8306374: (bf) Improve performance of DirectCharBuffer::append(CharSequence[,int,int])

Reviewed-by: liach, alanb

src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template

@@ -446,6 +446,69 @@ class Direct$Type$Buffer$RW$$BO$
 
     // --- Methods to support CharSequence ---
 
+#if[rw] 
+    private static final int APPEND_BUF_SIZE = 1024;
+
+    private $Type$Buffer appendChars(CharSequence csq, int start, int end) {
+        Objects.checkFromToIndex(start, end, csq.length());
+
+        int pos = position();
+        int lim = limit();
+        int rem = (pos <= lim) ? lim - pos : 0;
+        int length = end - start;
+        if (length > rem)
+            throw new BufferOverflowException();
+
+        char[] buf = new char[Math.min(APPEND_BUF_SIZE, length)];
+        int index = pos;
+        while (start < end) {
+            int count = end - start;
+            if (count > buf.length)
+                count = buf.length;
+
+            if (csq instanceof String str) {
+                str.getChars(start, start + count, buf, 0);
+            } else if (csq instanceof StringBuilder sb) {
+                sb.getChars(start, start + count, buf, 0);
+            } else if (csq instanceof StringBuffer sb) {
+                sb.getChars(start, start + count, buf, 0);
+            }
+
+            putArray(index, buf, 0, count);
+
+            start += count;
+            index += count;
+        }
+
+        position(pos + length);
+
+        return this;
+    }
+#end[rw] 
+
+    public $Type$Buffer append(CharSequence csq) {
+#if[rw] 
+        if (csq instanceof StringBuilder) 
+            return appendChars(csq, 0, csq.length());
+ 
+        return super.append(csq);
+#else[rw]
+        throw new ReadOnlyBufferException();
+#end[rw]
+    }
+ 
+    public $Type$Buffer append(CharSequence csq, int start, int end) { 
+#if[rw]
+        if (csq instanceof String || csq instanceof StringBuffer ||
+            csq instanceof StringBuilder)
+            return appendChars(csq, start, end);
+
+        return super.append(csq, start, end);
+#else[rw]
+        throw new ReadOnlyBufferException();
+#end[rw]
+    }
+
     public CharBuffer subSequence(int start, int end) {
         int pos = position();
         int lim = limit();

src/java.base/share/classes/java/nio/X-Buffer.java.template

@@ -1319,7 +1319,7 @@ public abstract sealed class $Type$Buffer
         return put(index, src, 0, src.length);
     }
 
-    private $Type$Buffer putArray(int index, $type$[] src, int offset, int length) {
+    $Type$Buffer putArray(int index, $type$[] src, int offset, int length) {
 #if[rw]
         if (
 #if[char]