Dependency Injection

[Bilal A. Siddiqui]

Hi All,

i am reading strutss 2 in action where they are integerating springs with struts. I am trying a lot but i am unable to understand what is dependency injection.

I am also not sure whether this question has to be post in springs forum or struts forum.

Regards
Bilal

[kurt hanni]

Dependency injection is done by the Spring framework.

Check this post about DI

[David Newton]

The nutshell version is that instead of an S2 action instantiating and using an implementation, like this:

public LoginAction extends ActionSupport {
    private User user; // And get/set.
    private UserService userService = new TestUserService();
    public String execute() {
        if (userService.login(user)) {
            // Process login.
            return SUCCESS;
        }
        return ERROR;
    }
}

actions will instead allow the implementation to be instantiated and injected by Spring. This is generally defined in a configuration file, but there are other ways. So the code would look more like this:

public LoginAction extends ActionSupport {
    private User user; // And get/set.
    private UserService userService; // And get/set.
    public String execute() {
        if (userService.login(user)) {
            // Process login.
            return SUCCESS;
        }
        return ERROR;
    }
}

Amongst other things, this means that the action can now be tested with various user service implementations--like one that always fails login, one that always succeeds, or one that succeeds/fails based on user information, whatever.

It's a simple concept, but very, very helpful.

[Bilal A. Siddiqui]

Thanks David & kurt

I think i need to study more. I am still not very comfortable with the concept.