[CSV-97] Allow the String value for null to be customized for the CSV printer.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1465768 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -63,6 +63,7 @@ public class CSVFormat implements Serializable {
         private boolean ignoreSurroundingSpaces; // Should leading/trailing spaces be ignored around values?
         private boolean ignoreEmptyLines;
         private String recordSeparator; // for outputs
+        private String nullToString; // for outputs
         private String[] header;
 
         /**
@@ -74,7 +75,7 @@ public class CSVFormat implements Serializable {
          */
         // package protected to give access without needing a synthetic accessor
         CSVFormatBuilder(final char delimiter){
-            this(delimiter, null, null, null, null, false, false, null, null);
+            this(delimiter, null, null, null, null, false, false, null, Constants.EMPTY, null);
         }
 
         /**
@@ -94,10 +95,11 @@ public class CSVFormat implements Serializable {
          *            <tt>true</tt> when whitespaces enclosing values should be ignored
          * @param ignoreEmptyLines
          *            <tt>true</tt> when the parser should skip empty lines
-         * @param recordSeparator
+         * @param nullToString TODO
-         *            the line separator to use for output
          * @param header
          *            the header
+         * @param recordSeparator
+         *            the line separator to use for output
          * @throws IllegalArgumentException if the delimiter is a line break character
          */
         // package protected for use by test code
@@ -105,7 +107,7 @@ public class CSVFormat implements Serializable {
                 final Quote quotePolicy, final Character commentStart,
                 final Character escape, final boolean ignoreSurroundingSpaces,
                 final boolean ignoreEmptyLines, final String lineSeparator,
-                final String[] header) {
+                String nullToString, final String[] header) {
             if (isLineBreak(delimiter)) {
                 throw new IllegalArgumentException("The delimiter cannot be a line break");
             }
@@ -117,6 +119,7 @@ public class CSVFormat implements Serializable {
             this.ignoreSurroundingSpaces = ignoreSurroundingSpaces;
             this.ignoreEmptyLines = ignoreEmptyLines;
             this.recordSeparator = lineSeparator;
+            this.nullToString = nullToString;
             this.header = header;
         }
 
@@ -132,7 +135,7 @@ public class CSVFormat implements Serializable {
             this(format.delimiter, format.quoteChar, format.quotePolicy,
                     format.commentStart, format.escape,
                     format.ignoreSurroundingSpaces, format.ignoreEmptyLines,
-                    format.recordSeparator, format.header);
+                    format.recordSeparator, format.nullToString, format.header);
         }
 
         /**
@@ -143,7 +146,7 @@ public class CSVFormat implements Serializable {
         public CSVFormat build() {
             validate();
             return new CSVFormat(delimiter, quoteChar, quotePolicy, commentStart, escape,
-                                 ignoreSurroundingSpaces, ignoreEmptyLines, recordSeparator, header);
+                                 ignoreSurroundingSpaces, ignoreEmptyLines, recordSeparator, nullToString, header);
         }
 
         /**
@@ -327,6 +330,19 @@ public class CSVFormat implements Serializable {
             return this;
         }
 
+        /**
+         * Sets the String to use for null values for output.
+         *
+         * @param nullToString
+         *            the String to use for null values for output.
+         *
+         * @return This builder with the the specified output record separator
+         */
+        public CSVFormatBuilder withNullToString(final String nullToString) {
+            this.nullToString = nullToString;
+            return this;
+        }
+
         /**
          * Sets the quoteChar of the format to the specified character.
          *
@@ -423,7 +439,8 @@ public class CSVFormat implements Serializable {
      * @return a standard comma separated format builder, as for {@link #RFC4180} but allowing empty lines.
      */
     public static CSVFormatBuilder newBuilder() {
-        return new CSVFormatBuilder(COMMA, DOUBLE_QUOTE_CHAR, null, null, null, false, true, CRLF, null);
+        return new CSVFormatBuilder(COMMA, DOUBLE_QUOTE_CHAR, null, null, null, false, true, CRLF, Constants.EMPTY, 
+                null);
     }
     private final char delimiter;
     private final Character quoteChar;
@@ -431,11 +448,12 @@ public class CSVFormat implements Serializable {
     private final Character commentStart;
     private final Character escape;
     private final boolean ignoreSurroundingSpaces; // Should leading/trailing spaces be ignored around values?
-
     private final boolean ignoreEmptyLines;
 
     private final String recordSeparator; // for outputs
 
+    private final String nullToString; // for outputs
+
     private final String[] header;
 
     /**
@@ -570,6 +588,7 @@ public class CSVFormat implements Serializable {
      *            <tt>true</tt> when the parser should skip empty lines
      * @param recordSeparator
      *            the line separator to use for output
+     * @param nullToString TODO
      * @param header
      *            the header
      * @throws IllegalArgumentException if the delimiter is a line break character
@@ -579,7 +598,7 @@ public class CSVFormat implements Serializable {
             final Quote quotePolicy, final Character commentStart,
             final Character escape, final boolean ignoreSurroundingSpaces,
             final boolean ignoreEmptyLines, final String recordSeparator,
-            final String[] header) {
+            String nullToString, final String[] header) {
         if (isLineBreak(delimiter)) {
             throw new IllegalArgumentException("The delimiter cannot be a line break");
         }
@@ -591,6 +610,7 @@ public class CSVFormat implements Serializable {
         this.ignoreSurroundingSpaces = ignoreSurroundingSpaces;
         this.ignoreEmptyLines = ignoreEmptyLines;
         this.recordSeparator = recordSeparator;
+        this.nullToString = nullToString;
         this.header = header == null ? null : header.clone();
     }
 
@@ -722,6 +742,15 @@ public class CSVFormat implements Serializable {
         return ignoreSurroundingSpaces;
     }
 
+    /**
+     * Returns the value to use for writing null values.
+     *
+     * @return the value to use for writing null values.
+     */
+    public String getNullToString() {
+        return nullToString;
+    }
+
     /**
      * Returns the character used to encapsulate values containing special characters.
      *

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

@@ -344,7 +344,7 @@ public class CSVPrinter implements Flushable, Closeable {
      */
     public void print(final Object value) throws IOException {
         // null values are considered empty
-        final String strValue = value == null ? EMPTY : value.toString();
+        final String strValue = value == null ? format.getNullToString() : value.toString();
         print(value, strValue, 0, strValue.length());
     }
 

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

@@ -41,7 +41,7 @@ public class CSVFormatBuilderTest {
 
     @Before
     public void setUp() throws Exception {
-        builder = new CSVFormatBuilder('+', Character.valueOf('!'), null, Character.valueOf('#'), Character.valueOf('!'), true, true, CRLF, null);
+        builder = new CSVFormatBuilder('+', Character.valueOf('!'), null, Character.valueOf('#'), Character.valueOf('!'), true, true, CRLF, Constants.EMPTY, null);
     }
 
     @Test

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

@@ -307,6 +307,15 @@ public class CSVPrinterTest {
         printer.close();
     }
 
+    @Test
+    public void testPrintCustomNullValues() throws IOException {
+        final StringWriter sw = new StringWriter();
+        final CSVPrinter printer = new CSVPrinter(sw, CSVFormat.DEFAULT.toBuilder().withNullToString("NULL").build());
+        printer.printRecord("a", null, "b");
+        assertEquals("a,NULL,b" + recordSeparator, sw.toString());
+        printer.close();
+    }
+
     @Test
     public void testQuoteAll() throws IOException {
         final StringWriter sw = new StringWriter();