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

我正在使用opencsv 3.6来从Java bean开始创建一个csv文件。

首先，我尝试了以下代码:

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();
        }

    }
}

但是我有以下错误:

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getColumnName类的HeaderColumnNameTranslateMappingStrategy方法中的opencsv源代码中，存在以下行:

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

因此，header为null。的确如此，事实上，该类是HeaderColumnNameMappingStrategy类的子类，其中包含从未初始化的header变量(String[]类型)。

我在此类中找到的唯一有用的方法是captureHeader，但不幸的是，它需要使用CSVReader作为输入。

因此，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几行:

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)我也不异常(exception)，但是在结果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文件中的正确列名称？

有没有不使用CSVReader类的方法？

最佳答案

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一个自定义策略(避免CSVReader)和一个自定义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); } } }}