Future Perfect Continuous (Future Tenses)

example:
"By the next year, I will have been working as a teacher for 30 years".

Use
Actions that will be in progress at a definite moment in the future.

The only use of this tense is to talk about future actions that will be in progress at some specified point in the future.

By tomorrow I will have been saving money for a new house for 4 years.

Examples:

• Before they come, we will have been cleaning the house for 5 hours.
• By the next year, Ben and his wife will have been living together for 50 years.

Common Time Expressions
Time expressions that are commonly used with the Future Perfect Perfect:

• By tomorrow / 8 o'clock
• This year / month / week
• Next year / month / week

Form
Contracted forms 
WILL = 'LL
Example: She'll have been = she will have been
WILL + NOT = WON'T
Example: She won't have been = she will not have been

Positive Sentences

Note
If duration of an activity (e.g. "since April", "for three hours") is unknown then the Future Continuous should be used instead of the Perfect Form.Example: 

- I will be taking a bath. 

- I will have been taking a bath.

Negative Sentences

Negative sentences sound rather unnatural. This is probably because the answer to a question like, "Will she have been teaching for 30 years this year?", would simply be, "No, I don't think so".

Questions

Good to know !!Questions beginning with "how long" are more common.
Examples:How long will you have been learning German this year?
How long will you have been trying to get your driving license this week? I hope you'll finally make it!