如果列表为空，使用 lombok getter 初始化列表？

Question

I am currently replacing all my standard POJO's to use Lombok for all the boilerplate code. I find myself keeping getters for lists because I want to return an empty list if the list has not been initialized. That is, I don't want the getter to return null. If there some lombok magic that I'm not aware of that can help me avoid doing this?

Example of generated code

private List<Object> list;
public Object getList(){ return list; }

What I would like instead:

private List<Object> list;
public Object getList(){
    if (list == null) {
        return new ArrayList();
    }
    return list;
}

Answer 1

You can achieve this by declaring and initializing the fields. The initialization will be done when the enclosing object is initialized.

private List<Object> list = new ArrayList();

Lomboks @Getter annotation provides an attribute lazy which allows lazy initialization.

 @Getter(lazy=true) private final double[] cached = expensiveInitMethod();

Documentation

Answer 2

I had the same questions as of this one. Though, the above answers are useful in some ways, the exact solution is to use @Builder and @Singular annotations of Lombok API like below given code.

It worked superb for me.

@Builder
class MyClass{
    @Singular
    private List<Type> myList;
}

This will initialize myList with a non-null List object. Though, this questions is an old one. But, still posting this answer to help someone like me who will refer this question in future.

Answer 3

That is, I don't want the getter to return null. If there some lombok magic that I'm not aware of that can help me avoid doing this?

You don't need any magic to be happen. Just initialize the list .

Answer 4

Newest versions of lombok do not generate a getter method if a getter method is provided with the same name and number of parameters.

With older versions of lombok, you can override the getter with anything you like by using AccessLevel.NONE on the field.

Note that merely initializing the field does not protect you from clients calling a constructor with nulls, or calling a setter with null (Still may be okay, depending on what you want).

Eg

// only necessary for older versions of lombok
@Getter(AccessLevel.NONE)
private Map<String, String> params;

public Map<String, String> getParams() {
    return (params == null) ? new HashMap<>() : params;
}

Answer 5

An old question, but this plugin does what you want:

https://github.com/dmak/jaxb-xew-plugin

Using this plugin generated the getter as:

public List<BaseVariableType> getVariables() {
    if (variables == null) {
        variables = new ArrayList<BaseVariableType>();
    }
    return variables;
}