3.x: CompositeException.printStackTrace to write directly into PS/PW (#7212)

Author: akarnokd

src/main/java/io/reactivex/rxjava3/exceptions/CompositeException.java

@@ -199,40 +199,41 @@ public void printStackTrace(PrintWriter s) {
      * Special handling for printing out a {@code CompositeException}.
      * Loops through all inner exceptions and prints them out.
      *
-     * @param s
+     * @param output
      *            stream to print to
      */
-    private void printStackTrace(PrintStreamOrWriter s) {
-        StringBuilder b = new StringBuilder(128);
-        b.append(this).append('\n');
+    private void printStackTrace(PrintStreamOrWriter output) {
+        output.append(this).append("\n");
         for (StackTraceElement myStackElement : getStackTrace()) {
-            b.append("\tat ").append(myStackElement).append('\n');
+            output.append("\tat ").append(myStackElement).append("\n");
         }
         int i = 1;
         for (Throwable ex : exceptions) {
-            b.append("  ComposedException ").append(i).append(" :\n");
-            appendStackTrace(b, ex, "\t");
+            output.append("  ComposedException ").append(i).append(" :\n");
+            appendStackTrace(output, ex, "\t");
             i++;
         }
-        s.println(b.toString());
+        output.append("\n");
     }
 
-    private void appendStackTrace(StringBuilder b, Throwable ex, String prefix) {
-        b.append(prefix).append(ex).append('\n');
+    private void appendStackTrace(PrintStreamOrWriter output, Throwable ex, String prefix) {
+        output.append(prefix).append(ex).append('\n');
         for (StackTraceElement stackElement : ex.getStackTrace()) {
-            b.append("\t\tat ").append(stackElement).append('\n');
+            output.append("\t\tat ").append(stackElement).append('\n');
         }
         if (ex.getCause() != null) {
-            b.append("\tCaused by: ");
-            appendStackTrace(b, ex.getCause(), "");
+            output.append("\tCaused by: ");
+            appendStackTrace(output, ex.getCause(), "");
         }
     }
 
     abstract static class PrintStreamOrWriter {
-        /** Prints the specified string as a line on this StreamOrWriter.
-         * @param o string to print
+        /**
+         * Prints the object's string representation via the underlying PrintStream or PrintWriter.
+         * @param o the object to print
+         * @return this
          */
-        abstract void println(Object o);
+        abstract PrintStreamOrWriter append(Object o);
     }
 
     /**
@@ -246,11 +247,15 @@ static final class WrappedPrintStream extends PrintStreamOrWriter {
         }
 
         @Override
-        void println(Object o) {
-            printStream.println(o);
+        WrappedPrintStream append(Object o) {
+            printStream.print(o);
+            return this;
         }
     }
 
+    /**
+     * Same abstraction and implementation as in JDK to allow PrintStream and PrintWriter to share implementation.
+     */
     static final class WrappedPrintWriter extends PrintStreamOrWriter {
         private final PrintWriter printWriter;
 
@@ -259,8 +264,9 @@ static final class WrappedPrintWriter extends PrintStreamOrWriter {
         }
 
         @Override
-        void println(Object o) {
-            printWriter.println(o);
+        WrappedPrintWriter append(Object o) {
+            printWriter.print(o);
+            return this;
         }
     }