src/java.base/share/classes/java/io/InputStream.java

@@ -27,10 +27,11 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
+import jdk.internal.io.IOSupport;
 
 /**
  * This abstract class is the superclass of all classes representing
  * an input stream of bytes.
  *

@@ -540,15 +541,8 @@
      *
      * @since 9
      */
     public long transferTo(OutputStream out) throws IOException {
         Objects.requireNonNull(out, "out");
-        long transferred = 0;
-        byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
-        int read;
-        while ((read = this.read(buffer, 0, DEFAULT_BUFFER_SIZE)) >= 0) {
-            out.write(buffer, 0, read);
-            transferred += read;
-        }
-        return transferred;
+        return IOSupport.copy(this, out);
     }
 }