如何更改方法中传递的Lambda表达式的值

Question

I have a class EmailServiceImpl which has a method sendMail(Cumsumer<EmailTemplate> template) .

EmailTemplate has 4 fileds

• to
• from
• body
• subject

I am setting three fields of EmailTemplate using Lambda expression and sending it to sendMail method, like below :

emailService.sendMail(mailer->
                mailer
                    .to("")
                    .subject("")
                    .body("")
                );

But I want to add it's 4th filed (from) inside sendMail method like below :

public String sendMail(Consumer<EmailTemplate> template) {
        template.from = "XYZ"; // cannot do this

    } 

I cannot access any field of EmailTemplate using this lambda (template).

I have following queries :

1. Is it possible to change values of passed lambda inside a method(like above)?
2. Is it good idea to do like that?
3. Any better approach to do this using lambda?

Answer 1

Is it possible to change values of passed lambda inside a method(like above)?

No. The sendMail() method accepts a consumer of emailTemplate. Which is NOT an emailTemplate itself. The consumer is a function that accepts an emailTemplate and does something with it. If you want to set the fourth field, you will need to do that inside of the lambda. The sendEmail() method is essentially receiving a class that can process an emailTemplate. It is not receiving an emailTemplate instance/state at all.

Is it good idea to do like that?

It depends on how you wish to design your sendMail() method and what responsibility do you want it to have. By the looks of it (and to keep it simple), the sendEmail() method should receive an emailTemplate object (and not a consumer). If you receive only the consumer, the only thing you can do it invoke/apply it on an emailTemplate object (which you currently are not sending to the sendEmail() method)

Any better approach to do this using lambda?

Lambdas define behavior/method-bodies. The act on an object that is supplied to them at a later time. In this example, I don't see the need for lambdas at all