Add ProxyOutputStream.setReference(OutputStream)

src/changes/changes.xml

@@ -59,6 +59,7 @@ The <action> type attribute can be add,update,fix,remove.
       <action dev="ggregory" type="add"                due-to="Gary Gregory">Add AbstractByteArrayOutputStream.write(byte[]).</action>
       <action dev="ggregory" type="add"                due-to="Gary Gregory">Add RandomAccessFileOutputStream.getRandomAccessFile().</action>
       <action dev="ggregory" type="add"                due-to="Gary Gregory">Add ProxyInputStream.setReference(InputStream), was package-private setIn(InputStream).</action>
+      <action dev="ggregory" type="add"                due-to="Gary Gregory">Add ProxyOutputStream.setReference(OutputStream).</action>
       <!-- UPDATE -->
       <action dev="ggregory" type="update"             due-to="Dependabot, Gary Gregory">Bump commons.bytebuddy.version from 1.15.10 to 1.15.11 #710.</action>
     </release>

src/main/java/org/apache/commons/io/output/ProxyOutputStream.java

@@ -116,6 +116,18 @@ protected void handleIOException(final IOException e) throws IOException {
         throw e;
     }
 
+    /**
+     * Sets the underlying output stream.
+     *
+     * @param out the underlying output stream.
+     * @return this instance.
+     * @since 2.19.0
+     */
+    public ProxyOutputStream setReference(final OutputStream out) {
+        this.out = out;
+        return this;
+    }
+
     /**
      * Invokes the delegate's {@code write(byte[])} method.
      * @param bts the bytes to write

src/test/java/org/apache/commons/io/output/ProxyOutputStreamTest.java

@@ -16,14 +16,15 @@
  */
 package org.apache.commons.io.output;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import java.io.OutputStream;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import org.apache.commons.lang3.ArrayUtils;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -34,7 +35,7 @@ public class ProxyOutputStreamTest {
 
     private ByteArrayOutputStream original;
 
-    private OutputStream proxied;
+    private ProxyOutputStream proxied;
 
     private final AtomicBoolean hit = new AtomicBoolean();
 
@@ -43,20 +44,31 @@ public void setUp() {
         original = new ByteArrayOutputStream() {
 
             @Override
-            public synchronized void write(final int ba) {
+            public void write(final byte[] ba) {
                 hit.set(true);
                 super.write(ba);
             }
 
             @Override
-            public void write(final byte[] ba) {
+            public synchronized void write(final int ba) {
                 hit.set(true);
                 super.write(ba);
             }
         };
         proxied = new ProxyOutputStream(original);
     }
 
+    @SuppressWarnings("resource")
+    @Test
+    public void testSetReference() throws Exception {
+        assertFalse(hit.get());
+        proxied.setReference(new ByteArrayOutputStream());
+        proxied.write('y');
+        assertFalse(hit.get());
+        assertEquals(0, original.size());
+        assertArrayEquals(ArrayUtils.EMPTY_BYTE_ARRAY, original.toByteArray());
+    }
+
     @Test
     public void testWrite() throws Exception {
         assertFalse(hit.get());