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 * Copyright (c) 2015, 2016, 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

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package java.lang.module;

import java.io.Closeable;

import java.io.IOException;

import java.io.InputStream;

import java.net.URI;

import java.nio.ByteBuffer;

import java.util.Objects;

import java.util.Optional;

/**

 * Provides access to the content of a module.

 *

 * <p> A module reader is intended for cases where access to the resources in a

 * module is required, regardless of whether the module has been loaded.

 * A framework that scans a collection of packaged modules on the file system,

 * for example, may use a module reader to access a specific resource in each

 * module. A module reader is also intended to be used by {@code ClassLoader}

 * implementations that load classes and resources from modules. </p>

 *

 * <p> A {@code ModuleReader} is {@linkplain ModuleReference#open open} upon

 * creation and is closed by invoking the {@link #close close} method.  Failure

 * to close a module reader may result in a resource leak.  The {@code

 * try-with-resources} statement provides a useful construct to ensure that

 * module readers are closed. </p>

 *

 * <p> A {@code ModuleReader} implementation may require permissions to access

 * resources in the module. Consequently the {@link #find find}, {@link #open

 * open} and {@link #read read} methods may throw {@code SecurityException} if

 * access is denied by the security manager. </p>

 *

 * @see ModuleReference

 * @since 9

 */

public interface ModuleReader extends Closeable {

    /**

     * Finds a resource, returning a URI to the resource in the module.

     *

     * @param  name

     *         The name of the resource to open for reading

     *

     * @return A URI to the resource; an empty {@code Optional} if the resource

     *         is not found or a URI cannot be constructed to locate the

     *         resource

     *

     * @throws IOException

     *         If an I/O error occurs or the module reader is closed

     * @throws SecurityException

     *         If denied by the security manager

     *

     * @see ClassLoader#getResource(String)

     */

    Optional<URI> find(String name) throws IOException;

    /**

     * Opens a resource, returning an input stream to read the resource in

     * the module.

     *

     * @implSpec The default implementation invokes the {@link #find(String)

     * find} method to get a URI to the resource. If found, then it attempts

     * to construct a {@link java.net.URL URL} and open a connection to the

     * resource.

     *

     * @param  name

     *         The name of the resource to open for reading

     *

     * @return An input stream to read the resource or an empty

     *         {@code Optional} if not found

     *

     * @throws IOException

     *         If an I/O error occurs or the module reader is closed

     * @throws SecurityException

     *         If denied by the security manager

     */

    default Optional<InputStream> open(String name) throws IOException {

        Optional<URI> ouri = find(name);

        if (ouri.isPresent()) {

            return Optional.of(ouri.get().toURL().openStream());

        } else {

            return Optional.empty();

        }

    }

    /**

     * Reads a resource, returning a byte buffer with the contents of the

     * resource.

     *

     * The element at the returned buffer's position is the first byte of the

     * resource, the element at the buffer's limit is the last byte of the

     * resource. Once consumed, the {@link #release(ByteBuffer) release} method

     * must be invoked. Failure to invoke the {@code release} method may result

     * in a resource leak.

     *

     * @apiNote This method is intended for high-performance class loading. It

     * is not capable (or intended) to read arbitrary large resources that

     * could potentially be 2GB or larger. The rational for using this method

     * in conjunction with the {@code release} method is to allow module reader

     * implementations manage buffers in an efficient manner.

     *

     * @implSpec The default implementation invokes the {@link #open(String)

     * open} method and reads all bytes from the input stream into a byte

     * buffer.

     *

     * @param  name

     *         The name of the resource to read

     *

     * @return A byte buffer containing the contents of the resource or an

     *         empty {@code Optional} if not found

     *

     * @throws IOException

     *         If an I/O error occurs or the module reader is closed

     * @throws SecurityException

     *         If denied by the security manager

     *

     * @see ClassLoader#defineClass(String, ByteBuffer, java.security.ProtectionDomain)

     */

    default Optional<ByteBuffer> read(String name) throws IOException {

        Optional<InputStream> oin = open(name);

        if (oin.isPresent()) {

            try (InputStream in = oin.get()) {

                return Optional.of(ByteBuffer.wrap(in.readAllBytes()));

            }

        } else {

            return Optional.empty();

        }

    }

    /**

     * Release a byte buffer. This method should be invoked after consuming

     * the contents of the buffer returned by the {@code read} method.

     * The behavior of this method when invoked to release a buffer that has

     * already been released, or the behavior when invoked to release a buffer

     * after a {@code ModuleReader} is closed is implementation specific and

     * therefore not specified.

     *

     * @param  bb

     *         The byte buffer to release

     *

     * @implSpec The default implementation doesn't do anything except check

     * if the byte buffer is null.

     */

    default void release(ByteBuffer bb) {

        Objects.requireNonNull(bb);

    }

    /**

     * Closes the module reader. Once closed then subsequent calls to locate or

     * read a resource will fail by returning {@code Optional.empty()} or

     * throwing {@code IOException}.

     *

     * <p> A module reader is not required to be asynchronously closeable. If a

     * thread is reading a resource and another thread invokes the close method,

     * then the second thread may block until the read operation is complete.

     *

     * <p> The behavior of {@code InputStream}s obtained using the {@link

     * #open(String) open} method and used after the module reader is closed

     * is implementation specific and therefore not specified.

     */

    @Override

    void close() throws IOException;

}