baeldung-articles : BAEL-6892

Commit to adding two mеthods to convert OutputStream to a byte array.

core-java-modules/core-java-io-5/src/test/java/com/baeldung/outputstreamtobytearray/OutputStreamtoByteArrayUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.outputstreamtobytearray;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.io.*;
+
+public class OutputStreamtoByteArrayUnitTest {
+
+    @Test
+    public void givenFileOutputStream_whenUsingFileUtilsToReadTheFile_thenReturnByteArray() throws IOException {
+        String data = "Welcome to Baeldung!";
+        String filePath = "file.txt";
+
+        try (FileOutputStream outputStream = new FileOutputStream(filePath)) {
+            outputStream.write(data.getBytes());
+        }
+
+        byte[] byteArray = FileUtils.readFileToByteArray(new File(filePath));
+        String result = new String(byteArray);
+
+        Assertions.assertEquals(data, result);
+    }
+
+
+    @Test
+    public void givenFileOutputStream_whenUsingDrainableOutputStream_thenReturnByteArray() throws IOException {
+        String data = "Welcome to Baeldung!";
+        String filePath = "file.txt";
+        DrainableOutputStream drainableOutputStream = new DrainableOutputStream(new FileOutputStream(filePath));
+        drainableOutputStream.write(data.getBytes());
+        byte[] intercepted = drainableOutputStream.toByteArray();
+        String result = new String(intercepted);
+        Assertions.assertEquals(data, result);
+    }
+
+    public class DrainableOutputStream extends FilterOutputStream {
+        private final ByteArrayOutputStream buffer;
+
+        public DrainableOutputStream(OutputStream out) {
+            super(out);
+            this.buffer = new ByteArrayOutputStream();
+        }
+
+        @Override
+        public void write(byte b[]) throws IOException {
+            this.buffer.write(b);
+            super.write(b);
+        }
+
+        public byte[] toByteArray() {
+            return this.buffer.toByteArray();
+        }
+    }
+}