Create Excel file in Java

You can use Apache POI for creating native binary xls files.

Or you can use JExcelApi which is another, and somewhat light-weight as far as I can remember, Java library for Excel.

Flat files do not allow providing meta information.

I would suggest writing out a HTML table containing the information you need, and let Excel read it instead. You can then use <b> tags to do what you ask for.

Changing the extension of a file does not in any way change its contents. The extension is just a label.

If you want to work with Excel spreadsheets using Java, read up on the Apache POI library.

I used also JXLS: it receives the data as a Map and a template EXCEL with the correct syntax and return the file correctly populated. The data in every cell must be a JavaBean with visibility public.

It not worws if you must insert data in more than 1 sheet: in this case I used POI.

To create a spreadsheet and format a cell using POI, see the Working with Fonts example, and use:

font.setBoldweight(Font.BOLDWEIGHT_BOLD);

POI works very well. There are some things you can't do (e.g. create VBA macros), but it'll read/write spreadsheets with macros, so you can create a suitable template sheet, read it and manipulate it with POI, and then write it out.

I've created the API "generator-excel" to create an Excel file, below the dependecy:

<dependency>
  <groupId>com.github.bld-commons.excel</groupId>
  <artifactId>generator-excel</artifactId>
  <version>3.1.0</version>
</dependency>

This library can to configure the styles, the functions, the charts, the pivot table and etc. through a series of annotations.
You can write rows by getting data from a datasource trough a query with or without parameters.
Below an example to develop

1. I created 2 classes that represents the row of the table.

package bld.generator.report.junit.entity;
    
    import java.util.Date;
    
    import org.apache.poi.ss.usermodel.HorizontalAlignment;
    
    import bld.generator.report.excel.RowSheet;
    import bld.generator.report.excel.annotation.ExcelCellLayout;
    import bld.generator.report.excel.annotation.ExcelColumn;
    import bld.generator.report.excel.annotation.ExcelDate;
    import bld.generator.report.excel.annotation.ExcelImage;
    import bld.generator.report.excel.annotation.ExcelRowHeight;
    
    @ExcelRowHeight(height = 3)
    public class UtenteRow implements RowSheet {
        
        @ExcelColumn(columnName = "Id", indexColumn = 0)
        @ExcelCellLayout(horizontalAlignment = HorizontalAlignment.RIGHT)
        private Integer idUtente; 
        @ExcelColumn(columnName = "Nome", indexColumn = 2)
        @ExcelCellLayout
        private String nome; 
        @ExcelColumn(columnName = "Cognome", indexColumn = 1)
        @ExcelCellLayout
        private String cognome;
        @ExcelColumn(columnName = "Data di nascita", indexColumn = 3)
        @ExcelCellLayout(horizontalAlignment = HorizontalAlignment.CENTER)
        @ExcelDate
        private Date dataNascita;
        @ExcelColumn(columnName = "Immagine", indexColumn = 4)
        @ExcelCellLayout
        @ExcelImage(resizeHeight = 0.7, resizeWidth = 0.6)
        private byte[] image;   
        
        @ExcelColumn(columnName = "Path", indexColumn = 5)
        @ExcelCellLayout
        @ExcelImage(resizeHeight = 0.7, resizeWidth = 0.6)
        private String path;    
        
    
        public UtenteRow() {
        }
    
    
        public UtenteRow(Integer idUtente, String nome, String cognome, Date dataNascita) {
            super();
            this.idUtente = idUtente;
            this.nome = nome;
            this.cognome = cognome;
            this.dataNascita = dataNascita;
        }
    
    
        public Integer getIdUtente() {
            return idUtente;
        }
    
    
        public void setIdUtente(Integer idUtente) {
            this.idUtente = idUtente;
        }
    
    
        public String getNome() {
            return nome;
        }
    
    
        public void setNome(String nome) {
            this.nome = nome;
        }
    
    
        public String getCognome() {
            return cognome;
        }
    
    
        public void setCognome(String cognome) {
            this.cognome = cognome;
        }
    
    
        public Date getDataNascita() {
            return dataNascita;
        }
    
    
        public void setDataNascita(Date dataNascita) {
            this.dataNascita = dataNascita;
        }
    
    
        public byte[] getImage() {
            return image;
        }
    
    
        public String getPath() {
            return path;
        }
    
    
        public void setImage(byte[] image) {
            this.image = image;
        }
    
    
        public void setPath(String path) {
            this.path = path;
        }
    
    }




package bld.generator.report.junit.entity;

import org.apache.poi.ss.usermodel.DataConsolidateFunction;
import org.apache.poi.ss.usermodel.HorizontalAlignment;

import bld.generator.report.excel.RowSheet;
import bld.generator.report.excel.annotation.ExcelCellLayout;
import bld.generator.report.excel.annotation.ExcelColumn;
import bld.generator.report.excel.annotation.ExcelFont;
import bld.generator.report.excel.annotation.ExcelSubtotal;
import bld.generator.report.excel.annotation.ExcelSubtotals;

@ExcelSubtotals(labelTotalGroup = "Total",endLabel = "total")
public class SalaryRow implements RowSheet {

    @ExcelColumn(columnName = "Name", indexColumn = 0)
    @ExcelCellLayout
    private String name;
    @ExcelColumn(columnName = "Amount", indexColumn = 1)
    @ExcelCellLayout(horizontalAlignment = HorizontalAlignment.RIGHT)
    @ExcelSubtotal(dataConsolidateFunction = DataConsolidateFunction.SUM,excelCellLayout = @ExcelCellLayout(horizontalAlignment = HorizontalAlignment.RIGHT,font=@ExcelFont(bold = true)))
    private Double amount;
    
    public SalaryRow() {
        super();
    }
    public SalaryRow(String name, Double amount) {
        super();
        this.name = name;
        this.amount = amount;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Double getAmount() {
        return amount;
    }
    public void setAmount(Double amount) {
        this.amount = amount;
    }
    
}

2. I created 2 class that represents the sheets.

package bld.generator.report.junit.entity;

import javax.validation.constraints.Size;

import bld.generator.report.excel.QuerySheetData;
import bld.generator.report.excel.annotation.ExcelHeaderLayout;
import bld.generator.report.excel.annotation.ExcelMarginSheet;
import bld.generator.report.excel.annotation.ExcelQuery;
import bld.generator.report.excel.annotation.ExcelSheetLayout;

@ExcelSheetLayout
@ExcelHeaderLayout
@ExcelMarginSheet(bottom = 1.5, left = 1.5, right = 1.5, top = 1.5)
@ExcelQuery(select = "SELECT id_utente, nome, cognome, data_nascita,image,path "
        + "FROM utente "
        + "WHERE cognome=:cognome "
        + "order by cognome,nome")
public class UtenteSheet extends QuerySheetData<UtenteRow> {
    

    public UtenteSheet(@Size(max = 31) String sheetName) {
        super(sheetName);
    }

    
}




package bld.generator.report.junit.entity;

import javax.validation.constraints.Size;

import bld.generator.report.excel.SheetData;
import bld.generator.report.excel.annotation.ExcelHeaderLayout;
import bld.generator.report.excel.annotation.ExcelMarginSheet;
import bld.generator.report.excel.annotation.ExcelSheetLayout;
@ExcelSheetLayout
@ExcelHeaderLayout
@ExcelMarginSheet(bottom = 1.5,left = 1.5,right = 1.5,top = 1.5)
public class SalarySheet extends SheetData<SalaryRow> {

    public SalarySheet(@Size(max = 31) String sheetName) {
        super(sheetName);
    }

}

3. Class test, in the test function there are antoher sheets

package bld.generator.report.junit;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.List;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import bld.generator.report.excel.BaseSheet;
import bld.generator.report.excel.GenerateExcel;
import bld.generator.report.excel.data.ReportExcel;
import bld.generator.report.junit.entity.AutoreLibriSheet;
import bld.generator.report.junit.entity.CasaEditrice;
import bld.generator.report.junit.entity.GenereSheet;
import bld.generator.report.junit.entity.SalaryRow;
import bld.generator.report.junit.entity.SalarySheet;
import bld.generator.report.junit.entity.TotaleAutoreLibriRow;
import bld.generator.report.junit.entity.TotaleAutoreLibriSheet;
import bld.generator.report.junit.entity.UtenteSheet;
import bld.generator.report.utils.ExcelUtils;

/**
 * The Class ReportTest.
 */
@RunWith(SpringRunner.class)
@SpringBootTest
@ConfigurationProperties
@ComponentScan(basePackages = {"bld.generator","bld.read"})
@EnableTransactionManagement
public class ReportTestJpa {

    /** The Constant PATH_FILE. */
    private static final String PATH_FILE = "/mnt/report/";

    /** The generate excel. */
    @Autowired
    private GenerateExcel generateExcel;

    /**
     * Sets the up.
     *
     * @throws Exception the exception
     */
    @Before
    public void setUp() throws Exception {
    }

    /**
     * Test.
     *
     * @throws Exception the exception
     */
    @Test
    public void test() throws Exception {
        List<BaseSheet> listBaseSheet = new ArrayList<>();
        
        UtenteSheet utenteSheet=new UtenteSheet("Utente");
        utenteSheet.getMapParameters().put("cognome", "Rossi");
        listBaseSheet.add(utenteSheet);
        
        CasaEditrice casaEditrice = new CasaEditrice("Casa Editrice","Mondadori", new GregorianCalendar(1955, Calendar.MAY, 10), "Roma", "/home/francesco/Documents/git-project/dev-excel/linux.jpg","Drammatico");
        listBaseSheet.add(casaEditrice);
        
        
        AutoreLibriSheet autoreLibriSheet = new AutoreLibriSheet("Libri d'autore","Test label");
        TotaleAutoreLibriSheet totaleAutoreLibriSheet=new TotaleAutoreLibriSheet();
        totaleAutoreLibriSheet.getListRowSheet().add(new TotaleAutoreLibriRow("Totale"));
        autoreLibriSheet.setSheetFunctionsTotal(totaleAutoreLibriSheet);
        listBaseSheet.add(autoreLibriSheet);
        GenereSheet genereSheet=new GenereSheet("Genere");
        listBaseSheet.add(genereSheet);
        SalarySheet salarySheet=new SalarySheet("salary");
        salarySheet.getListRowSheet().add(new SalaryRow("a",2.0));
        salarySheet.getListRowSheet().add(new SalaryRow("a",2.0));
        salarySheet.getListRowSheet().add(new SalaryRow("a",2.0));
        salarySheet.getListRowSheet().add(new SalaryRow("a",2.0));
        salarySheet.getListRowSheet().add(new SalaryRow("c",1.0));
        salarySheet.getListRowSheet().add(new SalaryRow("c",1.0));
        salarySheet.getListRowSheet().add(new SalaryRow("c",1.0));
        salarySheet.getListRowSheet().add(new SalaryRow("c",1.0));
        listBaseSheet.add(salarySheet);
        ReportExcel excel = new ReportExcel("Mondadori JPA", listBaseSheet);

        byte[] byteReport = this.generateExcel.createFileXlsx(excel);

        ExcelUtils.writeToFile(PATH_FILE,excel.getTitle(), ".xlsx", byteReport);

    }

    

}

4. Application yaml

logging:
  level:
    root: WARN
    org:
      springframework:
        web: DEBUG
      hibernate: ERROR



spring:
  datasource:
    url: jdbc:postgresql://localhost:5432/excel_db
    username: ${EXCEL_USER_DB}
    password: ${EXCEL_PASSWORD_DB}
  jpa:
    show-sql: true
    properties:
      hibernate:
        default_schema: public
        jdbc:
          lob:
            non_contextual_creation: true 
        format_sql: true    
        ddl-auto: auto
    database-platform: org.hibernate.dialect.PostgreSQLDialect
    generate-ddl: true

below the link of the project on github:

• https://github.com/bld-commons/dev-excel

I personally work with IntelliJ IDEA, where things are a little bit more complicated... I think.

So if you want to create and Excel File with extension: .CSV , .XLSX , .XLS , you must download the Apache Poi( last version ). https://www.apache.org/dyn/closer.lua/poi/release/bin/poi-bin-5.1.0-20211024.zip

After that you must create a project of MAVEN and in pom.xml you must add some dependency. https://www.tutorialspoint.com/maven/maven_external_dependencies.htm

And there you go. It worked for me, hope you'll be satisfied!

Best regards, TalladegaRS6