mcosta21 / excel-reader-java

This project is a simple Excel file reader using Apache POI and Java 11

Excel Reader

This project is a simple Excel file reader. Using the ExcelReader.java, and passing a xlsx file and a mapper class that implements the IRowMapper, you get a result list to yout own custom class.

ExcelReader class

The ExcelReader class uses a Generic class to return a typed list, uses only its own custom class, and pass the file and the mapper. The implementation is based in Apache POI resources to read the file, and it gets the rows and columns.

public class ExcelReader<T> {

    private InputStream file;
    private IRowMapper<T> rowMapper;
    private boolean skipFirstLine = true;

    public ExcelReader(InputStream inputStream, IRowMapper<T> rowMapper) {
        this.file = inputStream;
        this.rowMapper = rowMapper;
    }

    public ExcelReader(InputStream inputStream, IRowMapper<T> rowMapper, boolean skipFirstLine) {
        this.file = inputStream;
        this.rowMapper = rowMapper;
        this.skipFirstLine = skipFirstLine;
    }

    public List<T> read() throws Exception {
        if(file == null) {
            throw new Exception("File not found");
        }

        var items = new ArrayList<T>();

        try {
            XSSFWorkbook workbook = new XSSFWorkbook(file);
            XSSFSheet sheet = workbook.getSheetAt(0);

            var firstLine = this.skipFirstLine ? 1 : 0;
            for(int i = firstLine; i < sheet.getPhysicalNumberOfRows(); i++) {
                XSSFRow row = sheet.getRow(i);
                T item = rowMapper.map(row);
                items.add(item);
            }
        }
        catch (IOException e) {
            e.printStackTrace();
        }

        return items;
    }
}

IRowMapper interface

public interface IRowMapper<T> {
    T map(XSSFRow row);
}

Example

Import a list of students with name, email and level;

NAME	EMAIL	LEVEL
Marcio	[e-mail]	master
Teste	[e-mail]	smarter
Teste 2	[e-mail]	intermediate

java/resources/data/students.xlsx

StudentDTO

@Data
public class StudentDTO {
    private String email;
    private String name;
    private String level;
}

StudentDTORowMapper

public class StudentDTORowMapper implements IRowMapper<StudentDTO> {
    @Override
    public StudentDTO map(XSSFRow row) {
        StudentDTO student = new StudentDTO();
        student.setName(String.valueOf(row.getCell(0)));
        student.setEmail(String.valueOf(row.getCell(1)));
        student.setLevel(String.valueOf(row.getCell(2)));
        return student;
    }
}

Using the ExcelReader to StudentDTO

@SpringBootApplication
public class ExcelReaderApplication {
	public static void main(String[] args) throws Exception {
		SpringApplication.run(ExcelReaderApplication.class, args);

		var file = new ClassPathResource("data/students.xlsx");

		var excelReader = new ExcelReader<StudentDTO>(file.getInputStream(), new StudentDTORowMapper());
		var items = excelReader.read();
	}
}

Result

• StudentDTO(email=[e-mail], name=Marcio, level=master)
• StudentDTO(email=[e-mail], name=Teste, level=starter)
• StudentDTO(email=[e-mail], name=Teste 2, level=intermediate)

Developed by Marcio Costa.