public Map<Bank, List<Account>> findAllGroupByBank() {
     Map<Bank, List<Account>> result = new HashMap<>();
    
            this.accountService
                    .findAll()
                    .stream()
                    .forEach(a -> result.computeIfAbsent(a.getBank(), this::findAllByBank));
            return result;
   }

   private List<Account> findAllByBank(Bank aBank) {
       return this.accountService.findAll().stream().filter(account -> aBank.equals(account.getBank())).collect(Collectors.toList());
   }

package com.cyrgue.designpatterns.chain;

public abstract class ConflictChecker {

    protected UserModel anonymousUser;
    protected UserModel registeredUser;

    protected ConflictChecker nextChecker;

    public ConflictChecker(UserModel anonymousUser, UserModel registeredUser) {
        this.anonymousUser = anonymousUser;
        this.registeredUser = registeredUser;
    }

    public void setNextChecker(ConflictChecker nextChecker) {
        this.nextChecker = nextChecker;
    }

    public void check() throws Exception {
        if (this.hasConflict()) {
            process();
        }  // Possible d'avoir un else ici - La chaine s'arrete
        if (nextChecker != null) {
            nextChecker.check();
        }
    }

    abstract protected void process() throws Exception;

    abstract protected boolean hasConflict();
}