OpenCsv使用BeanToCsv + HeaderColumnNameTranslateMappingStrategy写入错误的列名称

问题描述

我使用 opencsv 3.6 为了从一个java bean开始创建一个csv文件。

I'm using opencsv 3.6 in order to create a csv file starting from a java bean.

首先，我尝试这个代码：

First of all, I tried this code:

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();
        }

    }
}

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

这发生是因为在 getColumnName $ c> HeaderColumnNameTranslateMappingStrategy 类有以下行：

This happens because in opencsv source code in getColumnName method in the HeaderColumnNameTranslateMappingStrategy class there is the following line:

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

因此， header 为null。这是真的，实际上这个类是 HeaderColumnNameMappingStrategy 的类，包含头变量（<$ c $

Therefore, header is null. This is true, in fact this class is a subclass of HeaderColumnNameMappingStrategy class that contains the header variable (String[] type) that is never initialized.

在这个类中找到的唯一有用的方法是 captureHeader ，但不幸的是它需要一个 CSVReader 作为输入。

The only useful method I found in this class is captureHeader, but unfortunately it takes a CSVReader as input.

创建了一个空的csv文件：

For this reason I created an empty csv file:

COLUMN1,COLUMN2

，我在try / catch块的开头添加了以下行：

and I added the following lines at the beginning of the try/catch block:

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）没有例外，但在结果csv文件中列的名称不遵循映射策略：

In this way (that I really don't like because I have to create a csv file) I have no exception, but in the result csv file the name of the columns does not follow the mapping strategy:

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

两个问题：

1. 如何获得预期结果，即csv文件中的正确列名？


2. 有一种方法不能使用 CSVReader 类？

1. How can I have the expected result, i.e. the right column names in the csv file?
2. There is a way to not use the CSVReader class?

推荐答案

查看 BeanToCsv 的源代码， processHeader（...）方法不提供所提供的头。您唯一的选择是创建一个自定义策略（避免 CSVReader ）和自定义 BeanToCsv 如下

Looking at the source code of BeanToCsv, the processHeader(...) method does nothing with the supplied headers. Your only option is to create a custom strategy ( to avoid CSVReader ) and a custom BeanToCsv as below

 

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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