带有列标题的 StatefulBeanToCsv

Question

我正在使用opencsv-4.0 编写一个 csv 文件，我需要在输出文件中添加列标题。

这是我的代码。

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());
    }

}

以上代码创建一个包含数据的 csv 文件。但它不包括该文件中的列标题。

如何添加列标题以输出 csv？

Answer 1

ColumnPositionMappingStrategy#generateHeader 返回空数组

/**
 * 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];
}

如果您从 BeanToCsv 构建器中删除 MappingStrategy

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

它将 Product 的类成员写为 CSV 标题

如果您的 Product 类成员名称是

"productCode", "MFD", "EXD"

这应该是正确的解决方案

否则，添加@CsvBindByName 注解

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;
        }
    }

}

输出：

"EXD","MFD","PRODUCTCODE"

"111","11","1"

"222","22","2"

"333","33","3"

注意；由于 OpenCSV 库使用反射，类、getter 和 setter 需要公开

Answer 2

你可以通过注解来追加

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;

}

Answer 3

我可能在这里遗漏了一些明显的东西，但你不能将你的标题字符串附加到 writer 对象吗？

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.

Answer 4

使用 HeaderColumnNameMappingStrategy 进行读取，然后使用相同的策略进行写入。在这种情况下，“相同”不仅意味着同一个类，而且实际上是同一个对象。

来自StatefulBeanToCsvBuilder.withMappingStrategy的javadoc：

读取 CSV 源代码，从读取操作中获取映射策略，并将其传递给此方法进行写入操作是完全合法的。这节省了一些处理时间，但更重要的是，保留了标头顺序。

这样您将获得一个包含标题的 CSV，其中列的顺序与原始 CSV 相同。

使用 OpenCSV 5.4 为我工作。

Answer 5

您也可以重写 generateHeaders 方法并返回设置的列映射，它将在 csv 中具有标题行

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