递归对象写入平面 csv 文件

Question

我需要写这样的对象

class User {
    UUID id;
    String name;
    Role role;
}

class Role {
    String name;
    LocalDate activeFrom;
    Authority owner;
}

class Authority {
    String name;
}

棘手的想法是 csv 写入应该通过对象树递归地工作。还需要将 LocalDate 写成字符串，如 2019-11-05 f.e.;

生成的 csv 文件应该是平面的，看起来像：

user.id,user.name,user.role.name,user.role.activeFrom,user.role.owner.name

// 示例值

我已经尝试过 OpenCsv:

        StatefulBeanToCsv<User> beanToCsv = new StatefulBeanToCsvBuilder<User>(printWriter).build();
        try {
            beanToCsv.write(users);
        } catch (CsvDataTypeMismatchException | CsvRequiredFieldEmptyException e) {
            e.printStackTrace();
        }
        printWriter.close();

和 Univocity 解析器：

CsvWriterSettings settings = new CsvWriterSettings();
        ObjectRowWriterProcessor processor = new ObjectRowWriterProcessor();
        settings.setRowWriterProcessor(processor);
        processor.convertType(User.class, );

到目前为止运气不好。他们只能序列化为 csv 顶级对象。同样在 OpenCsv 中，我在序列化 LocalDate 时遇到了问题。你能帮助我吗？建议方法或库？

Answer 1

由于我没有得到任何答案，我将描述我的解决方案。我使用了图书馆：

http://super-csv.github.io/super-csv/index.html

和扩展名：

https://super-csv.github.io/super-csv/dozer.html

代码：

import org.supercsv.io.dozer.CsvDozerBeanWriter;
import org.supercsv.prefs.CsvPreference;
import java.io.IOException;
import java.io.Writer;

static final String[] FIELD_MAPPING = new String[]{
    "user.id", "user.name", "user.role.name", "user.role.activeFrom", "user.role.owner.name"
};

    try (var beanWriter = new CsvDozerBeanWriter(printWriter, CsvPreference.STANDARD_PREFERENCE)) {
        beanWriter.configureBeanMapping(User.class, FIELD_MAPPING);
        beanWriter.writeHeader(FIELD_MAPPING);
        for (User user : users) {
            beanWriter.write(user);
        }
    }
    printWriter.close();

https://super-csv.github.io/super-csv/xref-test/org/supercsv/example/dozer/Writing.html

以及如何测试它：

@Test
void status_written_in_csv_format() {
    // Setup
    WriteCsvToResponse objectUnderTest = new WriteCsvToResponse ();
    StringWriter stringWriter = new StringWriter();
    PrintWriter printWriter = new PrintWriter(stringWriter);

    // Given
    Status status = ...

    // When
    objectUnderTest.writeStatus(printWriter, status);

    // Then
    String actualCsv = stringWriter.toString();
    assertThat(actualCsv.split("\n"))
       .as("Produced CSV")
       .containsExactly(
         "id,storeId,status",
         "42,142,OK");
}

Answer 2

在 univocity-parsers 上，无需任何映射，您只需使用 @Nested 注释嵌套对象即可。

class User {
    ...

    @Nested
    Role role;
}

递归对象写入平面 csv 文件

Recursive object write to flat csv file

csv

tree

recursion

hierarchy

univocity