(Collectors.toList());
  };

  @Test
  @DisplayName("should get classes recursively in given package")
  void test() {
    Collection<Class<?>> classes = findAllPackageClasses.apply(getClass().getPackage().getName());
    assertThat(classes).hasSizeGreaterThan(4);
    classes.stream().map(String::valueOf).forEach(log::info);
  }
}

PS:为了简化处理错误的样板文件等，我在这里使用了vavr和lombok库

其他实现可以在我的GitHub daggerok/java-reflection-find- annotation -classes-or-methods repo中找到

这是不可能的，因为包中的所有类都可能不会被加载，而你总是知道一个类的包。

如果您不使用任何动态类加载器，您可以搜索类路径，并为每个条目搜索目录或JAR文件。

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->{
        ...
    });

你需要查找类路径中的每个类装入器条目:

    String pkg = "org/apache/commons/lang";
    ClassLoader cl = ClassLoader.getSystemClassLoader();
    URL[] urls = ((URLClassLoader) cl).getURLs();
    for (URL url : urls) {
        System.out.println(url.getFile());
        File jar = new File(url.getFile());
        // ....
    }   

如果条目是目录，只需在右边的子目录中查找:

if (jar.isDirectory()) {
    File subdir = new File(jar, pkg);
    if (!subdir.exists())
        continue;
    File[] files = subdir.listFiles();
    for (File file : files) {
        if (!file.isFile())
            continue;
        if (file.getName().endsWith(".class"))
            System.out.println("Found class: "
                    + file.getName().substring(0,
                            file.getName().length() - 6));
    }
}   

如果条目是文件，并且它是jar，检查它的ZIP条目:

else {
    // try to open as ZIP
    try {
        ZipFile zip = new ZipFile(jar);
        for (Enumeration<? extends ZipEntry> entries = zip
                .entries(); entries.hasMoreElements();) {
            ZipEntry entry = entries.nextElement();
            String name = entry.getName();
            if (!name.startsWith(pkg))
                continue;
            name = name.substring(pkg.length() + 1);
            if (name.indexOf('/') < 0 && name.endsWith(".class"))
                System.out.println("Found class: "
                        + name.substring(0, name.length() - 6));
        }
    } catch (ZipException e) {
        System.out.println("Not a ZIP: " + e.getMessage());
    } catch (IOException e) {
        System.err.println(e.getMessage());
    }
}

现在，一旦包中有了所有的类名，就可以尝试用反射加载它们，并分析它们是类还是接口等等。