Incompatible types - Found void java.util.Optional

Question

There is a red underlined with the message: Incompatible types. Required: ...model.Constants Found: java.util.Optional on jpa findById method.

I use findById is here:

Constants constants=constantsRepository.findById(1L);

And my model is:

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "pkid")
private Long id;

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

Any help please?

Here is my all code

ConstantsRepository interface

package com.destek.salaryCalculation.repository;

import com.destek.salaryCalculation.model.Constants;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface ConstantsRepository extends  JpaRepository<Constants, Long>{

}

BesCreateController java

package com.destek.salaryCalculation.controller;

import com.destek.salaryCalculation.helper.BesCreateExcelHelper;
import com.destek.salaryCalculation.model.Personal;
import com.destek.salaryCalculation.repository.PersonalRepository;
import org.apache.poi.openxml4j.exceptions.InvalidFormatException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@RestController
@CrossOrigin(origins = "http://localhost:3000")
@RequestMapping("/salarycalc")
public class BesCreateController {

    @Autowired
    private PersonalRepository personalRepository;

    @GetMapping("/besexcel/{group}")
    public void exportToExcelByGroup(HttpServletResponse response,@PathVariable String group) throws IOException, InvalidFormatException {
        response.setContentType("application/octet-stream");

        String headerKey = "Content-Disposition";
        String headerValue = "attachment; filename=bes.xlsx";
        response.setHeader(headerKey, headerValue);
        List<Personal> listPersonal = personalRepository.getListPersonelByGroup(group);
        System.out.println(listPersonal);
        BesCreateExcelHelper excelExporter = new 
       BesCreateExcelHelper(listPersonal);
       excelExporter.export(response);
    }
}

And BesCreateHelper java

package com.destek.salaryCalculation.helper;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Calendar;
import java.util.List;
import java.util.Optional;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import com.destek.salaryCalculation.model.Constants;
import com.destek.salaryCalculation.model.Personal;
import com.destek.salaryCalculation.repository.ConstantsRepository;
import org.apache.poi.openxml4j.exceptions.InvalidFormatException;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFFont;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.springframework.beans.factory.annotation.Autowired;

public class BesCreateExcelHelper {
    private XSSFWorkbook workbook;
    private XSSFSheet sheet;
    private List<Personal> listPersonalBes;

    @Autowired
    private ConstantsRepository constantsRepository;
    public BesCreateExcelHelper(List<Personal> listPersonalBes) throws IOException, InvalidFormatException {
        FileInputStream inputStream = new FileInputStream(new File("bes.xlsx"));
        this.listPersonalBes = listPersonalBes;
        //workbook = new XSSFWorkbook();
        workbook = (XSSFWorkbook) WorkbookFactory.create(inputStream);
        sheet = workbook.getSheetAt(0);
        inputStream.close();
    }

    private void createCell(Row row, int columnCount, Object value, CellStyle style) {
        //sheet.autoSizeColumn(columnCount);
        Cell cell = row.createCell(columnCount);
        if (value instanceof Integer) {
            cell.setCellValue((Integer) value);
        } else if (value instanceof Boolean) {
            cell.setCellValue((Boolean) value);
        }else {
            cell.setCellValue((String) value);
        }
        cell.setCellStyle(style);
    }

    private void writeDataLines() {
        int rowCount = sheet.getLastRowNum();

        CellStyle style = workbook.createCellStyle();
        XSSFFont font = workbook.createFont();
        font.setFontHeight(15);
        style.setFont(font);

       Optional<Constants> constants2 = constantsRepository.findById(1L);
       Constants constants = constants2.orElseThrow(() ->new RuntimeException("No such data found"));;

        for (Personal personal : listPersonalBes) {
            Row row = sheet.createRow(++rowCount);
            int columnCount = 0;
            int i = 1;
            createCell(row, columnCount++, i++, style);
            createCell(row, columnCount++, personal.getName(), style);
            createCell(row, columnCount++, personal.getIdentity().toString(), style);
            double besAmount=0;
            if(personal.getBes()==1){
                int numberDayOfMonth=constants.getDayOfWork();
           int sanitaryPermit=personal.getSanitaryPermit();
            double grossWages=0;
           if(sanitaryPermit<numberDayOfMonth) {
                grossWages = constants.getDailyWage() * (numberDayOfMonth - sanitaryPermit);
           }
               float socialHelp=constants.getSocialHelp();
               float mealBonus=constants.getMealBonus();
               float tisSupport=constants.getTisSupport();
               double deservedVehicleHelp=0;
               if(numberDayOfMonth>0){
                   int dayOfWork=numberDayOfMonth-sanitaryPermit-personal.getAnnualPermit();
                   // TODO: 11.01.2021 busTicketHelp tekrar hesaplatılacak.
                   double busTicketHelp=3.25*numberDayOfMonth;
                    deservedVehicleHelp=busTicketHelp*dayOfWork/numberDayOfMonth;
               }
               double mealPrice=(constants.getDayOfWork()-(personal.getSanitaryPermit()- Math.floor(personal.getSanitaryPermit()/7)*2)-personal.getAnnualPermit())*constants.getMealBonus();
               double extraWorkHourPrice=Math.ceil(personal.getExtraWorkHour()*constants.getDailyWage()/5);
               double extraWorkHourPriceSpecial=Math.ceil(personal.getExtraWorkHourSpecial()*constants.getDailyWage()/7.5*1.5);
               double mealException=constants.getMinimumWage()/30*6/100*mealPrice;
               double sgkPrimBaseAmount=grossWages+socialHelp+mealBonus+tisSupport+deservedVehicleHelp+mealPrice+extraWorkHourPrice+extraWorkHourPriceSpecial+mealException;
               besAmount=sgkPrimBaseAmount*0.03;
               }
            createCell(row, columnCount++, String.valueOf(besAmount), style);
        }
    }
    public void export(HttpServletResponse response) throws IOException {
        //writeHeaderLine();
        writeDataLines();
        ServletOutputStream outputStream = response.getOutputStream();
        workbook.write(outputStream);
        // workbook.close();
        outputStream.close();
    }
}

Answer 1

As @AnishB states you need to resolve the value from the optional but I would not use

... = constants.get(); 

straight away since this is dangerous constants.get() would throw NoSuchElementException if value does not exist

You should use:

Constants value = constants.orElse(null); 

or even

Constants value = constants.orElseThrow(() -> new CustomException()); 

this line would throw exception but on that case you control the exception handling not something behind the scenes

BTW, You are getting a NullPointerException when try to call constantsRepository.findById(1L); because the BesCreateExcelHelper is not a Spring dependency so you can not inject other spring dependencies into it at that case constantsRepository will be null

You have 2 options:

#1, Annotate that BesCreateExcelHelper with @Component annotation this will make BesCreateExcelHelper a spring dependency thus constantsRepository will be injected normally BUT you must convert BesCreateExcelHelper constructor into a method since constructors are used by Spring starting from version 4.3 to inject dependencies.

BesCreateExcelHelper would be like :

@Component
public class BesCreateExcelHelper {
...
public void init(List<Personal> listPersonalBes) { // notice this was the constructor logic
  .......
}
}

And then you inject BesCreateExcelHelper into the BesCreateController and replace that ..new BesCreateController() line with besCreateExcelHelper.init(listPersonal)

---

#2 You can keep the BesCreateExcelHelper as it is but remove that Constant fetch line and pass the constant value from outside, ofcourse outside here means some other Spring component as you do in exportToExcelByGroup so simply you will execute constantsRepository.findById(1L); in the controller then pass it as a second constructor argument to the Helper class

...

constant = ...constantsRepository.findById(1L);
excelExporter = new 
       BesCreateExcelHelper(listPersonal, constant);

I like first option more

Answer 2

findById(ID id) method from JpaRepository returns a value of type Optional<T>.

To get the actual value from Optional<T>, you can use get() method but in some cases, data may not be there and you will get NoSuchElementException. So, you either return a default value with orElse() or you can throw an exception with orElseThrow().

Example :

With orElseThrow() :

Optional<Constants> constants = constantsRepository.findById(1L);
                           
Constants value = constants.orElseThrow(() -> 
                                new RuntimeException("No such data found"));

With orElse()

Optional<Constants> constants = constantsRepository.findById(1L);
                           
Constants value = constants.orElse(null);

if(value == null) {
  // write some logic
}

Answer 3

findById return a Optinal data.You need to get it like this.

Optional<Constants> constants=constantsRepository.findById(1L);