Classic simple fluent builder usually suffers from some annoyances.
Let's look a this example:
ComplexClass cc = ComplexClass.Builder()
.addThis(42).setThat("I'm that").addSomethingOther("I'm other")
.addYetAnother("yet yet yet").mixPudding(true).setChickenFeedingDevice(device)
.addThis(99).withTimeout(5000).setThat("I'm another that").build()
Disregarding silly and inconsistent method naming...
- large number of builder methods confuse user
- builder method can be mistakenly called multiple times
Having way to enforce order into method chaining will allow to build something more like wizzard or workflow which wiil simplify Builder usage greatly.
Let's introduce some interfaces according following rules- Any interface declares only subset of Builder methods
- Interface method return value is another interface instead of Builder instance
- Builder itself implements all interfaces
Together this basicaly forms very simple example of formal grammar where order in interface chaining represents production rules
To demonstrate idea just described, I built Selenium2/WebDriver WaitBuilder. It uses WbBegin interface as initial building point, WbAnd interface allowing to add multiple multiple conditions and finaly WbEnd with .seconds(int seconds) method instead of traditional .build().
Selenium has WebDriverWait class allowing conditional waits, which is very useful for testing pages, where elements appear dynamicaly or to perform assertion of Post/Redirect/Get (redirect after form submission) in time-boxed manner. SeleniumWaitBuilder allows to combine multiple conditions together.
It enables to write such cool chains such as...
//pass test if "results-table" element will appear in 5 seconds, fail otherwise
SeleniumWaitBuilder.with(driver)
.passOn().element(By.id("results-table")).seconds(5);
//pass test if title become "Example Domain" and in 5 seconds or fail immediately if it happen to contain "error" string
SeleniumWaitBuilder.with(driver).passOn()
.title().equals("Example Domain")
.and().failOn()
.title().contains("error")
.seconds(5);
SeleniumWaitBuilder.with(driver).passOn()
.title().endsWith("Example Domain")
.element(By.id("result-table"))
.and().failOn()
.title().contains("error")
.url().contains("/500")
.seconds(5);
And finally, hero of today's blog post - mighty SeleniumWaitBuilder itself!
I admit that this is overkill for most of the builders but still, it is neat...
Happy contitional waiting!