implementing BAEL-6833 (#14912)

Co-authored-by: technoddy <mail.technoddy@gmail.com>

libraries-io/pom.xml

@@ -5,6 +5,18 @@
     <modelVersion>4.0.0</modelVersion>
     <artifactId>libraries-io</artifactId>
     <name>libraries-io</name>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>17</source>
+                    <target>17</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
 
     <parent>
         <groupId>com.baeldung</groupId>
@@ -34,6 +46,11 @@
             <artifactId>zip4j</artifactId>
             <version>${zip4j.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.opencsv</groupId>
+            <artifactId>opencsv</artifactId>
+            <version>${opencsv.version}</version>
+        </dependency>
     </dependencies>
 
     <properties>
@@ -42,6 +59,10 @@
         <sshj.version>0.27.0</sshj.version>
         <vfs.version>2.4</vfs.version>
         <zip4j.version>2.9.0</zip4j.version>
+        <opencsv.version>5.7.1</opencsv.version>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
 
 </project>

libraries-io/src/main/java/com/baeldung/java/io/pojotocsv/Application.java

@@ -0,0 +1,4 @@
+package com.baeldung.java.io.pojotocsv;
+
+public record Application(String id, String name, Integer age, String created_at) {
+}

libraries-io/src/main/java/com/baeldung/java/io/pojotocsv/ApplicationWithAnnotation.java

@@ -0,0 +1,8 @@
+package com.baeldung.java.io.pojotocsv;
+
+import com.opencsv.bean.CsvBindByName;
+import com.opencsv.bean.CsvBindByPosition;
+
+public record ApplicationWithAnnotation(@CsvBindByName(column = "id", required = true) @CsvBindByPosition(position = 1) String id, @CsvBindByName(column = "name", required = true) @CsvBindByPosition(position = 0) String name,
+                                        @CsvBindByName(column = "age", required = true) @CsvBindByPosition(position = 2) Integer age, @CsvBindByName(column = "position", required = true) @CsvBindByPosition(position = 3) String created_at) {
+}

libraries-io/src/main/java/com/baeldung/java/io/pojotocsv/BeanToCsv.java

@@ -0,0 +1,55 @@
+package com.baeldung.java.io.pojotocsv;
+
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.List;
+
+import com.opencsv.CSVWriter;
+import com.opencsv.bean.StatefulBeanToCsvBuilder;
+import com.opencsv.exceptions.CsvDataTypeMismatchException;
+import com.opencsv.exceptions.CsvRequiredFieldEmptyException;
+
+public class BeanToCsv {
+
+    public void beanToCSVWithDefault(List<Application> applications) throws Exception {
+        try (FileWriter writer = new FileWriter("src/main/resources/application.csv")) {
+            var builder = new StatefulBeanToCsvBuilder<Application>(writer).withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
+                .withSeparator(',')
+                .build();
+            builder.write(applications);
+        }
+    }
+
+    public void beanToCSVWithCustomHeaderStrategy(List<Application> applications) throws IOException, CsvRequiredFieldEmptyException, CsvDataTypeMismatchException {
+        try (FileWriter writer = new FileWriter("src/main/resources/application2.csv")) {
+            var mappingStrategy = new CustomHeaderStrategy<Application>();
+            mappingStrategy.setType(Application.class);
+
+            var builder = new StatefulBeanToCsvBuilder<Application>(writer).withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
+                .withMappingStrategy(mappingStrategy)
+                .build();
+            builder.write(applications);
+        }
+    }
+
+    public void beanToCSVWithCustomPositionStrategy(List<ApplicationWithAnnotation> applications) throws Exception {
+        try (FileWriter writer = new FileWriter("src/main/resources/application3.csv")) {
+            var builder = new StatefulBeanToCsvBuilder<ApplicationWithAnnotation>(writer).withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
+                .build();
+            builder.write(applications);
+        }
+    }
+
+    public void beanToCSVWithCustomHeaderAndPositionStrategy(List<ApplicationWithAnnotation> applications) throws IOException, CsvRequiredFieldEmptyException, CsvDataTypeMismatchException {
+        try (FileWriter writer = new FileWriter("src/main/resources/application4.csv")) {
+            var mappingStrategy = new CustomColumnPositionStrategy<ApplicationWithAnnotation>();
+            mappingStrategy.setType(ApplicationWithAnnotation.class);
+
+            var builder = new StatefulBeanToCsvBuilder<ApplicationWithAnnotation>(writer).withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
+                .withMappingStrategy(mappingStrategy)
+                .build();
+            builder.write(applications);
+        }
+    }
+
+}

libraries-io/src/main/java/com/baeldung/java/io/pojotocsv/CustomColumnPositionStrategy.java

@@ -0,0 +1,12 @@
+package com.baeldung.java.io.pojotocsv;
+
+import com.opencsv.bean.ColumnPositionMappingStrategy;
+import com.opencsv.exceptions.CsvRequiredFieldEmptyException;
+
+public class CustomColumnPositionStrategy<T> extends ColumnPositionMappingStrategy<T> {
+    @Override
+    public String[] generateHeader(T bean) throws CsvRequiredFieldEmptyException {
+        super.generateHeader(bean);
+        return super.getColumnMapping();
+    }
+}

libraries-io/src/main/java/com/baeldung/java/io/pojotocsv/CustomHeaderStrategy.java

@@ -0,0 +1,16 @@
+package com.baeldung.java.io.pojotocsv;
+
+import java.util.Arrays;
+
+import com.opencsv.bean.HeaderColumnNameMappingStrategy;
+import com.opencsv.exceptions.CsvRequiredFieldEmptyException;
+
+public class CustomHeaderStrategy<T> extends HeaderColumnNameMappingStrategy<T> {
+    @Override
+    public String[] generateHeader(T bean) throws CsvRequiredFieldEmptyException {
+        String[] header = super.generateHeader(bean);
+        return Arrays.stream(header)
+            .map(String::toLowerCase)
+            .toArray(String[]::new);
+    }
+}

libraries-io/src/main/resources/application.csv

@@ -0,0 +1,4 @@
+AGE,CREATED_AT,ID,NAME
+34,2023-08-11,123,Sam
+44,2023-02-11,456,Tam
+54,2023-03-11,890,Jam

libraries-io/src/main/resources/application2.csv

@@ -0,0 +1,4 @@
+age,created_at,id,name
+34,2023-08-11,123,Sam
+44,2023-02-11,456,Tam
+54,2023-03-11,890,Jam

libraries-io/src/main/resources/application3.csv

@@ -0,0 +1,3 @@
+Sam,123,34,2023-08-11
+Tam,456,44,2023-02-11
+Jam,789,54,2023-03-11

libraries-io/src/main/resources/application4.csv

@@ -0,0 +1,4 @@
+name,id,age,created_at
+Sam,123,34,2023-08-11
+Tam,456,44,2023-02-11
+Jam,789,54,2023-03-11

libraries-io/src/test/java/com/baeldung/java/io/pojotocsv/BeanToCsvUnitTest.java

@@ -0,0 +1,80 @@
+package com.baeldung.java.io.pojotocsv;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import java.io.BufferedReader;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class BeanToCsvUnitTest {
+
+    List<Application> applications = new ArrayList<>();
+    List<ApplicationWithAnnotation> applicationsWithAnnotation = new ArrayList<>();
+
+    @BeforeEach
+    public void beforeEach() {
+        applications = List.of(new Application("123", "Sam", 34, "2023-08-11"), new Application("456", "Tam", 44, "2023-02-11"), new Application("890", "Jam", 54, "2023-03-11"));
+
+        applicationsWithAnnotation = List.of(new ApplicationWithAnnotation("123", "Sam", 34, "2023-08-11"), new ApplicationWithAnnotation("456", "Tam", 44, "2023-02-11"), new ApplicationWithAnnotation("789", "Jam", 54, "2023-03-11"));
+    }
+
+    @Test
+    public void givenApplicationPOJO_whenUsingDefaultStrategy_thenReceiveCSVFormatWithAscendingOrderOfField() throws Exception {
+        BeanToCsv beanToCsv = new BeanToCsv();
+        beanToCsv.beanToCSVWithDefault(applications);
+        try (BufferedReader bufferedReader = Files.newBufferedReader(Path.of("src/main/resources/application.csv"))) {
+            List<String> content = bufferedReader.lines()
+                .toList();
+            assertThat(content.get(0)).isEqualTo("AGE,CREATED_AT,ID,NAME");
+            assertThat(content.get(1)).isEqualTo("34,2023-08-11,123,Sam");
+            assertThat(content.get(2)).isEqualTo("44,2023-02-11,456,Tam");
+            assertThat(content.get(3)).isEqualTo("54,2023-03-11,890,Jam");
+        }
+    }
+
+    @Test
+    public void givenApplicationPOJO_whenUsingCustomHeaderStrategy_thenReceiveCSVFormatWithCustomHeaders() throws Exception {
+        BeanToCsv beanToCsv = new BeanToCsv();
+        beanToCsv.beanToCSVWithCustomHeaderStrategy(applications);
+        try (BufferedReader bufferedReader = Files.newBufferedReader(Path.of("src/main/resources/application2.csv"))) {
+            List<String> content = bufferedReader.lines()
+                .toList();
+            assertThat(content.get(0)).isEqualTo("age,created_at,id,name");
+            assertThat(content.get(1)).isEqualTo("34,2023-08-11,123,Sam");
+            assertThat(content.get(2)).isEqualTo("44,2023-02-11,456,Tam");
+            assertThat(content.get(3)).isEqualTo("54,2023-03-11,890,Jam");
+        }
+    }
+
+    @Test
+    public void givenApplicationPOJOWithAnnotation_whenUsingCustomPositionStrategy_thenReceiveCSVFormatWithCustomPosition() throws Exception {
+        BeanToCsv beanToCsv = new BeanToCsv();
+        beanToCsv.beanToCSVWithCustomPositionStrategy(applicationsWithAnnotation);
+        try (BufferedReader bufferedReader = Files.newBufferedReader(Path.of("src/main/resources/application3.csv"))) {
+            List<String> content = bufferedReader.lines()
+                .toList();
+            assertThat(content.get(0)).isEqualTo("Sam,123,34,2023-08-11");
+            assertThat(content.get(1)).isEqualTo("Tam,456,44,2023-02-11");
+            assertThat(content.get(2)).isEqualTo("Jam,789,54,2023-03-11");
+        }
+    }
+
+    @Test
+    public void givenApplicationPOJOWithAnnotation_whenUsingCustomHeaderPositionStrategy_thenReceiveCSVFormatWithCustomHeaderPosition() throws Exception {
+        BeanToCsv beanToCsv = new BeanToCsv();
+        beanToCsv.beanToCSVWithCustomHeaderAndPositionStrategy(applicationsWithAnnotation);
+        try (BufferedReader bufferedReader = Files.newBufferedReader(Path.of("src/main/resources/application4.csv"))) {
+            List<String> content = bufferedReader.lines()
+                .toList();
+            assertThat(content.get(0)).isEqualTo("name,id,age,created_at");
+            assertThat(content.get(1)).isEqualTo("Sam,123,34,2023-08-11");
+            assertThat(content.get(2)).isEqualTo("Tam,456,44,2023-02-11");
+            assertThat(content.get(3)).isEqualTo("Jam,789,54,2023-03-11");
+        }
+    }
+}