Java provides the Deflater class for general purpose compression using the ZLIB compression library. It also provides the DeflaterOutputStream which uses the Deflater class to filter a stream of data by compressing (deflating) it and then writing the compressed data to another output stream. There are equivalent Inflater and InflaterOutputStream classes to handle the decompression.
Compression
Here is an example of how to use the DeflatorOutputStream to compress a byte array.
1 2 3 4 | //Compress byte arraystatic byte[] compressBArray(byte [] bArray) throws IOException { ByteArrayOutputStream os = new ByteArrayOutputStream(); try (DeflaterOutputStream dos = new DeflaterOutputStream(os)) { dos.write(bArray); } return os.toByteArray();} |
Let’s test:
1 | //Testingbyte[] input = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA".getBytes();byte[] op = CompressionUtil.compressBArray(input);System.out.println("original data length " + input.length + ", compressed data length " + op.length); |
This results ‘original data length 71, compressed data length 12’
Decompression
1 2 3 4 5 | public static byte[] decompress(byte[] compressedTxt) throws IOException { ByteArrayOutputStream os = new ByteArrayOutputStream(); try (OutputStream ios = new InflaterOutputStream(os)) { ios.write(compressedTxt); } return os.toByteArray();} |
Let’s test:
1 2 3 4 | byte[] input = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA".getBytes();byte[] op = CompressionUtil.compress(input);byte[] org = CompressionUtil.decompress(op);System.out.println(new String(org, StandardCharsets.UTF_8)); |
This prints the original ‘input’ string.
Let’s convert the byte[] to Base64 to make it portable
In the above examples we are getting the compressed data in byte array format (byte []) which is an array of numbers.
But we might want to transmit the compressed data to a file or json or db right? So, in order to transmit, we can convert it to Base64 using the following
1 2 3 | { byte[] bytes = {}; //the byte array String b64Compressed = new String(Base64.getEncoder().encode(bytes)); byte[] decompressedBArray = Base64.getDecoder().decode(b64Compressed); new String(decompressedBArray, StandardCharsets.UTF_8); //convert to original string if input was string } |
Here’s the complete code and the test cases
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | package compress;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.OutputStream;import java.nio.charset.StandardCharsets;import java.util.Base64;import java.util.zip.Deflater;import java.util.zip.DeflaterOutputStream;import java.util.zip.InflaterOutputStream;public class CompressionUtil { public static String compressAndReturnB64(String text) throws IOException { return new String(Base64.getEncoder().encode(compress(text))); } public static String decompressB64(String b64Compressed) throws IOException { byte[] decompressedBArray = decompress(Base64.getDecoder().decode(b64Compressed)); return new String(decompressedBArray, StandardCharsets.UTF_8); } public static byte[] compress(String text) throws IOException { return compress(text.getBytes()); } public static byte[] compress(byte[] bArray) throws IOException { ByteArrayOutputStream os = new ByteArrayOutputStream(); try (DeflaterOutputStream dos = new DeflaterOutputStream(os)) { dos.write(bArray); } return os.toByteArray(); } public static byte[] decompress(byte[] compressedTxt) throws IOException { ByteArrayOutputStream os = new ByteArrayOutputStream(); try (OutputStream ios = new InflaterOutputStream(os)) { ios.write(compressedTxt); } return os.toByteArray(); }} |
Test case:
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 | package compress;import org.junit.jupiter.api.Test;import java.io.IOException;import java.nio.charset.StandardCharsets;public class CompressionTest { String testStr = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"; @Test void compressByte() throws IOException { byte[] input = testStr.getBytes(); byte[] op = CompressionUtil.compress(input); System.out.println("original data length " + input.length + ", compressed data length " + op.length); byte[] org = CompressionUtil.decompress(op); System.out.println(org.length); System.out.println(new String(org, StandardCharsets.UTF_8)); } @Test void compress() throws IOException { String op = CompressionUtil.compressAndReturnB64(testStr); System.out.println("Compressed data b64" + op); String org = CompressionUtil.decompressB64(op); System.out.println("Original text" + org); }} |
Note: Since the compress and decompress method operate on byte[], we can compress/decompress any data type.
Published on Java Code Geeks with permission by Ganesh Tiwari, partner at our JCG program. See the original article here: Java Compress/Decompress String/Data Opinions expressed by Java Code Geeks contributors are their own. |
byte[] input = “uNSsVqOV7SBPAfn36mQvyIWGP5BfjnH2GaagEq5XBOBMErY2fP8WTZKizueqLCB3”.getBytes();
byte[] op = compressBArray(input);
original data length 64, compressed data length 72