Spring – How to use spring annotations like @Autowired in kotlin

kotlinspring

Is it possible to do something like following in Kotlin?

@Autowired
internal var mongoTemplate: MongoTemplate

@Autowired
internal var solrClient: SolrClient

Best Answer

Recommended approach to do Dependency Injection in Spring is constructor injection:

@Component
class YourBean(
    private val mongoTemplate: MongoTemplate, 
    private val solrClient: SolrClient
) {
  // code
}

Prior to Spring 4.3 constructor should be explicitly annotated with Autowired:

@Component
class YourBean @Autowired constructor(
    private val mongoTemplate: MongoTemplate, 
    private val solrClient: SolrClient
) {
  // code
}

In rare cases, you might like to use field injection, and you can do it with the help of lateinit:

@Component
class YourBean {

    @Autowired
    private lateinit var mongoTemplate: MongoTemplate

    @Autowired
    private lateinit var solrClient: SolrClient
}

Constructor injection checks all dependencies at bean creation time and all injected fields is val, at other hand lateinit injected fields can be only var, and have little runtime overhead. And to test class with constructor, you don't need reflection.

Links:

  1. Documentation on lateinit
  2. Documentation on constructors
  3. Developing Spring Boot applications with Kotlin
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