Java

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• cloning Java objects
• creating a proxy objects
• speeding up EJB lookups
• ZIP compressing in Java
• writing a JUnit testcase
• serializing Java objects
• using Java logger
• looking up hostnames by IP in Java
• implementing a Queue in Java
• parsing XML files (DOM)
• reading files in java

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Compress in java using ZIP

This task will be illustrated by an example implementation of a ZIP compressor / decompressor class.

Takes an array of bytes, then returns a byte array containing the zip-compressed content. Works the same way with decompressing.

import java.util.zip.Deflater;
import java.util.zip.Inflater;
import java.io.ByteArrayOutputStream;
	
class Compressor {

    private int expectedUncompressedDataSize = 16384;
    private Deflater deflater;
    private Inflater inflater;
    private ByteArrayOutputStream bos;

    protected Compressor() {
        construct();
    }

    protected Compressor(int expectedUncompressedDataSize) {
        this.expectedUncompressedDataSize = expectedUncompressedDataSize;
        construct();
    }

    private void construct() {
        deflater = new Deflater();
        inflater = new Inflater();
        bos = new ByteArrayOutputStream(expectedUncompressedDataSize);
    }

    public byte[] compress(byte[] uncompressedData) {
        deflater.setInput(uncompressedData);
        deflater.finish();
        byte[] compressBuf = new byte[expectedUncompressedDataSize];
        while (!deflater.finished()) {
            int count = deflater.deflate(compressBuf);
            bos.write(compressBuf, 0, count);
        }
        byte[] compressedData = bos.toByteArray();
        reset();
        return compressedData;
    }

    public byte[] deCompress(byte[] compressedData) {
        try {
            inflater.setInput(compressedData);
            byte[] decompressBuf = new byte[expectedUncompressedDataSize];
            while (!inflater.finished()) {
                int count = inflater.inflate(decompressBuf);
                bos.write(decompressBuf, 0, count);
            }
            byte[] decompressedData = bos.toByteArray();
            reset();
            return decompressedData;
        } catch (Exception e) {
            throw new RuntimeException("Decompressing data failed", e);
        }
    }

    private void reset() {
        bos.reset();
        deflater.reset();
        inflater.reset();
    }
}

The class can be used like this:

import java.util.Arrays;

public class Test {
    public static void main(String[] args) {
        Compressor compressor = new Compressor();
        String myText =
            "In this test I want compress " +
            "a short text like this " +
            "using ZIP, and see if " +
            "it gets any smaller.";
			
        byte[] myData = myText.getBytes();
        byte[] myCompressedData = compressor.compress(myData);
        byte[] myDecompressedData = compressor.deCompress(myCompressedData);

        System.out.println("Uncompressed data size: " + myData.length);
        System.out.println("Compressed data size: " + myCompressedData.length);
        System.out.println(
            "Decompressed data is correct: " +
            Arrays.equals(myData, myDecompressedData
        ));
    }
}