How to parse a list of list of spring properties - spring-boot

Question

I have this Spring boot application.properties
list1=valueA,valueB
list2=valueC
list3=valueD,valueE
topics=list1,list2,list3
What I'm trying to do is to use in the topics element of #KafkaListener annotation the values of the values of topics property
Using the expression
#KafkaListener(topics={"#{'${topics}'.split(',')}"})
I get list1,list2,list3 as separated string
How can I loop on this list in order to get valueA,valueB,valueC,valueD,valueE?
Edit: I must parse topics properties in order that #KafkaListener registers for consuming message from topics valueA,valueB,valueC, etc.
I read that is possible call a method in this way:
#KafkaListener(topics="#parse(${topics})")
So, I wrote this method:
public String[] parse(String s) {
ExpressionParser parser = new SpelExpressionParser();
return Arrays.stream(s.split(",").map(key -> (String)(parser.parse(key).getValue())).toArray(String[]::new);
}
But the parse method is not invoked
So, I tried directly to do this into annotations
in this way:
#KafkaListener(topics="#{Arrays.stream('${topics}'.split(',')).map(key->${key}).toArray(String[]::new)}")
But also this solution give me errors.
Edit 2:
Modifying in this way the method is invoked
#KafkaListener(topics="parse()")
#Bean
public String[] parse(String s) {
...
}
The problems is how to get "topics" props inside the method

Answer 1

You can't invoke arbitrary methods like that; you need to reference a bean #someBean.parse(...); using #parse requires registering a static method as a function.
However, this works for me and is much simpler:
list1=valueA,valueB
list2=valueC
list3=valueD,valueE
topics=${list1},${list2},${list3}
and
#KafkaListener(id = "so64390079", topics = "#{'${topics}'.split(',')}")
EDIT
If you can't use placeholders in topics, this works...
#SpringBootApplication
public class So64390079Application {
public static void main(String[] args) {
SpringApplication.run(So64390079Application.class, args);
}
#KafkaListener(id = "so64390079", topics = "#{#parser.parse('${topics}')}")
public void listen(String in) {
System.out.println(in);
}
}
#Component
class Parser implements EnvironmentAware {
private Environment environmment;
#Override
public void setEnvironment(Environment environment) {
this.environmment = environment;
}
public String[] parse(String[] topics) {
StringBuilder sb = new StringBuilder();
for (String topic : topics) {
sb.append(this.environmment.getProperty(topic));
sb.append(',');
}
return StringUtils.commaDelimitedListToStringArray(sb.toString().substring(0, sb.length() - 1));
}
}