compression and decompression of string data in java

Question

I am using the following code to compress and decompress string data  but the problem which I am facing is  it is easily getting compressed without error  but decompress method throws following error    Exception in thread  main  java io IOException  Not in GZIP format  public static void main String   args  throws Exception           String string    I am what I am hhhhhhhhhhhhhhhhhhhhhhhhhhhhh                     bjggujhhhhhhhhh                     rggggggggggggggggggggggggg                     esfffffffffffffffffffffffffffffff                     esffffffffffffffffffffffffffffffff                     esfekfgy enter code here etd enter code here wdd                     heljwidgutwdbwdq8d                     skdfgysrdsdnjsvfyekbdsgcu                    jbujsbjvugsduddbdj           System out println  after compress             String compressed   compress string           System out println compressed           System out println  after decompress             String decomp   decompress compressed           System out println decomp                public static String compress String str  throws Exception           if  str    null    str length      0                return str                    System out println  String length       str length             ByteArrayOutputStream obj new ByteArrayOutputStream            GZIPOutputStream gzip   new GZIPOutputStream obj           gzip write str getBytes  UTF-8             gzip close            String outStr   obj toString  UTF-8            System out println  Output String length       outStr length             return outStr                public static String decompress String str  throws Exception           if  str    null    str length      0                return str                    System out println  Input String length       str length             GZIPInputStream gis   new GZIPInputStream new ByteArrayInputStream str getBytes  UTF-8              BufferedReader bf   new BufferedReader new InputStreamReader gis   UTF-8             String outStr               String line          while   line bf readLine     null              outStr    line                    System out println  Output String lenght       outStr length             return outStr           Still couldn t figure out how to fix this issue

User · Answer

The problem is this line       String outStr   obj toString  UTF-8      The byte array obj contains arbitrary binary data   You can t  decode  arbitrary binary data as if it was UTF-8   If you try you will get a String that cannot then be  encoded  back to bytes   Or at least  the bytes you get will be different to what you started with     to the extent that they are no longer a valid GZIP stream   The fix is to store or transmit the contents of the byte array as-is   Don t try to convert it into a String   It is binary data  not text

User · Answer

This is because of   String outStr   obj toString  UTF-8      Send the byte   which you can get from your ByteArrayOutputStream and use it as such in your ByteArrayInputStream to construct your GZIPInputStream  Following are the changes which need to be done in your code   byte   compressed   compress string     In the main method  public static byte   compress String str  throws Exception                       return obj toByteArray       public static String decompress byte   bytes  throws Exception               GZIPInputStream gis   new GZIPInputStream new ByteArrayInputStream bytes

User · Answer

Another example of correct compression and decompression    Slf4j public class GZIPCompression       public static byte   compress final String stringToCompress            if  isNull stringToCompress     stringToCompress length      0                return null                     try  final ByteArrayOutputStream baos   new ByteArrayOutputStream                final GZIPOutputStream gzipOutput   new GZIPOutputStream baos                 gzipOutput write stringToCompress getBytes UTF 8                gzipOutput finish                return baos toByteArray              catch  IOException e                throw new UncheckedIOException  Error while compression    e                        public static String decompress final byte   compressed            if  isNull compressed     compressed length    0                return null                     try  final GZIPInputStream gzipInput   new GZIPInputStream new ByteArrayInputStream compressed                 final StringWriter stringWriter   new StringWriter                  IOUtils copy gzipInput  stringWriter  UTF 8               return stringWriter toString              catch  IOException e                throw new UncheckedIOException  Error while decompression    e

User · Answer

The above Answer solves our problem but in addition to that   if we are trying to decompress a uncompressed  not a zip format   byte     we will get  Not in GZIP format  exception message   For solving that we can add addition code in our Class   public static boolean isCompressed final byte   compressed        return  compressed 0      byte   GZIPInputStream GZIP MAGIC    amp  amp   compressed 1      byte   GZIPInputStream GZIP MAGIC  gt  gt  8        My Complete Compression Class with compress decompress would look like   import java io BufferedReader  import java io ByteArrayInputStream  import java io ByteArrayOutputStream  import java io IOException  import java io InputStreamReader  import java util zip GZIPInputStream  import java util zip GZIPOutputStream   public class GZIPCompression     public static byte   compress final String str  throws IOException       if   str    null      str length      0           return null            ByteArrayOutputStream obj   new ByteArrayOutputStream        GZIPOutputStream gzip   new GZIPOutputStream obj       gzip write str getBytes  UTF-8         gzip flush        gzip close        return obj toByteArray           public static String decompress final byte   compressed  throws IOException       final StringBuilder outStr   new StringBuilder        if   compressed    null      compressed length    0           return               if  isCompressed compressed           final GZIPInputStream gis   new GZIPInputStream new ByteArrayInputStream compressed          final BufferedReader bufferedReader   new BufferedReader new InputStreamReader gis   UTF-8            String line        while   line   bufferedReader readLine       null            outStr append line                 else         outStr append compressed             return outStr toString           public static boolean isCompressed final byte   compressed        return  compressed 0      byte   GZIPInputStream GZIP MAGIC    amp  amp   compressed 1      byte   GZIPInputStream GZIP MAGIC  gt  gt  8

User · Answer

If you ever need to transfer the zipped content via network or store it as text  you have to use Base64 encoder such as apache commons codec Base64  to convert the byte array to a Base64 String  and decode the string back to byte array at remote client   Found an example at Use Zip Stream and Base64 Encoder to Compress Large String Data

User · Answer

You can t convert binary data to String  As a solution you can encode binary data and then convert to String  For example  look at this How do you convert binary data to Strings and back in Java

User · Answer

Client send some messages need be compressed  server  kafka  decompress the string meesage  Below is my sample   compress      public static String compress String str  String inEncoding            if  str    null    str length      0                return str                    try               ByteArrayOutputStream out   new ByteArrayOutputStream                GZIPOutputStream gzip   new GZIPOutputStream out               gzip write str getBytes inEncoding                gzip close                return URLEncoder encode out toString  ISO-8859-1     UTF-8              catch  IOException e                e printStackTrace                      return null          decompress       public static String decompress String str  String outEncoding            if  str    null    str length      0                return str                     try               String decode   URLDecoder decode str   UTF-8                 ByteArrayOutputStream out   new ByteArrayOutputStream                ByteArrayInputStream in   new ByteArrayInputStream decode getBytes  ISO-8859-1                 GZIPInputStream gunzip   new GZIPInputStream in               byte   buffer   new byte 256               int n              while   n   gunzip read buffer    gt   0                    out write buffer  0  n                             return out toString outEncoding             catch  IOException e                e printStackTrace                      return null

[java] compression and decompression of string data in java

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