src/java.base/share/classes/jdk/internal/module/ModulePath.java
changeset 47216 71c04702a3d5
parent 45652 33342314ce89
child 47866 39db80b32b69
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/jdk/internal/module/ModulePath.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,791 @@
+/*
+ * Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.internal.module;
+
+import java.io.BufferedInputStream;
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.UncheckedIOException;
+import java.lang.module.FindException;
+import java.lang.module.InvalidModuleDescriptorException;
+import java.lang.module.ModuleDescriptor;
+import java.lang.module.ModuleDescriptor.Builder;
+import java.lang.module.ModuleFinder;
+import java.lang.module.ModuleReference;
+import java.net.URI;
+import java.nio.file.DirectoryStream;
+import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.jar.Attributes;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+import java.util.jar.Manifest;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+import java.util.zip.ZipException;
+import java.util.zip.ZipFile;
+
+import jdk.internal.jmod.JmodFile;
+import jdk.internal.jmod.JmodFile.Section;
+import jdk.internal.perf.PerfCounter;
+import jdk.internal.util.jar.VersionedStream;
+
+
+/**
+ * A {@code ModuleFinder} that locates modules on the file system by searching
+ * a sequence of directories or packaged modules. The ModuleFinder can be
+ * created to work in either the run-time or link-time phases. In both cases it
+ * locates modular JAR and exploded modules. When created for link-time then it
+ * additionally locates modules in JMOD files. The ModuleFinder can also
+ * optionally patch any modules that it locates with a ModulePatcher.
+ */
+
+public class ModulePath implements ModuleFinder {
+    private static final String MODULE_INFO = "module-info.class";
+
+    // the version to use for multi-release modular JARs
+    private final Runtime.Version releaseVersion;
+
+    // true for the link phase (supports modules packaged in JMOD format)
+    private final boolean isLinkPhase;
+
+    // for patching modules, can be null
+    private final ModulePatcher patcher;
+
+    // the entries on this module path
+    private final Path[] entries;
+    private int next;
+
+    // map of module name to module reference map for modules already located
+    private final Map<String, ModuleReference> cachedModules = new HashMap<>();
+
+
+    private ModulePath(Runtime.Version version,
+                       boolean isLinkPhase,
+                       ModulePatcher patcher,
+                       Path... entries) {
+        this.releaseVersion = version;
+        this.isLinkPhase = isLinkPhase;
+        this.patcher = patcher;
+        this.entries = entries.clone();
+        for (Path entry : this.entries) {
+            Objects.requireNonNull(entry);
+        }
+    }
+
+    /**
+     * Returns a ModuleFinder that that locates modules on the file system by
+     * searching a sequence of directories and/or packaged modules. The modules
+     * may be patched by the given ModulePatcher.
+     */
+    public static ModuleFinder of(ModulePatcher patcher, Path... entries) {
+        return new ModulePath(JarFile.runtimeVersion(), false, patcher, entries);
+    }
+
+    /**
+     * Returns a ModuleFinder that that locates modules on the file system by
+     * searching a sequence of directories and/or packaged modules.
+     */
+    public static ModuleFinder of(Path... entries) {
+        return of((ModulePatcher)null, entries);
+    }
+
+    /**
+     * Returns a ModuleFinder that that locates modules on the file system by
+     * searching a sequence of directories and/or packaged modules.
+     *
+     * @param version The release version to use for multi-release JAR files
+     * @param isLinkPhase {@code true} if the link phase to locate JMOD files
+     */
+    public static ModuleFinder of(Runtime.Version version,
+                                  boolean isLinkPhase,
+                                  Path... entries) {
+        return new ModulePath(version, isLinkPhase, null, entries);
+    }
+
+
+    @Override
+    public Optional<ModuleReference> find(String name) {
+        Objects.requireNonNull(name);
+
+        // try cached modules
+        ModuleReference m = cachedModules.get(name);
+        if (m != null)
+            return Optional.of(m);
+
+        // the module may not have been encountered yet
+        while (hasNextEntry()) {
+            scanNextEntry();
+            m = cachedModules.get(name);
+            if (m != null)
+                return Optional.of(m);
+        }
+        return Optional.empty();
+    }
+
+    @Override
+    public Set<ModuleReference> findAll() {
+        // need to ensure that all entries have been scanned
+        while (hasNextEntry()) {
+            scanNextEntry();
+        }
+        return cachedModules.values().stream().collect(Collectors.toSet());
+    }
+
+    /**
+     * Returns {@code true} if there are additional entries to scan
+     */
+    private boolean hasNextEntry() {
+        return next < entries.length;
+    }
+
+    /**
+     * Scans the next entry on the module path. A no-op if all entries have
+     * already been scanned.
+     *
+     * @throws FindException if an error occurs scanning the next entry
+     */
+    private void scanNextEntry() {
+        if (hasNextEntry()) {
+
+            long t0 = System.nanoTime();
+
+            Path entry = entries[next];
+            Map<String, ModuleReference> modules = scan(entry);
+            next++;
+
+            // update cache, ignoring duplicates
+            int initialSize = cachedModules.size();
+            for (Map.Entry<String, ModuleReference> e : modules.entrySet()) {
+                cachedModules.putIfAbsent(e.getKey(), e.getValue());
+            }
+
+            // update counters
+            int added = cachedModules.size() - initialSize;
+            moduleCount.add(added);
+
+            scanTime.addElapsedTimeFrom(t0);
+        }
+    }
+
+
+    /**
+     * Scan the given module path entry. If the entry is a directory then it is
+     * a directory of modules or an exploded module. If the entry is a regular
+     * file then it is assumed to be a packaged module.
+     *
+     * @throws FindException if an error occurs scanning the entry
+     */
+    private Map<String, ModuleReference> scan(Path entry) {
+
+        BasicFileAttributes attrs;
+        try {
+            attrs = Files.readAttributes(entry, BasicFileAttributes.class);
+        } catch (NoSuchFileException e) {
+            return Collections.emptyMap();
+        } catch (IOException ioe) {
+            throw new FindException(ioe);
+        }
+
+        try {
+
+            if (attrs.isDirectory()) {
+                Path mi = entry.resolve(MODULE_INFO);
+                if (!Files.exists(mi)) {
+                    // assume a directory of modules
+                    return scanDirectory(entry);
+                }
+            }
+
+            // packaged or exploded module
+            ModuleReference mref = readModule(entry, attrs);
+            if (mref != null) {
+                String name = mref.descriptor().name();
+                return Collections.singletonMap(name, mref);
+            }
+
+            // not recognized
+            String msg;
+            if (!isLinkPhase && entry.toString().endsWith(".jmod")) {
+                msg = "JMOD format not supported at execution time";
+            } else {
+                msg = "Module format not recognized";
+            }
+            throw new FindException(msg + ": " + entry);
+
+        } catch (IOException ioe) {
+            throw new FindException(ioe);
+        }
+    }
+
+
+    /**
+     * Scans the given directory for packaged or exploded modules.
+     *
+     * @return a map of module name to ModuleReference for the modules found
+     *         in the directory
+     *
+     * @throws IOException if an I/O error occurs
+     * @throws FindException if an error occurs scanning the entry or the
+     *         directory contains two or more modules with the same name
+     */
+    private Map<String, ModuleReference> scanDirectory(Path dir)
+        throws IOException
+    {
+        // The map of name -> mref of modules found in this directory.
+        Map<String, ModuleReference> nameToReference = new HashMap<>();
+
+        try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
+            for (Path entry : stream) {
+                BasicFileAttributes attrs;
+                try {
+                    attrs = Files.readAttributes(entry, BasicFileAttributes.class);
+                } catch (NoSuchFileException ignore) {
+                    // file has been removed or moved, ignore for now
+                    continue;
+                }
+
+                ModuleReference mref = readModule(entry, attrs);
+
+                // module found
+                if (mref != null) {
+                    // can have at most one version of a module in the directory
+                    String name = mref.descriptor().name();
+                    ModuleReference previous = nameToReference.put(name, mref);
+                    if (previous != null) {
+                        String fn1 = fileName(mref);
+                        String fn2 = fileName(previous);
+                        throw new FindException("Two versions of module "
+                                                 + name + " found in " + dir
+                                                 + " (" + fn1 + " and " + fn2 + ")");
+                    }
+                }
+            }
+        }
+
+        return nameToReference;
+    }
+
+
+    /**
+     * Reads a packaged or exploded module, returning a {@code ModuleReference}
+     * to the module. Returns {@code null} if the entry is not recognized.
+     *
+     * @throws IOException if an I/O error occurs
+     * @throws FindException if an error occurs parsing its module descriptor
+     */
+    private ModuleReference readModule(Path entry, BasicFileAttributes attrs)
+        throws IOException
+    {
+        try {
+
+            // exploded module
+            if (attrs.isDirectory()) {
+                return readExplodedModule(entry); // may return null
+            }
+
+            // JAR or JMOD file
+            if (attrs.isRegularFile()) {
+                String fn = entry.getFileName().toString();
+                boolean isDefaultFileSystem = isDefaultFileSystem(entry);
+
+                // JAR file
+                if (fn.endsWith(".jar")) {
+                    if (isDefaultFileSystem) {
+                        return readJar(entry);
+                    } else {
+                        // the JAR file is in a custom file system so
+                        // need to copy it to the local file system
+                        Path tmpdir = Files.createTempDirectory("mlib");
+                        Path target = Files.copy(entry, tmpdir.resolve(fn));
+                        return readJar(target);
+                    }
+                }
+
+                // JMOD file
+                if (isDefaultFileSystem && isLinkPhase && fn.endsWith(".jmod")) {
+                    return readJMod(entry);
+                }
+            }
+
+            return null;
+
+        } catch (InvalidModuleDescriptorException e) {
+            throw new FindException("Error reading module: " + entry, e);
+        }
+    }
+
+    /**
+     * Returns a string with the file name of the module if possible.
+     * If the module location is not a file URI then return the URI
+     * as a string.
+     */
+    private String fileName(ModuleReference mref) {
+        URI uri = mref.location().orElse(null);
+        if (uri != null) {
+            if (uri.getScheme().equalsIgnoreCase("file")) {
+                Path file = Paths.get(uri);
+                return file.getFileName().toString();
+            } else {
+                return uri.toString();
+            }
+        } else {
+            return "<unknown>";
+        }
+    }
+
+    // -- JMOD files --
+
+    private Set<String> jmodPackages(JmodFile jf) {
+        return jf.stream()
+            .filter(e -> e.section() == Section.CLASSES)
+            .map(JmodFile.Entry::name)
+            .map(this::toPackageName)
+            .flatMap(Optional::stream)
+            .collect(Collectors.toSet());
+    }
+
+    /**
+     * Returns a {@code ModuleReference} to a module in JMOD file on the
+     * file system.
+     *
+     * @throws IOException
+     * @throws InvalidModuleDescriptorException
+     */
+    private ModuleReference readJMod(Path file) throws IOException {
+        try (JmodFile jf = new JmodFile(file)) {
+            ModuleInfo.Attributes attrs;
+            try (InputStream in = jf.getInputStream(Section.CLASSES, MODULE_INFO)) {
+                attrs  = ModuleInfo.read(in, () -> jmodPackages(jf));
+            }
+            return ModuleReferences.newJModModule(attrs, file);
+        }
+    }
+
+
+    // -- JAR files --
+
+    private static final String SERVICES_PREFIX = "META-INF/services/";
+
+    private static final Attributes.Name AUTOMATIC_MODULE_NAME
+        = new Attributes.Name("Automatic-Module-Name");
+
+    /**
+     * Returns the service type corresponding to the name of a services
+     * configuration file if it is a legal type name.
+     *
+     * For example, if called with "META-INF/services/p.S" then this method
+     * returns a container with the value "p.S".
+     */
+    private Optional<String> toServiceName(String cf) {
+        assert cf.startsWith(SERVICES_PREFIX);
+        int index = cf.lastIndexOf("/") + 1;
+        if (index < cf.length()) {
+            String prefix = cf.substring(0, index);
+            if (prefix.equals(SERVICES_PREFIX)) {
+                String sn = cf.substring(index);
+                if (Checks.isClassName(sn))
+                    return Optional.of(sn);
+            }
+        }
+        return Optional.empty();
+    }
+
+    /**
+     * Reads the next line from the given reader and trims it of comments and
+     * leading/trailing white space.
+     *
+     * Returns null if the reader is at EOF.
+     */
+    private String nextLine(BufferedReader reader) throws IOException {
+        String ln = reader.readLine();
+        if (ln != null) {
+            int ci = ln.indexOf('#');
+            if (ci >= 0)
+                ln = ln.substring(0, ci);
+            ln = ln.trim();
+        }
+        return ln;
+    }
+
+    /**
+     * Treat the given JAR file as a module as follows:
+     *
+     * 1. The value of the Automatic-Module-Name attribute is the module name
+     * 2. The version, and the module name when the  Automatic-Module-Name
+     *    attribute is not present, is derived from the file ame of the JAR file
+     * 3. All packages are derived from the .class files in the JAR file
+     * 4. The contents of any META-INF/services configuration files are mapped
+     *    to "provides" declarations
+     * 5. The Main-Class attribute in the main attributes of the JAR manifest
+     *    is mapped to the module descriptor mainClass if possible
+     */
+    private ModuleDescriptor deriveModuleDescriptor(JarFile jf)
+        throws IOException
+    {
+        // Read Automatic-Module-Name attribute if present
+        Manifest man = jf.getManifest();
+        Attributes attrs = null;
+        String moduleName = null;
+        if (man != null) {
+            attrs = man.getMainAttributes();
+            if (attrs != null) {
+                moduleName = attrs.getValue(AUTOMATIC_MODULE_NAME);
+            }
+        }
+
+        // Derive the version, and the module name if needed, from JAR file name
+        String fn = jf.getName();
+        int i = fn.lastIndexOf(File.separator);
+        if (i != -1)
+            fn = fn.substring(i + 1);
+
+        // drop ".jar"
+        String name = fn.substring(0, fn.length() - 4);
+        String vs = null;
+
+        // find first occurrence of -${NUMBER}. or -${NUMBER}$
+        Matcher matcher = Patterns.DASH_VERSION.matcher(name);
+        if (matcher.find()) {
+            int start = matcher.start();
+
+            // attempt to parse the tail as a version string
+            try {
+                String tail = name.substring(start + 1);
+                ModuleDescriptor.Version.parse(tail);
+                vs = tail;
+            } catch (IllegalArgumentException ignore) { }
+
+            name = name.substring(0, start);
+        }
+
+        // Create builder, using the name derived from file name when
+        // Automatic-Module-Name not present
+        Builder builder;
+        if (moduleName != null) {
+            try {
+                builder = ModuleDescriptor.newAutomaticModule(moduleName);
+            } catch (IllegalArgumentException e) {
+                throw new FindException(AUTOMATIC_MODULE_NAME + ": " + e.getMessage());
+            }
+        } else {
+            builder = ModuleDescriptor.newAutomaticModule(cleanModuleName(name));
+        }
+
+        // module version if present
+        if (vs != null)
+            builder.version(vs);
+
+        // scan the names of the entries in the JAR file
+        Map<Boolean, Set<String>> map = VersionedStream.stream(jf)
+                .filter(e -> !e.isDirectory())
+                .map(JarEntry::getName)
+                .filter(e -> (e.endsWith(".class") ^ e.startsWith(SERVICES_PREFIX)))
+                .collect(Collectors.partitioningBy(e -> e.startsWith(SERVICES_PREFIX),
+                                                   Collectors.toSet()));
+
+        Set<String> classFiles = map.get(Boolean.FALSE);
+        Set<String> configFiles = map.get(Boolean.TRUE);
+
+        // the packages containing class files
+        Set<String> packages = classFiles.stream()
+                .map(this::toPackageName)
+                .flatMap(Optional::stream)
+                .distinct()
+                .collect(Collectors.toSet());
+
+        // all packages are exported and open
+        builder.packages(packages);
+
+        // map names of service configuration files to service names
+        Set<String> serviceNames = configFiles.stream()
+                .map(this::toServiceName)
+                .flatMap(Optional::stream)
+                .collect(Collectors.toSet());
+
+        // parse each service configuration file
+        for (String sn : serviceNames) {
+            JarEntry entry = jf.getJarEntry(SERVICES_PREFIX + sn);
+            List<String> providerClasses = new ArrayList<>();
+            try (InputStream in = jf.getInputStream(entry)) {
+                BufferedReader reader
+                    = new BufferedReader(new InputStreamReader(in, "UTF-8"));
+                String cn;
+                while ((cn = nextLine(reader)) != null) {
+                    if (cn.length() > 0) {
+                        String pn = packageName(cn);
+                        if (!packages.contains(pn)) {
+                            String msg = "Provider class " + cn + " not in module";
+                            throw new InvalidModuleDescriptorException(msg);
+                        }
+                        providerClasses.add(cn);
+                    }
+                }
+            }
+            if (!providerClasses.isEmpty())
+                builder.provides(sn, providerClasses);
+        }
+
+        // Main-Class attribute if it exists
+        if (attrs != null) {
+            String mainClass = attrs.getValue(Attributes.Name.MAIN_CLASS);
+            if (mainClass != null) {
+                mainClass = mainClass.replace("/", ".");
+                if (Checks.isClassName(mainClass)) {
+                    String pn = packageName(mainClass);
+                    if (packages.contains(pn)) {
+                        builder.mainClass(mainClass);
+                    }
+                }
+            }
+        }
+
+        return builder.build();
+    }
+
+    /**
+     * Patterns used to derive the module name from a JAR file name.
+     */
+    private static class Patterns {
+        static final Pattern DASH_VERSION = Pattern.compile("-(\\d+(\\.|$))");
+        static final Pattern NON_ALPHANUM = Pattern.compile("[^A-Za-z0-9]");
+        static final Pattern REPEATING_DOTS = Pattern.compile("(\\.)(\\1)+");
+        static final Pattern LEADING_DOTS = Pattern.compile("^\\.");
+        static final Pattern TRAILING_DOTS = Pattern.compile("\\.$");
+    }
+
+    /**
+     * Clean up candidate module name derived from a JAR file name.
+     */
+    private static String cleanModuleName(String mn) {
+        // replace non-alphanumeric
+        mn = Patterns.NON_ALPHANUM.matcher(mn).replaceAll(".");
+
+        // collapse repeating dots
+        mn = Patterns.REPEATING_DOTS.matcher(mn).replaceAll(".");
+
+        // drop leading dots
+        if (mn.length() > 0 && mn.charAt(0) == '.')
+            mn = Patterns.LEADING_DOTS.matcher(mn).replaceAll("");
+
+        // drop trailing dots
+        int len = mn.length();
+        if (len > 0 && mn.charAt(len-1) == '.')
+            mn = Patterns.TRAILING_DOTS.matcher(mn).replaceAll("");
+
+        return mn;
+    }
+
+    private Set<String> jarPackages(JarFile jf) {
+        return VersionedStream.stream(jf)
+                .filter(e -> !e.isDirectory())
+                .map(JarEntry::getName)
+                .map(this::toPackageName)
+                .flatMap(Optional::stream)
+                .collect(Collectors.toSet());
+    }
+
+    /**
+     * Returns a {@code ModuleReference} to a module in modular JAR file on
+     * the file system.
+     *
+     * @throws IOException
+     * @throws FindException
+     * @throws InvalidModuleDescriptorException
+     */
+    private ModuleReference readJar(Path file) throws IOException {
+        try (JarFile jf = new JarFile(file.toFile(),
+                                      true,               // verify
+                                      ZipFile.OPEN_READ,
+                                      releaseVersion))
+        {
+            ModuleInfo.Attributes attrs;
+            JarEntry entry = jf.getJarEntry(MODULE_INFO);
+            if (entry == null) {
+
+                // no module-info.class so treat it as automatic module
+                try {
+                    ModuleDescriptor md = deriveModuleDescriptor(jf);
+                    attrs = new ModuleInfo.Attributes(md, null, null, null);
+                } catch (RuntimeException e) {
+                    throw new FindException("Unable to derive module descriptor for "
+                                            + jf.getName(), e);
+                }
+
+            } else {
+                attrs = ModuleInfo.read(jf.getInputStream(entry),
+                                        () -> jarPackages(jf));
+            }
+
+            return ModuleReferences.newJarModule(attrs, patcher, file);
+        } catch (ZipException e) {
+            throw new FindException("Error reading " + file, e);
+        }
+    }
+
+
+    // -- exploded directories --
+
+    private Set<String> explodedPackages(Path dir) {
+        try {
+            return Files.find(dir, Integer.MAX_VALUE,
+                    ((path, attrs) -> attrs.isRegularFile() && !isHidden(path)))
+                    .map(path -> dir.relativize(path))
+                    .map(this::toPackageName)
+                    .flatMap(Optional::stream)
+                    .collect(Collectors.toSet());
+        } catch (IOException x) {
+            throw new UncheckedIOException(x);
+        }
+    }
+
+    /**
+     * Returns a {@code ModuleReference} to an exploded module on the file
+     * system or {@code null} if {@code module-info.class} not found.
+     *
+     * @throws IOException
+     * @throws InvalidModuleDescriptorException
+     */
+    private ModuleReference readExplodedModule(Path dir) throws IOException {
+        Path mi = dir.resolve(MODULE_INFO);
+        ModuleInfo.Attributes attrs;
+        try (InputStream in = Files.newInputStream(mi)) {
+            attrs = ModuleInfo.read(new BufferedInputStream(in),
+                                    () -> explodedPackages(dir));
+        } catch (NoSuchFileException e) {
+            // for now
+            return null;
+        }
+        return ModuleReferences.newExplodedModule(attrs, patcher, dir);
+    }
+
+    /**
+     * Maps a type name to its package name.
+     */
+    private static String packageName(String cn) {
+        int index = cn.lastIndexOf('.');
+        return (index == -1) ? "" : cn.substring(0, index);
+    }
+
+    /**
+     * Maps the name of an entry in a JAR or ZIP file to a package name.
+     *
+     * @throws InvalidModuleDescriptorException if the name is a class file in
+     *         the top-level directory of the JAR/ZIP file (and it's not
+     *         module-info.class)
+     */
+    private Optional<String> toPackageName(String name) {
+        assert !name.endsWith("/");
+        int index = name.lastIndexOf("/");
+        if (index == -1) {
+            if (name.endsWith(".class") && !name.equals(MODULE_INFO)) {
+                String msg = name + " found in top-level directory"
+                             + " (unnamed package not allowed in module)";
+                throw new InvalidModuleDescriptorException(msg);
+            }
+            return Optional.empty();
+        }
+
+        String pn = name.substring(0, index).replace('/', '.');
+        if (Checks.isPackageName(pn)) {
+            return Optional.of(pn);
+        } else {
+            // not a valid package name
+            return Optional.empty();
+        }
+    }
+
+    /**
+     * Maps the relative path of an entry in an exploded module to a package
+     * name.
+     *
+     * @throws InvalidModuleDescriptorException if the name is a class file in
+     *         the top-level directory (and it's not module-info.class)
+     */
+    private Optional<String> toPackageName(Path file) {
+        assert file.getRoot() == null;
+
+        Path parent = file.getParent();
+        if (parent == null) {
+            String name = file.toString();
+            if (name.endsWith(".class") && !name.equals(MODULE_INFO)) {
+                String msg = name + " found in top-level directory"
+                             + " (unnamed package not allowed in module)";
+                throw new InvalidModuleDescriptorException(msg);
+            }
+            return Optional.empty();
+        }
+
+        String pn = parent.toString().replace(File.separatorChar, '.');
+        if (Checks.isPackageName(pn)) {
+            return Optional.of(pn);
+        } else {
+            // not a valid package name
+            return Optional.empty();
+        }
+    }
+
+    /**
+     * Returns true if the given file exists and is a hidden file
+     */
+    private boolean isHidden(Path file) {
+        try {
+            return Files.isHidden(file);
+        } catch (IOException ioe) {
+            return false;
+        }
+    }
+
+
+    /**
+     * Return true if a path locates a path in the default file system
+     */
+    private boolean isDefaultFileSystem(Path path) {
+        return path.getFileSystem().provider()
+                .getScheme().equalsIgnoreCase("file");
+    }
+
+
+    private static final PerfCounter scanTime
+        = PerfCounter.newPerfCounter("jdk.module.finder.modulepath.scanTime");
+    private static final PerfCounter moduleCount
+        = PerfCounter.newPerfCounter("jdk.module.finder.modulepath.modules");
+}