Jakarta EE Instance Arayüzü

Giriş

Açıklaması şöyle

A more powerful solution is Instance (resembles Spring’s ObjectProvider, and extends Provider) because it comes with

an iterator, which allows running for-loops over multi-valued dependencies (0..n)

a stream() method

methods for checking the availability and uniqueness of the dependency

Açıklaması şöyle

The following table summarizes the return value of the three boolean check methods, depending on the number of provided bean instances:                               

# OF INSTANCES ISRESOLVABLE ISUNSATISFIED ISAMBIGUOUS

0                         false                 true                         false

1                         true                         false                 false

>1                         false                 false                 true

Instance also allows applying additional filters (based on type and qualifier) when invoking its “select()” method, which is most useful in combination with programmatic injection

Örnek

Şöyle yaparız

@Inject
Instance<Pet> petInstances;

...

// loop over instances:
for (Pet pet : petInstances) {
  ...
}

// instance stream:
petInstances.stream().forEach(...);

// boolean check methods:
petInstances.isResolvable();
petInstances.isUnsatisfied();
petInstances.isAmbiguous();