java - How to implement this nested flow with optionals? -

i've have method takes string input , should return string.

the following ascii art presents logical flow:

option<a> opta = finder.finda(input);            opta            /\ isempty() /  \ isdefined()            /    \  "err_1"       option<b> optb = finder.findb(opta.get().bid);                       / \            isempty() /   \ isdefined()                     /     \                 "err_2"    opt2.get().id 

basically given input i'm looking a object returned wrapped in option. a present i'm looking b - wrapped in option too, otherwise return err_1. if b present return it's id, otherwise return err_2.

i'm wondering how implemented using optionals (or pattern matching maybe?) in nice , concise way (without ifology) - possibly in one-liner.

could please suggest something?

source code try out can found here.

it looks have 3 possible exit points:

1. opta empty -> "err_1"
2. opta not empty && optb empty -> "err_2"
3. both not empty -> optb.get().bid

you can achieve doing javaslang:

 opta    .map(a -> finder.findb(a.bid)       .map(b -> b.bid)       .getorelse("err_2"))    .getorelse("err_1"); 

if opta empty, jump straight orelse("err_1")

if opta not empty, using value stored inside getting value b.bid or "err_2" in case of optb emptiness.

also, in pure java 8, this:

opta   .map(a -> finder.findb(a.bid)     .map(b -> b.bid)     .orelse("err_2"))   .orelse("err_1");