Compressing and Decompressing strings in Java

[Chitra Raji]

Hi

I compressed a string using GZIPOutputStream. Now when i try to uncompress it using GZIPInputStream throws the following exception "java.util.zip.ZipException: invalid bit length repeat" while reading from the stream.

Anyone who has compressed and or uncompressed strings, please help.

[Kalai Selvan]

Hi Chitra,
I just tried the following code and it works......

  
import java.util.zip.GZIPOutputStream;
import java.util.zip.GZIPInputStream;
 
import java.io.*;
 
class StringEg {
 
public static void main(String[] args) throws IOException {

String str = "Test String";

FileOutputStream fos = new FileOutputStream("str.txt");
GZIPOutputStream gzos = new GZIPOutputStream(fos);
gzos.write(str.getBytes());
gzos.close(); 
FileInputStream fis = new FileInputStream("str.txt");
GZIPInputStream gzis = new GZIPInputStream(fis);
                //I am taken the size of array as 11 since i know the size.
                //But it should be fetched dynamically.
byte arr[] = new byte[11];

gzis.read(arr);
str = new String(arr);
System.out.println("==> " + str);
}
}
 

Please while sending such question also provide the code. So the problem will be easy to undestand.


Regards,
Kalai Selvan T.

[Chitra Raji]

Thanx.

But the problem is i dont want to use files. i want to compress/decompress a string. Following is my code.

private static String compress(String str)
{
String str1 = null;
ByteArrayOutputStream bos = null;
try
{
bos = new ByteArrayOutputStream();
BufferedOutputStream dest = null;

byte b[] = str.getBytes();
GZIPOutputStream gz = new GZIPOutputStream(bos,b.length);
gz.write(b,0,b.length);
bos.close();
gz.close();

}
catch(Exception e) {
System.out.println(e);
e.printStackTrace();
}
byte b1[] = bos.toByteArray();
return new String(b1);
}

private static String deCompress(String str)
{
String s1 = null;

try
{
byte b[] = str.getBytes();
InputStream bais = new ByteArrayInputStream(b);
GZIPInputStream gs = new GZIPInputStream(bais);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int numBytesRead = 0;
byte [] tempBytes = new byte[6000];
try
{
while ((numBytesRead = gs.read(tempBytes, 0, tempBytes.length)) != -1)
{
baos.write(tempBytes);
}
s1 = new String(baos.toByteArray());
s1= baos.toString();
}
catch(ZipException e)
{
e.printStackTrace();
}
}
catch(Exception e) {
e.printStackTrace();
}
return s1;
}

[Kalai Selvan]

Hi Chitra,
U can refer java doc of java.util.zip.Deflater and ava.util.zip.Inflator,
some examples were given there.

I hope that will help you.

Regards,
Kalai Selvan T.

[Chitra Raji]

i tried that also. it gives the same exception. any other alternative?

[Greg T Robertson]

You may need to base 64 encode the strings first depending upon what exactly is in them. There are severl Base 64 encoders out there (may be one in standard J2SE now not sure) but if not check apache's website.

[Dirk Schreckmann]

When posting code, please be sure to surround the code with the [code] and [/code] UBB Tags. This will help to preserve the formatting of the code, thus making it easier to read and understand.

[Susanta Chatterjee]

Hi Chitra,

Change the line containing:

 baos.write(tempBytes);

to

  baos.write(tempBytes, 0, numBytesRead); 

in deCompress method.

I tried that with your two methods and works perfectly.

What happening is: you are writing more bytes to your output stream, than you read in from inputstream and thereby corrupting the stream.

Also, in future, when you post, please follow the advices made to you already by others.

Susanta
[ September 23, 2004: Message edited by: Susanta Chatterjee ]

[Chitra Raji]

Hi susanta

i tried the code that u sent. it is not working. i am still getting the same exception.

thanx.
Chitra

[Chitra Raji]

Hi Greg T Robertson

Thanx for the information. It worked.

Thanx and Regards
Chitra

[Alexandr Erofeev]

Chitra Raji wrote:
But the problem is i dont want to use files. i want to compress/decompress a string. Following is my code.

private static String compress(String str) 
   {
String str1 = null;
ByteArrayOutputStream bos = null;
try
{
bos = new ByteArrayOutputStream();
BufferedOutputStream dest = null;
 
byte b[] = str.getBytes();
GZIPOutputStream gz = new GZIPOutputStream(bos,b.length);
gz.write(b,0,b.length);
bos.close();
gz.close();

}
catch(Exception e) {
System.out.println(e);
  e.printStackTrace();
   }
   byte b1[] = bos.toByteArray();
   return new String(b1);
   }
   
   private static String deCompress(String str)
   {
String s1 = null;
 
try
{
byte b[] = str.getBytes();
InputStream bais = new ByteArrayInputStream(b);
GZIPInputStream gs = new GZIPInputStream(bais);
ByteArrayOutputStream baos  = new ByteArrayOutputStream();
int numBytesRead = 0;
byte [] tempBytes = new byte[6000];
try
{
while ((numBytesRead = gs.read(tempBytes, 0, tempBytes.length)) != -1)
{   
baos.write(tempBytes);
}
s1 = new String(baos.toByteArray());
s1= baos.toString();
}
catch(ZipException e)
{
e.printStackTrace();
}
}
catch(Exception e) {
  e.printStackTrace();
 }
return s1;
 }

Your code generates an error.

java.io.IOException: unknown format (magic number ef1f)
GZIPInputStream gs = new GZIPInputStream(bais);

Сode:

String str = "{\"ErrorCode\":12,\"Message\":\"How to decompres!\"}";
String cmpr = compress(str);
String dcmpr = deCompress(cmpr);

[Jesper de Jong]

Hello Alexandr, welcome to the Ranch!

Thanks for you answer. Please note that the original question was asked in 2004. The person who asked the question is probably not still waiting for an answer eight years later.

[Alexandr Erofeev]

public String unZip(String zipped) throws DataFormatException, IOException {
        byte[] bytes = zipped.getBytes("WINDOWS-1251");
        Inflater decompressed = new Inflater();
        decompressed.setInput(bytes);

        byte[] result = new byte[100];
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();

        while (decompressed.inflate(result) != 0)
            buffer.write(result);

        decompressed.end();

        return new String(buffer.toByteArray(), charset);
    }

It's work

[Winston Gutkowski]

Alexandr Erofeev wrote:It's work

Did you read Jesper's post? It might work, but it's 8 years too late.

Winston