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Indexer Reader is a dependency-less library that is able to read published (remote) index with incremental update support, making usable to integrate published Maven Indexes into any engine without depending on maven-indexer-core and its transitive dependencies.

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package org.apache.maven.index.reader;

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

import java.io.IOException;
import java.io.OutputStream;

/**
 * Maven Index writable {@link ResourceHandler}, is capable of saving resources too. Needed only if incremental index
 * updates are wanted, to store the index state locally, and be able to calculate incremental diffs on next {@link
 * IndexReader} invocation. Is used by single thread only.
 *
 * @see ResourceHandler
 * @since 5.1.2
 */
public interface WritableResourceHandler
        extends ResourceHandler
{
    /**
     * Resource that is writable.
     */
    interface WritableResource
            extends Resource
    {
        /**
         * Returns the {@link OutputStream} stream of the resource, if exists, it will replace the existing content, or
         * if not exists, the resource will be created. The stream should be closed by caller, otherwise resource leaks
         * might be introduced. How and when content is written is left to implementation, but it is guaranteed that
         * this method is called only once, and will be followed by {@link #close()} on the resource itself.
         * Implementation does not have to be "read consistent", in a way to worry what subsequent {@link #read()}
         * method will return, as mixed calls will not happen on same instance of resource.
         */
        OutputStream write() throws IOException;
    }

    /**
     * Returns the {@link WritableResource} with {@code name}. Returned locator should be handled as
     * resource.
     *
     * @param name Resource name, guaranteed to be non-{@code null} and is FS and URL safe string.
     */
    WritableResource locate( String name ) throws IOException;
}