[BAEL-7659] Compress and Create a Byte Array Using GZip (#16451)

* [BAEL-7659] Compress and create a byte array using GZip

* [BAEL-7659] Compress and Create a Byte Array Using GZip

* [BAEL-7659] Compress and Create a Byte Array Using GZip

* [BAEL-7659] Compress and Create a Byte Array Using GZip

* [BAEL-7659] Compress and create a byte array using GZip

---------

Co-authored-by: p.kostopoulos <p.kostopoulos@astynomia.gr>

core-java-modules/core-java-io-5/src/main/java/com/baeldung/gzipbytearray/GZip.java

@@ -0,0 +1,22 @@
+package com.baeldung.gzipbytearray;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.zip.GZIPOutputStream;
+
+public class GZip {
+
+    private static final int BUFFER_SIZE = 512;
+
+    public static void gzip(InputStream is, OutputStream os) throws IOException {
+        GZIPOutputStream gzipOs = new GZIPOutputStream(os);
+        byte[] buffer = new byte[BUFFER_SIZE];
+        int bytesRead = 0;
+        while ((bytesRead = is.read(buffer)) > -1) {
+            gzipOs.write(buffer, 0, bytesRead);
+        }
+        gzipOs.close();
+    }
+
+}

core-java-modules/core-java-io-5/src/test/java/com/baeldung/gzipbytearray/GZipUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.gzipbytearray;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+
+import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class GZipUnitTest {
+
+    Logger logger = LoggerFactory.getLogger(GZipUnitTest.class);
+
+    @Test
+    void whenCompressingUsingGZip_thenGetCompressedByteArray() throws IOException {
+        String payload = "This is a sample text to test method gzip. The gzip algorithm will compress this string. "
+            + "The result will be smaller than this string.";
+        ByteArrayOutputStream os = new ByteArrayOutputStream();
+        GZip.gzip(new ByteArrayInputStream(payload.getBytes()), os);
+        byte[] compressed = os.toByteArray();
+        assertTrue(payload.getBytes().length > compressed.length);
+        assertEquals("1f", Integer.toHexString(compressed[0] & 0xFF));
+        assertEquals("8b", Integer.toHexString(compressed[1] & 0xFF));
+    }
+
+}