Why am I getting a NullPointerException?

Question

Java

For some reason, I get a NullPointerException
complaining about the interface method of the findById() repository

(THIS IS NOT BECAUSE OF LONG, I TRIED Integer, my method is highlighted in red)
Repositories:

package com.blrmyfc.repos;

import com.blrmyfc.domain.XmlFileEntity;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.Optional;
public interface XmlFileRepo extends CrudRepository<XmlFileEntity, Integer> {
    XmlFileEntity findById(Long id);
//    XmlFileEntity findOne(int id);
//    XmlFileEntity findByFilename(String filename);
}

Essence:

package com.blrmyfc.domain;


import org.hibernate.validator.constraints.Length;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class XmlFileEntity {

    @Id
    @GeneratedValue(strategy= GenerationType.AUTO)
    private Integer id;

    public Integer getId() {
        return id;
    }

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

    private String fileName;
    private String fileLink;



    private String valid;

    @Length(max = 4096)
    private String fileStrings;



    public String getValid() {
        return valid;
    }

    public void setValid(String valid) {
        this.valid = valid;
    }

    public String getFileStrings() {
        return fileStrings;
    }

    public void setFileStrings(String fileStrings) {
        this.fileStrings = fileStrings;
    }

    public XmlFileEntity() {
    }

    public XmlFileEntity(String fileName, String fileLink) {
        this.fileName = fileName;
        this.fileLink = fileLink;
    }



    public String getFileName() {
        return fileName;
    }

    public void setFileName(String fileName) {
        this.fileName = fileName;
    }

    public String getFileLink() {
        return fileLink;
    }

    public void setFileLink(String fileLink) {
        this.fileLink = fileLink;
    }
}

The controller in which the method works (and in all other classes, controllers, and even in public static void main(String[] args) DOES NOT WORK :( ):

package com.blrmyfc.controller;


import com.blrmyfc.domain.XmlFileEntity;
import com.blrmyfc.logic.SchemaValidator;
import com.blrmyfc.logic.XmlViewer;
import com.blrmyfc.repos.XmlFileRepo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.xml.sax.SAXException;

import java.io.IOException;

//@Controller
@RestController
public class ShowController {

    @Value("${upload.path}")
    private String uploadPath;

    @Autowired
    private XmlFileRepo xmlFileRepo;

    @PostMapping("/validate")
    public String validateFiles(@RequestParam("xmls") String xmls, @RequestParam("xsds") String xsds, Model model){
        SchemaValidator schemaValidator = new SchemaValidator();
        boolean flag = true;
        try{
            schemaValidator.validate(uploadPath+"/"+(xmlFileRepo.findById(Integer.parseInt(xmls)).get().getFileLink()),
                    uploadPath+"/"+(xmlFileRepo.findById(Integer.parseInt(xsds)).get().getFileLink()));
//            schemaValidator.validate("./upload-dir/students.xml",
//                    "./upload-dir/students.xsd");
        }catch (SAXException e){
            flag=false;
            e.printStackTrace();
        }catch (IOException e){
            flag=false;
            e.printStackTrace();
        }catch (NullPointerException e){
            flag=false;
            e.printStackTrace();
        }
        if(flag){
            XmlFileEntity xmlFileEntity = xmlFileRepo.findById(Integer.parseInt(xmls)).get();
            xmlFileEntity.setValid("true");
            XmlViewer xmlViewer = new XmlViewer();
            xmlFileEntity.setFileStrings(xmlViewer.getStrings(uploadPath+"/"+(xmlFileRepo.findById(Integer.parseInt(xmls)).get().getFileLink())));
            xmlFileRepo.save(xmlFileEntity);
        }else {
            xmlFileRepo.findById(Integer.parseInt(xmls)).get().setValid("false");
        }
        return "Валидация: "+flag;
//        return "Воть (xmls)(xsds)==>"+xmls+xsds+"+_=-=-=-"+uploadPath+"/"+(xmlFileRepo.findById(Integer.parseInt(xmls)).get().getFileLink() )+"-------"+uploadPath+"/"+(xmlFileRepo.findById(Integer.parseInt(xsds)).get().getFileLink());
    }
}

The class in which I want it to work (ValidateFromDBAndSave):

package com.blrmyfc.logic;

import com.blrmyfc.repos.XmlFileRepo;
import org.springframework.beans.factory.annotation.Autowired;

public class ValidateFromDBAndSave {

    @Autowired
    public XmlFileRepo xmlFileRepo;

    public String printXmlFileStringFromDB(){
        String xmlFileString="";
        System.out.println(xmlFileRepo.findById(13).get().getFileStrings());
        return xmlFileString;
    }
}

Answer 1

We need to initialize the repository like this:
thanks for the help

@Service
public class ValidateFromDBAndSave {

    private final XmlFileRepo xmlFileRepo;

    @Autowired
    public ValidateFromDBAndSave(XmlFileRepo xmlFileRepo) {
        this.xmlFileRepo = xmlFileRepo;
    }

    public String printXmlFileStringFromDB(){
        String xmlFileString="";
        xmlFileString=xmlFileRepo.findById(13).get().getFileStrings();
        return xmlFileString;
    }
}

Controller

@GetMapping("/soli")
    public String soli(){
        return new ValidateFromDBAndSave(xmlFileRepo).printXmlFileStringFromDB();
//        return xmlFileRepo.findById(13).get().getFileStrings();
    }