Currently I learn Springboot.

    @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {
        Collection<GrantedAuthority> collection = new ArrayList<GrantedAuthority>();
        collection.add(()-> user.getRole().getKey());
        return collection;
    }

In this code

collection.add(()-> user.getRole().getKey());

I know this is lambda expression but I don't get raw code. This is not my code. Could you let me know the raw code?

CodePudding user response：

The code is hard to follow because the collection is supposed to be a collection of GrantedAuthority objects. A GrantedAuthority is a single method interface with a getAuthority() function - https://docs.spring.io/spring-security/site/docs/current/api/org/springframework/security/core/GrantedAuthority.html#getAuthority()

So what the code is trying to do here is create a single element collection with a GrantedAuthority whose getAuthority method returns the value of user.getRole().getKey() - whatever that happens to be in this context.

You might find it easier to think of there being a single-use class here:

GrantedAuthority theOneAuthority = new GrantedAuthority() {
   String getAuthority() {
      return user.getRole().getKey();
   }
}
return List.of(theOneAuthority); // a single entry list

To understand the above, however, you'd need to understand the concept of an anonymous inner class - in other words a temporary type whose job it is to subclass an interface or other class to do something a particular method wants us to do.

In this instance, a lambda is a better alternative.

// as there's only one method, taking 0 parameters and returning string
// then this 0 parameter string-returning lambda can BE a `GrantedAuthority`
GrantedAuthority authFromLambda = () -> user.getRole().getKey();

CodePudding user response：

There are some types of lambda expressions:

1. (int x, int y) -> { return x y; }
2. x -> x * x
3. ( ) -> x

So, your case is third one. It is used when you get no parameters as a method arguments and return a value. In your example, it just returns the value of user.getRole().getKey()); and it added to the Collection<GrantedAuthority>