GZIP compression to a byte array

问题:

I am trying to write a class that can compress data. The below code fails (no exception is thrown, but the target .gz file is empty.)
Besides: I don't want to generate the .gz file directly like it is done in all examples. I only want to get the compressed data, so that I can e.g. encrypt it before writting the data to a file.

If I write directly to a file everything works fine:

import java.io.*;
import java.util.zip.*;
import java.nio.charset.*;

public class Zipper
{
  public static void main(String[] args)
  {    
    byte[] dataToCompress = "This is the test data."
      .getBytes(StandardCharsets.ISO_8859_1);

    GZIPOutputStream zipStream = null;
    FileOutputStream fileStream = null;
    try
    {
      fileStream = new FileOutputStream("C:/Users/UserName/Desktop/zip_file.gz");
      zipStream = new GZIPOutputStream(fileStream);
      zipStream.write(dataToCompress);

      fileStream.write(compressedData);
    }
    catch(Exception e)
    {
      e.printStackTrace();
    }
    finally
    {
      try{ zipStream.close(); }
        catch(Exception e){ }
      try{ fileStream.close(); }
        catch(Exception e){ }
    }
  }
}

But, if I want to 'bypass' it to the byte array stream it does not produce a single byte - compressedData is always empty.

import java.io.*;
import java.util.zip.*;
import java.nio.charset.*;

public class Zipper
{
  public static void main(String[] args)
  {    
    byte[] dataToCompress = "This is the test data."
      .getBytes(StandardCharsets.ISO_8859_1);
    byte[] compressedData = null;

    GZIPOutputStream zipStream = null;
    ByteArrayOutputStream byteStream = null;
    FileOutputStream fileStream = null;
    try
    {
      byteStream = new ByteArrayOutputStream(dataToCompress.length);
      zipStream = new GZIPOutputStream(byteStream);
      zipStream.write(dataToCompress);

      compressedData = byteStream.toByteArray();

      fileStream = new FileOutputStream("C:/Users/UserName/Desktop/zip_file.gz");
      fileStream.write(compressedData);
    }
    catch(Exception e)
    {
      e.printStackTrace();
    }
    finally
    {
      try{ zipStream.close(); }
        catch(Exception e){ }
      try{ byteStream.close(); }
        catch(Exception e){ }
      try{ fileStream.close(); }
        catch(Exception e){ }
    }
  }
}

回答1:

The problem is that you are not closing the GZIPOutputStream. Until you close it the output will be incomplete.

You just need to close it before reading the byte array. You need to reorder the finally blocks to achieve this.

import java.io.*;
import java.util.zip.*;
import java.nio.charset.*;

public class Zipper
{
  public static void main(String[] args)
  {    
    byte[] dataToCompress = "This is the test data."
      .getBytes(StandardCharsets.ISO_8859_1);

    try
    {
      ByteArrayOutputStream byteStream =
        new ByteArrayOutputStream(dataToCompress.length);
      try
      {
        GZIPOutputStream zipStream =
          new GZIPOutputStream(byteStream);
        try
        {
          zipStream.write(dataToCompress);
        }
        finally
        {
          zipStream.close();
        }
      }
      finally
      {
        byteStream.close();
      }

      byte[] compressedData = byteStream.toByteArray();

      FileOutputStream fileStream =
        new FileOutputStream("C:/Users/UserName/Desktop/zip_file.gz");
      try
      {
        fileStream.write(compressedData);
      }
      finally
      {
        try{ fileStream.close(); }
          catch(Exception e){ /* We should probably delete the file now? */ }
      }
    }
    catch(Exception e)
    {
      e.printStackTrace();
    }
  }
}

I do not recommend inititalizing the stream variables to null, because it means your finally block can also throw a NullPointerException.

Also note that you can declare main to throw IOException (then you would not need the outermost try statement.)

There is little point in swallowing exceptions from zipStream.close();, because if it throws an exception you will not have a valid .gz file (so you should not proceed to write it.)

Also I would not swallow exceptions from byteStream.close(); but for a different reason - they should never be thrown (i.e. there is a bug in your JRE and you would want to know about that.)

回答2:

If you are still looking an answer you can use the below code to get the compressed byte[] using deflater and decompress it using inflater.

public static void main(String[] args) {
        //Some string for testing
        String sr = new String("fsdfesfsfdddddddsfdsfssdfdsfdsfdsfdsfdsdfggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggghghghghggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggfsdfesfsfdddddddsfdsfssdfdsfdsfdsfdsfdsdfggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggghghghghggggggggggggggggggggggggggggggggggggggggg");
        byte[] data = sr.getBytes();
        System.out.println("src size "+data.length);
        try {
            compress(data);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static byte[] compress(byte[] data) throws IOException { 
        Deflater deflater = new Deflater(); 
        deflater.setInput(data); 
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream(data.length);  

        deflater.finish(); 
        byte[] buffer = new byte[1024];  
        while (!deflater.finished()) { 
        int count = deflater.deflate(buffer);  
        outputStream.write(buffer, 0, count);  
        } 
        outputStream.close(); 
        byte[] output = outputStream.toByteArray(); 

        System.out.println("Original: " + data.length  ); 
        System.out.println("Compressed: " + output.length ); 
        return output; 
        }   

回答3:

I've improved JITHINRAJ's code - used try-with-resources:

private static byte[] gzipCompress(byte[] uncompressedData) {
        byte[] result = new byte[]{};
        try (ByteArrayOutputStream bos = new ByteArrayOutputStream(uncompressedData.length);
             GZIPOutputStream gzipOS = new GZIPOutputStream(bos)) {
            gzipOS.write(uncompressedData);
            gzipOS.close();
            result = bos.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }

private static byte[] gzipUncompress(byte[] compressedData) {
        byte[] result = new byte[]{};
        try (ByteArrayInputStream bis = new ByteArrayInputStream(compressedData);
             ByteArrayOutputStream bos = new ByteArrayOutputStream();
             GZIPInputStream gzipIS = new GZIPInputStream(bis)) {
            byte[] buffer = new byte[1024];
            int len;
            while ((len = gzipIS.read(buffer)) != -1) {
                bos.write(buffer, 0, len);
            }
            result = bos.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }

回答4:

Try with this code..

try {
    String inputFileName = "test.txt";  //may use your file_Path
    String zipFileName = "compressed.zip";

    //Create input and output streams
    FileInputStream inStream = new FileInputStream(inputFileName);
    ZipOutputStream outStream = new ZipOutputStream(new FileOutputStream(zipFileName));

    // Add a zip entry to the output stream
    outStream.putNextEntry(new ZipEntry(inputFileName));

    byte[] buffer = new byte[1024];
    int bytesRead;

    //Each chunk of data read from the input stream
    //is written to the output stream
    while ((bytesRead = inStream.read(buffer)) > 0) {
        outStream.write(buffer, 0, bytesRead);
    }

    //Close zip entry and file streams
    outStream.closeEntry();

    outStream.close();
    inStream.close();

} catch (IOException ex) {
    ex.printStackTrace();
}

Also may be helpful this one..

• http://www.java-samples.com/java/zip_files_in_a_folder_using_java.htm

回答5:

You can use the below function, it is tested and working fine.

In general, your code has serious problem of ignoring the exceptions! returning null or simply not printing anything in the catch block will make it very difficult to debug

You do not have to write the zip output to a file if you want to process it further (e.g. encrypt it), you can easily modify the code to write the output to in-memory stream

public static String zip(File inFile, File zipFile) throws IOException {        
    FileInputStream fis = new FileInputStream(inFile);
    FileOutputStream fos = new FileOutputStream(zipFile);
    ZipOutputStream zout = new ZipOutputStream(fos);

    try {
        zout.putNextEntry(new ZipEntry(inFile.getName()));
        byte[] buffer = new byte[BUFFER_SIZE];
        int len;
        while ((len = fis.read(buffer)) > 0) {
            zout.write(buffer, 0, len);
        }
        zout.closeEntry();
    } catch (Exception ex) {
        ex.printStackTrace();
        return null;
    } finally {
        try{zout.close();}catch(Exception ex){ex.printStackTrace();}
        try{fis.close();}catch(Exception ex){ex.printStackTrace();}         
    }
    return zipFile.getAbsolutePath();
}

回答6:

To compress

private static byte[] compress(byte[] uncompressedData) {
        ByteArrayOutputStream bos = null;
        GZIPOutputStream gzipOS = null;
        try {
            bos = new ByteArrayOutputStream(uncompressedData.length);
            gzipOS = new GZIPOutputStream(bos);
            gzipOS.write(uncompressedData);
            gzipOS.close();
            return bos.toByteArray();

        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            try {
                assert gzipOS != null;
                gzipOS.close();
                bos.close();
            }
            catch (Exception ignored) {
            }
        }
        return new byte[]{};
    }

To uncompress

private byte[] uncompress(byte[] compressedData) {
        ByteArrayInputStream bis = null;
        ByteArrayOutputStream bos = null;
        GZIPInputStream gzipIS = null;

        try {
            bis = new ByteArrayInputStream(compressedData);
            bos = new ByteArrayOutputStream();
            gzipIS = new GZIPInputStream(bis);

            byte[] buffer = new byte[1024];
            int len;
            while((len = gzipIS.read(buffer)) != -1){
                bos.write(buffer, 0, len);
            }
            return bos.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            try {
                assert gzipIS != null;
                gzipIS.close();
                bos.close();
                bis.close();
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }
        return new byte[]{};
    }