example code for Article How to Write to a CSV File in Java

core-java-io/src/main/java/com/baeldung/csv/WriteCsvFileExample.java

@@ -0,0 +1,29 @@
+package com.baeldung.csv;
+
+import java.io.BufferedWriter;
+import java.io.IOException;
+
+public class WriteCsvFileExample {
+
+    public void writeLine(BufferedWriter writer, String[] data) throws IOException {
+        StringBuilder csvLine = new StringBuilder();
+
+        for (int i = 0; i < data.length; i++) {
+            if (i > 0) {
+                csvLine.append(",");
+            }
+            csvLine.append(escapeSpecialCharacters(data[i]));
+        }
+
+        writer.write(csvLine.toString());
+    }
+
+    public String escapeSpecialCharacters(String data) {
+        String escapedData = data.replaceAll("\\R", " ");
+        if (data.contains(",") || data.contains("\"") || data.contains("'")) {
+            data = data.replace("\"", "\"\"");
+            escapedData = "\"" + data + "\"";
+        }
+        return escapedData;
+    }
+}

core-java-io/src/test/java/com/baeldung/csv/WriteCsvFileExampleUnitTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.csv;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class WriteCsvFileExampleUnitTest {
+    private static final Logger LOG = LoggerFactory.getLogger(WriteCsvFileExampleUnitTest.class);
+
+    private static final String CSV_FILE_NAME = "src/test/resources/exampleOutput.csv";
+    private WriteCsvFileExample csvExample;
+
+    @Before
+    public void setupClass() {
+        csvExample = new WriteCsvFileExample();
+    }
+
+    @Test
+    public void givenCommaContainingData_whenEscapeSpecialCharacters_stringReturnedInQuotes() {
+        String data = "three,two,one";
+        String escapedData = csvExample.escapeSpecialCharacters(data);
+
+        String expectedData = "\"three,two,one\"";
+        assertEquals(expectedData, escapedData);
+    }
+
+    @Test
+    public void givenQuoteContainingData_whenEscapeSpecialCharacters_stringReturnedFormatted() {
+        String data = "She said \"Hello\"";
+        String escapedData = csvExample.escapeSpecialCharacters(data);
+
+        String expectedData = "\"She said \"\"Hello\"\"\"";
+        assertEquals(expectedData, escapedData);
+    }
+
+    @Test
+    public void givenNewlineContainingData_whenEscapeSpecialCharacters_stringReturnedInQuotes() {
+        String dataNewline = "This contains\na newline";
+        String dataCarriageReturn = "This contains\r\na newline and carriage return";
+        String escapedDataNl = csvExample.escapeSpecialCharacters(dataNewline);
+        String escapedDataCr = csvExample.escapeSpecialCharacters(dataCarriageReturn);
+
+        String expectedData = "This contains a newline";
+        assertEquals(expectedData, escapedDataNl);
+        String expectedDataCr = "This contains a newline and carriage return";
+        assertEquals(expectedDataCr, escapedDataCr);
+    }
+
+    @Test
+    public void givenNonSpecialData_whenEscapeSpecialCharacters_stringReturnedUnchanged() {
+        String data = "This is nothing special";
+        String returnedData = csvExample.escapeSpecialCharacters(data);
+
+        assertEquals(data, returnedData);
+    }
+
+    @Test
+    public void givenBufferedWriter_whenWriteLine_thenOutputCreated() {
+        List<String[]> dataLines = new ArrayList<String[]>();
+        dataLines.add(new String[] { "John", "Doe", "38", "Comment Data\nAnother line of comment data" });
+        dataLines.add(new String[] { "Jane", "Doe, Jr.", "19", "She said \"I'm being quoted\"" });
+
+        File csvOutputFile = new File(CSV_FILE_NAME);
+        try (BufferedWriter writer = new BufferedWriter(new FileWriter(csvOutputFile))) {
+            for (Iterator<String[]> dataIterator = dataLines.iterator(); dataIterator.hasNext();) {
+                csvExample.writeLine(writer, dataIterator.next());
+                if (dataIterator.hasNext()) {
+                    writer.newLine();
+                }
+            }
+            writer.flush();
+        } catch (IOException e) {
+            LOG.error("IOException " + e.getMessage());
+        }
+
+        assertTrue(csvOutputFile.exists());
+    }
+}

core-java-io/src/test/resources/exampleOutput.csv

@@ -0,0 +1,2 @@
+John,Doe,38,Comment Data Another line of comment data
+Jane,"Doe, Jr.",19,"She said ""I'm being quoted"""