add modifying input example

docs/src/content/docs/guides/Examples/modifying-input.mdx

@@ -0,0 +1,28 @@
+---
+title: Modifying input
+---
+
+import {Code} from '@astrojs/starlight/components';
+import sourceCode from '../../../../../../example/src/main/java/example/ExampleCsvReaderWithFieldModifier.java?raw';
+
+The CSV specification ([section 2.4. of RFC 4180](https://www.rfc-editor.org/rfc/rfc4180#section-2)) explicitly states:
+
+> Spaces are considered part of a field and should not be ignored.
+
+However, in some cases, you might want to remove leading and trailing spaces from fields while reading a CSV file
+or modify the fields in another way (e.g., converting them to lower- or uppercase). FastCSV allows you to do this
+using a field modifier that can be used together with a `CsvRecordHandler`.
+
+:::tip
+If you want to read fields not as string but as a specific type (e.g., `Boolean`, `Long`, `LocalDate`, etc.),
+you should check out the [Custom Callback handler example](../custom-callback-handler/).
+:::
+
+## Example
+
+In the following example, fields are modified while reading a CSV file.
+
+<Code code={sourceCode} title="ExampleCsvReaderWithFieldModifier.java" lang="java"/>
+
+You also find this source code example in the
+[FastCSV GitHub repository](https://github.com/osiegmar/FastCSV/blob/main/example/src/main/java/example/ExampleCsvReaderWithFieldModifier.java).

example/src/main/java/example/ExampleCsvReaderWithFieldModifier.java

@@ -16,28 +16,36 @@ public class ExampleCsvReaderWithFieldModifier {
 
     public static void main(final String[] args) {
         System.out.println("Trim fields:");
-        CsvReader.builder().build(new CsvRecordHandler(FieldModifiers.TRIM), DATA)
+        CsvReader.builder()
+            .build(new CsvRecordHandler(FieldModifiers.TRIM), DATA)
             .forEach(System.out::println);
 
-        System.out.println("Trim and lowercase fields:");
-        CsvReader.builder().build(new CsvRecordHandler(combinedModifier()), DATA)
+        System.out.println("Combine modifiers (trim/lowercase):");
+        CsvReader.builder()
+            .build(new CsvRecordHandler(combinedModifier()), DATA)
             .forEach(System.out::println);
 
-        System.out.println("Trim and lowercase fields of first record (by using a custom modifier):");
-        CsvReader.builder().build(new CsvRecordHandler(customModifier()), DATA)
+        System.out.println("Custom modifier (trim/lowercase on first record):");
+        CsvReader.builder()
+            .build(new CsvRecordHandler(customModifier()), DATA)
             .forEach(System.out::println);
     }
 
     private static FieldModifier combinedModifier() {
-        return FieldModifiers.TRIM.andThen(FieldModifiers.lower(Locale.ENGLISH));
+        return FieldModifiers.TRIM
+            .andThen(FieldModifiers.lower(Locale.ENGLISH));
     }
 
     private static FieldModifier customModifier() {
         return new FieldModifier() {
             @Override
-            public String modify(final long startingLineNumber, final int fieldIdx, final boolean quoted,
+            public String modify(final long startingLineNumber,
+                                 final int fieldIdx,
+                                 final boolean quoted,
                                  final String field) {
-                return startingLineNumber == 1 ? field.trim().toLowerCase(Locale.ENGLISH) : field;
+                return startingLineNumber == 1
+                    ? field.trim().toLowerCase(Locale.ENGLISH)
+                    : field;
             }
         };
     }