Determines whether the specified stream contains gzipped data, by checking for the GZIP magic number, and returns a stream capable of reading those data. - Java File Path IO

Java examples for File Path IO:GZIP

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Description

Determines whether the specified stream contains gzipped data, by checking for the GZIP magic number, and returns a stream capable of reading those data.

Demo Code

/**//from w ww  . jav a 2s .c o  m
 * Copy of the code from github.com/bndtools/bnd, reason: not available at Maven central or other repository
 *
 * Licensed 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 com.java2s;
import java.io.*;
import java.util.zip.*;

public class Main {
    /**
     * Determines whether the specified stream contains gzipped data, by
     * checking for the GZIP magic number, and returns a stream capable of
     * reading those data.
     *
     * @throws IOException
     */
    public static InputStream detectCompression(InputStream stream)
            throws IOException {
        InputStream buffered;
        if (stream.markSupported())
            buffered = stream;
        else
            buffered = new BufferedInputStream(stream);

        buffered.mark(2);
        int magic = readUShort(buffered);
        buffered.reset();

        InputStream result;
        if (magic == GZIPInputStream.GZIP_MAGIC)
            result = new GZIPInputStream(buffered);
        else
            result = buffered;
        return result;
    }

    private static int readUShort(InputStream in) throws IOException {
        int b = readUByte(in);
        return (readUByte(in) << 8) | b;
    }

    private static int readUByte(InputStream in) throws IOException {
        int b = in.read();
        if (b == -1) {
            throw new EOFException();
        }
        if (b < -1 || b > 255) {
            // Report on this.in, not argument in; see read{Header, Trailer}.
            throw new IOException(in.getClass().getName()
                    + ".read() returned value out of range -1..255: " + b);
        }
        return b;
    }
}

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