Java11 openCSV只写入文件特定的bean属性

Question

如何只向csv文件(使用openCSV)写入特定的bean属性

即给学生上课

public class MyEntry {

private String propOne;
private Long propTwo;
private int propThree;
private String propFour;
private String propFive;
...
private String propFifteen;

//getters and setter omitted for brevity

}

在其他情况下，我可能需要创建一个包含从propFour到propTen字段的csv文件，可能需要创建一个具有所有bean属性的csv。可能有许多情况需要将不同的字段导出到csv文件。如何在不为不同情况创建自定义类的情况下实现它？

Answer 1

您可以创建CSVWriter.java并使用反射概念读取类的属性。记住调用setAccesible(true)，以便从外部访问私有字段

虚拟对象

import java.util.List;

public class Dummy {
  public static final List<String> GROUP_1 = List.of("prop1", "prop2");
  public static final List<String> GROUP_2 = List.of("prop1", "prop3");
  private String prop1;
  private Integer prop2;
  private String prop3;

  public String getProp1() {
      return prop1;
  }

  public Integer getProp2() {
      return prop2;
  }

  public String getProp3() {
    return prop3;
  }

  public void setProp1(String prop1) {
      this.prop1 = prop1;
  }

  public void setProp2(Integer prop2) {
      this.prop2 = prop2;
  }

  public void setProp3(String prop3) {
      this.prop3 = prop3;
  }
}

CSV编写器

import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.List;

public class CSVWriter<T> {
    private List<T> dataList;

    CSVWriter(List<T> dataList){
        this.dataList = dataList;
    }

    public void setDataList(List<T> dataList) {
        this.dataList = dataList;
    }

    public List<T> getDataList() {
        return dataList;
    }

    void save(FileWriter fileWriter) {
        if(dataList == null) {
            throw new RuntimeException("the data was not initialized");
        }

        //TODO Write all attributes into csv file
    }

    void save(FileWriter fileWriter, List<String> attributeNames) throws NoSuchFieldException, IllegalAccessException, IOException {
        if(dataList == null) {
            throw new RuntimeException("the data was not initialized");
        }

        //TODO improve errors handle

        for (T data : dataList) {
            Class<?> c = data.getClass();
            for (String attribute : attributeNames) {
                Field field = c.getDeclaredField(attribute);
                String valueString = getValue(field, data);
                fileWriter.write(valueString + ",");
            }
            fileWriter.write("\n");
            fileWriter.flush();
        }

        fileWriter.close();
    }

    private String getValue(Field field, T data) throws IllegalAccessException {
        field.setAccessible(true); //due to private field
        return field.get(data).toString();
    }
}

如何使用它？

public static void main(String[] args) throws Exception {
    List<Dummy> dummyList = new ArrayList<>();
    Dummy dummy1 = new Dummy();
    dummy1.setProp1("prop 1 value");
    dummy1.setProp2(2);
    dummy1.setProp3("prop 3 value");


    dummyList.add(dummy1);

    CSVWriter<Dummy> csvWriter = new CSVWriter<>(dummyList);

    csvWriter.save(new FileWriter("group1.csv"), Dummy.GROUP_1);
    csvWriter.save(new FileWriter("group2.csv"), Dummy.GROUP_2);
    System.out.println("Hello World!");
}

我知道你需要使用OpenCSV来做这件事。我以前从未使用过这个库，但是这个概念应该是相同的。