如何编写List< String>到csv文件&使用supercsv读回 [英] How to write List<String> to csv file & read it back using supercsv

问题描述

我使用supercsv CsvBeanWriter将值写入csv文件。

Am using supercsv CsvBeanWriter to write values to csv file.

示例类：

public class Employee {
    private String name;

    private int empId;

    List<String> phoneNumbers;
}

我得到的输出是：

name,empId,phoneNumbers
vijay,1,"[123, 456]"

注意 List< String> phoneNumbers 写在 []

我的问题是如何读回到Employee类（bean）使用supercsv。

My Question is how do I read it back to Employee class(bean)using supercsv.

我尝试使用 CsvBeanReader & CsvDozerBeanReader ，但无法读取列表< String> 。

I tried using CsvBeanReader & CsvDozerBeanReader but not able to read the List<String>.

我收到非法报价例外。

Am getting illegalargument exception. Will be thankful for any pointers !

完成代码：

public class DozerBeanReader {
public static void main(String [] args){
    ICsvDozerBeanReader beanReader = null;

    try {
        beanReader = new CsvDozerBeanReader(new FileReader("Employee.csv"), 
                CsvPreference.STANDARD_PREFERENCE);

        String [] header = beanReader.getHeader(true); // ignore the header

        Class<?> [] hintTypes = {String.class, Integer.class, List.class};

        beanReader.configureBeanMapping(Employee.class, header, hintTypes);

        Employee readEmp1 = beanReader.read(Employee.class);
        readEmp1.toString();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }


}
}

推荐答案

您依赖于您的列表的电话号码被写为单个CSV列使用列表的 toString（）格式，例如 [123，456] 。

You're relying on the fact that your List of phone numbers is written as a single CSV column using the List's toString()format, e.g. [123, 456].

您会收到类似以下的例外：

You will be getting an exception something like the following:

org.dozer.MappingException: Illegal object type 
for the method 'setPhoneNumbers'. 
Expected types: 
java.util.List
Actual types: 
java.lang.String

因为Dozer不知道如何将String [123，456] 转换为 List 。您可以执行此操作，但您需要撰写单元处理器将该字符串转换回 List 。如果你的电话号码纯粹是数字，不应该太难，但如果你的电话号码有逗号，那么事情会变得麻烦！

because Dozer has no idea how to convert the String [123, 456] to a List. You can do this, but you'll need to write a cell processor to convert that String back to a List. If your phone numbers are purely numbers that shouldn't be too hard, but if your phone numbers have commas then things are going to get messy!

我建议写每个电话号码作为一个单独的列 - 这使得它更容易（对于任何人阅读您的文件，包括你！）

I'd recommend writing each phone number as a separate column - it makes it so much easier (for anyone reading your file, including you!).

所有你需要做的是使用CsvDozerBeanReader和CsvDozerBeanWriter和索引映射。

All you'll need to do is use CsvDozerBeanReader and CsvDozerBeanWriter with indexed mapping.

下面是一个例子 - 关键部分是索引映射：

Here's an example - the key part is the indexed mapping:

String[] fieldMapping = new String[] { "name",
    "empId", "phoneNumbers[0]", "phoneNumbers[1]" };

• 我已定义了2个电话号码列 -


• 我可以为标题使用fieldMapping，但选择使用更易读的自定义标题




• 我使用StringReader / StringWriter只是为了简化示例


• I've defined 2 phone number columns - if your List will have more, then just add more columns
• I could have used the fieldMapping for the header, but chose to use a more readable custom header
• You shouldn't need the hints as you've got in your question
• I've used StringReader/StringWriter just to make the example simple

示例：

// create employee to write/read
Employee employee = new Employee();
employee.setEmpId(1234);
employee.setName("Vijay");
employee.setPhoneNumbers(Arrays.asList("123", "456"));

// the CSV header
String[] header = new String[] { "name",
    "empId", "phoneNumber1", "phoneNumber2" };

// the field mapping
String[] fieldMapping = new String[] { "name",
    "empId", "phoneNumbers[0]", "phoneNumbers[1]" };

// write the employee
StringWriter out = new StringWriter();
ICsvDozerBeanWriter writer = 
    new CsvDozerBeanWriter(out,
    CsvPreference.STANDARD_PREFERENCE);
writer.configureBeanMapping(Employee.class, fieldMapping);
writer.writeHeader(header);
writer.write(employee);
writer.flush();

// read the employee
ICsvDozerBeanReader reader = 
    new CsvDozerBeanReader(new StringReader(out.toString()),
    CsvPreference.STANDARD_PREFERENCE);
reader.configureBeanMapping(Employee.class, fieldMapping);
reader.getHeader(true); // ignore header
Employee e = reader.read(Employee.class);
System.out.println(e);

假设你写了 toString（）方法，这应该打印

Assuming you've written the toString() method, this should print

Employee [name=Vijay, empId=1234, phoneNumbers=[123, 456]]

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