如何用java读取php的gzencode函数输出的压缩字符?

输入的字符串为php的gzencode压缩的字符串，可以用gzdecode解开，但是用java的java.util.zip.GZIPInputStream读入字符串时，总是提示：
java.util.zip.ZipException: Not in GZIP format
希望有经验的朋友帮我解答一下，我的代码如下：
JAVA

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;
public class Gzdecode {
    public static void decompress(InputStream is, OutputStream os)
            throws Exception {
        GZIPInputStream gis = new GZIPInputStream(is);
        int count;
        byte data[] = new byte[BUFFER];
        while ((count = gis.read(data, 0, BUFFER)) != -1) {
            os.write(data, 0, count);
        }
        gis.close();
    }
    public static byte[] decompress(byte[] data) throws Exception {  
        ByteArrayInputStream bais = new ByteArrayInputStream(data);  
        ByteArrayOutputStream baos = new ByteArrayOutputStream();   
        // 解压缩   
        decompress(bais, baos);   
        data = baos.toByteArray();  
        baos.flush();  
        baos.close();   
        bais.close();   
        return data;  
    }
        public static void main(String[] args) throws Exception
    {
        String input="";
        byte[] data=input.getBytes("UTF-8");
        byte[] data_decompress=decompress(data);
        System.out.write(data_decompress);