Autowire all interfaces keyed by type - spring

Question

I've a an interface and there are multiple implementations of the interface. There can be only one type of implementation for each interface type and I want to collect all the interface implementations per type, i.e.
Map<String, InterfaceExample>
public interface InterfaceExample {
String getType();
ClassA getClassA();
}
If I had to get in this form Map<String, List<InterfaceExample>> I would have done in the following way:
#Autowired
private List<InterfaceExample> interfaceExamples;
#Bean
public Map<String, List<IntefaceExample>> getExamples() {
return interfaceExamples.stream()
.map(x -> new AbstractMap.SimpleEntry<>(x.getType(), x))
.collect(Collectors.groupingBy(Map.Entry::getKey, Collectors.mapping(Map.Entry::getValue, Collectors.toList())));
}
Now that I've to ensure there is only one implementation per type I can do in following way:
#Bean
public Map<String, IntefaceExample> getExamples() {
Map<String, List<IntefaceExample>> examples = interfaceExamples.stream()
.map(x -> new AbstractMap.SimpleEntry<>(x.getType(), x))
.collect(Collectors.groupingBy(Map.Entry::getKey, Collectors.mapping(Map.Entry::getValue, Collectors.toList())));
Map<String, InterfaceExample> output = new HashMap<>();
examples.forEach((key, value) -> {
if(value.size() > 1) {
throw new RuntimeException("Wrongly configured!! ");
} else if(value.size() == 1) {
output.put(key, value.get(0));
}
});
return output;
}
Is there a different way to ensure that there is only implementation per type and create the bean in a "streamified way" without explicitly creating the output map?

Answer 1

After groupingby you can check if there are multiple beans of same type and collect them into List
List<InterfaceExample> res = interfaceExamples.stream().collect(Collectors.groupingBy(InterfaceExample::getType)).values()
.stream().map(value -> {
if (value.size() == 1) {
return value.get(0);
}
throw new RuntimeException("Wrongly configured!! ");
}).collect(Collectors.toList());
The best way is write a custom method that does the validation logic
public InterfaceExample conditionCheck(List<InterfaceExample> value) {
if (value.size() == 1) {
return value.get(0);
}
throw new RuntimeException("Wrongly configured!! ");
}
And then simply use stream
List<InterfaceExample> res = interfaceExamples.stream()
.collect(Collectors.groupingBy(InterfaceExample::getType))
.values()
.stream()
.map(this::conditionCheck)
.collect(Collectors.toList());