add multiple flushing capabilities

Author: osiegmar

CHANGELOG.md

@@ -5,7 +5,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
-- Nothing yet
+### Added
+- Implement `Flushable` interface for `CsvWriter` to allow flushing the underlying writer
+- Implement `autoFlush` option for `CsvWriter` to automatically flush the writer after writing a record
+- Implement `toConsole` method for `CsvWriter` to write records to the console
 
 ## [3.2.0] - 2024-06-15
 ### Added

example/src/main/java/example/ExampleCsvWriterWithComments.java

@@ -1,7 +1,5 @@
 package example;
 
-import java.io.StringWriter;
-
 import de.siegmar.fastcsv.writer.CsvWriter;
 
 /**
@@ -10,13 +8,10 @@
 public class ExampleCsvWriterWithComments {
 
     public static void main(final String[] args) {
-        final StringWriter sw = new StringWriter();
-        CsvWriter.builder().build(sw)
+        CsvWriter.builder().toConsole()
             .writeComment("A comment can be placed\nanywhere")
             .writeRecord("field 1", "field 2", "field 3\n#with a line break")
             .writeComment("in the CSV file");
-
-        System.out.println(sw);
     }
 
 }

example/src/main/java/example/ExampleCsvWriterWithDataTransformation.java

@@ -1,7 +1,6 @@
 package example;
 
 import java.io.IOException;
-import java.io.StringWriter;
 
 import de.siegmar.fastcsv.reader.CsvReader;
 import de.siegmar.fastcsv.reader.NamedCsvRecord;
@@ -15,10 +14,8 @@ public class ExampleCsvWriterWithDataTransformation {
     private static final String DATA = "firstname,initial,lastname,age\njohn,h.,smith";
 
     public static void main(final String[] args) throws IOException {
-        final StringWriter out = new StringWriter();
-
         try (CsvReader<NamedCsvRecord> reader = CsvReader.builder().ofNamedCsvRecord(DATA);
-             CsvWriter writer = CsvWriter.builder().build(out)) {
+             CsvWriter writer = CsvWriter.builder().toConsole()) {
 
             // transform firstname, initial, lastname to lastname, firstname
             writer.writeRecord("lastname", "firstname");
@@ -28,8 +25,6 @@ public static void main(final String[] args) throws IOException {
                 writer.writeRecord(lastname, firstname);
             }
         }
-
-        System.out.println(out);
     }
 
 }

example/src/main/java/example/ExampleCsvWriterWithNonStandardControlCharacters.java

@@ -1,7 +1,5 @@
 package example;
 
-import java.io.StringWriter;
-
 import de.siegmar.fastcsv.writer.CsvWriter;
 import de.siegmar.fastcsv.writer.LineDelimiter;
 
@@ -11,20 +9,16 @@
 public class ExampleCsvWriterWithNonStandardControlCharacters {
 
     public static void main(final String[] args) {
-        final StringWriter sw = new StringWriter();
-
         // The default configuration uses a comma as field separator,
         // a double quote as quote character and
         // a CRLF as line delimiter.
         CsvWriter.builder()
             .fieldSeparator(';')
             .quoteCharacter('\'')
             .lineDelimiter(LineDelimiter.LF)
-            .build(sw)
+            .toConsole()
             .writeRecord("header1", "header2")
             .writeRecord("value1", "value;2");
-
-        System.out.println(sw);
     }
 
 }

example/src/main/java/example/ExampleCsvWriterWithQuoteStrategy.java

@@ -1,8 +1,5 @@
 package example;
 
-import java.io.PrintWriter;
-import java.nio.charset.StandardCharsets;
-
 import de.siegmar.fastcsv.writer.CsvWriter;
 import de.siegmar.fastcsv.writer.QuoteStrategies;
 import de.siegmar.fastcsv.writer.QuoteStrategy;
@@ -13,33 +10,29 @@
 public class ExampleCsvWriterWithQuoteStrategy {
 
     public static void main(final String[] args) {
-        final PrintWriter pw = new PrintWriter(System.out, false, StandardCharsets.UTF_8);
-
-        pw.println("Quote always");
+        System.out.println("Quote always");
         CsvWriter.builder()
             .quoteStrategy(QuoteStrategies.ALWAYS)
-            .build(pw)
+            .toConsole()
             .writeRecord("value1", "", null, "value,4");
 
-        pw.println("Quote non-empty");
+        System.out.println("Quote non-empty");
         CsvWriter.builder()
             .quoteStrategy(QuoteStrategies.NON_EMPTY)
-            .build(pw)
+            .toConsole()
             .writeRecord("value1", "", null, "value,4");
 
-        pw.println("Quote empty");
+        System.out.println("Quote empty");
         CsvWriter.builder()
             .quoteStrategy(QuoteStrategies.EMPTY)
-            .build(pw)
+            .toConsole()
             .writeRecord("value1", "", null, "value,4");
 
-        pw.println("Quote custom");
+        System.out.println("Quote custom");
         CsvWriter.builder()
             .quoteStrategy(customQuote())
-            .build(pw)
+            .toConsole()
             .writeRecord("value1", "", null, "value,4");
-
-        pw.flush();
     }
 
     // A quote strategy can be used to force quote fields that would otherwise not be quoted.

example/src/main/java/example/ExampleCsvWriterWithSingleFields.java

@@ -1,7 +1,5 @@
 package example;
 
-import java.io.StringWriter;
-
 import de.siegmar.fastcsv.writer.CsvWriter;
 
 /**
@@ -10,12 +8,9 @@
 public class ExampleCsvWriterWithSingleFields {
 
     public static void main(final String[] args) {
-        final StringWriter sw = new StringWriter();
-        CsvWriter.builder().build(sw)
+        CsvWriter.builder().toConsole()
             .writeRecord("header1", "header2")
             .writeRecord().writeField("value1").writeField("value2").endRecord();
-
-        System.out.println(sw);
     }
 
 }

example/src/main/java/example/ExampleCsvWriterWithStringOutput.java

@@ -15,7 +15,8 @@ public static void main(final String[] args) {
             .writeRecord("header1", "header2")
             .writeRecord("value1", "value2");
 
-        System.out.println(sw);
+        final String csv = sw.toString();
+        System.out.println(csv);
     }
 
 }

lib/src/intTest/java/blackbox/writer/ConsoleWriterTest.java

@@ -0,0 +1,40 @@
+package blackbox.writer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.nio.charset.StandardCharsets;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import de.siegmar.fastcsv.writer.CsvWriter;
+
+class ConsoleWriterTest {
+
+    @SuppressWarnings("checkstyle:RegexpMultiline")
+    private final PrintStream standardOut = System.out;
+    private final ByteArrayOutputStream capturedOut = new ByteArrayOutputStream();
+
+    @BeforeEach
+    public void setUp() {
+        System.setOut(new PrintStream(capturedOut, true, StandardCharsets.UTF_8));
+    }
+
+    @AfterEach
+    public void tearDown() {
+        System.setOut(standardOut);
+    }
+
+    @Test
+    void console() {
+        CsvWriter.builder().toConsole()
+            .writeRecord("foo", "bar");
+
+        assertThat(capturedOut).asString()
+            .isEqualTo("foo,bar\r\n");
+    }
+
+}

lib/src/intTest/java/blackbox/writer/CsvWriterTest.java

@@ -1,11 +1,14 @@
 package blackbox.writer;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
+import java.io.FilterWriter;
 import java.io.IOException;
 import java.io.StringWriter;
 import java.io.UncheckedIOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.List;
@@ -260,13 +263,49 @@ void disableBuffer() {
         assertThat(stringWriter).asString().isEqualTo("foo,bar\n");
     }
 
+    // autoFlush
+
+    @Test
+    void noAutoFlush() {
+        final CsvWriter csvWriter = CsvWriter.builder().build(flushFailWriter());
+        assertThatCode(() -> csvWriter.writeRecord("foo"))
+            .doesNotThrowAnyException();
+    }
+
+    @Test
+    void manualFlush(@TempDir final Path tempDir) throws IOException {
+        final Path file = tempDir.resolve("fastcsv.csv");
+        CsvWriter.builder().build(file)
+            .writeRecord("foo")
+            .flush();
+
+        assertThat(Files.readString(file))
+            .isEqualTo("foo\r\n");
+    }
+
+    @Test
+    void autoFlush() {
+        final CsvWriter csvWriter = CsvWriter.builder().autoFlush(true).build(flushFailWriter());
+        assertThatThrownBy(() -> csvWriter.writeRecord("foo"))
+            .isInstanceOf(UnsupportedOperationException.class);
+    }
+
+    private static FilterWriter flushFailWriter() {
+        return new FilterWriter(FilterWriter.nullWriter()) {
+            @Override
+            public void flush() {
+                throw new UnsupportedOperationException();
+            }
+        };
+    }
+
     // toString()
 
     @Test
     void builderToString() {
         assertThat(crw).asString()
             .isEqualTo("CsvWriterBuilder[fieldSeparator=,, quoteCharacter=\", "
-                + "commentCharacter=#, quoteStrategy=null, lineDelimiter=\n, bufferSize=8192]");
+                + "commentCharacter=#, quoteStrategy=null, lineDelimiter=\n, bufferSize=8192, autoFlush=false]");
     }
 
     @Test