带有列标题的StatefulBeanToCsv

问题描述 投票：0回答：7

我正在使用 

opencsv-4.0
编写 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());
    }

}

上面的代码创建了一个包含数据的 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？

java csv opencsv
7个回答
23
投票

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();

它将把 Product 的类成员写入 CSV header

如果您的产品类成员名称是

"productCode", "MFD", "EXD"

这应该是正确的解决方案

否则，添加@CsvBindByName注释

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”、“产品代码”

“111”、“11”、“1”

“222”，“22”，“2”

“333”，“33”，“3”

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

9
投票

您可以通过注释追加

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;

}
5
投票

我可能在这里错过了一些明显的东西，但是你不能将标题字符串附加到 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.
0
投票

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，而且意味着同一个对象。

来自

StatefulBeanToCsvBuilder.withMappingStrategy
的javadoc：

读取 CSV 源、从读取操作中获取映射策略并将其传递给此方法以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，保留了标头排序。

这样您将获得包含标题的 CSV，其中列的顺序与原始 CSV 相同。

使用 OpenCSV 5.4 为我工作。

0
投票

使用自定义策略

    static class CustomStrategy<T> extends ColumnPositionMappingStrategy<T> {
    public String[] generateHeader() {
        return this.getColumnMapping();
    }
}

在您编写的 CSV 对象上，不要忘记同时提供两者

@CsvBindByName(column="UID")
@CsvBindByPosition(position = 3)
0
投票

对于那些想要同时使用 HeaderName 和 Position 而不先读取 csv 文件的人。

使用自定义映射策略很容易实现。

static class NameAndPositionMappingStrategy<T> extends HeaderNameBaseMappingStrategy<T> {
        public NameAndPositionMappingStrategy(Class<T> clazz) {
            setType(clazz);
            setColumnOrderOnWrite(new Comparator<String>() {
                @Override
                public int compare(String o1, String o2) {
                    CsvBindByPosition pos1 = getFieldMap().get(o1).getField().getAnnotation(CsvBindByPosition.class);
                    CsvBindByPosition pos2 = getFieldMap().get(o2).getField().getAnnotation(CsvBindByPosition.class);
                    return Integer.compare(
                       pos1 != null ? pos1.position() : 0,
                       pos2 != null ? pos2.position() : 0
                    );
                }
            });
        }
    }

在你的 bean 中你现在可以定义两个注释

 public static class Product {
        @CsvBindByPosition(position = 0)
        @CsvBindByName(column = "ID")
        String id;

        @CsvBindByPosition(position = 1)
        @CsvBindByName(column = "FIELD2")
        String member2;

        @CsvBindByPosition(position = 2)
        @CsvBindByName(column = "FIELD3")
        String member3;
    

}

作家应该是这样的：


builder.withMappingStrategy(new NameAndPositionMappingStrategy<Product>(Product.class).build()

这将同时使用 CsvBindByName 和 CsvBindByPosition。

（或者，您也可以只使用 HeaderNameBaseMappingStrategy 并设置 ColumnOrderOnWrite 而不使用继承）

-1
投票

您还可以重写generateHeaders方法并返回设置的列映射，该映射将在csv中包含标题行

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