Write from java to excel

import java.io.File;

import org.apache.poi.ss.usermodel.Cell;

import org.apache.poi.xssf.usermodel.XSSFRow;

import org.apache.poi.xssf.usermodel.XSSFSheet;

import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import java.io.FileOutputStream;

import java.util.Map;

import java.util.Set;

import java.util.TreeMap;

public class WriteDataToExcel {

    public static void main(String[] args) throws Exception

    {

        XSSFWorkbook workbook = new XSSFWorkbook();

        XSSFSheet spreadsheet

            = workbook.createSheet(" Student Data ");

        XSSFRow row;

        Map<String, Object[]> studentData

            = new TreeMap<String, Object[]>();

        studentData.put(

            "1",

            new Object[] { "Roll No", "NAME", "Year" });

        studentData.put("2", new Object[] { "128", "Aditya",

                                            "2nd year" });

        studentData.put(

            "3",

            new Object[] { "129", "Narayana", "2nd year" });

        studentData.put("4", new Object[] { "130", "Mohan",

                                            "2nd year" });

        studentData.put("5", new Object[] { "131", "Radha",

                                            "2nd year" });

        studentData.put("6", new Object[] { "132", "Gopal",

                                            "2nd year" });

        Set<String> keyid = studentData.keySet();

        int rowid = 0;

        for (String key : keyid) {

            row = spreadsheet.createRow(rowid++);

            Object[] objectArr = studentData.get(key);

            int cellid = 0;

            for (Object obj : objectArr) {

                Cell cell = row.createCell(cellid++);

                cell.setCellValue((String)obj);

            }

        }

        FileOutputStream out = new FileOutputStream(

            new File("C:/savedexcel/GFGsheet.xlsx"));

        workbook.write(out);

        out.close();

    }

}

Learn to read excel, write excel, evaluate formula cells and apply custom formatting to the generated excel files using Apache POI library with examples.

If we are building software for the HR or Finance domain, there is usually a requirement for generating excel reports across management levels. Apart from reports, we can also expect some input data for the applications coming in the form of excel sheets and the application is expected to support this requirement.

Apache POI is a well-trusted library among many other open-source libraries to handle such usecases involving excel files. Please note that, in addition, we can read and write MS Word and MS PowerPoint files also using the Apache POI library.

This Apache POI tutorial will discuss some everyday excel operations in real-life applications.

1. Maven Dependency

If we are working on a maven project, we can include the Apache POI dependencies in pom.xml file using this:

<dependency>
  <groupId>org.apache.poi</groupId>
  <artifactId>poi</artifactId>
  <version>5.2.2</version>
</dependency>

<dependency>
  <groupId>org.apache.poi</groupId>
  <artifactId>poi-ooxml</artifactId>
  <version>5.2.2</version>
</dependency>

2. Important Classes in POI Library

1. HSSF, XSSF and XSSF classes

   Apache POI main classes usually start with either HSSF, XSSF or SXSSF.

   • HSSF – is the POI Project’s pure Java implementation of the Excel 97(-2007) file format. e.g., HSSFWorkbook, HSSFSheet.
   • XSSF – is the POI Project’s pure Java implementation of the Excel 2007 OOXML (.xlsx) file format. e.g., XSSFWorkbook, XSSFSheet.
   • SXSSF (since 3.8-beta3) – is an API-compatible streaming extension of XSSF to be used when huge spreadsheets have to be produced and heap space is limited. e.g., SXSSFWorkbook, SXSSFSheet. SXSSF achieves its low memory footprint by limiting access to the rows within a sliding window, while XSSF gives access to all rows in the document.

2. Row and Cell

   Apart from the above classes, Row and Cell interact with a particular row and a particular cell in an excel sheet.

3. Styling Related Classes

   A wide range of classes like CellStyle, BuiltinFormats, ComparisonOperator, ConditionalFormattingRule, FontFormatting, IndexedColors, PatternFormatting, SheetConditionalFormatting etc. are used when you have to add formatting to a sheet, primarily based on some rules.

4. FormulaEvaluator

   Another helpful class FormulaEvaluator is used to evaluate the formula cells in an excel sheet.

3. Writing an Excel File

I am taking this example first so we can reuse the excel sheet created by this code in further examples.

Writing excel using POI is very simple and involves the following steps:

1. Create a workbook
2. Create a sheet in workbook
3. Create a row in sheet
4. Add cells to sheet
5. Repeat steps 3 and 4 to write more data

It seems very simple, right? Let’s have a look at the code doing these steps.

Java program to write an excel file using Apache POI library.

package com.howtodoinjava.demo.poi;
//import statements
public class WriteExcelDemo 
{
    public static void main(String[] args) 
    {
        //Blank workbook
        XSSFWorkbook workbook = new XSSFWorkbook(); 
         
        //Create a blank sheet
        XSSFSheet sheet = workbook.createSheet("Employee Data");
          
        //This data needs to be written (Object[])
        Map<String, Object[]> data = new TreeMap<String, Object[]>();
        data.put("1", new Object[] {"ID", "NAME", "LASTNAME"});
        data.put("2", new Object[] {1, "Amit", "Shukla"});
        data.put("3", new Object[] {2, "Lokesh", "Gupta"});
        data.put("4", new Object[] {3, "John", "Adwards"});
        data.put("5", new Object[] {4, "Brian", "Schultz"});
          
        //Iterate over data and write to sheet
        Set<String> keyset = data.keySet();
        int rownum = 0;
        for (String key : keyset)
        {
            Row row = sheet.createRow(rownum++);
            Object [] objArr = data.get(key);
            int cellnum = 0;
            for (Object obj : objArr)
            {
               Cell cell = row.createCell(cellnum++);
               if(obj instanceof String)
                    cell.setCellValue((String)obj);
                else if(obj instanceof Integer)
                    cell.setCellValue((Integer)obj);
            }
        }
        try
        {
            //Write the workbook in file system
            FileOutputStream out = new FileOutputStream(new File("howtodoinjava_demo.xlsx"));
            workbook.write(out);
            out.close();
            System.out.println("howtodoinjava_demo.xlsx written successfully on disk.");
        } 
        catch (Exception e) 
        {
            e.printStackTrace();
        }
    }
}

See Also: Appending Rows to Excel

4. Reading an Excel File

Reading an excel file using POI is also very simple if we divide this into steps.

1. Create workbook instance from an excel sheet
2. Get to the desired sheet
3. Increment row number
4. iterate over all cells in a row
5. repeat steps 3 and 4 until all data is read

Let’s see all the above steps in code. I am writing the code to read the excel file created in the above example. It will read all the column names and the values in it – cell by cell.

Java program to read an excel file using Apache POI library.

package com.howtodoinjava.demo.poi;
//import statements
public class ReadExcelDemo 
{
    public static void main(String[] args) 
    {
        try
        {
            FileInputStream file = new FileInputStream(new File("howtodoinjava_demo.xlsx"));
 
            //Create Workbook instance holding reference to .xlsx file
            XSSFWorkbook workbook = new XSSFWorkbook(file);
 
            //Get first/desired sheet from the workbook
            XSSFSheet sheet = workbook.getSheetAt(0);
 
            //Iterate through each rows one by one
            Iterator<Row> rowIterator = sheet.iterator();
            while (rowIterator.hasNext()) 
            {
                Row row = rowIterator.next();
                //For each row, iterate through all the columns
                Iterator<Cell> cellIterator = row.cellIterator();
                 
                while (cellIterator.hasNext()) 
                {
                    Cell cell = cellIterator.next();
                    //Check the cell type and format accordingly
                    switch (cell.getCellType()) 
                    {
                        case Cell.CELL_TYPE_NUMERIC:
                            System.out.print(cell.getNumericCellValue() + "t");
                            break;
                        case Cell.CELL_TYPE_STRING:
                            System.out.print(cell.getStringCellValue() + "t");
                            break;
                    }
                }
                System.out.println("");
            }
            file.close();
        } 
        catch (Exception e) 
        {
            e.printStackTrace();
        }
    }
}

Program Output:

ID      NAME        LASTNAME
1.0     Amit        Shukla  
2.0     Lokesh      Gupta   
3.0     John        Adwards 
4.0     Brian       Schultz 

See Also: Apache POI – Read an Excel File using SAX Parser

5. Add and Evaluate Formula Cells

When working on complex excel sheets, we encounter many cells with formulas to calculate their values. These are formula cells. Apache POI also has excellent support for adding formula cells and evaluating already present formula cells.

Let’s see one example of how to add formula cells in excel?

The sheet has four cells in a row and the fourth one in the multiplication of all the previous 3 rows. So the formula will be: A2*B2*C2 (in the second row)

Java program to add formula in an excel file using Apache POI library.

public static void main(String[] args) 
{
    XSSFWorkbook workbook = new XSSFWorkbook();
    XSSFSheet sheet = workbook.createSheet("Calculate Simple Interest");
  
    Row header = sheet.createRow(0);
    header.createCell(0).setCellValue("Pricipal");
    header.createCell(1).setCellValue("RoI");
    header.createCell(2).setCellValue("T");
    header.createCell(3).setCellValue("Interest (P r t)");
      
    Row dataRow = sheet.createRow(1);
    dataRow.createCell(0).setCellValue(14500d);
    dataRow.createCell(1).setCellValue(9.25);
    dataRow.createCell(2).setCellValue(3d);
    dataRow.createCell(3).setCellFormula("A2*B2*C2");
      
    try {
        FileOutputStream out =  new FileOutputStream(new File("formulaDemo.xlsx"));
        workbook.write(out);
        out.close();
        System.out.println("Excel with foumula cells written successfully");
          
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Similarly, we want to read a file with formula cells and use the following logic to evaluate formula cells.

Java program to evaluate formula in an excel file using Apache POI library.

public static void readSheetWithFormula()
{
    try
    {
        FileInputStream file = new FileInputStream(new File("formulaDemo.xlsx"));
 
        //Create Workbook instance holding reference to .xlsx file
        XSSFWorkbook workbook = new XSSFWorkbook(file);
 
        FormulaEvaluator evaluator = workbook.getCreationHelper().createFormulaEvaluator();
         
        //Get first/desired sheet from the workbook
        XSSFSheet sheet = workbook.getSheetAt(0);
 
        //Iterate through each rows one by one
        Iterator<Row> rowIterator = sheet.iterator();
        while (rowIterator.hasNext()) 
        {
            Row row = rowIterator.next();
            //For each row, iterate through all the columns
            Iterator<Cell> cellIterator = row.cellIterator();
             
            while (cellIterator.hasNext()) 
            {
                Cell cell = cellIterator.next();
                //Check the cell type after eveluating formulae
                //If it is formula cell, it will be evaluated otherwise no change will happen
                switch (evaluator.evaluateInCell(cell).getCellType()) 
                {
                    case Cell.CELL_TYPE_NUMERIC:
                        System.out.print(cell.getNumericCellValue() + "tt");
                        break;
                    case Cell.CELL_TYPE_STRING:
                        System.out.print(cell.getStringCellValue() + "tt");
                        break;
                    case Cell.CELL_TYPE_FORMULA:
                        //Not again
                        break;
                }
            }
            System.out.println("");
        }
        file.close();
    } 
    catch (Exception e) 
    {
        e.printStackTrace();
    }
}

Program Output:

Pricipal        RoI         T       Interest (P r t)        
14500.0         9.25        3.0     402375.0  

6. Formatting the Cells

So far we have seen examples of reading/writing and excel files using Apache POI. But, when creating a report in an excel file, it is essential to add formatting on cells that fit into any pre-determined criteria.

This formatting can be a different coloring based on a specific value range, expiry date limit etc.

In the below examples, we are taking a couple of such cell formatting examples for various purposes.

6.1. Cell value in a specific range

This code will color any cell in a range whose value is between a configured range. [e.g., between 50 and 70]

static void basedOnValue(Sheet sheet) 
{
    //Creating some random values
    sheet.createRow(0).createCell(0).setCellValue(84);
    sheet.createRow(1).createCell(0).setCellValue(74);
    sheet.createRow(2).createCell(0).setCellValue(50);
    sheet.createRow(3).createCell(0).setCellValue(51);
    sheet.createRow(4).createCell(0).setCellValue(49);
    sheet.createRow(5).createCell(0).setCellValue(41);
 
    SheetConditionalFormatting sheetCF = sheet.getSheetConditionalFormatting();
 
    //Condition 1: Cell Value Is   greater than  70   (Blue Fill)
    ConditionalFormattingRule rule1 = sheetCF.createConditionalFormattingRule(ComparisonOperator.GT, "70");
    PatternFormatting fill1 = rule1.createPatternFormatting();
    fill1.setFillBackgroundColor(IndexedColors.BLUE.index);
    fill1.setFillPattern(PatternFormatting.SOLID_FOREGROUND);
 
    //Condition 2: Cell Value Is  less than      50   (Green Fill)
    ConditionalFormattingRule rule2 = sheetCF.createConditionalFormattingRule(ComparisonOperator.LT, "50");
    PatternFormatting fill2 = rule2.createPatternFormatting();
    fill2.setFillBackgroundColor(IndexedColors.GREEN.index);
    fill2.setFillPattern(PatternFormatting.SOLID_FOREGROUND);
 
    CellRangeAddress[] regions = {
            CellRangeAddress.valueOf("A1:A6")
    };
 
    sheetCF.addConditionalFormatting(regions, rule1, rule2);
}

6.2. Highlight Duplicate Values

Highlight all cells which have duplicate values in observed cells.

static void formatDuplicates(Sheet sheet) {
    sheet.createRow(0).createCell(0).setCellValue("Code");
    sheet.createRow(1).createCell(0).setCellValue(4);
    sheet.createRow(2).createCell(0).setCellValue(3);
    sheet.createRow(3).createCell(0).setCellValue(6);
    sheet.createRow(4).createCell(0).setCellValue(3);
    sheet.createRow(5).createCell(0).setCellValue(5);
    sheet.createRow(6).createCell(0).setCellValue(8);
    sheet.createRow(7).createCell(0).setCellValue(0);
    sheet.createRow(8).createCell(0).setCellValue(2);
    sheet.createRow(9).createCell(0).setCellValue(8);
    sheet.createRow(10).createCell(0).setCellValue(6);
 
    SheetConditionalFormatting sheetCF = sheet.getSheetConditionalFormatting();
 
    // Condition 1: Formula Is   =A2=A1   (White Font)
    ConditionalFormattingRule rule1 = sheetCF.createConditionalFormattingRule("COUNTIF($A$2:$A$11,A2)>1");
    FontFormatting font = rule1.createFontFormatting();
    font.setFontStyle(false, true);
    font.setFontColorIndex(IndexedColors.BLUE.index);
 
    CellRangeAddress[] regions = {
            CellRangeAddress.valueOf("A2:A11")
    };
 
    sheetCF.addConditionalFormatting(regions, rule1);
 
    sheet.getRow(2).createCell(1).setCellValue("<== Duplicates numbers in the column are highlighted.  " +
            "Condition: Formula Is =COUNTIF($A$2:$A$11,A2)>1   (Blue Font)");
}

6.3. Alternate Color Rows in Different Colors

A simple code to color each alternate row in a different color.

static void shadeAlt(Sheet sheet) {
    SheetConditionalFormatting sheetCF = sheet.getSheetConditionalFormatting();
 
    // Condition 1: Formula Is   =A2=A1   (White Font)
    ConditionalFormattingRule rule1 = sheetCF.createConditionalFormattingRule("MOD(ROW(),2)");
    PatternFormatting fill1 = rule1.createPatternFormatting();
    fill1.setFillBackgroundColor(IndexedColors.LIGHT_GREEN.index);
    fill1.setFillPattern(PatternFormatting.SOLID_FOREGROUND);
 
    CellRangeAddress[] regions = {
            CellRangeAddress.valueOf("A1:Z100")
    };
 
    sheetCF.addConditionalFormatting(regions, rule1);
 
    sheet.createRow(0).createCell(1).setCellValue("Shade Alternating Rows");
    sheet.createRow(1).createCell(1).setCellValue("Condition: Formula Is  =MOD(ROW(),2)   (Light Green Fill)");
}

6.4. Color amounts that are going to expire in the next 30 days

A handy code for financial projects which keeps track of deadlines.

static void expiryInNext30Days(Sheet sheet) 
{
    CellStyle style = sheet.getWorkbook().createCellStyle();
    style.setDataFormat((short)BuiltinFormats.getBuiltinFormat("d-mmm"));
 
    sheet.createRow(0).createCell(0).setCellValue("Date");
    sheet.createRow(1).createCell(0).setCellFormula("TODAY()+29");
    sheet.createRow(2).createCell(0).setCellFormula("A2+1");
    sheet.createRow(3).createCell(0).setCellFormula("A3+1");
 
    for(int rownum = 1; rownum <= 3; rownum++) sheet.getRow(rownum).getCell(0).setCellStyle(style);
 
    SheetConditionalFormatting sheetCF = sheet.getSheetConditionalFormatting();
 
    // Condition 1: Formula Is   =A2=A1   (White Font)
    ConditionalFormattingRule rule1 = sheetCF.createConditionalFormattingRule("AND(A2-TODAY()>=0,A2-TODAY()<=30)");
    FontFormatting font = rule1.createFontFormatting();
    font.setFontStyle(false, true);
    font.setFontColorIndex(IndexedColors.BLUE.index);
 
    CellRangeAddress[] regions = {
            CellRangeAddress.valueOf("A2:A4")
    };
 
    sheetCF.addConditionalFormatting(regions, rule1);
 
    sheet.getRow(0).createCell(1).setCellValue("Dates within the next 30 days are highlighted");
}

I am ending this apache poi tutorial here to keep the post within a limit.

7. Conclusion

In this tutorial, we learned to read excel, write excel, set and evaluate formula cells, and format the cells with color codings using the Apache POI library.

Happy Learning !!

Source Code on Github

In this tutorial, I’d love to share with you guys some examples of writing data to Excel files using the Apache POI library. If today is the first day you get to know Apache POI and you haven’t written any code snippet to read/write Excel files yet, I recommend you to read the sections 1 and 2 in the tutorial How to Read Excel Files in Java using Apache POI to understand the fundamentals of Apache POI.

Or if you are a kind of person who likes getting your hands-dirty first, let jump directly into the following examples.

1. Apache POI API Basics for Writing Excel Files

The fundamental interfaces include Workbook, Sheet, Row and Cell. For basic formatting, use the CellStyle and Font interfaces. Concrete implementing classes include:

• Excel 2003: HSSFWorkbook, HSSFSheet, HSSFRow, HSSFCell, etc.
• Excel 2007: XSSFWorkbook, XSSFSheet, XSSFRow, XSSFCell, etc.

But I recommend using the common interfaces for greater flexibility with both Excel formats 2003 (XLS) and 2007(XLSX).

Here are the basic steps for writing an Excel file:

1. Create a Workbook.
2. Create a Sheet.
3. Repeat the following steps until all data is processed:
   1. Create a Row.
   2. Create Cellsin a Row. Apply formatting using CellStyle.
4. Write to an OutputStream.
5. Close the output stream.

Now, let’s see some examples that demonstrate writing a list of books to an Excel file.

2. A Simple Example to create an Excel file in Java

The following code snippet is a very simple program that demonstrates writing a list of books to an Excel file in the simplest and dirty form:

package net.codejava.excel;

import java.io.FileOutputStream;
import java.io.IOException;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

/**
 * A very simple program that writes some data to an Excel file
 * using the Apache POI library.
 * @author www.codejava.net
 *
 */
public class SimpleExcelWriterExample {

	public static void main(String[] args) throws IOException {
		XSSFWorkbook workbook = new XSSFWorkbook();
		XSSFSheet sheet = workbook.createSheet("Java Books");
		
		Object[][] bookData = {
				{"Head First Java", "Kathy Serria", 79},
				{"Effective Java", "Joshua Bloch", 36},
				{"Clean Code", "Robert martin", 42},
				{"Thinking in Java", "Bruce Eckel", 35},
		};

		int rowCount = 0;
		
		for (Object[] aBook : bookData) {
			Row row = sheet.createRow(++rowCount);
			
			int columnCount = 0;
			
			for (Object field : aBook) {
				Cell cell = row.createCell(++columnCount);
				if (field instanceof String) {
					cell.setCellValue((String) field);
				} else if (field instanceof Integer) {
					cell.setCellValue((Integer) field);
				}
			}
			
		}
		
		
		try (FileOutputStream outputStream = new FileOutputStream("JavaBooks.xlsx")) {
			workbook.write(outputStream);
		}
	}

}

This program creates an Excel 2007 document which looks like the following screenshot (File: JavaBooks.xlsx):

3. A More Object-Oriented Example to create an Excel file in Java

The following code snippets demonstrate a nicer program that focuses on OOP approach. That makes the program more flexible and easy to extend or upgrade in the future.

• Create the model class (Book.java):

  package net.codejava.excel;
  
  public class Book {
  	private String title;
  	private String author;
  	private float price;
  
  	public Book() {
  	}
  
  	public Book(String title, String author, double price) {
  		this.title = title;
  		this.author = author;
  		this.price = price;
  	}
  
  	// getters and setters
  }

• The method that writes a list of books to an Excel file (in 2003 format):

  public void writeExcel(List<Book> listBook, String excelFilePath) throws IOException {
  	Workbook workbook = new HSSFWorkbook();
  	Sheet sheet = workbook.createSheet();
  
  	int rowCount = 0;
  
  	for (Book aBook : listBook) {
  		Row row = sheet.createRow(++rowCount);
  		writeBook(aBook, row);
  	}
  
  	try (FileOutputStream outputStream = new FileOutputStream(excelFilePath)) {
  		workbook.write(outputStream);
  	}
  }

• The method that writes information of a book to cells:

  private void writeBook(Book aBook, Row row) {
  	Cell cell = row.createCell(1);
  	cell.setCellValue(aBook.getTitle());
  
  	cell = row.createCell(2);
  	cell.setCellValue(aBook.getAuthor());
  
  	cell = row.createCell(3);
  	cell.setCellValue(aBook.getPrice());
  }

• The following method creates some dummy data (a list of books):

  private List<Book> getListBook() {
  	Book book1 = new Book("Head First Java", "Kathy Serria", 79);
  	Book book2 = new Book("Effective Java", "Joshua Bloch", 36);
  	Book book3 = new Book("Clean Code", "Robert Martin", 42);
  	Book book4 = new Book("Thinking in Java", "Bruce Eckel", 35);
  
  	List<Book> listBook = Arrays.asList(book1, book2, book3, book4);
  
  	return listBook;
  }

• And the following code snippet is for testing:

  NiceExcelWriterExample excelWriter = new NiceExcelWriterExample();
  
  List<Book> listBook = excelWriter.getListBook();
  String excelFilePath = "NiceJavaBooks.xls";
  
  excelWriter.writeExcel(listBook, excelFilePath);

4. Formatting Cells of the Excel file

Of course you may need to format the Excel file to make it looks nicely and professionally. Formatting is diversity and quite complex so in this introductory tutorial, I just show you how to format the basics like setting font style. Here are the steps:

• Create a CellStyle object what holds formatting information:

  CellStyle cellStyle = sheet.getWorkbook().createCellStyle();

• Invoke the appropriate setters to apply the formatting you want. For example:

  cellStyle.setAlignment(CellStyle.ALIGN_CENTER);
  cellStyle.setFont(font);
  cellStyle.setWrapText(true);

For example, the following method writes a header row for the document with font style bold and size is 16:

private void createHeaderRow(Sheet sheet) {

	CellStyle cellStyle = sheet.getWorkbook().createCellStyle();
	Font font = sheet.getWorkbook().createFont();
	font.setBold(true);
	font.setFontHeightInPoints((short) 16);
	cellStyle.setFont(font);

	Row row = sheet.createRow(0);
	Cell cellTitle = row.createCell(1);

	cellTitle.setCellStyle(cellStyle);
	cellTitle.setCellValue("Title");

	Cell cellAuthor = row.createCell(2);
	cellAuthor.setCellStyle(cellStyle);
	cellAuthor.setCellValue("Author");

	Cell cellPrice = row.createCell(3);
	cellPrice.setCellStyle(cellStyle);
	cellPrice.setCellValue("Price");
}

You can see the complete program (FormattedExcelWriterExample.java) which can be found in the source code attached to this article.

5. Writing both Excel 2003 and Excel 2007 formats in Java

For better flexibility (supporting both common Excel formats), I recommend writing a factory method that either returns a HSSFWorkbook or XSSFWorkbook, depending on the extension of the file (.xls or .xlsx). Here’s the method:

private Workbook getWorkbook(String excelFilePath)
		throws IOException {
	Workbook workbook = null;

	if (excelFilePath.endsWith("xlsx")) {
		workbook = new XSSFWorkbook();
	} else if (excelFilePath.endsWith("xls")) {
		workbook = new HSSFWorkbook();
	} else {
		throw new IllegalArgumentException("The specified file is not Excel file");
	}

	return workbook;
}

You can see the complete program (FlexibleExcelWriterExample.java) which can be found in the source code attached to this article.

That’s how to read Excel files in Java programmatically. To learn more in-depth about Java programming, this Java software developers course would be good choice.

Related Java Excel Tutorials:

• How to Read Excel Files in Java using Apache POI
• Java Example to Read Password-protected Excel Files Using Apache POI
• Java Example to Update Existing Excel Files Using Apache POI
• Working with Formula Cells in Excel using Apache POI

References

• Apache POI — the Java API for Microsoft Documents
• POI API Documentation (Javadocs)
• Apache POI Quick Guide
• Apache POI HOWTO

Рассказывает автор блога javarevisited.blogspot.ru

Из этой статьи вы сможете узнать о записи и чтении данных из Excel файлов в Java (будет рассмотрен как XLS, так и XLSX формат). Мы будем использовать библиотеку Apache POI и сосредоточимся на работе с типами String и Date, работа с последним происходит достаточно хитро. Напомню, что работу с числами мы уже рассмотрели в другой статье.

Библиотеку poi-XX.jar вы можете использовать для всех старых (xls, doc, ppt) файлов Microsoft Office, для новых (xlsx, docx, pptx) вам понадобится poi-ooxml-XX.jar. Очень важно понимать, что к чему относится, т.к. используемые классы тоже разные — для старых расширений это HSSFWorkbook, а для новых — XSSFWorkbook.

Подготовка: загрузка библиотек и зависимостей

Конечно, существует достаточно много открытых библиотек, которые позволяют работать с Excel файлами в Java, например, JXL, но мы будем использовать имеющую самый обширный API и самую популярную — Apache POI. Чтобы её использовать, вам нужно скачать jar файлы и добавить их через Eclipse вручную, или вы можете предоставить это Maven.

Во втором случае вам нужно просто добавить следующие две зависимости:

<dependencies>
    <dependency>
        <groupId>org.apache.poi</groupId>
        <artifactId>poi</artifactId>
        <version>3.12</version>
    </dependency>
    <dependency>
        <groupId>org.apache.poi</groupId>
        <artifactId>poi-ooxml</artifactId>
        <version>3.12</version>
    </dependency>
  </dependencies>

Самое удобное в Maven — что он загрузит не только указанные poi.jar и poi-ooxml.jar, но и все jar файлы, которые используются внутри, то есть xmlbeans-2.6.0.jar, stax-api-1.0.1.jar, poi-ooxml-schemas-3.12.jar и commons-codec-1.9.jar.

Если вы будете добавлять библиотеки вручную — не забудьте о вышеназванных файлах. Скачать всё можно отсюда. Помните — если вы загрузите только poi-XX.jar, то ваш код скомпилируется без ошибок, но потом упадёт с java.lang.NoClassDefFoundError: org/apache/xmlbeans/XmlObject, так как внутри будет вызываться xmlbeans.jar.

Запись

В этом примере мы запишем в xls файл следующие данные: в первую ячейку — строку с именем, а во вторую — дату рождения. Вот пошаговая инструкция:

• Создаём объект HSSFWorkBook;
• Создаём лист, используя на объекте, созданном в предыдущем шаге, createSheet();
• Создаём на листе строку, используя createRow();
• Создаём в строке ячейку — createCell();
• Задаём значение ячейки через setCellValue();
• Записываем workbook в File через FileOutputStream;
• Закрываем workbook, вызывая close().

Для записи строк или чисел этого вполне достаточно, но чтобы записать дату, нам понадобится сделать ещё кое-что:

• Создать DateFormat;
• Создать CellStyle;
• Записать DateFormat в CellStyle;
• Записать CellStyle в ячейку;
• Теперь в эту ячейку можно записать объект Date через всё тот же setCellValue;
• Чтобы дата поместилась в ячейку, нам нужно добавить столбцу свойство автоматически менять размер: sheet.autoSizeColumn(1).

Всё вместе это будет выглядеть так:

@SuppressWarnings("deprecation")
    public static void writeIntoExcel(String file) throws FileNotFoundException, IOException{
        Workbook book = new HSSFWorkbook();
        Sheet sheet = book.createSheet("Birthdays");

        // Нумерация начинается с нуля
        Row row = sheet.createRow(0); 
        
        // Мы запишем имя и дату в два столбца
        // имя будет String, а дата рождения --- Date,
        // формата dd.mm.yyyy
        Cell name = row.createCell(0);
        name.setCellValue("John");
        
        Cell birthdate = row.createCell(1);
        
        DataFormat format = book.createDataFormat();
        CellStyle dateStyle = book.createCellStyle();
        dateStyle.setDataFormat(format.getFormat("dd.mm.yyyy"));
        birthdate.setCellStyle(dateStyle);
        
 
        // Нумерация лет начинается с 1900-го
        birthdate.setCellValue(new Date(110, 10, 10));
        
        // Меняем размер столбца
        sheet.autoSizeColumn(1);
        
        // Записываем всё в файл
        book.write(new FileOutputStream(file));
        book.close();
    }

Чтение

Теперь мы считаем из только что созданного файла то, что мы туда записали.

• Для начала создадим HSSFWorkBook, передав в конструктор FileInputStream;
• Получаем лист, передавая в getSheet() его номер или название;
• Получаем строку, используя getRow();
• Получаем ячейку, используя getCell();
• Узнаём тип ячейки, используя на ней getCellType();
• В зависимости от типа ячейки, читаем её значения, используя getStringCellValue(), getNumericCellValue() или getDateCellValue();
• Закрываем workbook используя close().

Напомню, что дату Excel хранит как числа, т.е. тип ячейки всё равно будет CELL_TYPE_NUMERIC.

В виде кода это будет выглядеть следующим образом:

public static void readFromExcel(String file) throws IOException{
        HSSFWorkbook myExcelBook = new HSSFWorkbook(new FileInputStream(file));
        HSSFSheet myExcelSheet = myExcelBook.getSheet("Birthdays");
        HSSFRow row = myExcelSheet.getRow(0);
        
        if(row.getCell(0).getCellType() == HSSFCell.CELL_TYPE_STRING){
            String name = row.getCell(0).getStringCellValue();
            System.out.println("name : " + name);
        }
        
        if(row.getCell(1).getCellType() == HSSFCell.CELL_TYPE_NUMERIC){
            Date birthdate = row.getCell(1).getDateCellValue();
            System.out.println("birthdate :" + birthdate);
        }
        
        myExcelBook.close();
        
    }

В заключение

Как уже упомналось выше, чтение из xlsx файлов ничем принципиально не отличается — нужно только вместо HSSFWorkBook, HSSFSheet, HSSFRow (и прочих) из poi-XX.jar использовать XSSFWorkBook, XSSFSheet, XSSFRow из poi-ooxml-XX.jar. Это всё, что вам нужно знать для чтения и записи в файлы Excel. Разумеется, с помощью библиотеки Apache POI вы можете сделать гораздо больше, но эта статья должна помочь вам быстрее в ней освоиться.

_{Перевод статьи «How to Read Write Excel file in Java — POI Example»}

In this Java Apache POI tutorial we learn step by step to implement a Java program to export data from Java objects to an Excel file using the Apache POI library.

Table of contents

1. Add Apache POI dependencies to Java project
2. Create New Entity Class
3. Implement Excel File Exporter Class
4. How to use ExcelFileExporter class to export Excel file

Add Apache POI dependencies to Java project

First step, we add the Apache POI dependencies to the Java project.

If you use Gradle build project, add the following dependencies to the build.gradle file.

implementation group: 'org.apache.poi', name: 'poi', version: '5.2.2'
implementation group: 'org.apache.poi', name: 'poi-ooxml', version: '5.2.2'

If you use Maven build project, add the following dependencies to the pom.xml file.

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi</artifactId>
    <version>5.2.2</version>
</dependency>
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-ooxml</artifactId>
    <version>5.2.2</version>
</dependency>

Create New Entity Class

For example, we want to implement a Java application to export a list of contacts data to an Excel file. At this step we implement a new Java class named Contact to represent the contact information which needs to be exported.

Contact.java

public class Contact {
    private String firstName;
    private String lastName;
    private String email;

    public Contact(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

Implement Excel File Exporter Class

At this step we implement a new Java class named ExcelFileExporter with the following steps to export an Excel file from given data.

• Create a new Workbook object which represent an Excel workbook.
• Create a new Sheet object which represent an Excel worksheet.
• Create a new header Row from given header texts. At this step we use CellStyle class to define header foreground color and border.
• Create new data rows from given list of Contact objects. At this step we use CellStyle class to define cell border for data rows.
• Using Sheet.autoSizeColumn(int column) method to adjusts column width to fit the contents for three first columns.
• Using the Workbook.write(OutputStream stream) method to write Excel file with given name.

ExcelFileExporter.java

import org.apache.poi.ss.usermodel.BorderStyle;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellStyle;
import org.apache.poi.ss.usermodel.FillPatternType;
import org.apache.poi.ss.usermodel.IndexedColors;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.List;

/**
 * Excel File Exporter
 */
public class ExcelFileExporter {

    public void exportExcelFile(List<Contact> contacts, String[] headers, String fileName) {
        // create a new Workbook
        Workbook workbook = new XSSFWorkbook();

        // Create a new Sheet named "Contacts"
        Sheet sheet = workbook.createSheet("Contacts");

        // Create header row
        createHeaderRow(workbook, sheet, headers);

        // Create rows
        for(int i = 0; i < contacts.size(); i++) {
            // row index equals i + 1 because the first row of Excel file is the header row.
            int rowIndex = i + 1;
            createNewRow(workbook, sheet, rowIndex, contacts.get(i));
        }

        // Adjusts 3 columns to set the width to fit the contents.
        sheet.autoSizeColumn(0);
        sheet.autoSizeColumn(1);
        sheet.autoSizeColumn(2);

        // Write to file
        try (OutputStream outputStream = new FileOutputStream(fileName)) {
            workbook.write(outputStream);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * Create header row
     * @param workbook the Workbook object
     * @param sheet the Sheet object
     * @param headers the headers text
     */
    private void createHeaderRow(Workbook workbook, Sheet sheet, String[] headers) {
        Row headerRow = sheet.createRow(0);
        CellStyle headerCellStyle = workbook.createCellStyle();
        headerCellStyle.setFillForegroundColor(IndexedColors.LIGHT_YELLOW.index);
        headerCellStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
        headerCellStyle.setBorderTop(BorderStyle.THIN);
        headerCellStyle.setTopBorderColor(IndexedColors.BLACK.index);
        headerCellStyle.setBorderRight(BorderStyle.THIN);
        headerCellStyle.setRightBorderColor(IndexedColors.BLACK.index);
        headerCellStyle.setBorderBottom(BorderStyle.THIN);
        headerCellStyle.setBottomBorderColor(IndexedColors.BLACK.index);
        headerCellStyle.setBorderLeft(BorderStyle.THIN);
        headerCellStyle.setLeftBorderColor(IndexedColors.BLACK.index);

        for(int i = 0; i < headers.length; i++) {
            Cell cell = headerRow.createCell(i);
            cell.setCellValue(headers[i]);
            cell.setCellStyle(headerCellStyle);
        }
    }

    /**
     * Create a new row
     * @param workbook the Workbook object
     * @param sheet the Sheet object
     * @param rowIndex the index of row to create
     * @param contact the Contact object which represent information to write to row.
     */
    private void createNewRow(Workbook workbook, Sheet sheet, int rowIndex, Contact contact) {
        Row row = sheet.createRow(rowIndex);
        CellStyle cellStyle = workbook.createCellStyle();
        cellStyle.setBorderTop(BorderStyle.THIN);
        cellStyle.setTopBorderColor(IndexedColors.BLACK.index);
        cellStyle.setBorderRight(BorderStyle.THIN);
        cellStyle.setRightBorderColor(IndexedColors.BLACK.index);
        cellStyle.setBorderBottom(BorderStyle.THIN);
        cellStyle.setBottomBorderColor(IndexedColors.BLACK.index);
        cellStyle.setBorderLeft(BorderStyle.THIN);
        cellStyle.setLeftBorderColor(IndexedColors.BLACK.index);

        Cell cell = row.createCell(0);
        cell.setCellValue(contact.getFirstName());
        cell.setCellStyle(cellStyle);

        cell = row.createCell(1);
        cell.setCellValue(contact.getLastName());
        cell.setCellStyle(cellStyle);

        cell = row.createCell(2);
        cell.setCellValue(contact.getEmail());
        cell.setCellStyle(cellStyle);
    }

}

How to use ExcelFileExporter class to export Excel file

At this final step we implement a Main class and use the ExcelFileExporter above to export Excel file named contacts.xlsx as the following Java code.

Main.java

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String... args) {
        // List of contacts to export to Excel file.
        List<Contact> contacts = new ArrayList<>();
        contacts.add(new Contact("Rayhan", "Harmon", "rayhan@simplesolution.dev"));
        contacts.add(new Contact("Paddy", "Sheridan", "paddy@simplesolution.dev"));
        contacts.add(new Contact("Clara", "Callaghan", "clara@simplesolution.dev"));
        contacts.add(new Contact("Josephine", "Amos", "josephine@simplesolution.dev"));
        contacts.add(new Contact("Sheikh", "Tucker", "sheikh@simplesolution.dev"));

        // Header text
        String[] headers = new String[] {"First Name", "Last Name", "Email"};

        // File name
        String fileName = "contacts.xlsx";

        // Export Excel file
        ExcelFileExporter excelFileExporter = new ExcelFileExporter();
        excelFileExporter.exportExcelFile(contacts, headers, fileName);
    }
}

Execute the the above Java application we have the output contacts.xlsx file as below.

Happy Coding 😊

Related Articles

Java Apache POI Tutorial

Spring Boot Download Excel File Export from MySQL Database

Spring Boot Web Application Download Excel File

Java Read Excel File using Apache POI

Java Read Excel Workbook from File using Apache POI

Java Read Excel Workbook from InputStream using Apache POI

Java Read Password Protected Excel File using Apache POI

Java How to Iterate over Sheets Rows and Cells of Excel file using Apache POI

Java Add Rows to Existing Excel File using Apache POI

Java Add Sheet to Existing Excel File using Apache POI

Java Remove Sheet from Existing Excel File using Apache POI

Java Create Formula Excel Cells using Apache POI