java GZIP的压缩解压缩问题

public static String compress(String str) throws IOException {
if (str == null || str.length() == 0) {
return str;
}
ByteArrayOutputStream out = new ByteArrayOutputStream();
GZIPOutputStream gzip = new GZIPOutputStream(out);
gzip.write(str.getBytes());
gzip.close();
gzip.finish();
// return out.toString("ISO-8859-1");
return out.toString("UTF-8");
}

// 解压缩   
  public static String uncompress(String str) throws IOException {   
    if (str == null || str.length() == 0) {   
      return str;   
    }   
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    ByteArrayInputStream in = new ByteArrayInputStream(str.getBytes("utf-8"));   
    GZIPInputStream gunzip = new GZIPInputStream(in);   
    byte[] buffer = new byte[256];   
    int n;   
    while ((n = gunzip.read(buffer))>=0) {   
      out.write(buffer, 0, n);   
    }   
    // toString()使用平台默认编码，也可以显式的指定如toString("GBK")  
    return out.toString();   
  }   

    Exception in thread "main" java.io.IOException: Not in GZIP format
at java.util.zip.GZIPInputStream.readHeader(GZIPInputStream.java:141)
at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:56)
at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:65)
at Util.ZipUtil2.uncompress(ZipUtil2.java:106)
at Util.ZipUtil2.main(ZipUtil2.java:126)

public static byte[] compress(String str) throws IOException {
if (str == null || str.length() == 0) {
return null;
}
byte[] outPut = null;
ByteArrayOutputStream out = new ByteArrayOutputStream();
GZIPOutputStream gzip = new GZIPOutputStream(out);
gzip.write(str.getBytes());
gzip.close();
gzip.finish();
outPut = out.toByteArray();
// return out.toString("ISO-8859-1");
return outPut;
}

// 解压缩
public static String uncompress(byte[] str) throws IOException {

    ByteArrayInputStream in = new ByteArrayInputStream(str);
    GZIPInputStream gunzip = new GZIPInputStream(in);
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    byte[] buffer = new byte[256];
    int n;
    while ((n = gunzip.read(buffer)) >= 0) {
        out.write(buffer, 0, n);
    }
    // toString()使用平台默认编码，也可以显式的指定如toString("GBK")
    return out.toString();
}

public static void main(String[] args) {
    try {
        byte[] b=Test.compress("111111111111");
        System.out.println(Test.uncompress(b));
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    };
}

改成上面的就好了，已测