在Java 9中运行时扫描类路径/模块路径

以下代码实现了Java 9+中的模块路径扫描（拼图）。它找到callstack上的所有类，然后为每个类引用调用 classRef.getModule（）。getLayer（）。getConfiguration（）。modules（），返回aa 列表< ResolvedModule> ，而不仅仅是列表< Module> 。 （ ResolvedModule 允许您访问模块资源，而模块则不允许。）给定 ResolvedModule 每个模块的引用，你可以调用 .reference（）方法来获取 ModuleReference 对于一个模块。 ModuleReference＃open（）为您提供 ModuleReader ，它允许您使用 ModuleReader #list（），或者使用打开资源> Optional< InputStream> ModuleReader #open（resourcePath）或可选< ByteBuffer> ModuleReader＃读取（resourcePath）。然后，在完成模块后，关闭 ModuleReader 。这在我见过的任何地方都没有记录。要弄清楚这一切是非常困难的。但这里是代码，希望其他人能从中受益。

The following code achieves module path scanning in Java 9+ (Jigsaw). It finds all classes on the callstack, then for each class reference, calls classRef.getModule().getLayer().getConfiguration().modules(), which returns a a List<ResolvedModule>, rather than just a List<Module>. (ResolvedModule gives you access to the module resources, whereas Module does not.) Given a ResolvedModule reference for each module, you can call the .reference() method to get the ModuleReference for a module. ModuleReference#open() gives you a ModuleReader, which allows you to list the resources in a module, using ModuleReader#list(), or to open a resource using Optional<InputStream> ModuleReader#open(resourcePath) or Optional<ByteBuffer> ModuleReader#read(resourcePath). You then close the ModuleReader when you're done with the module. This is not documented anywhere that I have seen. It was very difficult to figure all this out. But here is the code, in the hope that someone else will benefit from this.

请注意，即使在JDK9 +中，您仍然可以使用传统的classpath元素和模块路径元素，对于完整的模块路径+类路径扫描，您应该使用适当的类路径扫描解决方案，例如 ClassGraph ，支持使用以下机制进行模块扫描（免责声明，我是作者）。

Note that even in JDK9+, you can still utilize traditional classpath elements along with module path elements, so for a complete module path + classpath scan, you should probably use a proper classpath scanning solution, such as ClassGraph, which supports module scanning using the below mechanism (disclaimer, I am the author).

package main;

import java.lang.StackWalker.Option;
import java.lang.module.ModuleReader;
import java.lang.module.ModuleReference;
import java.lang.module.ResolvedModule;
import java.net.URI;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Deque;
import java.util.HashSet;
import java.util.List;
import java.util.Map.Entry;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Stream;

public class Java9Scanner {

    private static final class CallerResolver extends SecurityManager {
        /** Get classes in the call stack. */
        @Override
        protected Class<?>[] getClassContext() {
            return super.getClassContext();
        }
    }

    /** Recursively find the topological sort order of ancestral layers. */
    private static void findLayerOrder(ModuleLayer layer,
            Set<ModuleLayer> visited, Deque<ModuleLayer> layersOut) {
        if (visited.add(layer)) {
            List<ModuleLayer> parents = layer.parents();
            for (int i = 0; i < parents.size(); i++) {
                findLayerOrder(parents.get(i), visited, layersOut);
            }
            layersOut.push(layer);
        }
    }

    /** Get ModuleReferences from a Class reference. */
    private static List<Entry<ModuleReference, ModuleLayer>> findModuleRefs(
            Class<?>[] callStack) {
        Deque<ModuleLayer> layerOrder = new ArrayDeque<>();
        Set<ModuleLayer> visited = new HashSet<>();
        for (int i = 0; i < callStack.length; i++) {
            ModuleLayer layer = callStack[i].getModule().getLayer();
            findLayerOrder(layer, visited, layerOrder);
        }
        Set<ModuleReference> addedModules = new HashSet<>();
        List<Entry<ModuleReference, ModuleLayer>> moduleRefs = new ArrayList<>();
        for (ModuleLayer layer : layerOrder) {
            Set<ResolvedModule> modulesInLayerSet = layer.configuration()
                    .modules();
            final List<Entry<ModuleReference, ModuleLayer>> modulesInLayer =
                    new ArrayList<>();
            for (ResolvedModule module : modulesInLayerSet) {
                modulesInLayer
                        .add(new SimpleEntry<>(module.reference(), layer));
            }
            // Sort modules in layer by name for consistency
            Collections.sort(modulesInLayer,
                    (e1, e2) -> e1.getKey().descriptor().name()
                            .compareTo(e2.getKey().descriptor().name()));
            // To be safe, dedup ModuleReferences, in case a module occurs in multiple
            // layers and reuses its ModuleReference (no idea if this can happen)
            for (Entry<ModuleReference, ModuleLayer> m : modulesInLayer) {
                if (addedModules.add(m.getKey())) {
                    moduleRefs.add(m);
                }
            }
        }
        return moduleRefs;
    }

    /** Get the classes in the call stack. */
    private static Class<?>[] getCallStack() {
        // Try StackWalker (JDK 9+)
        PrivilegedAction<Class<?>[]> stackWalkerAction = new PrivilegedAction<Class<?>[]>() {
            @Override
            public Class<?>[] run() {
                List<Class<?>> stackFrameClasses = new ArrayList<>();
                StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE)
                        .forEach(sf -> stackFrameClasses
                                .add(sf.getDeclaringClass()));
                return stackFrameClasses.toArray(new Class<?>[0]);
            }
        };
        try {
            // Try with doPrivileged()
            return AccessController
                    .doPrivileged(stackWalkerAction);
        } catch (Exception e) {
        }
        try {
            // Try without doPrivileged()
            return stackWalkerAction.run();
        } catch (Exception e) {
        }

        // Try SecurityManager
        PrivilegedAction<Class<?>[]> callerResolverAction = new PrivilegedAction<Class<?>[]>() {
            @Override
            public Class<?>[] run() {
                return new CallerResolver().getClassContext();
            }
        };
        try {
            // Try with doPrivileged()
            return AccessController
                    .doPrivileged(callerResolverAction);
        } catch (Exception e) {
        }
        try {
            // Try without doPrivileged()
            return callerResolverAction.run();
        } catch (Exception e) {
        }

        // As a fallback, use getStackTrace() to try to get the call stack
        try {
            throw new Exception();
        } catch (final Exception e) {
            final List<Class<?>> classes = new ArrayList<>();
            for (final StackTraceElement elt : e.getStackTrace()) {
                try {
                    classes.add(Class.forName(elt.getClassName()));
                } catch (final Throwable e2) {
                    // Ignore
                }
            }
            if (classes.size() > 0) {
                return classes.toArray(new Class<?>[0]);
            } else {
                // Last-ditch effort -- include just this class in the call stack
                return new Class<?>[] { Java9Scanner.class };
            }
        }
    }

    /**
     * Return true if the given module name is a system module. There can be
     * system modules in layers above the boot layer.
     */
    private static boolean isSystemModule(
            final ModuleReference moduleReference) {
        URI location = moduleReference.location().orElse(null);
        if (location == null) {
            return true;
        }
        final String scheme = location.getScheme();
        return scheme != null && scheme.equalsIgnoreCase("jrt");
    }

    public static void main(String[] args) throws Exception {
        // Get ModuleReferences for modules of all classes in call stack,
        List<Entry<ModuleReference, ModuleLayer>> systemModuleRefs = new ArrayList<>();
        List<Entry<ModuleReference, ModuleLayer>> nonSystemModuleRefs = new ArrayList<>();

        Class<?>[] callStack = getCallStack();
        List<Entry<ModuleReference, ModuleLayer>> moduleRefs = findModuleRefs(
                callStack);
        // Split module refs into system and non-system modules based on module name
        for (Entry<ModuleReference, ModuleLayer> m : moduleRefs) {
            (isSystemModule(m.getKey()) ? systemModuleRefs
                    : nonSystemModuleRefs).add(m);
        }

        // List system modules
        System.out.println("\nSYSTEM MODULES:\n");
        for (Entry<ModuleReference, ModuleLayer> e : systemModuleRefs) {
            ModuleReference ref = e.getKey();
            System.out.println("  " + ref.descriptor().name());
        }

        // Show info for non-system modules
        System.out.println("\nNON-SYSTEM MODULES:");
        for (Entry<ModuleReference, ModuleLayer> e : nonSystemModuleRefs) {
            ModuleReference ref = e.getKey();
            ModuleLayer layer = e.getValue();
            System.out.println("\n  " + ref.descriptor().name());
            System.out.println(
                    "    Version: " + ref.descriptor().toNameAndVersion());
            System.out.println(
                    "    Packages: " + ref.descriptor().packages());
            System.out.println("    ClassLoader: "
                    + layer.findLoader(ref.descriptor().name()));
            Optional<URI> location = ref.location();
            if (location.isPresent()) {
                System.out.println("    Location: " + location.get());
            }
            try (ModuleReader moduleReader = ref.open()) {
                Stream<String> stream = moduleReader.list();
                stream.forEach(s -> System.out.println("      File: " + s));
            }
        }
    }
}