使用 OpenCSV 将 CSV 解析为多个/嵌套 bean 类型？

2023-11-24

我有各种 CSV，其中包含一些标准列和一些完全随机的字段：

firstname, lastname, dog_name, fav_hat, fav_color
bill,smith,fido,porkpie,blue
james,smith,rover,bowler,purple


firstname, lastname, car_type, floor_number
tom, collins, ford, 14
jim, jones, toyota, 120

所以我试图将它们解析为 Person.class bean，它保存名字和姓氏，然后我有一个名为 PersonAttribute.class 的第二个类来保存......其他什么。

两个类的基本概要：

class Person {
 public String firstname;
 public String lastname;
 public List<PersonAttribute> attribs;
}

class PersonAttribute {
 public Person p;
 public String key; // header name, ex. 'car_type'
 public String value; // column value, ex. 'ford'
}

我一直在 opencsv 中使用 CsvToBean 函数：

public static List<Person> parseToBeans(File csvFile, HashMap<String, String> mapStrategy, Class beanClass) throws IOException {
    CSVReader reader = null;
    try {
        reader = new CSVReader(new BufferedReader(new FileReader(csvFile)));

        HeaderColumnNameTranslateMappingStrategy<Person> strategy = new HeaderColumnNameTranslateMappingStrategy<>();
        strategy.setType(beanClass);
        strategy.setColumnMapping(mapStrategy);

        final CsvToBean<Person> csv = new CsvToBean<Person>() {
            @Override
            protected Object convertValue(String value, PropertyDescriptor prop) throws InstantiationException, IllegalAccessException {
                value = value.trim().replaceAll(" +", " ");
                return super.convertValue(value, prop);
            }
        };
        return csv.parse(strategy, reader);
    }
...

但是，我不确定在解析 Person.class beans 的 csv 时如何处理创建 PersonAttribute.class beans。我碰到这个帖子我想知道我是否需要切换到 supercsv 才能轻松处理我想做的事情？

您当然可以使用 Super CSV 来实现这一目标。

您可以使用

CsvBeanReader- 不支持索引映射，因此您需要在 bean 中创建一个辅助方法才能使用它
CsvDozerBeanReader- 支持开箱即用的索引映射，因此将完全满足您的需求（需要最近发布的 Super CSV 2.1.0）

使用 CsvBeanReader

如果您不想使用 Dozer 并且能够修改您的 bean 类，最简单的选择是在您的 bean 上添加一个虚拟 setterCsvBeanReader将用于填充属性。我假设你的Person and PersonAttributebeans 有一个公共的无参数构造函数和为每个字段定义的 getters/setters（这是必需的）。

将以下虚拟设置器添加到您的Person bean:

public void setAddAttribute(PersonAttribute attribute){
    if (attribs == null){
        attribs = new ArrayList<PersonAttribute>();
    }
    attribs.add(attribute);
}

创建自定义细胞处理器这将填充一个PersonAttribute使用 CSV 标头中的相应键以及 CSV 列中的值。

package org.supercsv.example;

import org.supercsv.cellprocessor.CellProcessorAdaptor;
import org.supercsv.util.CsvContext;

/**
 * Creates a PersonAttribute using the corresponding header as the key.
 */
public class ParsePersonAttribute extends CellProcessorAdaptor {

    private final String[] header;

    public ParsePersonAttribute(final String[] header) {
        this.header = header;
    }

    public Object execute(Object value, CsvContext context) {

        if( value == null ) {
            return null;
        }

        PersonAttribute attribute = new PersonAttribute();
        // columns start at 1
        attribute.setKey(header[context.getColumnNumber() - 1]);
        attribute.setValue((String) value);
        return attribute;
    }

}

我认为下面的例子已经很能说明问题了，但我应该指出以下几点：

我必须使用自定义首选项，因为您的 CSV 包含不属于数据的空格
我必须动态组装字段映射和单元处理器数组，因为您的数据具有未知数量的属性（此设置通常并不复杂）
属性使用的所有字段映射addAttribute，对应于setAddAttribute()我们添加到您的 bean 中的方法
我使用我们的定制细胞处理器创建了一个PersonAttribute每个属性列的 bean

这是代码：

package org.supercsv.example;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

import org.supercsv.cellprocessor.Optional;
import org.supercsv.cellprocessor.constraint.NotNull;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.io.CsvBeanReader;
import org.supercsv.io.ICsvBeanReader;
import org.supercsv.prefs.CsvPreference;

public class ReadWithCsvBeanReader {

    private static final String CSV = 
            "firstname, lastname, dog_name, fav_hat, fav_color\n"
            + "bill,smith,fido,porkpie,blue\n"
            + "james,smith,rover,bowler,purple";

    private static final String CSV2 = 
            "firstname, lastname, car_type, floor_number\n"
            + "tom, collins, ford, 14\n" + "jim, jones, toyota, 120";

    // attributes start at element 2 of the header array
    private static final int ATT_START_INDEX = 2;

    // custom preferences required because CSV contains 
    spaces that aren't part of the data
    private static final CsvPreference PREFS = 
        new CsvPreference.Builder(
            CsvPreference.STANDARD_PREFERENCE)
            .surroundingSpacesNeedQuotes(true).build();

    public static void main(String[] args) throws IOException {
        System.out.println("CsvBeanReader with first CSV input:");
        readWithCsvBeanReader(new StringReader(CSV));
        System.out.println("CsvBeanReader with second CSV input:");
        readWithCsvBeanReader(new StringReader(CSV2));
    }

    private static void readWithCsvBeanReader(final Reader reader)
            throws IOException {
        ICsvBeanReader beanReader = null;
        try {
            beanReader = new CsvBeanReader(reader, PREFS);

            final String[] header = beanReader.getHeader(true);

            // set up the field mapping and processors dynamically
            final String[] fieldMapping = new String[header.length];
            final CellProcessor[] processors = 
                    new CellProcessor[header.length];
            for (int i = 0; i < header.length; i++) {
                if (i < ATT_START_INDEX) {
                    // normal mappings
                    fieldMapping[i] = header[i];
                    processors[i] = new NotNull();
                } else {
                    // attribute mappings
                    fieldMapping[i] = "addAttribute";
                    processors[i] = 
                            new Optional(new ParsePersonAttribute(header));
                }
            }

            Person person;
            while ((person = beanReader.read(Person.class, fieldMapping,
                    processors)) != null) {
                System.out.println(String.format(
                        "lineNo=%s, rowNo=%s, person=%s",
                        beanReader.getLineNumber(), beanReader.getRowNumber(),
                        person));
            }

        } finally {
            if (beanReader != null) {
                beanReader.close();
            }
        }
    }

}

输出（我添加了toString()方法到你的豆子）：

CsvBeanReader with first CSV input:
lineNo=2, rowNo=2, person=Person [firstname=bill, lastname=smith, attribs=[PersonAttribute [key=dog_name, value=fido], PersonAttribute [key=fav_hat, value=porkpie], PersonAttribute [key=fav_color, value=blue]]]
lineNo=3, rowNo=3, person=Person [firstname=james, lastname=smith, attribs=[PersonAttribute [key=dog_name, value=rover], PersonAttribute [key=fav_hat, value=bowler], PersonAttribute [key=fav_color, value=purple]]]
CsvBeanReader with second CSV input:
lineNo=2, rowNo=2, person=Person [firstname=tom, lastname=collins, attribs=[PersonAttribute [key=car_type, value=ford], PersonAttribute [key=floor_number, value=14]]]
lineNo=3, rowNo=3, person=Person [firstname=jim, lastname=jones, attribs=[PersonAttribute [key=car_type, value=toyota], PersonAttribute [key=floor_number, value=120]]]

使用 CsvDozerBeanReader

如果你不能，或者不想修改你的bean，那么我建议使用CsvDozerBeanReader in the 超级 CSV 推土机扩展装置项目，因为它支持嵌套和索引字段映射。查看一些正在使用的示例here.

下面是一个使用的示例CsvDozerBeanReader。你会发现它几乎与CsvBeanReader示例，但是：

它使用不同的阅读器（废话！）
它使用索引映射，例如attribs[0]
它通过调用来设置映射configureBeanMapping()（而不是接受字符串数组read()方法就像CsvBeanReader
它还设置了一些提示（更多内容见下文）

Code:

package org.supercsv.example;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

import org.supercsv.cellprocessor.Optional;
import org.supercsv.cellprocessor.constraint.NotNull;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.io.dozer.CsvDozerBeanReader;
import org.supercsv.io.dozer.ICsvDozerBeanReader;
import org.supercsv.prefs.CsvPreference;

public class ReadWithCsvDozerBeanReader {

    private static final String CSV = 
            "firstname, lastname, dog_name, fav_hat, fav_color\n"
            + "bill,smith,fido,porkpie,blue\n" 
            + "james,smith,rover,bowler,purple";

    private static final String CSV2 = 
            "firstname, lastname, car_type, floor_number\n" 
            + "tom, collins, ford, 14\n"
            + "jim, jones, toyota, 120";

    // attributes start at element 2 of the header array
    private static final int ATT_START_INDEX = 2;

    // custom preferences required because CSV contains spaces that aren't part of the data
    private static final CsvPreference PREFS = new CsvPreference.Builder(CsvPreference.STANDARD_PREFERENCE)
        .surroundingSpacesNeedQuotes(true).build();

    public static void main(String[] args) throws IOException {
        System.out.println("CsvDozerBeanReader with first CSV input:");
        readWithCsvDozerBeanReader(new StringReader(CSV));
        System.out.println("CsvDozerBeanReader with second CSV input:");
        readWithCsvDozerBeanReader(new StringReader(CSV2));
    }

    private static void readWithCsvDozerBeanReader(final Reader reader) throws IOException {
        ICsvDozerBeanReader beanReader = null;
        try {
            beanReader = new CsvDozerBeanReader(reader, PREFS);

            final String[] header = beanReader.getHeader(true);

            // set up the field mapping, processors and hints dynamically
            final String[] fieldMapping = new String[header.length];
            final CellProcessor[] processors = new CellProcessor[header.length];
            final Class<?>[] hintTypes = new Class<?>[header.length];
            for( int i = 0; i < header.length; i++ ) {
                if( i < ATT_START_INDEX ) {
                    // normal mappings
                    fieldMapping[i] = header[i];
                    processors[i] = new NotNull();
                } else {
                    // attribute mappings
                    fieldMapping[i] = String.format("attribs[%d]", i - ATT_START_INDEX);
                    processors[i] = new Optional(new ParsePersonAttribute(header));
                    hintTypes[i] = PersonAttribute.class;
                }
            }

            beanReader.configureBeanMapping(Person.class, fieldMapping, hintTypes);

            Person person;
            while( (person = beanReader.read(Person.class, processors)) != null ) {
                System.out.println(String.format("lineNo=%s, rowNo=%s, person=%s", 
                    beanReader.getLineNumber(),
                    beanReader.getRowNumber(), person));
            }

        }
        finally {
            if( beanReader != null ) {
                beanReader.close();
            }
        }
    }

}

Output:

CsvDozerBeanReader with first CSV input:
lineNo=2, rowNo=2, person=Person [firstname=bill, lastname=smith, attribs=[PersonAttribute [key=dog_name, value=fido], PersonAttribute [key=fav_hat, value=porkpie], PersonAttribute [key=fav_color, value=blue]]]
lineNo=3, rowNo=3, person=Person [firstname=james, lastname=smith, attribs=[PersonAttribute [key=dog_name, value=rover], PersonAttribute [key=fav_hat, value=bowler], PersonAttribute [key=fav_color, value=purple]]]
CsvDozerBeanReader with second CSV input:
lineNo=2, rowNo=2, person=Person [firstname=tom, lastname=collins, attribs=[PersonAttribute [key=car_type, value=ford], PersonAttribute [key=floor_number, value=14]]]
lineNo=3, rowNo=3, person=Person [firstname=jim, lastname=jones, attribs=[PersonAttribute [key=car_type, value=toyota], PersonAttribute [key=floor_number, value=120]]]

在整理这个例子时，我发现了一个错误CsvDozerBeanReader在 Super CSV 2.0.1 中，当您组合细胞处理器（例如我在上面的示例中创建的用于解析每个人属性键/值的），具有索引映射，例如：

"firstname","lastname","attribs[0]","attribs[1]"

我刚刚发布了 Super CSV 2.1.0 修复了这个问题。事实证明，Dozer 需要配置一个提示才能使索引映射正常工作。我不是 100% 确定为什么，因为它完全有能力创建每个PersonAttribute并在摆脱自定义单元处理器并使用以下（深度）映射时将其添加到正确的索引：

"firstname","lastname","attribs[0].value","attribs[1].value"

我希望这有帮助：）

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