java - OpenCsv 用 BeanToCsv + HeaderColumnNameTranslateMappingStrategy 写错列名

Question

我正在使用 opencsv 3.6 从 java bean 开始创建一个 csv 文件。

首先，我试过这段代码:

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。这是真的，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，但不幸的是它需要一个 CSVReader 作为输入。

因此我创建了一个空的 csv 文件:

COLUMN1,COLUMN2

我在 try/catch block 的开头添加了以下行:

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

以这种方式(我真的不喜欢，因为我必须创建一个 csv 文件)我也不异常(exception)，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:

1. 如何获得预期的结果，即 csv 文件中的正确列名？
2. 有没有办法不使用 CSVReader 类？

Answer 1

查看BeanToCsv的源代码, processHeader(...)方法对提供的 header 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

 

public class CustomBean {
   ...
   public static void main(String[] args) {
     ...
     HeaderColumnNameTranslateMappingStrategy strategy = new <b>CustomStrategy</b><CustomBean>();
     strategy.setType(CustomBean.class);
     strategy.setColumnMapping(mapping);
     ...

     BeanToCsv bean = new <b>CustomBeanToCsv</b><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);
         }
     }
   }
}