Compressing and Decompressing files in Java

Compressing a File using DeflaterOutputStream

• void close() : Writes remaining compressed data to the output stream and closes the underlying stream.
• protected void deflate() : Writes next block of compressed data to the output stream.
• void finish() : Finishes writing compressed data to the output stream without closing the underlying stream.
• void flush() : Flushes the compressed output stream.
• void write(byte[] b, int off, int len) : Writes an array of bytes to the compressed output stream where off is the start offset of data and len is total number of bytes.
• void write(int b) : Writes a byte to the compressed output stream.

• Take an input file ‘file 1’ to FileInputStream for reading data.
• Take the output file ‘file 2’ and assign it to FileOutputStream . This will help to write data into ‘file2’.
• Assign FileOutputStream to DeflaterOutputStream for Compressing the data.
• Now, read data from FileInputStream and write it into DeflaterOutputStream. It will compress the data and send it to FileOutputStream which stores the compressed data into the output file.

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.Deflater;
import java.util.zip.DeflaterOutputStream;

class zip
{
    public static void main(String[] args) throws IOException {
        //Assign the original file : file to
        //FileInputStream for reading data
        FileInputStream fis=new FileInputStream("file1");

        //Assign compressed file:file2 to FileOutputStream
        FileOutputStream fos=new FileOutputStream("file2");

        //Assign FileOutputStream to DeflaterOutputStream
        DeflaterOutputStream dos=new DeflaterOutputStream(fos);

        //read data from FileInputStream and write it into DeflaterOutputStream
        int data;
        while ((data=fis.read())!=-1)
        {
            dos.write(data);
        }

        //close the file
        fis.close();
        dos.close();
    }
}

Decompressing a File using InflaterInputStream

• int available() : Returns 0 after EOF has been reached, otherwise always return 1.
• void close() : Closes the input stream and releases any system resources associated with the stream.
• protected void fill() : Fills input buffer with more data to decompress.
• void mark(int readlimit) : Marks the current position in the input stream.
• boolean markSupported() : Tests if the input stream supports the mark and reset methods.
• int read() : Reads a byte of uncompressed data.
• int read(byte[] b, int off, int len) : Reads decompressed data into an array of bytes to the compressed output stream where off is the start offset of data and len is total number of bytes.
• void reset() : Re-positions this stream to the position at the time the mark method was last called on this input stream.

• File with the name ‘file2’ now contains compressed data and we need to obtain original decompressed data from this file.
• Assign the compressed file ‘file2’ to FileInputStream. This helps to read data from ‘file2’.
• Assign the output file ‘file3’ to FileOutputStream. This will help to write uncompressed data into ‘file3’.
• Now, read uncompressed data from InflaterInputStream and write it into FileOutputStream. This will write the uncompressed data to ‘file3’.

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.InflaterInputStream;

//Uncompressing a file using an InflaterInputStream
class unzip
{
    public static void main(String[] args) throws IOException {
        //assign Input File : file2 to FileInputStream for reading data
        FileInputStream fis=new FileInputStream("file2");

        //assign output file: file3 to FileOutputStream for reading the data
        FileOutputStream fos=new FileOutputStream("file3");
        
        //assign inflaterInputStream to FileInputStream for uncompressing the data
        InflaterInputStream iis=new InflaterInputStream(fis);
        
        //read data from inflaterInputStream and write it into FileOutputStream 
        int data;
        while((data=iis.read())!=-1)
        {
            fos.write(data);
        }
        
        //close the files
        fos.close();
        iis.close();
        
    }
}