How to extend already defined lists and maps in Spring application context?

Question

Imagine a staged application context with different phases. We start with an early phase to define the necessary infrastructure. The xml application contexts are loaded sequenti

Answer 1

You can define exampleMapping is the second definition is in a separate file, and you use to import one file into another, but it's a fragile approach, and easily broken.

I suggest a more robust strategy. Replace the exampleMapping with a Registry class, which in turn contains and manages the mappings:

public MappingRegistry {

   private final Map mappings = new HashMap();

   public void addMapping(K key, V value) {
      mappings.put(key, value);
   }

   public Map getMappings() {
      return Collections.unmodifiableMap(mappings);
   }
}

Then, write a class which registers a mapping with the registry:

public class MappingRegistrar {

   private final MappingRegistry registry;

   private K key;
   private V value;

   @Autowired
   public MappingRegistrar(MappingRegistry registry) {
      this.registry = registry;
   }

   public void setKey(K key) {
      this.key = key;
   }

   public void setValue(V value) {
      this.value = value;
   }

   @PostConstruct
   public void registerMapping() {
      registry.addMapping(key, value);
   }
}

The your config becomes something like this:

These mappings can now be scattered throughout your config in any way you see fit, and they will self-assemble. ExampleServcie is then injected with the MappingRegistry and extracts the mappings accordingly.

It's a bit more work than what you already have, but it's a lot more flexible and less error prone. This is particularly valuable if you're trying to build an extensible framework of some kind; you want to put fewer constraints on how people use it.