StatefulBeanToCsv with Column headers

Question

I am using opencsv-4.0 to write a csv file and I need to add column headers in output file.

Here is my code.

public static void buildProductCsv(final List<Product> product,
        final String filePath) {

    try {

        Writer writer = new FileWriter(filePath);

        // mapping of columns with their positions
        ColumnPositionMappingStrategy<Product> mappingStrategy = new ColumnPositionMappingStrategy<Product>();
        // Set mappingStrategy type to Product Type
        mappingStrategy.setType(Product.class);
        // Fields in Product Bean
        String[] columns = new String[] { "productCode", "MFD", "EXD" };
        // Setting the colums for mappingStrategy
        mappingStrategy.setColumnMapping(columns);

        StatefulBeanToCsvBuilder<Product> builder = new StatefulBeanToCsvBuilder<Product>(writer);

        StatefulBeanToCsv<Product> beanWriter = builder.withMappingStrategy(mappingStrategy).build();
        // Writing data to csv file
        beanWriter.write(product);
        writer.close();

        log.info("Your csv file has been generated!");

    } catch (Exception ex) {
        log.warning("Exception: " + ex.getMessage());
    }

}

Above code create a csv file with data. But it not include column headers in that file.

How could I add column headers to output csv?

score 20 · Accepted Answer · edited Jun 20 '20 at 09:12

ColumnPositionMappingStrategy#generateHeader returns empty array

/**
 * This method returns an empty array.
 * The column position mapping strategy assumes that there is no header, and
 * thus it also does not write one, accordingly.
 * @return An empty array
 */
@Override
public String[] generateHeader() {
    return new String[0];
}

If you remove MappingStrategy from BeanToCsv builder

// replace 
StatefulBeanToCsv<Product> beanWriter = builder.withMappingStrategy(mappingStrategy).build();
// with
StatefulBeanToCsv<Product> beanWriter = builder.build();

It will write Product's class members as CSV header

If your Product class members names are

"productCode", "MFD", "EXD"

This should be the right solution

Else, add @CsvBindByName annotation

import com.opencsv.bean.CsvBindByName;
import com.opencsv.bean.StatefulBeanToCsv;
import com.opencsv.bean.StatefulBeanToCsvBuilder;

import java.io.FileWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.List;

public class CsvTest {

    public static void main(String[] args) throws Exception {
        Writer writer = new FileWriter(fileName);

        StatefulBeanToCsvBuilder<Product> builder = new StatefulBeanToCsvBuilder<>(writer);
        StatefulBeanToCsv<Product> beanWriter = builder.build();

        List<Product> products = new ArrayList<>();
        products.add(new Product("1", "11", "111"));
        products.add(new Product("2", "22", "222"));
        products.add(new Product("3", "33", "333"));
        beanWriter.write(products);
        writer.close();
    }

    public static class Product {
        @CsvBindByName(column = "productCode")
        String id;
        @CsvBindByName(column = "MFD")
        String member2;
        @CsvBindByName(column = "EXD")
        String member3;

        Product(String id, String member2, String member3) {
            this.id = id;
            this.member2 = member2;
            this.member3 = member3;
        }

        public String getId() {
            return id;
        }

        public void setId(String id) {
            this.id = id;
        }

        public String getMember2() {
            return member2;
        }

        public void setMember2(String member2) {
            this.member2 = member2;
        }

        public String getMember3() {
            return member3;
        }

        public void setMember3(String member3) {
            this.member3 = member3;
        }
    }

}

Output:

"EXD","MFD","PRODUCTCODE"

"111","11","1"

"222","22","2"

"333","33","3"

Pay attention; class, getters & setters needs to be public due to the use of Reflection by OpenCSV library

Thanks for your answer. This worked. But Is there any way to change the column order? As you can see columns are ordered in alphabetical. I need to customize the order like `"PRODUCTCODE", "EXD","MFD"` — Bishan, Sep 07 '17 at 04:14
@Bishan you can add to each member the annotation @CsvBindByPosition(position = 0), position is zero based. — whoopdedoo, Sep 07 '17 at 08:38
Can't I use both `@CsvBindByPosition` and `@CsvBindByName`? I have added `@CsvBindByPosition`. Now column order is ok. But column names are missing in output file. — Bishan, Sep 07 '17 at 10:26
it seems like you are right, i've been traveling all around the source code, consider open a ticket at https://sourceforge.net/p/opencsv/feature-requests/ — whoopdedoo, Sep 07 '17 at 11:27
no problem, if annotations CsvBindByPosition or CsvCustomBindByPosition are present, ColumnPositionMappingStrategy is chosen, which does not generate headers, ColumnPositionMappingStrategy#generateHeader returns empty array — whoopdedoo, Sep 07 '17 at 11:29
@Bishan it will be nice if you accept my answer as a solution, there are many and might be more suitable CSV libraries for your product, take a look https://github.com/search?l=Java&o=desc&q=CSV+library&s=stars&type=Repositories — whoopdedoo, Sep 07 '17 at 12:32
@Bishan Please have a look at [my answer to similar question](https://stackoverflow.com/questions/45203867/how-to-write-from-bean-to-csv-using-opencsv-by-specfying-custom-column-headers/46185186#46185186). It shows how to write CSV and have both custom header column names and ordering — sebast26, Sep 12 '17 at 21:17
Is there anyway to get the exact name in the CsvBindByName annotation? and not the UPPERCASE of it? — Udi, Feb 11 '19 at 07:56
@Iddo how can i remove the double quotes from the output value ? — Pranav MS, Apr 30 '19 at 09:02
Some solution how to control custom naming and ordering: https://stackoverflow.com/a/58731084/7230670 — Vladyslav Vynnyk, Nov 06 '19 at 13:24

score 5 · Answer 2 · answered Jun 11 '18 at 12:15

I may have missed something obvious here but couldn't you just append your header String to the writer object?

Writer writer = new FileWriter(filePath);
writer.append("header1, header2, header3, ...etc \n");

// This will be followed by your code with BeanToCsvBuilder 
// Note: the terminating \n might differ pending env.

Bruno Muehlbauer de Souza · Answer 3 · 2020-04-17T12:00:49.630

You can append by annotation

public void export(List<YourObject> list, PrintWriter writer) throws Exception {
        writer.append( buildHeader( YourObject.class ) );
        StatefulBeanToCsvBuilder<YourObject> builder = new StatefulBeanToCsvBuilder<>( writer );
        StatefulBeanToCsv<YourObject> beanWriter = builder.build();
        beanWriter.write( mapper.map( list ) );
        writer.close();
    }

    private String buildHeader(Class<YourObject> clazz) {
        return Arrays.stream( clazz.getDeclaredFields() )
                .filter( f -> f.getAnnotation( CsvBindByPosition.class ) != null
                        && f.getAnnotation( CsvBindByName.class ) != null )
                .sorted( Comparator.comparing( f -> f.getAnnotation( CsvBindByPosition.class ).position() ) )
                .map( f -> f.getAnnotation( CsvBindByName.class ).column() )
                .collect( Collectors.joining( "," ) ) + "\n";
    }

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class YourObject {

    @CsvBindByPosition(position = 0)
    @CsvBindByName(column = "A")
    private Long a;

    @CsvBindByPosition(position = 1)
    @CsvBindByName(column = "B")
    private String b;

    @CsvBindByPosition(position = 2)
    @CsvBindByName(column = "C")
    private String c;

}

Elegant use of stream. This seems the best implementation. – sympatric greg Apr 16 '20 at 05:26 — sympatric greg, Apr 16 '20 at 05:26

score 0 · Answer 4 · answered Mar 31 '21 at 08:21

Use a HeaderColumnNameMappingStrategy for reading, then use the same strategy for writing. "Same" in this case meaning not just the same class, but really the same object.

From the javadoc of StatefulBeanToCsvBuilder.withMappingStrategy:

It is perfectly legitimate to read a CSV source, take the mapping strategy from the read operation, and pass it in to this method for a write operation. This conserves some processing time, but, more importantly, preserves header ordering.

This way you will get a CSV including headers, with columns in the same order as the original CSV.

Worked for me using OpenCSV 5.4.

score -1 · Answer 5 · answered Jan 26 '21 at 20:53

You could also override the generateHeaders method and return the column mapping that is set, which will have header row in csv

ColumnPositionMappingStrategy<Product> mappingStrategy = new ColumnPositionMappingStrategy<Product>() {
            @Override
            public String[] generateHeader(Product bean) throws CsvRequiredFieldEmptyException {
                return this.getColumnMapping();
            }
        };

StatefulBeanToCsv with Column headers

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