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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
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/* ====================================================================
   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.
==================================================================== */
package org.apache.poi.openxml4j.util;

import java.io.IOException;
import java.io.InputStream;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.compress.archivers.zip.ZipArchiveEntry;

/**
 * Provides a way to get at all the ZipEntries
 *  from a ZipInputStream, as many times as required.
 * Allows a ZipInputStream to be treated much like
 *  a ZipFile, for a price in terms of memory.
 * Be sure to call {@link #close()} as soon as you're
 *  done, to free up that memory!
 */
public class ZipInputStreamZipEntrySource implements ZipEntrySource {
    private static int thresholdForTempFiles = -1;
    private static boolean encryptTempFiles = false;
    private final Map zipEntries = new HashMap<>();

    private InputStream streamToClose;

    /**
     * Set the threshold at which a zip entry is regarded as too large for holding in memory
     * and the data is put in a temp file instead
     * @param thresholdBytes number of bytes at which a zip entry is regarded as too large for holding in memory
     *                       and the data is put in a temp file instead - defaults to -1 meaning temp files are not used
     *                       and that zip entries with more than 2GB of data after decompressing will fail, 0 means all
     *                       zip entries are stored in temp files. A threshold like 50000000 (approx 50Mb is recommended)
     * @since POI 5.1.0
     * @see #setEncryptTempFiles(boolean)
     */
    public static void setThresholdBytesForTempFiles(int thresholdBytes) {
        thresholdForTempFiles = thresholdBytes;
    }

    /**
     * Get the threshold at which it a zip entry is regarded as too large for holding in memory
     * and the data is put in a temp file instead (defaults to -1 meaning temp files are not used)
     * @return threshold in bytes
     * @since POI 5.1.0
     */
    public static int getThresholdBytesForTempFiles() {
        return thresholdForTempFiles;
    }

    /**
     * Encrypt temp files when they are used. Only affects temp files related to zip entries.
     * @param encrypt whether temp files should be encrypted
     * @since POI 5.1.0
     * @see #setThresholdBytesForTempFiles(int)
     */
    public static void setEncryptTempFiles(boolean encrypt) {
        encryptTempFiles = encrypt;
    }

    /**
     * Whether temp files should be encrypted (default false). Only affects temp files related to zip entries.
     * @since POI 5.1.0
     */
    public static boolean shouldEncryptTempFiles() {
        return encryptTempFiles;
    }

    /**
     * Reads all the entries from the ZipInputStream 
     *  into memory, and don't close (since POI 4.0.1) the source stream.
     * We'll then eat lots of memory, but be able to
     *  work with the entries at-will.
     * @see #setThresholdBytesForTempFiles
     */
    public ZipInputStreamZipEntrySource(ZipArchiveThresholdInputStream inp) throws IOException {
        for (;;) {
            final ZipArchiveEntry zipEntry = inp.getNextEntry();
            if (zipEntry == null) {
                break;
            }
            zipEntries.put(zipEntry.getName(), new ZipArchiveFakeEntry(zipEntry, inp));
        }

        streamToClose = inp;
    }

    @Override
    public Enumeration getEntries() {
        return Collections.enumeration(zipEntries.values());
    }

    @Override
    public InputStream getInputStream(ZipArchiveEntry zipEntry) throws IOException {
        assert (zipEntry instanceof ZipArchiveFakeEntry);
        return ((ZipArchiveFakeEntry)zipEntry).getInputStream();
    }

    @Override
    public void close() throws IOException {
        for (ZipArchiveFakeEntry entry : zipEntries.values()) {
            entry.close();
        }

        // Free the memory
        zipEntries.clear();

        streamToClose.close();
    }

    @Override
    public boolean isClosed() {
        return zipEntries.isEmpty();
    }

    @Override
    public ZipArchiveEntry getEntry(final String path) {
        final String normalizedPath = path.replace('\\', '/');
        final ZipArchiveEntry ze = zipEntries.get(normalizedPath);
        if (ze != null) {
            return ze;
        }

        for (final Map.Entry fze : zipEntries.entrySet()) {
            if (normalizedPath.equalsIgnoreCase(fze.getKey())) {
                return fze.getValue();
            }
        }

        return null;
    }
}