Apache POI Tutorial

Published on August 4, 2022

Welcome to Apache POI Tutorial. Sometimes we need to read data from Microsoft Excel Files or we need to generate reports in Excel format, mostly for Business or Finance purposes. Java doesn’t provide built-in support for working with excel files, so we need to look for open source APIs for the job. When I started the hunt for Java APIs for excel, most of the people recommended JExcel or Apache POI. After further research, I found that Apache POI is the way to go for following main reasons. There are some other reasons related to advanced features but let’s not go into that much detail.

Backing of Apache foundation.
JExcel doesn’t support xlsx format whereas POI supports both xls and xlsx formats.
Apache POI provides stream-based processing, that is suitable for large files and requires less memory.

Apache POI

Apache POI provides excellent support for working with Microsoft Excel documents. Apache POI is able to handle both XLS and XLSX formats of spreadsheets. Some important points about Apache POI API are:

Apache POI contains HSSF implementation for Excel '97(-2007) file format i.e XLS.
Apache POI XSSF implementation should be used for Excel 2007 OOXML (.xlsx) file format.
Apache POI HSSF and XSSF API provides mechanisms to read, write or modify excel spreadsheets.
Apache POI also provides SXSSF API that is an extension of XSSF to work with very large excel sheets. SXSSF API requires less memory and is suitable when working with very large spreadsheets and heap memory is limited.
There are two models to choose from - event model and user model. Event model requires less memory because the excel file is read in tokens and requires processing them. User model is more object oriented and easy to use and we will use this in our examples.
Apache POI provides excellent support for additional excel features such as working with Formulas, creating cell styles by filling colors and borders, fonts, headers and footers, data validations, images, hyperlinks etc.

Apache POI Maven Dependencies

If you are using maven, add below Apache POI dependencies.

<dependency>
	<groupId>org.apache.poi</groupId>
	<artifactId>poi</artifactId>
	<version>3.10-FINAL</version>
</dependency>
<dependency>
	<groupId>org.apache.poi</groupId>
	<artifactId>poi-ooxml</artifactId>
	<version>3.10-FINAL</version>
</dependency>

Current version of Apache POI is 3.10-FINAL. If you are having standalone java application, include jars from below image.

Apache POI Example - Read Excel File

Let’s say we have an excel file “Sample.xlsx” with two sheets and having data like below image. We want to read the excel file and create the list of Countries. Sheet1 has some additional data, that we will ignore while parsing it. Our Country java bean code is: Country.java

package com.journaldev.excel.read;

public class Country {

	private String name;
	private String shortCode;
	
	public Country(String n, String c){
		this.name=n;
		this.shortCode=c;
	}
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getShortCode() {
		return shortCode;
	}
	public void setShortCode(String shortCode) {
		this.shortCode = shortCode;
	}
	
	@Override
	public String toString(){
		return name + "::" + shortCode;
	}
	
}

Apache POI example program to read excel file to the list of countries looks like below. ReadExcelFileToList.java

package com.journaldev.excel.read;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

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

public class ReadExcelFileToList {

	public static List<Country> readExcelData(String fileName) {
		List<Country> countriesList = new ArrayList<Country>();
		
		try {
			//Create the input stream from the xlsx/xls file
			FileInputStream fis = new FileInputStream(fileName);
			
			//Create Workbook instance for xlsx/xls file input stream
			Workbook workbook = null;
			if(fileName.toLowerCase().endsWith("xlsx")){
				workbook = new XSSFWorkbook(fis);
			}else if(fileName.toLowerCase().endsWith("xls")){
				workbook = new HSSFWorkbook(fis);
			}
			
			//Get the number of sheets in the xlsx file
			int numberOfSheets = workbook.getNumberOfSheets();
			
			//loop through each of the sheets
			for(int i=0; i < numberOfSheets; i++){
				
				//Get the nth sheet from the workbook
				Sheet sheet = workbook.getSheetAt(i);
				
				//every sheet has rows, iterate over them
				Iterator<Row> rowIterator = sheet.iterator();
				while (rowIterator.hasNext()) 
		        {
					String name = "";
					String shortCode = "";
					
					//Get the row object
					Row row = rowIterator.next();
					
					//Every row has columns, get the column iterator and iterate over them
					Iterator<Cell> cellIterator = row.cellIterator();
		             
		            while (cellIterator.hasNext()) 
		            {
		            	//Get the Cell object
		            	Cell cell = cellIterator.next();
		            	
		            	//check the cell type and process accordingly
		            	switch(cell.getCellType()){
		            	case Cell.CELL_TYPE_STRING:
		            		if(shortCode.equalsIgnoreCase("")){
		            			shortCode = cell.getStringCellValue().trim();
		            		}else if(name.equalsIgnoreCase("")){
		            			//2nd column
		            			name = cell.getStringCellValue().trim();
		            		}else{
		            			//random data, leave it
		            			System.out.println("Random data::"+cell.getStringCellValue());
		            		}
		            		break;
		            	case Cell.CELL_TYPE_NUMERIC:
		            		System.out.println("Random data::"+cell.getNumericCellValue());
		            	}
		            } //end of cell iterator
		            Country c = new Country(name, shortCode);
		            countriesList.add(c);
		        } //end of rows iterator
				
				
			} //end of sheets for loop
			
			//close file input stream
			fis.close();
			
		} catch (IOException e) {
			e.printStackTrace();
		}
		
		return countriesList;
	}

	public static void main(String args[]){
		List<Country> list = readExcelData("Sample.xlsx");
		System.out.println("Country List\n"+list);
	}

}

The program is very easy to understand and contains following steps:

Create Workbook instance based on the file type. XSSFWorkbook for xlsx format and HSSFWorkbook for xls format. Notice that we could have created a wrapper class with factory pattern to get the workbook instance based on the file name.
Use workbook getNumberOfSheets() to get the number of sheets and then use for loop to parse each of the sheets. Get the Sheet instance using getSheetAt(int i) method.
Get Row iterator and then Cell iterator to get the Cell object. Apache POI is using iterator pattern here.
Use switch-case to read the type of Cell and the process it accordingly.

Now when we run above Apache POI example program, it produces following output on console.

Random data::1.0
Random data::2.0
Random data::3.0
Random data::4.0
Country List
[India::IND, Afghanistan::AFG, United States of America::USA, Anguilla::AIA, 
Denmark ::DNK, Dominican Republic ::DOM, Algeria ::DZA, Ecuador ::ECU]

Apache POI Example - Write Excel File

Writing excel file in apache POI is similar to reading, except that here we first create the workbook. Then set sheets, rows and cells values and use FileOutputStream to write it to file. Let’s write a simple apache POI example where we will use list of countries from the above method to save into another file in a single sheet. WriteListToExcelFile.java

package com.journaldev.excel.read;

import java.io.FileOutputStream;
import java.util.Iterator;
import java.util.List;

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

public class WriteListToExcelFile {

	public static void writeCountryListToFile(String fileName, List<Country> countryList) throws Exception{
		Workbook workbook = null;
		
		if(fileName.endsWith("xlsx")){
			workbook = new XSSFWorkbook();
		}else if(fileName.endsWith("xls")){
			workbook = new HSSFWorkbook();
		}else{
			throw new Exception("invalid file name, should be xls or xlsx");
		}
		
		Sheet sheet = workbook.createSheet("Countries");
		
		Iterator<Country> iterator = countryList.iterator();
		
		int rowIndex = 0;
		while(iterator.hasNext()){
			Country country = iterator.next();
			Row row = sheet.createRow(rowIndex++);
			Cell cell0 = row.createCell(0);
			cell0.setCellValue(country.getName());
			Cell cell1 = row.createCell(1);
			cell1.setCellValue(country.getShortCode());
		}
		
		//lets write the excel data to file now
		FileOutputStream fos = new FileOutputStream(fileName);
		workbook.write(fos);
		fos.close();
		System.out.println(fileName + " written successfully");
	}
	
	public static void main(String args[]) throws Exception{
		List<Country> list = ReadExcelFileToList.readExcelData("Sample.xlsx");
		WriteListToExcelFile.writeCountryListToFile("Countries.xls", list);
	}
}

When I execute above apache POI example program, the excel file generated looks like below image.

Apache POI Example - Read Excel Formula

Sometimes we need to handle complex excel files with formulas, let’s see a simple apache POI example to read the formula of a cell with it’s value. ReadExcelFormula.java

package com.journaldev.excel.read;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Iterator;

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

public class ReadExcelFormula {

	public static void readExcelFormula(String fileName) throws IOException{
		
		FileInputStream fis = new FileInputStream(fileName);
		
		//assuming xlsx file
		Workbook workbook = new XSSFWorkbook(fis);
		Sheet sheet = workbook.getSheetAt(0);
		Iterator<Row> rowIterator = sheet.iterator();
		while (rowIterator.hasNext()) 
        {
			Row row = rowIterator.next();
			Iterator<Cell> cellIterator = row.cellIterator();
            
            while (cellIterator.hasNext()) 
            {
            	Cell cell = cellIterator.next();
            	switch(cell.getCellType()){
            	case Cell.CELL_TYPE_NUMERIC:
            		System.out.println(cell.getNumericCellValue());
            		break;
            	case Cell.CELL_TYPE_FORMULA:
            		System.out.println("Cell Formula="+cell.getCellFormula());
            		System.out.println("Cell Formula Result Type="+cell.getCachedFormulaResultType());
            		if(cell.getCachedFormulaResultType() == Cell.CELL_TYPE_NUMERIC){
            			System.out.println("Formula Value="+cell.getNumericCellValue());
            		}
            	}
            }
        }
	}
	
	public static void main(String args[]) throws IOException {
		readExcelFormula("FormulaMultiply.xlsx");
	}
}

When we execute above apache poi example program, we get following output.

1.0
2.0
3.0
4.0
Cell Formula=A1*A2*A3*A4
Cell Formula Result Type=0
Formula Value=24.0

Apache POI Example - Excel Write Formula

Sometimes, we need to do some calculations and then write the cell values. We can use the excel formulas to do this calculation and that will make it more accurate because values will change if the cell values used in calculations are changed. Let’s see a simple example to write excel file with formulas using apache poi api. WriteExcelWithFormula.java

package com.journaldev.excel.read;

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

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;

public class WriteExcelWithFormula {

	public static void writeExcelWithFormula(String fileName) throws IOException{
		Workbook workbook = new XSSFWorkbook();
		Sheet sheet = workbook.createSheet("Numbers");
		Row row = sheet.createRow(0);
		row.createCell(0).setCellValue(10);
		row.createCell(1).setCellValue(20);
		row.createCell(2).setCellValue(30);
		//set formula cell
		row.createCell(3).setCellFormula("A1*B1*C1");
		
		//lets write to file
		FileOutputStream fos = new FileOutputStream(fileName);
		workbook.write(fos);
		fos.close();
		System.out.println(fileName + " written successfully");
	}
	
	public static void main(String[] args) throws IOException {
		writeExcelWithFormula("Formulas.xlsx");
	}
}

The excel file produced with above Apache POI API example program looks like below image. That’s all on Apache POI tutorial for working with excel files, look into Apache POI classes methods to learn more features of it. References: Apache POI Developers Guide

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About the author

Pankaj Kumar

Author

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Java and Python Developer for 20+ years, Open Source Enthusiast, Founder of https://www.askpython.com/, https://www.linuxfordevices.com/, and JournalDev.com (acquired by DigitalOcean). Passionate about writing technical articles and sharing knowledge with others. Love Java, Python, Unix and related technologies. Follow my X @PankajWebDev

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Category:

Tutorial

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Java

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Apache POI Tutorial

Apache POI

Apache POI Maven Dependencies

Apache POI Example - Read Excel File

Apache POI Example - Write Excel File

Apache POI Example - Read Excel Formula

Apache POI Example - Excel Write Formula

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