Easyexcel exports according to the filter column (not empty in the middle, the order can be adjusted)

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Use EasyExel According to the way the filter column is exported, there is one in the official document “ Export only the specified columns according to the parameters ” Example , But in this case, I tested the derived Excel That's true .

EasyExcel Official documents ：https://www.yuque.com/easyexcel/doc

“ name ” and “ Birthday ” In the middle, there's a column , But if you need to export according to which fields are displayed on the front end , And the order should be as shown on the front end （ The front end implements drag and drop as well as filter to specify which fields to display , Therefore, the export format should be consistent ...）, The example given in this official document does not seem to satisfy , So I wrote an example that uses no object creation + An example of how reflection works .

This is one I wrote Person Test object

public class Person {

    @ExcelIgnore
    private Long id;

    @ExcelProperty(" name ")
    private String name;

    @ExcelProperty(" Age ")
    private int age;

    @ExcelProperty(" Birthday ")
    @DateTimeFormat("yyyy year MM month dd Japan ")
    private Date birthday;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
}

Using official documents “ Do not create write for objects ” Example , Encapsulate the , Use reflection to return the fields to be filtered

package com.example.demo.utils;

import com.alibaba.excel.EasyExcel;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

/**
 * @author  Bean sprouts 
 * @version 1.0
 * @Date 2020-11-09 09:13
 */
public class EasyExcelUtils {
    private static final Logger logger = LoggerFactory.getLogger(EasyExcelUtils.class);

    /**
     * @param fileName   File pathname 
     * @param sheetName sheet name 
     * @param data       The data from the query 
     * @param headList   Incoming Excel head （ for example ： full name , Birthday ）
     * @param fileList   Pass in the fields to be displayed （ for example ： The field corresponding to the name is name, The corresponding field of birthday is birthday）
     */
    public static void noModelWrite(String fileName, String sheetName, List data, List<String> headList, List<String> fileList){
        EasyExcel.write(fileName).head(head(headList)).sheet(sheetName).doWrite(dataList(data,fileList));
    }

    /**
     *  Set up Excel head 
     * @param headList  Excel Header information 
     * @return
     */
    private static List<List<String>> head(List<String> headList) {
        List<List<String>> list = new ArrayList<>();

        for (String value : headList) {
            List<String> head = new ArrayList<>();
            head.add(value);
            list.add(head);
        }
        return list;
    }

    /**
     *  Set table information 
     * @param dataList   The data found 
     * @param fileList   Fields to display 
     * @return
     */
    private static List<List<Object>> dataList(List<Object> dataList, List<String> fileList) {
        List<List<Object>> list = new ArrayList<>();
        for (Object person : dataList) {
            List<Object> data = new ArrayList<>();
            for (String fieldName : fileList) {
                /** By reflecting the fields that are displayed as needed , Get the corresponding property value */
                data.add(getFieldValue(fieldName, person));
            }
            list.add(data);
        }
        return list;
    }

    /**
     *  According to the field passed in, get the corresponding get Method , Such as name, Corresponding getName Method 
     * @param fieldName   Field name 
     * @param person     object 
     * @return
     */
    private static Object getFieldValue(String fieldName, Object person) {
        try {

            String firstLetter = fieldName.substring(0, 1).toUpperCase();
            String getter = "get" + firstLetter + fieldName.substring(1);
            Method method = person.getClass().getMethod(getter);
            return method.invoke(person);
        } catch (Exception e) {
            logger.error(" Failed to get object property value using reflection ", e);
            return null;
        }

    }


}

controller Layer uses this tool class to write Excel.

@RequestMapping(value = "/auth/downloadList",method = {RequestMethod.GET, RequestMethod.POST})
    public void downloadList(String filedNames,String filedCodes){
        List<Person> list = personServiceImpl.findPersonAll();

        /**Excel head , Parameter format ： full name , Birthday */
        String[] head = filedNames.split(",");
        List<String> headList = new ArrayList<>(Arrays.asList(head));

        /**Excel Form and content , Parameter format ：name,birthday*/
        String[] file = filedCodes.split(",");
        List<String> fileList = new ArrayList<>(Arrays.asList(file));

        EasyExcelUtils.noModelWrite("E:/data/ Test example .xls"," Test example ",list,headList,fileList);
    }

test 1 The incoming parameter is ：

filedNames ： name , Birthday

filedCodes ： name,birthday

The effect is as follows ：

test 2 The incoming parameter is ：

filedNames :  Birthday , name

filedCodes :  birthday,name

The effect is as follows ：

Through the code above , Use EasyExcel Does not create object write for + Reflection technology can be implemented without leaving one or more columns empty Excel, The dynamic column display can be realized according to the order of the front-end input parameters .

Be careful ：

1. To use this method, you need to pass in Excel Header information and corresponding field information ;

2. Because we use reflection to call the corresponding property name get Method to get the value , You need to check the properties corresponding to get Whether the method is named canonically , If not, it needs to be dealt with separately .