BAEL-8276: Convert Between ByteBuffer and Byte Array in Java

Author: azhwani

core-java-modules/core-java-nio-3/src/test/java/com/baeldung/bytebuffer/ByteBufferToByteArrayConversionUnitTest.java

@@ -0,0 +1,105 @@
+package com.baeldung.bytebuffer;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.nio.BufferUnderflowException;
+import java.nio.ByteBuffer;
+import java.nio.ReadOnlyBufferException;
+
+import org.junit.jupiter.api.Test;
+
+class ByteBufferToByteArrayConversionUnitTest {
+    
+    @Test
+    void givenByteBuffer_whenUsingArrayMethod_thenConvertToByteArray() {
+        byte[] givenBytes = {1, 6, 3};
+        ByteBuffer buffer = ByteBuffer.wrap(givenBytes);
+        byte[] bytes = buffer.array();
+        
+        assertArrayEquals(givenBytes, bytes);
+    }
+    
+    @Test
+    void givenBufferWithoutBackingArray_whenCallingArray_thenThrowUnsupportedOperationException() {
+        ByteBuffer buffer = ByteBuffer.allocateDirect(4);
+
+        assertThrows(UnsupportedOperationException.class, buffer::array);
+    }
+    
+    @Test
+    void givenReadOnlyBuffer_whenCallingArray_thenThrowReadOnlyBufferException() {
+        ByteBuffer buffer = ByteBuffer.wrap(new byte[] {1, 2, 3});
+        ByteBuffer readOnlyBuffer = buffer.asReadOnlyBuffer();
+
+        assertThrows(ReadOnlyBufferException.class, readOnlyBuffer::array);
+    }
+    
+    @Test
+    void givenByteBuffer_whenUsingGetMethod_thenConvertToByteArray() {
+        byte[] givenBytes = {5, 4, 2};
+        ByteBuffer buffer = ByteBuffer.wrap(givenBytes);
+        byte[] bytes = new byte[buffer.remaining()];
+        buffer.get(bytes);
+        
+        assertArrayEquals(givenBytes, bytes);
+    }
+    
+    @Test
+    void givenByteBuffer_whenUsingGetWithParamsMethod_thenConvertToByteArray() {
+        byte[] givenBytes = {5, 4, 2, 7};
+        ByteBuffer buffer = ByteBuffer.wrap(givenBytes);
+        byte[] bytes = new byte[2];
+        buffer.get(bytes, 0, 2);
+        
+        assertArrayEquals(new byte[] {5, 4}, bytes);
+    }
+    
+    @Test
+    void givenByteArray_whenUsingWrapMethod_thenConvertToByteBuffer() {
+        byte[] givenBytes = {1, 2, 3};
+        ByteBuffer buffer = ByteBuffer.wrap(givenBytes);
+        
+        assertArrayEquals(givenBytes, buffer.array());
+    }
+    
+    @Test
+    void givenByteArray_whenUsingWrapWithParamsMethod_thenConvertToByteBuffer() {
+        byte[] givenBytes = {1, 2, 3, 7, 8};
+        ByteBuffer buffer = ByteBuffer.wrap(givenBytes, 1, 2);
+        
+        byte[] actualBytes = new byte[buffer.remaining()];
+        buffer.get(actualBytes);
+        
+        assertArrayEquals(new byte[] {2, 3}, actualBytes);
+    }
+    
+    @Test
+    void givenByteArray_whenUsingAllocateAndPutMethods_thenConvertToByteBuffer() {
+        byte[] givenBytes = {1, 9, 7};
+        ByteBuffer buffer = ByteBuffer.allocate(givenBytes.length);
+        buffer.put(givenBytes);
+        
+        assertArrayEquals(givenBytes, buffer.array());
+    }
+    
+    @Test
+    void givenByteArray_whenUsingPutWithFlip_thenCorrect() {
+        byte[] givenBytes = {3, 8};
+        ByteBuffer buffer = ByteBuffer.allocate(givenBytes.length);
+        buffer.put(givenBytes);
+        buffer.flip();
+        
+        assertEquals(3, buffer.get());
+    }
+    
+    @Test
+    void givenByteArray_whenUsingPutWithoutFlip_thenThrowBufferUnderflowException() {
+        byte[] givenBytes = {1, 5};
+        ByteBuffer buffer = ByteBuffer.allocate(givenBytes.length);
+        buffer.put(givenBytes);
+        
+        assertThrows(BufferUnderflowException.class, buffer::get);
+    }
+}