如何用Open CSV实现单CSV列到多DTO字段的映射？

当前实现代码 #

MyDto类 #

public class MyDto {
    @CsvBindByName(column = "AFBP")
    String placeholderA;
    @CsvBindByNames({
            @CsvBindByName(column = "ABCD"),
            @CsvBindByName(column = "AFEL")
    })
    String placeholderB;

    @CsvBindByNames({
            @CsvBindByName(column = "ABCD"),
            @CsvBindByName(column = "ALTM")
    })
    String placeholderC;

    @Override
    public String toString() {
        return "placeholder A = " + placeholderA + ", placeholderB = " + placeholderB + ", placeholderC = " + placeholderC;
    }
}

待反序列化的CSV内容 #

var csv = "AFBP,ABCD\nthis is A,this is B and C";

实际反序列化结果 #

placeholder A = this is A, placeholderB = null, placeholderC = this is B and C

期望结果 #

placeholder A = this is A, placeholderB = this is B and C, placeholderC = this is B and C

问题 #

能否通过OpenCSV或其他支持注解的CSV库，实现单CSV列到多个DTO字段的映射反序列化？

解决方案 #

针对OpenCSV的解决方法 #

OpenCSV默认的@CsvBindByNames注解处理多字段映射同一列时，只会给其中一个字段赋值，无法自动同步到多个字段。可以通过以下方式实现需求：

1. 利用Setter方法同步值
   放弃在多个字段上直接绑定注解，转而通过一个绑定目标列的Setter方法，同时给多个字段赋值：

   public class MyDto {
       @CsvBindByName(column = "AFBP")
       String placeholderA;
       
       String placeholderB;
       String placeholderC;
   
       @CsvBindByName(column = "ABCD")
       public void setCommonValue(String value) {
           this.placeholderB = value;
           this.placeholderC = value;
       }
   
       @Override
       public String toString() {
           return "placeholder A = " + placeholderA + ", placeholderB = " + placeholderB + ", placeholderC = " + placeholderC;
       }
   }
   

   这种方式绕过注解的限制，通过手动赋值实现多字段同步。

2. 自定义MappingStrategy
   继承HeaderColumnNameMappingStrategy，重写populateBean方法，在完成默认映射逻辑后，主动将指定列的值赋值给需要同步的多个字段。

其他注解式CSV库的替代方案 #

如果不想修改OpenCSV的使用逻辑，可以尝试Jackson CSV，它支持将同一列名映射到多个字段：

public class MyDto {
    @JsonProperty("AFBP")
    String placeholderA;
    
    @JsonProperty("ABCD")
    String placeholderB;
    
    @JsonProperty("ABCD")
    String placeholderC;

    @Override
    public String toString() {
        return "placeholder A = " + placeholderA + ", placeholderB = " + placeholderB + ", placeholderC = " + placeholderC;
    }
}

使用Jackson CSV的CsvMapper执行反序列化时，会自动将ABCD列的值同时赋值给placeholderB和placeholderC。

内容的提问来源于stack exchange，提问作者michal