How to Merge Two List in Java Spring

This is my controller:

List<Equipement> equipements = equipementService.findEquipmentsByAssignment(affectationId);
List<Equipement> equipements2 = equipementService.selectSotck();

How can you merge two lists into one?

It depends on which version of java you use and if you are allowed to use external libs (like Guava), but here you will find few examples for most scenarios https://www.techiedelight.com/join-two-lists-java/

package com.elfayq.stock.services.impl;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import org.springframework.transaction.annotation.Transactional;
import com.elfayq.stock.dao.IEquipementDao;
import com.elfayq.stock.entities.Equipement;
import com.elfayq.stock.services.IEquipementService;
//L'annotation transactionnel pour dire que la classe contient des m�thode de transaction avec la base de donn�es
@Transactional
public class EquipementServiceImpl implements IEquipementService{
private IEquipementDao equipementsDao;
public void setEquipementsDao(IEquipementDao equipementsDao) {
this.equipementsDao = equipementsDao;
}
@Override
public Equipement save(Equipement entity) {
return equipementsDao.save(entity);
}
@Override
public Equipement update(Equipement entity) {	
return equipementsDao.update(entity);
}
@Override
public List<Equipement> selectAll() {	
return equipementsDao.selectAll();
}
@Override
public List<Equipement> selectAll(String sortField, String sort) {		
return equipementsDao.selectAll(sortField, sort);
}
@Override
public void remove(Long id) {
equipementsDao.remove(id);	
}
@Override
public List<Equipement> selectSotck() {		
return equipementsDao.selectAllByField("alloted", "0");
}
@Override
public List<Equipement> findEquipmentsByAssignment(Long affectionId) {		
return equipementsDao.selectAllByField("idAffectation",String.valueOf(affectionId));
}
@Override
public Equipement getById(Long id) {		
return equipementsDao.getById(id);
}
@Override
public Equipement findOne(String paramName, Object paramValue) {
return equipementsDao.findOne(paramName, paramValue);
}
@Override
public Equipement findOne(String[] paramNames, Object[] paramValues) {	
return equipementsDao.findOne(paramNames, paramValues);
}
@Override
public int findCountBy(String paramName, String paramValue) {	
return equipementsDao.findCountBy(paramName, paramValue);
}
public List<Equipement> addAll() {
{
List<Equipement> list = list1.stream().collect(Collectors.toList());
list.addAll(list2);
return list;
}
}

You could use Stream.concat for the streams of the two lists:

public List<Equipement> addAll() {
    return Stream.concat(list1.stream(), list2.stream()).collect(Collectors.toList());
}

or flatMap for the list of lists:

public List<Equipement> addAll() {
    return Arrays.stream(Arrays.asList(list1, list2))
                 .flatMap(List::stream)
                 .collect(Collectors.toList());
}

or simply List.addAll:

public List<Equipement> addAll() {
    List<Equipement> all = new ArrayList<>(list1);
    all.addAll(list2);
    return all;
}

Easiest way, if you don't need deduplication:

List<String> x = ...;
List<String> y = ...;
x.addAll(y);