Spring Boot中Groovy DSL如何注入Autowired Bean？

场景说明 #

你正在运行一个依赖AWS的Spring Boot Java应用，使用Groovy实现DSL，需要在DSL的send()方法中调用Spring容器里的SNSService Bean。

期望的DSL用法 #

sendNotification{
  topic 'topic'
  payload 'payload'
  send()
}

现有代码 #

Groovy DSL类（src/main/groovy）

class SNSDsl{
  String topic
  String payload
  void topic(String topic) {
    this.topic = topic
  }
  void payload(String payload) {
    this.payload = payload
  }

  void send(){
    // 需要调用SNSService的sendNotification方法
  }
}

Spring服务类（src/main/java）

@Named
public class SNSService {
  private final SnsOperations snsOperations;
  
  SNSService (SnsOperations snsOperations){
    this.snsOperations = snsOperations;
  }
  
  public void sendNotification(final String payload, final String topic) {
        SnsNotification<String> notification = SnsNotification.builder(payload)
                .build();
        snsOperations.sendNotification(topic, notification);
    }
}

解决方案 #

Spring的依赖注入仅对容器内管理的Bean生效，这里提供两种可行方案：

方案一：将SNSDsl声明为Spring Bean，通过构造器注入SNSService #

直接把SNSDsl纳入Spring容器管理，利用构造器注入SNSService，就能在send()方法中直接调用：

修改后的SNSDsl：

import org.springframework.stereotype.Component
import javax.inject.Inject

@Component
class SNSDsl{
  String topic
  String payload
  private final SNSService snsService

  // 构造器注入SNSService
  @Inject
  SNSDsl(SNSService snsService) {
    this.snsService = snsService
  }

  void topic(String topic) {
    this.topic = topic
  }

  void payload(String payload) {
    this.payload = payload
  }

  void send(){
    snsService.sendNotification(payload, topic)
  }
}

定义DSL入口方法（Spring Bean），用来启动DSL上下文：

import org.springframework.stereotype.Component
import javax.inject.Inject

@Component
class SNSDslExecutor {
  private final SNSDsl snsDsl

  @Inject
  SNSDslExecutor(SNSDsl snsDsl) {
    this.snsDsl = snsDsl
  }

  void sendNotification(@DelegatesTo(SNSDsl) Closure closure) {
    closure.delegate = snsDsl
    closure.resolveStrategy = Closure.DELEGATE_FIRST
    closure.call()
  }
}

之后在任意Spring管理的Bean中注入SNSDslExecutor，即可使用期望的DSL语法：

// 在某个Spring Bean中
@Inject
private SNSDslExecutor dslExecutor

// 使用DSL
dslExecutor.sendNotification {
  topic 'my-topic'
  payload 'hello-world'
  send()
}

方案二：手动传递SNSService到SNSDsl实例（不将SNSDsl纳入Spring容器） #

如果不想让SNSDsl成为Spring Bean，可以在创建DSL实例时手动传入容器中的SNSService：

修改SNSDsl，添加带参数的构造器：

class SNSDsl{
  String topic
  String payload
  private final SNSService snsService

  SNSDsl(SNSService snsService) {
    this.snsService = snsService
  }

  void topic(String topic) {
    this.topic = topic
  }

  void payload(String payload) {
    this.payload = payload
  }

  void send(){
    snsService.sendNotification(payload, topic)
  }
}

定义DSL入口，从Spring容器获取SNSService并传递给SNSDsl：

import org.springframework.stereotype.Component
import javax.inject.Inject

@Component
class SNSDslExecutor {
  private final SNSService snsService

  @Inject
  SNSDslExecutor(SNSService snsService) {
    this.snsService = snsService
  }

  void sendNotification(@DelegatesTo(SNSDsl) Closure closure) {
    def snsDsl = new SNSDsl(snsService)
    closure.delegate = snsDsl
    closure.resolveStrategy = Closure.DELEGATE_FIRST
    closure.call()
  }
}

使用方式和方案一完全一致，注入SNSDslExecutor即可调用DSL。

内容的提问来源于stack exchange，提问作者Pranesh Radhakrishnan