BAEL-5196 - Split a comma-separated string while ignoring commas in quotes (#11432)

* Creating the module 'core-java-string-operations-4' for new string related code samples. Implemented code samples for the article BAEL-5196

* including new module 'core-java-string-operations-4 in the parent project

* fixing spacing in the pom file

* fixing the maven configuration for our new project core-java-string-operations-4

core-java-modules/core-java-string-operations-4/src/main/java/com/baeldung/commaseparatedstring/SplitCommaSeparatedString.java

@@ -0,0 +1,66 @@
+package com.baeldung.commaseparatedstring;
+
+import java.io.IOException;
+import java.io.StringReader;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.regex.Pattern;
+
+import com.google.common.base.Splitter;
+import com.opencsv.CSVParser;
+import com.opencsv.CSVParserBuilder;
+import com.opencsv.CSVReader;
+import com.opencsv.CSVReaderBuilder;
+
+public class SplitCommaSeparatedString {
+
+    public static List<String> splitWithParser(String input) {
+
+        List<String> tokens = new ArrayList<String>();
+        int startPosition = 0;
+        boolean isInQuotes = false;
+        for (int currentPosition = 0; currentPosition < input.length(); currentPosition++) {
+            if (input.charAt(currentPosition) == '\"') {
+                isInQuotes = !isInQuotes;
+            } else if (input.charAt(currentPosition) == ',' && !isInQuotes) {
+                tokens.add(input.substring(startPosition, currentPosition));
+                startPosition = currentPosition + 1;
+            }
+        }
+
+        String lastToken = input.substring(startPosition);
+        if (lastToken.equals(",")) {
+            tokens.add("");
+        } else {
+            tokens.add(lastToken);
+        }
+
+        return tokens;
+    }
+
+    public static List<String> splitWithRegex(String input) {
+        String[] tokens = input.split(",(?=(?:[^\"]*\"[^\"]*\")*[^\"]*$)", -1);
+        return Arrays.asList(tokens);
+    }
+
+    public static List<String> splitWithGuava(String input) {
+        Pattern pattern = Pattern.compile(",(?=(?:[^\"]*\"[^\"]*\")*[^\"]*$)");
+        Splitter splitter = Splitter.on(pattern);
+        return splitter.splitToList(input);
+    }
+
+    public static List<String[]> splitMultiLineWithOpenCSV(String input) throws IOException {
+        CSVParser parser = new CSVParserBuilder().withSeparator(',')
+            .build();
+
+        CSVReader reader = new CSVReaderBuilder(new StringReader(input)).withCSVParser(parser)
+            .build();
+
+        List<String[]> list = new ArrayList<>();
+        list = reader.readAll();
+        reader.close();
+
+        return list;
+    }
+}

core-java-modules/core-java-string-operations-4/src/test/java/com/baeldung/commaseparatedstring/SplitCommaSeparatedStringUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.commaseparatedstring;
+
+import static com.baeldung.commaseparatedstring.SplitCommaSeparatedString.splitMultiLineWithOpenCSV;
+import static com.baeldung.commaseparatedstring.SplitCommaSeparatedString.splitWithGuava;
+import static com.baeldung.commaseparatedstring.SplitCommaSeparatedString.splitWithParser;
+import static com.baeldung.commaseparatedstring.SplitCommaSeparatedString.splitWithRegex;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.hasSize;
+import static org.junit.Assert.assertArrayEquals;
+
+import java.io.IOException;
+import java.util.List;
+
+import org.junit.Test;
+
+public class SplitCommaSeparatedStringUnitTest {
+    
+    @Test
+    public void givenSingleLineInput_whenParsing_shouldIgnoreCommasInsideDoubleQuotes() {
+        String input = "baeldung,tutorial,splitting,text,\"ignoring this comma,\"";
+
+        var matcher = contains("baeldung", "tutorial", "splitting", "text", "\"ignoring this comma,\"");
+        assertThat(splitWithParser(input), matcher);
+        assertThat(splitWithRegex(input), matcher);
+        assertThat(splitWithGuava(input), matcher);
+    }
+    
+    @Test
+    public void givenMultiLineInput_whenParsing_shouldIgnoreCommasInsideDoubleQuotes() throws IOException {
+        String input = "baeldung,tutorial,splitting,text,\"ignoring this comma,\"" + System.lineSeparator()
+        + "splitting,a,regular,line,no double quotes";
+
+        String[] firstLine = new String[]{"baeldung", "tutorial", "splitting", "text", "ignoring this comma,"};
+        String[] secondLine = new String[]{"splitting", "a", "regular", "line", "no double quotes"};
+        
+        List<String[]> result = splitMultiLineWithOpenCSV(input);
+        
+        assertThat(result, hasSize(2));
+        assertArrayEquals(firstLine, result.get(0));
+        assertArrayEquals(secondLine, result.get(1));
+    }
+
+}