Fix #45

Author: cowtowncoder

release-notes/VERSION

@@ -6,7 +6,8 @@ Version: 2.4.0 (xx-xxx-2014)
 #32: Allow disabling of quoteChar
  (suggested by Jason D)
 #40: Allow (re)ordering of columns of Schema, using `CsvSchema.sortedBy(...)`
-#45: Change Default Outputting Behavior to Include Final Comma Regardless of Value.
+#45: Change outputting behavior to include final commas even if values are
+ missing; also add `CsvGenerator.OMIT_MISSING_TAIL_COLUMNS`
 
 ------------------------------------------------------------------------
 === History: ===

src/main/java/com/fasterxml/jackson/dataformat/csv/CsvGenerator.java

@@ -39,6 +39,17 @@ public enum Feature {
          * @since 2.4
          */
         STRICT_CHECK_FOR_QUOTING(false),
+
+        /**
+         * Feature that determines whether columns without matching value may be omitted,
+         * when they are the last values of the row.
+         * If <code>true</code>, values and separators between values may be omitted, to slightly reduce
+         * length of the row; if <code>false</code>, separators need to stay in place and values
+         * are indicated by empty Strings.
+         * 
+         * @since 2.4
+         */
+        OMIT_MISSING_TAIL_COLUMNS(false),
         ;
 
         protected final boolean _defaultState;

src/main/java/com/fasterxml/jackson/dataformat/csv/impl/CsvWriter.java

@@ -64,9 +64,16 @@ public class CsvWriter
     /**
      * Marker flag used to determine if to do optimal (aka "strict") quoting
      * checks or not (looser conservative check)
+     * 
+     * @since 2.4
      */
     protected boolean _cfgOptimalQuoting;
-    
+
+    /**
+     * @since 2.4
+     */
+    protected boolean _cfgIncludeMissingTail;
+
     /*
     /**********************************************************
     /* Output state
@@ -142,6 +149,7 @@ public CsvWriter(IOContext ctxt, int csvFeatures, Writer out, CsvSchema schema)
         _ioContext = ctxt;
         _csvFeatures = csvFeatures;
         _cfgOptimalQuoting = CsvGenerator.Feature.STRICT_CHECK_FOR_QUOTING.enabledIn(csvFeatures);
+        _cfgIncludeMissingTail = !CsvGenerator.Feature.OMIT_MISSING_TAIL_COLUMNS.enabledIn(_csvFeatures);
 
         _outputBuffer = ctxt.allocConcatBuffer();
         _bufferRecyclable = true;
@@ -174,6 +182,7 @@ public CsvWriter(IOContext ctxt, int csvFeatures, Writer out,
         _ioContext = ctxt;
         _csvFeatures = csvFeatures;
         _cfgOptimalQuoting = CsvGenerator.Feature.STRICT_CHECK_FOR_QUOTING.enabledIn(csvFeatures);
+        _cfgIncludeMissingTail = !CsvGenerator.Feature.OMIT_MISSING_TAIL_COLUMNS.enabledIn(_csvFeatures);
 
         _outputBuffer = ctxt.allocConcatBuffer();
         _bufferRecyclable = true;
@@ -198,6 +207,7 @@ public CsvWriter(CsvWriter base, CsvSchema newSchema)
         _ioContext = base._ioContext;
         _csvFeatures = base._csvFeatures;
         _cfgOptimalQuoting = base._cfgOptimalQuoting;
+        _cfgIncludeMissingTail = base._cfgIncludeMissingTail;
 
         _outputBuffer = base._outputBuffer;
         _bufferRecyclable = base._bufferRecyclable;
@@ -356,9 +366,11 @@ public void endRow() throws IOException
         }
         // Any missing values?
         if (_nextColumnToWrite < _columnCount) {
-            do {
-                appendColumnSeparator();
-            } while (++_nextColumnToWrite < _columnCount);
+            if (_cfgIncludeMissingTail) {
+                do {
+                    appendColumnSeparator();
+                } while (++_nextColumnToWrite < _columnCount);
+            }
         }
         // write line separator
         _nextColumnToWrite = 0;

src/test/java/com/fasterxml/jackson/dataformat/csv/TestWriterWithMissingValues.java

@@ -45,11 +45,19 @@ public void testWrite_NullSecondColumn() throws JsonProcessingException {
     }
 
     @Test
-    public void testWrite_NullThirdColumn() throws JsonProcessingException {
-        final String csv = WRITER.writeValueAsString(
+    public void testWrite_NullThirdColumn() throws JsonProcessingException
+    {
+        CsvMapper mapper = new CsvMapper();
+        assertFalse(mapper.getFactory().isEnabled(CsvGenerator.Feature.OMIT_MISSING_TAIL_COLUMNS));
+        String csv = mapper.writer().withSchema(SCHEMA).writeValueAsString(
                 ImmutableMap.of("timestamp", "2014-03-10T23:32:47+00:00",
                         "value", 42));
 
         assertEquals("\"2014-03-10T23:32:47+00:00\",42,\n", csv);
+        mapper.getFactory().enable(CsvGenerator.Feature.OMIT_MISSING_TAIL_COLUMNS);
+        csv = mapper.writer().withSchema(SCHEMA).writeValueAsString(
+                ImmutableMap.of("timestamp", "2014-03-10T23:32:47+00:00",
+                        "value", 42));
+        assertEquals("\"2014-03-10T23:32:47+00:00\",42\n", csv);
     }
 }