Question

I am compressing a string using gzip, then uncompress the result, however I got the following exception, why?

 output:
Exception in thread "main" java.util.zip.ZipException: oversubscribed dynamic bit lengths tree
 at java.util.zip.InflaterInputStream.read(Unknown Source)
 at java.util.zip.GZIPInputStream.read(Unknown Source)
 at Test.main(Test.java:25)

public class Test {
 public static void main(String[]args) throws IOException{
  String s="helloworldthisisatestandtestonlydsafsdafdsfdsafadsfdsfsdfdsfdsfdsfdsfsadfdsfdasfassdfdfdsfdsdssdfdsfdsfd";
  byte[]bs=s.getBytes();
  ByteArrayOutputStream outstream = new ByteArrayOutputStream();

  GZIPOutputStream gzipOut = new GZIPOutputStream(outstream);
  gzipOut.write(bs);
  gzipOut.finish();
  String out=outstream.toString();
  System.out.println(out);
  System.out.println(out.length());

  ByteArrayInputStream in = new ByteArrayInputStream(out.getBytes());
  GZIPInputStream gzipIn=new GZIPInputStream(in);
  byte[]uncompressed = new byte[100000];
  int len=10, offset=0, totalLen=0;
  while((len = gzipIn.read(uncompressed, offset, len)) >0){ // this line
   offset+=len;
   totalLen+=len;
  }

  String uncompressedString=new String(uncompressed,0,totalLen);
  System.out.println(uncompressedString);
 }
}

Answer 1

According to this page, a likely cause is that the ZIP file you are trying to read is corrupted. (I know it is not an exact match to your circumstances … but I’m sure that the exception message is indicative.)

In your case, the problem is that you are converting the gzip stream from a byte array into a String and then back to a byte array. This is almost certainly a lossy operation, resulting a corrupted GZIP stream.

If you want to convert an arbitrary byte array to a string form and back, you will need to use one of the string encoding formats designed for that purpose; e.g. base64.

Alternatively, just change this:

    String out = outstream.toString();
    ByteArrayInputStream in = new ByteArrayInputStream(out.getBytes());

to this:

    byte[] out = outstream.toByteArray();
    ByteArrayInputStream in = new ByteArrayInputStream(out);