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OpenCsv使用BeanToCsv HeaderColumnNameTranslateMappingStrategy写错了列名

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我正在使用 opencsv 3.6 来从java bean开始创建一个csv文件 .

首先,我尝试了这段代码:

import com.opencsv.CSVReader;
import com.opencsv.CSVWriter;
import com.opencsv.bean.BeanToCsv;
import com.opencsv.bean.HeaderColumnNameTranslateMappingStrategy;

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class CustomBean {

    private String name;
    private String surname;

    public CustomBean(String n, String s) {
        this.name = n;
        this.surname = s;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }

    public String getSurname() {
        return surname;
    }

    public static void main(String[] args) {
        Map<String,String> mapping = new HashMap<String,String>();
        mapping.put("COLUMN1","name");
        mapping.put("COLUMN2","surname");

        HeaderColumnNameTranslateMappingStrategy<CustomBean> strategy = new HeaderColumnNameTranslateMappingStrategy<CustomBean>();
        strategy.setType(CustomBean.class);
        strategy.setColumnMapping(mapping);

        ArrayList<CustomBean> customUsers = new ArrayList<CustomBean>();
        customUsers.add(new CustomBean("Kobe","Bryant"));

        BeanToCsv<CustomBean> bean = new BeanToCsv<CustomBean>();

        try {            
            CSVWriter writer = new CSVWriter(new FileWriter("testOut.csv"));
            bean.write(strategy, writer, customUsers);
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

但我有以下错误:

Exception in thread "main" java.lang.RuntimeException: Error writing CSV !
    at com.opencsv.bean.BeanToCsv.write(BeanToCsv.java:74)
    at test.CustomBean.main(CustomBean.java:63)
Caused by: java.lang.NullPointerException
    at com.opencsv.bean.HeaderColumnNameTranslateMappingStrategy.getColumnName(HeaderColumnNameTranslateMappingStrategy.java:45)
    at com.opencsv.bean.HeaderColumnNameMappingStrategy.findDescriptor(HeaderColumnNameMappingStrategy.java:112)
    at com.opencsv.bean.BeanToCsv.processHeader(BeanToCsv.java:103)
    at com.opencsv.bean.BeanToCsv.write(BeanToCsv.java:69)
    ... 1 more

发生这种情况是因为在 HeaderColumnNameTranslateMappingStrategy 类的 getColumnName 方法中的opencsv源代码中有以下行:

return col < header.length ? columnMapping.get(header[col].toUpperCase()) : null;

因此, header 为空 . 这是事实,实际上这个类是 HeaderColumnNameMappingStrategy 类的子类,它包含从未初始化的 header 变量( String[] 类型) .

我在这个类中找到的唯一有用的方法是 captureHeader ,但不幸的是它需要 CSVReader 作为输入 .

出于这个原因,我创建了一个空的csv文件:

COLUMN1,COLUMN2

我在try / catch块的开头添加了以下行:

CSVReader reader = new CSVReader(new FileReader("testIn.csv"));
strategy.captureHeader(reader);

这样(我真的不喜欢,因为我必须创建一个csv文件)我没有异常,但在结果csv文件中,列的名称不遵循映射策略:

"name","surname"
"Kobe","Bryant"

两个问题:

  • 如何获得预期的结果,即csv文件中的右列名?

  • 有一种方法可以不使用 CSVReader 类吗?

2 回答

  • 3

    我已经使用openCSV五年了,我还在学习它的内容 . 问题是HeaderColumnNameMappingStrategy和HeaderColumnNameTranslateMappingStrategy是为CsvToBean创建的 . 它想要一个文件读取以获取 Headers ,以查看读者应该从哪里读取 .

    对于BeanToCsv类,请使用ColumnPositionMappingStrategy类 . 您可以为其提供要映射的类以及要映射的列的列表,并为您完成剩下的工作 .

    这是我编写的一个小测试方法 .

    public void createUsingBeanToCsv(int numRecords, FileWriter fos) {
        List<SmallRecord> smallRecords = new ArrayList<>(numRecords);
        for (int i = 0; i < numRecords; i++) {
            smallRecords.add(SmallRecordGenerator.createRecord(i));
        }
    
        BeanToCsv<SmallRecord> beanToCsv = new BeanToCsv<>();
        ColumnPositionMappingStrategy<SmallRecord> strategy = new ColumnPositionMappingStrategy<>();
        strategy.setType(SmallRecord.class);
        String[] columns = new String[]{"bigDecimal_1", "name_1", "intNumber_1"};
        strategy.setColumnMapping(columns);
    
        beanToCsv.write(strategy, fos, smallRecords);
    
    }
    
  • 2

    查看 BeanToCsv 的源代码, processHeader(...) 方法对提供的标头不执行任何操作 . 您唯一的选择是创建自定义策略(以避免 CSVReader )和自定义 BeanToCsv ,如下所示

    public class CustomBean {
       ...
       public static void main(String[] args) {
         ...
         HeaderColumnNameTranslateMappingStrategy strategy = new CustomStrategy<CustomBean>();
         strategy.setType(CustomBean.class);
         strategy.setColumnMapping(mapping);
         ...
    
         BeanToCsv bean = new CustomBeanToCsv<CustomBean>();
         ...
       }
    
       static class CustomStrategy<T> extends HeaderColumnNameTranslateMappingStrategy {
    
        @Override
        public void setColumnMapping(Map columnMapping) {
            super.setColumnMapping(columnMapping);
            header = new String[columnMapping.size()];
            int i = 0;
            for (Map.Entry entry : columnMapping.entrySet()) {
                header[i] = entry.getKey().toUpperCase();
                i++;
            }
        }
    
         public String[] getHeader() {
             return header;
         }
       }
    
       static class CustomBeanToCsv<T> extends BeanToCsv {
         @Override
         protected String[] processHeader(MappingStrategy mapper) throws IntrospectionException {
             if (mapper instanceof CustomStrategy) {
                 return ((CustomStrategy) mapper).getHeader();
             } else {
                 return super.processHeader(mapper);
             }
         }
       }
    }
    

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