Import export simple

 EasyExcel It's based on Java Simple 、 Save memory for reading and writing Excel Open source projects for

There are basically two ways to read and write

1. By creating objects
2. Do not create objects for operation

Import dependence ：

    <!-- https://mvnrepository.com/artifact/com.alibaba/easyexcel -->
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>easyexcel</artifactId>
      <version>2.0.5</version>
    </dependency>

This article will myql in city Table as read / write demo Data source

Mode one ： Don't create objects

    write in Excel

mybatis: Statement writing

   <sql id="exportSql">
        c.ID " City Numbers ",c.Name " The city name ",c.CountryCode " City Code ",
        c.District " Geographical area ",
        c.Population " population size ",
        status " state ",sex " Gender ",birthday " Birthday ",createTime " Time "
    </sql>

    <select id="getAll" parameterType="map" resultType="map">
        select
        <include refid="exportSql"/>
        from city as c
    </select>

  Data needs to be processed ：

    /**
     *  Do not create objects to get data 
     *
     * @return
     */
    private List<List<Object>> dataList2() {
        List<List<Object>> list = new ArrayList<List<Object>>();
        List<Map<String, Object>> all = cityDao.getAll();
        all.forEach(t -> {
            Map<String, Object> t1 = t;
            List<Object> data = new ArrayList<Object>();
            List<List<String>> lists = head2();
            lists.forEach(s -> {
                Object o = t1.get(s.get(0));
                if (o instanceof Date) { // Time type cannot be processed , Go straight to String type 
                    String s1 = String.valueOf(o);
                    o=s1;
                }
                data.add(o);
            });
            list.add(data);
        });
        return list;
    }

    /**
     * excel  The first line of data 
     *
     * @return
     */
    private List<List<String>> head2() {
        List<String> strings = Arrays.asList(new String[]
                {" City Numbers ", " The city name ", " City Code ", " Geographical area ", " population size ", " state ", " Gender ", " Birthday ", " Time "});
        List<List<String>> list = new ArrayList<List<String>>();
        strings.forEach(t -> {
            list.add(Collections.singletonList(t));
        });
        return list;
    }

  test ：

    /**
     *  Simple export without creating objects -----------------------------------
     */
    @Test
    public void exportByData() {
//        dataList2();
        String file = "C:\\Users\\lhl\\Desktop\\tem.xlsx";
        EasyExcel.write(file).head(head2()).sheet(" Templates ").doWrite(dataList2());
    }

result ： There is too much data below, so don't expand it

   Read Excel

  Create a listening class ： Every row of data is read

public class NoModelDataListener extends AnalysisEventListener<Map<Integer, Object>> {
    /**
     *  every other 100 Storage database , It can be used in practice 3000 strip , Then clean up list , Convenient for memory recycling 
     */
    private static final int BATCH_COUNT = 100;
    List<Map<Integer, Object>> list = new ArrayList<Map<Integer, Object>>();
    @Override
    public void invoke(Map<Integer, Object> data, AnalysisContext context) {
        System.out.println("---------------- Read excel data -------------------------");
        System.out.println(data);
        list.add(data);
        if (list.size() >= BATCH_COUNT) {
            saveData();
            list.clear();
        }
    }


    @Override

    public void doAfterAllAnalysed(AnalysisContext context) {
        saveData();
    }


    /**
     *  Plus the storage database 
     */

    private void saveData() {
        System.out.println(" Storage database ");

    }


    @Test
    public  void fadfda(){
//        System.out.println("hello world !!!");
        try {
            // Create a URL example 
            URL url = new URL("https://mp.weixin.qq.com/s/ZGjVb3gwYuj3mGv0sCyAbw");
            try {
                // adopt URL Of openStrean Method to get URL The voluntary byte input stream represented by the 
                InputStream is = url.openStream();
                InputStreamReader isr = new InputStreamReader(is,"utf-8");

                // Add a buffer to the character input stream 
                BufferedReader br = new BufferedReader(isr);
                String data = br.readLine();// Reading data 

                while (data!=null){// Loop read data 
                    System.out.println(data);// Output data 
                    data = br.readLine();
                }
                br.close();
                isr.close();
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        }
    }

    
}

  test ：

  /**
     *  Read excel
     */
    @Test
    public void readExcelByNoObj(){
        //  here   as long as , Then read the first sheet  Synchronous reading will automatically finish
        String file = "C:\\Users\\lhl\\Desktop\\tem.xlsx";
        EasyExcel.read(file, new NoModelDataListener()).sheet().doRead();
    }

effect ：

excel Easy read to this , There is no complicated processing . When we encounter complex data processing , It is more important to create objects to implement excel Data import and reading .

Mode two ： Create objects

          write in Excel

Create entity class ：ExportExcel,get 、set The method will not repeat

@ContentRowHeight(10)
@HeadRowHeight(20)
@ColumnWidth(25)
public class ExportExcel {
    @ExcelProperty(" City Numbers ")
    private Integer id;
    @ExcelProperty(" The city name ")
    private String name;
    /**
     *  Width is 50
     */
//    @ColumnWidth(50)  It can be set in a single column 
    @ExcelProperty(" City Code ")
    private String countryCode;
    @ExcelProperty(" region ")
    private String district;
    @ExcelProperty(" Population ")
    private Integer population;
    @ExcelProperty(" state ")
    private Integer status;
    @ExcelProperty(" Gender ")
    private String sex;
    @DateTimeFormat("yyyy year MM month dd Japan ")
    @ExcelProperty(" Birthday ")
    private Date birthday;
    @DateTimeFormat("yyyy year MM month dd Japan HH when mm branch ss second ")
    @ExcelProperty(" Time ")
    private Date createTime;

...................................
}

test ： The effect is the same , I won't repeat

mybatis layer ：sql Is to query all the information that will not be repeated ：

    /**
     * ---------------------------------------------
     *  Create an object export ----- Very convenient 
     */
    @Test
    public void fdsasfa() {
        List<ExportExcel> list = cityDao.exportAll();
        String file = "C:\\Users\\lhl\\Desktop\\tem.xlsx";
        EasyExcel.write(file, ExportExcel.class).sheet(" Templates ").doWrite(list);
    }

Read Excel

Create a listening class ：

//  There is a very important point  ModelDataListener  Can not be spring management , Every time you read excel Both new, And then it uses spring You can construct methods to pass in 
public class ModelDataListener extends AnalysisEventListener<ExportExcel> {
    /**
     *  every other 5 Storage database , It can be used in practice 3000 strip , Then clean up list , Convenient for memory recycling 
     */
    private static final int BATCH_COUNT = 5;
    List<ExportExcel> list = new ArrayList<ExportExcel>();

    private CityDao cityDao;// You can operate the database to store data 

    public ModelDataListener(CityDao demoDAO) {
        System.out.println("------- This gets the incoming dao layer -------");
        List<ExportExcel> all = demoDAO.exportAll();
        all.forEach(t-> System.out.println(t));
        this.cityDao=demoDAO;
    }
    /**
     *  Every data parsing will call 
     * @param data
     * one row value. Is is same as {@link AnalysisContext#readRowHolder()}
     */
    @Override
    public void invoke(ExportExcel data, AnalysisContext analysisContext) {
//        System.out.println(data);
        list.add(data);
        //  achieve BATCH_COUNT 了 , Need to store the database once , Prevent tens of thousands of data in memory , Easy to OOM
        if (list.size() >= BATCH_COUNT) {
            saveData();
            //  Storage complete cleaning  list
            list.clear();
        }
    }

    /**
     *  All data analysis is done   Will call 
     *
     * @param context
     */
    @Override

    public void doAfterAllAnalysed(AnalysisContext context) {
        //  We also need to save data here , Make sure that the last legacy data is also stored in the database 
        saveData();
    }
    /**
     *  Plus the storage database 
     */
    private void saveData() {
    }
}

test ： Results the correct

    /**
     *  Read according to the created object 
     */
    @Test
    public void readByModel(){
        String file = "C:\\Users\\lhl\\Desktop\\tem.xlsx";
        //  here   You need to specify which to read class To read , Then read the first sheet  The file stream closes automatically 
        EasyExcel.read(file, ExportExcel.class, new ModelDataListener(cityDao)).sheet().doRead();
    }

Particular attention ： Because no objects are created , I didn't use it correctly , The date and other formats are converted into strings , Don't string , Otherwise, a listening error will be reported .

More rigorous usage , Listening classes can use generics , You don't have to create each .

Other more uses ： Instructions · Language sparrow

ServletOutputStream fo=response.getOutputStream();
response.addHeader("Content-Disposition","attachment; filename=" + URLEncoder.encode(fileName, "UTF-8"));
response.setContentType("application/vnd.ms-excel;charset=utf-8");