java/11 : java.base/java/lang/module/ModuleFinder.java

ModuleFinder
https://openjdk.java.net/
GPLv2 + Classpath Exception
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package java.lang.module;

import java.nio.file.Path;
import java.security.AccessController;
import java.security.Permission;
import java.security.PrivilegedAction;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;

import jdk.internal.module.ModulePath;
import jdk.internal.module.SystemModuleFinders;

A finder of modules. A ModuleFinder is used to find modules during resolution or
service binding.
 A ModuleFinder can only find one module with a given name. A ModuleFinder that finds modules in a sequence of directories, for example, will locate the first occurrence of a module of a given name and will ignore other modules of that name that appear in directories later in the sequence. 
 Example usage: 

    Path dir1, dir2, dir3;
    ModuleFinder finder = ModuleFinder.of(dir1, dir2, dir3);
    Optional<ModuleReference> omref = finder.find("jdk.foo");
    omref.ifPresent(mref -> ... );

 The find and findAll methods defined here can fail for several reasons. These include I/O errors, errors detected parsing a module descriptor (module-info.class), or in the case of ModuleFinder returned by ModuleFinder.of, that two or more modules with the same name are found in a directory. When an error is detected then these methods throw 
FindException with an appropriate cause. The behavior of a ModuleFinder after a FindException is thrown is undefined. For example, invoking find after an exception is thrown may or may not scan the same modules that lead to the exception. It is recommended that a module finder be discarded after an exception is thrown. 
 A ModuleFinder is not required to be thread safe. 
Since: 9
@spec JPMS/**
 * A finder of modules. A {@code ModuleFinder} is used to find modules during
 * <a href="package-summary.html#resolution">resolution</a> or
 * <a href="Configuration.html#service-binding">service binding</a>.
 *
 * <p> A {@code ModuleFinder} can only find one module with a given name. A
 * {@code ModuleFinder} that finds modules in a sequence of directories, for
 * example, will locate the first occurrence of a module of a given name and
 * will ignore other modules of that name that appear in directories later in
 * the sequence. </p>
 *
 * <p> Example usage: </p>
 *
 * <pre>{@code
 *     Path dir1, dir2, dir3;
 *
 *     ModuleFinder finder = ModuleFinder.of(dir1, dir2, dir3);
 *
 *     Optional<ModuleReference> omref = finder.find("jdk.foo");
 *     omref.ifPresent(mref -> ... );
 *
 * }</pre>
 *
 * <p> The {@link #find(String) find} and {@link #findAll() findAll} methods
 * defined here can fail for several reasons. These include I/O errors, errors
 * detected parsing a module descriptor ({@code module-info.class}), or in the
 * case of {@code ModuleFinder} returned by {@link #of ModuleFinder.of}, that
 * two or more modules with the same name are found in a directory.
 * When an error is detected then these methods throw {@link FindException
 * FindException} with an appropriate {@link Throwable#getCause cause}.
 * The behavior of a {@code ModuleFinder} after a {@code FindException} is
 * thrown is undefined. For example, invoking {@code find} after an exception
 * is thrown may or may not scan the same modules that lead to the exception.
 * It is recommended that a module finder be discarded after an exception is
 * thrown. </p>
 *
 * <p> A {@code ModuleFinder} is not required to be thread safe. </p>
 *
 * @since 9
 * @spec JPMS
 */

public interface ModuleFinder {

    Finds a reference to a module of a given name.
 A ModuleFinder provides a consistent view of the modules that it locates. If find is invoked several times to locate the same module (by name) then it will return the same result each time. If a module is located then it is guaranteed to be a member of the set of modules returned by the findAll method. 
Params: name – 
        The name of the module to find
Throws: FindException – 
        If an error occurs finding the module
SecurityException – 
        If denied by the security manager
Returns: A reference to a module with the given name or an empty Optional if not found/**
     * Finds a reference to a module of a given name.
     *
     * <p> A {@code ModuleFinder} provides a consistent view of the
     * modules that it locates. If {@code find} is invoked several times to
     * locate the same module (by name) then it will return the same result
     * each time. If a module is located then it is guaranteed to be a member
     * of the set of modules returned by the {@link #findAll() findAll}
     * method. </p>
     *
     * @param  name
     *         The name of the module to find
     *
     * @return A reference to a module with the given name or an empty
     *         {@code Optional} if not found
     *
     * @throws FindException
     *         If an error occurs finding the module
     *
     * @throws SecurityException
     *         If denied by the security manager
     */
    Optional<ModuleReference> find(String name);

    Returns the set of all module references that this finder can locate.
 A ModuleFinder provides a consistent view of the modules that it locates. If findAll is invoked several times then it will return the same (equals) result each time. For each 
ModuleReference element in the returned set then it is guaranteed that find will locate the ModuleReference if invoked to find that module. 
Throws: FindException – 
        If an error occurs finding all modules
SecurityException – 
        If denied by the security manager
API Note: This is important to have for methods such as resolveAndBind that need to scan the module path to find modules that provide a specific service.
Returns: The set of all module references that this finder locates/**
     * Returns the set of all module references that this finder can locate.
     *
     * <p> A {@code ModuleFinder} provides a consistent view of the modules
     * that it locates. If {@link #findAll() findAll} is invoked several times
     * then it will return the same (equals) result each time. For each {@code
     * ModuleReference} element in the returned set then it is guaranteed that
     * {@link #find find} will locate the {@code ModuleReference} if invoked
     * to find that module. </p>
     *
     * @apiNote This is important to have for methods such as {@link
     * Configuration#resolveAndBind resolveAndBind} that need to scan the
     * module path to find modules that provide a specific service.
     *
     * @return The set of all module references that this finder locates
     *
     * @throws FindException
     *         If an error occurs finding all modules
     *
     * @throws SecurityException
     *         If denied by the security manager
     */
    Set<ModuleReference> findAll();

    Returns a module finder that locates the system modules. The system modules are the modules in the Java run-time image. The module finder will always find java.base.  If there is a security manager set then its checkPermission method is invoked to check that the caller has been granted RuntimePermission("accessSystemModules") to access the system modules. 
Throws: SecurityException – 
        If denied by the security manager
Returns: A ModuleFinder that locates the system modules/**
     * Returns a module finder that locates the <em>system modules</em>. The
     * system modules are the modules in the Java run-time image.
     * The module finder will always find {@code java.base}.
     *
     * <p> If there is a security manager set then its {@link
     * SecurityManager#checkPermission(Permission) checkPermission} method is
     * invoked to check that the caller has been granted
     * {@link RuntimePermission RuntimePermission("accessSystemModules")}
     * to access the system modules. </p>
     *
     * @return A {@code ModuleFinder} that locates the system modules
     *
     * @throws SecurityException
     *         If denied by the security manager
     */
    static ModuleFinder ofSystem() {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(new RuntimePermission("accessSystemModules"));
            PrivilegedAction<ModuleFinder> pa = SystemModuleFinders::ofSystem;
            return AccessController.doPrivileged(pa);
        } else {
            return SystemModuleFinders.ofSystem();
        }
    }

    Returns a module finder that locates modules on the file system by
searching a sequence of directories and/or packaged modules.
Each element in the given array is one of:

     A path to a directory of modules.
     A path to the top-level directory of an
        exploded module. 
     A path to a packaged module. 

The module finder locates modules by searching each directory, exploded
module, or packaged module in array index order. It finds the first
occurrence of a module with a given name and ignores other modules of
that name that appear later in the sequence.
 If an element is a path to a directory of modules then each entry in the directory is a packaged module or the top-level directory of an exploded module. It is an error if a directory contains more than one module with the same name. If an element is a path to a directory, and that directory contains a file named module-info.class, then the directory is treated as an exploded module rather than a directory of modules. 
 The module finder returned by this method supports modules packaged as JAR files. A JAR file with a 
module-info.class in its top-level directory, or in a versioned entry in a multi-release JAR file, is a modular JAR file and thus defines an explicit module. A JAR file that does not have a module-info.class in its top-level directory defines an automatic module, as follows:


     If the JAR file has the attribute "Automatic-Module-Name" in its main manifest then its value is the module name. The module name is otherwise derived from the name of the JAR file. 
     The version, and the module name when the attribute "Automatic-Module-Name" is not present, are derived from the file name of the JAR file as follows: 
    
         The ".jar" suffix is removed. 
         If the name matches the regular expression 
        "-(\\d+(\\.|$))" then the module name will be derived from the subsequence preceding the hyphen of the first occurrence. The subsequence after the hyphen is parsed as a Version and ignored if it cannot be parsed as a Version. 
         All non-alphanumeric characters ([^A-Za-z0-9]) in the module name are replaced with a dot ("."), all repeating dots are replaced with one dot, and all leading and trailing dots are removed. 
         As an example, a JAR file named "foo-bar.jar" will derive a module name "foo.bar" and no version. A JAR file named "foo-bar-1.2.3-SNAPSHOT.jar" will derive a module name "foo.bar" and "1.2.3-SNAPSHOT" as the version. 
    
     The set of packages in the module is derived from the non-directory entries in the JAR file that have names ending in ".class". A candidate package name is derived from the name using the characters up to, but not including, the last forward slash. All remaining forward slashes are replaced with dot ("."). If the resulting string is a legal package name then it is assumed to be a package name. For example, if the JAR file contains the entry "p/q/Foo.class" then the package name derived is "p.q".
     The contents of entries starting with 
    META-INF/services/ are assumed to be service configuration files (see ServiceLoader). If the name of a file (that follows META-INF/services/) is a legal class name then it is assumed to be the fully-qualified class name of a service type. The entries in the file are assumed to be the fully-qualified class names of provider classes. 
     If the JAR file has a Main-Class attribute in its main manifest, its value is a legal class name, and its package is in the set of packages derived for the module, then the value is the module main class. 

 If a ModuleDescriptor cannot be created (by means of the ModuleDescriptor.Builder API) for an automatic module then FindException is thrown. This can arise when the value of the "Automatic-Module-Name" attribute is not a legal module name, a legal module name cannot be derived from the file name of the JAR file, where the JAR file contains a .class in the top-level directory of the JAR file, where an entry in a service configuration file is not a legal class name or its package name is not in the set of packages derived for the module. 
 In addition to JAR files, an implementation may also support modules that are packaged in other implementation specific module formats. If an element in the array specified to this method is a path to a directory of modules then entries in the directory that not recognized as modules are ignored. If an element in the array is a path to a packaged module that is not recognized then a FindException is thrown when the file is encountered. Paths to files that do not exist are always ignored. 
 As with automatic modules, the contents of a packaged or exploded
module may need to be scanned in order to determine the packages in the module. Whether 
hidden files are ignored or not is implementation specific and therefore not specified. If a .class file (other than 
module-info.class) is found in the top-level directory then it is assumed to be a class in the unnamed package and so FindException is thrown. 
 Finders created by this method are lazy and do not eagerly check that the given file paths are directories or packaged modules. Consequently, the find or findAll methods will only fail if invoking these methods results in searching a directory or packaged module and an error is encountered. 
Params: entries – 
       A possibly-empty array of paths to directories of modules
       or paths to packaged or exploded modules
Returns: A ModuleFinder that locates modules on the file system/**
     * Returns a module finder that locates modules on the file system by
     * searching a sequence of directories and/or packaged modules.
     *
     * Each element in the given array is one of:
     * <ol>
     *     <li><p> A path to a directory of modules.</p></li>
     *     <li><p> A path to the <em>top-level</em> directory of an
     *         <em>exploded module</em>. </p></li>
     *     <li><p> A path to a <em>packaged module</em>. </p></li>
     * </ol>
     *
     * The module finder locates modules by searching each directory, exploded
     * module, or packaged module in array index order. It finds the first
     * occurrence of a module with a given name and ignores other modules of
     * that name that appear later in the sequence.
     *
     * <p> If an element is a path to a directory of modules then each entry in
     * the directory is a packaged module or the top-level directory of an
     * exploded module. It is an error if a directory contains more than one
     * module with the same name. If an element is a path to a directory, and
     * that directory contains a file named {@code module-info.class}, then the
     * directory is treated as an exploded module rather than a directory of
     * modules. </p>
     *
     * <p id="automatic-modules"> The module finder returned by this method
     * supports modules packaged as JAR files. A JAR file with a {@code
     * module-info.class} in its top-level directory, or in a versioned entry
     * in a {@linkplain java.util.jar.JarFile#isMultiRelease() multi-release}
     * JAR file, is a modular JAR file and thus defines an <em>explicit</em>
     * module. A JAR file that does not have a {@code module-info.class} in its
     * top-level directory defines an <em>automatic module</em>, as follows:
     * </p>
     *
     * <ul>
     *
     *     <li><p> If the JAR file has the attribute "{@code Automatic-Module-Name}"
     *     in its main manifest then its value is the {@linkplain
     *     ModuleDescriptor#name() module name}. The module name is otherwise
     *     derived from the name of the JAR file. </p></li>
     *
     *     <li><p> The {@link ModuleDescriptor#version() version}, and the
     *     module name when the attribute "{@code Automatic-Module-Name}" is not
     *     present, are derived from the file name of the JAR file as follows: </p>
     *
     *     <ul>
     *
     *         <li><p> The "{@code .jar}" suffix is removed. </p></li>
     *
     *         <li><p> If the name matches the regular expression {@code
     *         "-(\\d+(\\.|$))"} then the module name will be derived from the
     *         subsequence preceding the hyphen of the first occurrence. The
     *         subsequence after the hyphen is parsed as a {@link
     *         ModuleDescriptor.Version Version} and ignored if it cannot be
     *         parsed as a {@code Version}. </p></li>
     *
     *         <li><p> All non-alphanumeric characters ({@code [^A-Za-z0-9]})
     *         in the module name are replaced with a dot ({@code "."}), all
     *         repeating dots are replaced with one dot, and all leading and
     *         trailing dots are removed. </p></li>
     *
     *         <li><p> As an example, a JAR file named "{@code foo-bar.jar}" will
     *         derive a module name "{@code foo.bar}" and no version. A JAR file
     *         named "{@code foo-bar-1.2.3-SNAPSHOT.jar}" will derive a module
     *         name "{@code foo.bar}" and "{@code 1.2.3-SNAPSHOT}" as the version.
     *         </p></li>
     *
     *     </ul></li>
     *
     *     <li><p> The set of packages in the module is derived from the
     *     non-directory entries in the JAR file that have names ending in
     *     "{@code .class}". A candidate package name is derived from the name
     *     using the characters up to, but not including, the last forward slash.
     *     All remaining forward slashes are replaced with dot ({@code "."}). If
     *     the resulting string is a legal package name then it is assumed to be
     *     a package name. For example, if the JAR file contains the entry
     *     "{@code p/q/Foo.class}" then the package name derived is
     *     "{@code p.q}".</p></li>
     *
     *     <li><p> The contents of entries starting with {@code
     *     META-INF/services/} are assumed to be service configuration files
     *     (see {@link java.util.ServiceLoader}). If the name of a file
     *     (that follows {@code META-INF/services/}) is a legal class name
     *     then it is assumed to be the fully-qualified class name of a service
     *     type. The entries in the file are assumed to be the fully-qualified
     *     class names of provider classes. </p></li>
     *
     *     <li><p> If the JAR file has a {@code Main-Class} attribute in its
     *     main manifest, its value is a legal class name, and its package is
     *     in the set of packages derived for the module, then the value is the
     *     module {@linkplain ModuleDescriptor#mainClass() main class}. </p></li>
     *
     * </ul>
     *
     * <p> If a {@code ModuleDescriptor} cannot be created (by means of the
     * {@link ModuleDescriptor.Builder ModuleDescriptor.Builder} API) for an
     * automatic module then {@code FindException} is thrown. This can arise
     * when the value of the "{@code Automatic-Module-Name}" attribute is not a
     * legal module name, a legal module name cannot be derived from the file
     * name of the JAR file, where the JAR file contains a {@code .class} in
     * the top-level directory of the JAR file, where an entry in a service
     * configuration file is not a legal class name or its package name is not
     * in the set of packages derived for the module. </p>
     *
     * <p> In addition to JAR files, an implementation may also support modules
     * that are packaged in other implementation specific module formats. If
     * an element in the array specified to this method is a path to a directory
     * of modules then entries in the directory that not recognized as modules
     * are ignored. If an element in the array is a path to a packaged module
     * that is not recognized then a {@code FindException} is thrown when the
     * file is encountered. Paths to files that do not exist are always ignored.
     * </p>
     *
     * <p> As with automatic modules, the contents of a packaged or exploded
     * module may need to be <em>scanned</em> in order to determine the packages
     * in the module. Whether {@linkplain java.nio.file.Files#isHidden(Path)
     * hidden files} are ignored or not is implementation specific and therefore
     * not specified. If a {@code .class} file (other than {@code
     * module-info.class}) is found in the top-level directory then it is
     * assumed to be a class in the unnamed package and so {@code FindException}
     * is thrown. </p>
     *
     * <p> Finders created by this method are lazy and do not eagerly check
     * that the given file paths are directories or packaged modules.
     * Consequently, the {@code find} or {@code findAll} methods will only
     * fail if invoking these methods results in searching a directory or
     * packaged module and an error is encountered. </p>
     *
     * @param entries
     *        A possibly-empty array of paths to directories of modules
     *        or paths to packaged or exploded modules
     *
     * @return A {@code ModuleFinder} that locates modules on the file system
     */
    static ModuleFinder of(Path... entries) {
        // special case zero entries
        if (entries.length == 0) {
            return new ModuleFinder() {
                @Override
                public Optional<ModuleReference> find(String name) {
                    Objects.requireNonNull(name);
                    return Optional.empty();
                }

                @Override
                public Set<ModuleReference> findAll() {
                    return Set.of();
                }
            };
        }

        return ModulePath.of(entries);
    }

    Returns a module finder that is composed from a sequence of zero or more module finders. The find method of the resulting module finder will locate a module by invoking the find method of each module finder, in array index order, until either the module is found or all module finders have been searched. The 
findAll method of the resulting module finder will return a set of modules that includes all modules located by the first module finder. The set of modules will include all modules located by the second or subsequent module finder that are not located by previous module finders in the sequence.  When locating modules then any exceptions or errors thrown by the find or findAll methods of the underlying module finders will be propagated to the caller of the resulting module finder's find or findAll methods. 
Params: finders – 
       The array of module finders
Returns: A ModuleFinder that composes a sequence of module finders/**
     * Returns a module finder that is composed from a sequence of zero or more
     * module finders. The {@link #find(String) find} method of the resulting
     * module finder will locate a module by invoking the {@code find} method
     * of each module finder, in array index order, until either the module is
     * found or all module finders have been searched. The {@link #findAll()
     * findAll} method of the resulting module finder will return a set of
     * modules that includes all modules located by the first module finder.
     * The set of modules will include all modules located by the second or
     * subsequent module finder that are not located by previous module finders
     * in the sequence.
     *
     * <p> When locating modules then any exceptions or errors thrown by the
     * {@code find} or {@code findAll} methods of the underlying module finders
     * will be propagated to the caller of the resulting module finder's
     * {@code find} or {@code findAll} methods. </p>
     *
     * @param finders
     *        The array of module finders
     *
     * @return A {@code ModuleFinder} that composes a sequence of module finders
     */
    static ModuleFinder compose(ModuleFinder... finders) {
        // copy the list and check for nulls
        final List<ModuleFinder> finderList = List.of(finders);

        return new ModuleFinder() {
            private final Map<String, ModuleReference> nameToModule = new HashMap<>();
            private Set<ModuleReference> allModules;

            @Override
            public Optional<ModuleReference> find(String name) {
                // cached?
                ModuleReference mref = nameToModule.get(name);
                if (mref != null)
                    return Optional.of(mref);
                Optional<ModuleReference> omref = finderList.stream()
                        .map(f -> f.find(name))
                        .flatMap(Optional::stream)
                        .findFirst();
                omref.ifPresent(m -> nameToModule.put(name, m));
                return omref;
            }

            @Override
            public Set<ModuleReference> findAll() {
                if (allModules != null)
                    return allModules;
                // seed with modules already found
                Set<ModuleReference> result = new HashSet<>(nameToModule.values());
                finderList.stream()
                          .flatMap(f -> f.findAll().stream())
                          .forEach(mref -> {
                              String name = mref.descriptor().name();
                              if (nameToModule.putIfAbsent(name, mref) == null) {
                                  result.add(mref);
                              }
                          });
                allModules = Collections.unmodifiableSet(result);
                return allModules;
            }
        };
    }

}
Params:	name – The name of the module to find
Throws:	FindException – If an error occurs finding the module SecurityException – If denied by the security manager
Returns:	A reference to a module with the given name or an empty `Optional` if not found
Throws:	FindException – If an error occurs finding all modules SecurityException – If denied by the security manager
API Note:	This is important to have for methods such as `resolveAndBind` that need to scan the module path to find modules that provide a specific service.
Returns:	The set of all module references that this finder locates
Throws:	SecurityException – If denied by the security manager
Returns:	A `ModuleFinder` that locates the system modules
Params:	entries – A possibly-empty array of paths to directories of modules or paths to packaged or exploded modules
Returns:	A `ModuleFinder` that locates modules on the file system
Params:	finders – The array of module finders
Returns:	A `ModuleFinder` that composes a sequence of module finders
/

java/ 11/ java.base/java/lang/module/ModuleFinder.java
