Merge pull request #309 from SethFalco/header-docs

(doc): Document duplicate header behavior

Author: garydgregory

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

@@ -88,7 +88,7 @@ public String get(final int i) {
     }
 
     /**
-     * Returns a value by name.
+     * Returns a value by name. If multiple instances of the header name exists, only the last occurence is returned.
      *
      * <p>
      * Note: This requires a field mapping obtained from the original parser.
@@ -311,7 +311,9 @@ public List<String> toList() {
     }
 
     /**
-     * Copies this record into a new Map of header name to record value.
+     * Copies this record into a new Map of header name to record value. If multiple instances of a header name exists,
+     * only the last occurence is mapped.
+     *
      * <p>
      * Editing the map does not update this instance.
      * </p>

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

@@ -23,6 +23,7 @@
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertAll;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
@@ -341,6 +342,37 @@ public void testToString() {
         assertTrue(recordWithHeader.toString().contains("values="));
     }
 
+    @Test
+    public void testDuplicateHeaderGet() throws IOException {
+        final String csv = "A,A,B,B\n1,2,5,6\n";
+        final CSVFormat format = CSVFormat.DEFAULT.builder().setHeader().build();
+
+        try (final CSVParser parser = CSVParser.parse(csv, format)) {
+            final CSVRecord record = parser.nextRecord();
+
+            assertAll("Test that it gets the last instance of a column when there are duplicate headings",
+                () -> assertEquals("2", record.get("A")),
+                () -> assertEquals("6", record.get("B"))
+            );
+        }
+    }
+
+    @Test
+    public void testDuplicateHeaderToMap() throws IOException {
+        final String csv = "A,A,B,B\n1,2,5,6\n";
+        final CSVFormat format = CSVFormat.DEFAULT.builder().setHeader().build();
+
+        try (final CSVParser parser = CSVParser.parse(csv, format)) {
+            final CSVRecord record = parser.nextRecord();
+            final Map<String, String> map = record.toMap();
+
+            assertAll("Test that it gets the last instance of a column when there are duplicate headings",
+                () -> assertEquals("2", map.get("A")),
+                () -> assertEquals("6", map.get("B"))
+            );
+        }
+    }
+
     private void validateMap(final Map<String, String> map, final boolean allowsNulls) {
         assertTrue(map.containsKey(EnumHeader.FIRST.name()));
         assertTrue(map.containsKey(EnumHeader.SECOND.name()));