通过检查GZIP幻数来确定指定的流是否包含压缩的数据，并返回能够读取这些数据的流。

/**

 * 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.

 */
 /** 
 来 自 
 n  o  w  j  a  v  a . c o m
 **/

//package com.nowjava;

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/** 时代Java公众号 提 供 **/

            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