如何创建通用的FlatFileItemReader以读取具有不同标题的CSV文件? [英] How to create a generic FlatFileItemReader to read CSV files with different headers?

问题描述

我正在创建一个作业，该作业将基于输入参数读取和处理不同的.csv文件.有3种不同类型的.csv文件，它们的标题不同.我想使用通用的 FlatFileItemReader 将文件的每一行映射到POJO.

I'm creating a job that will read and process different .csv files based on an input parameter. There are 3 different types of .csv files with different headers. I want to map each line of a file to a POJO using a generic FlatFileItemReader.

每种文件类型都有其自己的POJO实现，并且所有特定于文件的POJO"都从抽象的 GenericFilePOJO 子类化.

Each type of file will have its own POJO implementation, and all "File Specific POJOs" are subclassed from an abstract GenericFilePOJO.

tasklet首先将读取输入参数，以确定需要读取的文件类型，然后使用适当的标题列构造LineTokenizer.它将此信息放置在infoHolder中以在阅读器步骤中进行检索.

A tasklet will first read the input parameter to decide which file type needs to be read, and construct a LineTokenizer with the appropriate header columns. It places this information in the infoHolder for retrieval at the reader step.

@Bean
public FlatFileItemReader<GenericFilePOJO> reader() {
    FlatFileItemReader<RawFile> reader = new FlatFileItemReader<GenericFilePOJO>();
    reader.setLinesToSkip(1); // header

    reader.setLineMapper(new DefaultLineMapper() {
        {
            // The infoHolder will contain the file-specific LineTokenizer
            setLineTokenizer(infoHolder.getLineTokenizer());
            setFieldSetMapper(new BeanWrapperFieldSetMapper<GenericFilePOJO>() {
                {
                    setTargetType(GenericFilePOJO.class);
                }
            });
        }
    });
    return reader;
}

尽管返回 GenericFilePOJO ，该读者仍可以处理不同的文件特定POJO吗?

Can this reader handle the different File Specific POJOs despite returning the GenericFilePOJO?

推荐答案

您写道:

tasklet 将首先读取输入参数以确定哪个文件类型需要阅读.

A tasklet will first read the input parameter to decide which file type needs to be read.

由于 tasklet 或 infoHolder 知道文件的类型，因此可以实现创建特定的 FieldSetMapper 实例.

Because the tasklet or infoHolder knows about type of file you can implement the creation of specific FieldSetMapper instance.

这是一个演示示例，该示例如何实现:

This is a demo example how it can be implemented:

public class Solution<T extends GenericFilePOJO> {
    private InfoHolder infoHolder = new InfoHolder();

    @Bean
    public FlatFileItemReader<T> reader()
    {
        FlatFileItemReader<T> reader = new FlatFileItemReader<T>();
        reader.setLinesToSkip(1);

        reader.setLineMapper(new DefaultLineMapper() {
            {
                setLineTokenizer(infoHolder.getLineTokenizer());
                setFieldSetMapper(infoHolder.getFieldSetMapper());
            }
        });
        return reader;
    }

    private class InfoHolder {
        DelimitedLineTokenizer getLineTokenizer() {
            return <some already existent logic>;
        }

        FieldSetMapper<T> getFieldSetMapper() {
            if (some condition for specific file POJO 1){
                return new BeanWrapperFieldSetMapper<T>() {
                    {
                        setTargetType(FileSpecificPOJO_1.class);
                    }
                };
            } else if (some condition for specific file POJO 2){
                return new BeanWrapperFieldSetMapper<T>() {
                    {
                        setTargetType(FileSpecificPOJO_2.class);
                    }
                };
            }
        }
    }
}

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