private void loadUsers() throws IOException {
        ObjectMapper mapper = new ObjectMapper();

        File file = new File(this.contextPath + "data"+ java.io.File.separator +"admins.json");
        String json = "";
        String temp;

        if(file.exists())
        {
            try(BufferedReader br = new BufferedReader(new FileReader(file))){
                while ((temp = br.readLine()) != null) {
                    json += temp;
                }
            }

            List<Admin> list = mapper.readValue(json,
                    new TypeReference<ArrayList<Admin>>() {});

            this.users.clear();
            for(Admin admin: list) {
                this.users.put(admin.getEmail(), admin);
            }
        }


        file = new File(this.contextPath + "data"+ java.io.File.separator +"sellers.json");
        json = "";

        if(file.exists())
        {
            try(BufferedReader br = new BufferedReader(new FileReader(file))){
                while ((temp = br.readLine()) != null) {
                    json += temp;
                }
            }
            List<Seller> list2 = mapper.readValue(json,
                    new TypeReference<ArrayList<Seller>>() {});

            for(Seller salesman: list2) {
                this.users.put(salesman.getEmail(), salesman);
            }

        }


        file = new File(this.contextPath + "data"+ java.io.File.separator +"buyers.json");
        json = "";

        System.out.println("Here");
        if(file.exists())
        {
            try(BufferedReader br = new BufferedReader(new FileReader(file))){
                while ((temp = br.readLine()) != null) {
                    json += temp;
                }
            }
            System.out.println("Inside");
            List<Buyer> list3 = mapper.readValue(json,
                    new TypeReference<ArrayList<Buyer>>() {});
            System.out.println(list3.size());
            for(Buyer customer: list3) {
                System.out.println(customer.getEmail());
                this.users.put(customer.getEmail(), customer);
            }
        }
    }

    public void saveUsers() {
        ObjectMapper mapper = new ObjectMapper();

        ArrayList<Admin> list = new ArrayList<Admin>();
        for (User user: this.users.values()) {
            if (user.getRole().equals(Role.Admin)) {
                list.add( (Admin)user );
            }
        }
        File file = new File(this.contextPath + "data"+ java.io.File.separator +"admins.json");
        try {
            mapper.writerWithDefaultPrettyPrinter().writeValue(file, list);
        } catch (IOException e) {
            e.printStackTrace();
        }

        ArrayList<Seller> list2 = new ArrayList<Seller>();
        for (User user: this.users.values()) {
            if (user.getRole().equals(Role.Seller)) {
                list2.add( (Seller)user );
            }
        }
        File file2 = new File(this.contextPath + "data"+ java.io.File.separator +"sellers.json");
        try {
            mapper.writerWithDefaultPrettyPrinter().writeValue(file2, list2);
        } catch (IOException e) {
            e.printStackTrace();
        }

        ArrayList<Buyer> list3 = new ArrayList<Buyer>();
        for (User user: this.users.values()) {
            if (user.getRole().equals(Role.Buyer)) {
                list3.add( (Buyer)user );
            }
        }
        File file3 = new File(this.contextPath + "data"+ java.io.File.separator +"buyers.json");
        try {
            mapper.writerWithDefaultPrettyPrinter().writeValue(file3, list3);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }