检查输入流是否被压缩。

/*

 * Copyright 2014 davidherod.

 *

 * 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.nowjava;

/* from 
时代Java公众号 - nowjava.com*/

import java.io.IOException;

import java.io.InputStream;

import java.io.PushbackInputStream;


import java.util.zip.GZIPInputStream;


public class Main {

    /**

     * Checks if an input stream is gzipped.

     *

     * @param in

     * @return

     */

    public static InputStream decompressStream(InputStream input)

            throws IOException {

        PushbackInputStream pb = new PushbackInputStream(input, 2); //we need a pushbackstream to look ahead

        byte[] signature = new byte[2];

        pb.read(signature); //read the signature

        pb.unread(signature); //push back the signature to the stream

        if (signature[0] == (byte) 0x1f && signature[1] == (byte) 0x8b)