Java wrapper class with dynamic List type

Question

I need to create some kind of response wrapper (in Rest controller). All mappings should return some necessary fields and some field specific to each class.

For example I have a mapping that returns list of objects of class User and one that returns a list of objects of type Account . Result is always of type List (that I'm getting from JdbcTemplate ) because it could contain more that one User/Account:

public class User {

    private String name;
    private String jobTitle;

    // constructor, getters, setters
}

public class Account {

    private String id;
    private String type;

    // constructor, getters, setters
}

And I have a wrapper:

public class Wrapper {
    public String requestDate;
    public String result;
    public List<?> resultObject; // should be User or Account

    // constructor, getters, setters
}

How can I make it possible to create an instance of wrapper like this:

//suppose I have a List of User objects called myUserList;
Wrapper wrapper = new Wrapper(today, "success", User.class, myUserList);

It looks similar to Spring's BeanPropertyRowMapper<T> but I stucked on implementing such for me.

Answer 1

i don't know if i correctly understood your question but you can use generics in this way

public class Wrapper<T> {
    public String requestDate;
    public String result;
    public List<T> resultObject; 

    // constructor, getters, setters
}

As yuo can see you defined wrapper in a "generic way"; now everytime you build a wrapper instance you can specify a class; for example if you want to create a wrapper of User:

List<User> myUserList = new ArrayList<User>();
Wrapper<User> usrWrap = new Wrapper(today, "success", myUserList);

I hope it is usefull

Angelo

Answer 2

What about using something like this:

Wrapper abstract class:

public abstract class Wrapper {
    public String requestDate;
    public String result;

    // constructor, getters, setters
}

User Wrapper class:

public class UserWrapper extends Wrapper {

    public List<User> resultObject; 

    // constructor, getters, setters
}

Account Wrapper class:

public class AccountWrapper extends Wrapper {

    public List<Account> resultObject; 

    // constructor, getters, setters
}

Consumption:

UserWrapper userWrapper = new Wrapper(today, "success", myUserList);

AccountWrapper accountWrapper = new Wrapper(today, "success", myAccountList);

List<Wrapper> wrapperList = Array.asList(userWrapper, accountWrapper);