StreamEncoder provides CharBuffer fast-path in append

Author: mkarg

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

@@ -232,11 +232,7 @@ public Writer append(CharSequence csq, int start, int end) throws IOException {
 
     @Override
     public Writer append(CharSequence csq) throws IOException {
-        if (csq instanceof CharBuffer) {
-            se.write((CharBuffer) csq);
-        } else {
-            se.append(csq);
-        }
+        se.append(csq);
         return this;
     }
 

src/java.base/share/classes/sun/nio/cs/StreamEncoder.java

@@ -151,14 +151,22 @@ public void write(CharBuffer cb) throws IOException {
     }
 
     public Writer append(CharSequence csq) throws IOException {
-        if (csq == null) csq = "null";
-        implWrite(csq, 0, csq.length());
+        if (csq instanceof CharBuffer cb) {
+            write(cb);
+        } else {
+            if (csq == null) csq = "null";
+            implWrite(csq, 0, csq.length());
+        }
         return this;
     }
 
     public Writer append(CharSequence csq, int start, int end) throws IOException {
-        if (csq == null) csq = "null";
-        implWrite(csq, start, end - start);
+        if (csq instanceof CharBuffer cb) {
+            write(cb.subSequence(start, end));
+        } else {
+            if (csq == null) csq = "null";
+            implWrite(csq, start, end - start);
+        }
         return this;
     }