Java- Passing unknown DAO

Question

I created a common method in which I will pass a DAO but it will not be a one DAO. Like i will be passing not only StudentDao but also TeachersDao and ClubsDao.

Originally, this is my method:

    public static String getSomething(StudentDao, String id){

        Properties proFind = new Properties();
        proFind.put(StudentDao.ID, id);

        dao.select(proFind).get(0);

        return somethingINeed;
    }

But then I've decided that to use only one method, make it something generic.. Somthing like this:

    public static <T> String getSomething(Class<T> dao, String id){

        Properties proFind = new Properties();
        proFind.put(StudentDao.ID, id);

        dao.select(proFind).get(0);

        return somethingINeed;
    }

but this is not correct.

So my objective is to pass any Dao in that method. Did i miss something in java? Any idea or enlightenment is greatly appreciated.

[EDIT]

All my Daos extends Dao which is and interface. My concern is just this method in which how I can use any Dao. The attributes used can be found in the interface Dao also.

Answer 1

I agree with Kayaman's comment above.

Your service/business tier should be interfacing with multiple DAOs to perform CRUD operations on different entities eg Student, Teacher.

public class MyService {

    private StudentDao studentDao;
    private TeacherDao teacherDao;

    // Daos injected

    public Student findStudent(Long id) {
        return this.studentDao.find(id);
    }

    // Other methods involving students or teachers
}

Trying to have one generic DAO is cumbersome and not good design in my opinion.

If you have a base DAO and base entity classes, you can still push a lot of the boilerplate CRUD code into the base classes. When I first started using DAOs, I found the following article very useful: Don't repeat the DAO!

Answer 2

thats why java created Interface enter link description here or Inheritance

just create a DAO interface or base class and change your method to

public static String getSomething(Dao dao, String id)

Answer 3

Use this

public static String getSomething(Object dao, String id){

if(dao instanceOf StudentDao){
 // do your code
 }
else if(dao instanceOf AnotherDao){
 // do your code
 }

and so on.............