Fix CSV-331: CSVFormat ignores trim when printing a Reader value

src/main/java/org/apache/commons/csv/CSVFormat.java

@@ -2264,6 +2264,11 @@ private void print(final InputStream inputStream, final Appendable out, final bo
      * Prints the {@code value} as the next value on the line to {@code out}. The value will be escaped or encapsulated as needed. Useful when one wants to
      * avoid creating CSVPrinters. Trims the value if {@link #getTrim()} is true.
      *
+     * <p>
+     * If {@code value} is a {@link Reader} and {@link #getTrim()} is true, the reader is fully read into memory so the value can be trimmed before printing;
+     * otherwise the value is streamed without holding it in memory. The reader is never closed by this method.
+     * </p>
+     *
      * @param value     value to output.
      * @param out       where to print the value.
      * @param newRecord if this a new record.
@@ -2287,8 +2292,15 @@ public void print(final Object value, final Appendable out, final boolean newRec
             } else if (value instanceof CharSequence) {
                 charSequence = (CharSequence) value;
             } else if (value instanceof Reader) {
-                print((Reader) value, out, newRecord);
-                return;
+                // CSV-331: the streaming path cannot apply trim(), so when trimming is enabled the reader
+                // is fully read into memory first; trim() is applied below on the regular path.
+                // The reader is not closed here: closing it remains the caller's responsibility.
+                if (getTrim()) {
+                    charSequence = IOUtils.toString((Reader) value);
+                } else {
+                    print((Reader) value, out, newRecord);
+                    return;
+                }
             } else if (value instanceof InputStream) {
                 print((InputStream) value, out, newRecord);
                 return;
@@ -2348,6 +2360,13 @@ public CSVPrinter print(final Path out, final Charset charset) throws IOExceptio
         return print(Files.newBufferedWriter(out, charset));
     }
 
+    /**
+     * Prints a Reader value by streaming it without holding the whole value in memory.
+     * <p>
+     * Trimming is NOT applied here: when {@link #getTrim()} is true, {@link #print(Object, Appendable, boolean)}
+     * buffers the reader in memory and takes the regular CharSequence path instead (CSV-331).
+     * </p>
+     */
     private void print(final Reader reader, final Appendable out, final boolean newRecord) throws IOException {
         // Reader is never null here
         if (!newRecord) {

src/test/java/org/apache/commons/csv/CSVFormatTest.java

@@ -1373,6 +1373,66 @@ void testTrim() throws IOException {
         assertEquals("header", out.toString());
     }
 
+    /**
+     * Tests <a href="https://issues.apache.org/jira/browse/CSV-331">CSV-331</a>: trim must also be applied when
+     * printing a Reader value.
+     */
+    @Test
+    void testTrimReaderValue() throws IOException {
+        final CSVFormat formatWithTrim = CSVFormat.DEFAULT.withDelimiter(',').withTrim().withQuote(null).withRecordSeparator(CRLF);
+
+        Reader in = new StringReader("a,b,c");
+        final StringBuilder out = new StringBuilder();
+        formatWithTrim.print(in, out, true);
+        assertEquals("a,b,c", out.toString());
+
+        in = new StringReader("  x,y,z  ");
+        out.setLength(0);
+        formatWithTrim.print(in, out, true);
+        assertEquals("x,y,z", out.toString());
+
+        in = new StringReader("");
+        out.setLength(0);
+        formatWithTrim.print(in, out, true);
+        assertEquals("", out.toString());
+
+        in = new StringReader("header\r\n");
+        out.setLength(0);
+        formatWithTrim.print(in, out, true);
+        assertEquals("header", out.toString());
+
+        // CSV-331 reproduction: ORACLE enables trim.
+        final StringBuilder oracleOut = new StringBuilder();
+        CSVFormat.ORACLE.print(new StringReader("  Alice  "), oracleOut, true);
+        assertEquals("Alice", oracleOut.toString());
+    }
+
+    /**
+     * Tests <a href="https://issues.apache.org/jira/browse/CSV-331">CSV-331</a>: a Reader value must still be
+     * encapsulated when needed after trimming.
+     */
+    @Test
+    void testTrimReaderValueWithQuotes() throws IOException {
+        final CSVFormat formatWithTrim = CSVFormat.DEFAULT.withDelimiter(',').withTrim().withRecordSeparator(CRLF);
+        final Reader in = new StringReader("  \"a,b\"  ");
+        final StringBuilder out = new StringBuilder();
+        formatWithTrim.print(in, out, true);
+        assertEquals("\"\"\"a,b\"\"\"", out.toString());
+    }
+
+    /**
+     * Tests <a href="https://issues.apache.org/jira/browse/CSV-331">CSV-331</a>: without trim a Reader value must
+     * keep streaming as-is.
+     */
+    @Test
+    void testNoTrimReaderValue() throws IOException {
+        final CSVFormat formatWithoutTrim = CSVFormat.DEFAULT.withDelimiter(',').withQuote(null).withRecordSeparator(CRLF);
+        final Reader in = new StringReader("  Alice  ");
+        final StringBuilder out = new StringBuilder();
+        formatWithoutTrim.print(in, out, true);
+        assertEquals("  Alice  ", out.toString());
+    }
+
     @Test
     void testWithCommentStart() {
         final CSVFormat formatWithCommentStart = CSVFormat.DEFAULT.withCommentMarker('#');