带列标题的StatefulBeanToCsv [英] StatefulBeanToCsv with Column headers

问题描述

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

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

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());
    }

}

上面的代码用数据创建一个csv文件.但该文件中不包括列标题.

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

如何添加列标题以输出csv?

How could I add column headers to output csv?

推荐答案

ColumnPositionMappingStrategy#generateHeader返回空数组

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];
}

如果您从BeanToCsv构建器中删除MappingStrategy

If you remove MappingStrategy from BeanToCsv builder

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

它将产品类的成员写为CSV标头

It will write Product's class members as CSV header

如果您的Product类成员名称是

If your Product class members names are

"productCode", "MFD", "EXD"

这应该是正确的解决方案

This should be the right solution

否则，添加@CsvBindByName批注

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;
        }
    }

}

输出:

"EXD"，"MFD"，"PRODUCTCODE"

"EXD","MFD","PRODUCTCODE"

"111"，"11"，"1"

"111","11","1"

"222"，"22"，"2"

"222","22","2"

"333"，"33"，"3"

"333","33","3"

注意；类，吸气剂设置者需要公开，因为OpenCSV库使用了Reflection

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

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