Spring中的多种实现

Question

我有 TopicGenerator 接口：

public interface TopicGenerator {
    File create(MultiValueMap params);
    boolean accept(MultiValueMap params);
}

还有 3 个实现：

@RequiredArgsConstructor
public class JavaTopicGenerator implements TopicGenerator {
//implementation ommited for readability

@RequiredArgsConstructor
public class PhpTopicGenerator implements TopicGenerator {
//implementation ommited for readability

@RequiredArgsConstructor
public class CppTopicGenerator implements TopicGenerator {
//implementation ommited for readability

现在我尝试做的是根据我的参数使用它们，这就是我创建特殊 TopicFacade 的原因。

@RequiredArgsConstructor
public class TopicFacade {

    @NonNull
    private final TopicService topicService;

    @NonNull
    private final List<TopicGenerator> topicGenerators;

    public void generate(MultiValueMap<String, String> params, HttpServletResponse response) {
        for (TopicGenerator topicGenerator : topicGenerators) {
            if (topicGenerator.accept(params)) {
                File tempFile = topicService.generate(params);
                //do something else.
            }
        }
    }
}

在我的 TopicServiceImpl 上我有什么：

@Service
@RequiredArgsConstructor
public class TopicServiceImpl implements TopicService {

    @NonNull
    private final List<TopicGenerator> reportGenerators;

        public File generate(MultiValueMap params) {
        for (TopicGenerator topicGenerator : topicGenerators) {
            if (topicGenerator.create(params)) {
                return topicGenerator.export(params);
            }
        }

我收到如下错误： Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'topicServiceImpl': Unsatisfied dependency expressed through field 'topicGenerators'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'java.util.List<com.topic.service.TopicGenerator>' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

（早些时候，当我使用字段注入而不是构造函数时，我能够在 3 个实现之一之前添加 @Service，并且代码正在处理该单个实现，但它不是我想要的）

Answer 1

可以定义List<TopicGenerator> 类型的bean，如下所示：

@Configuration
public class AppConfig {

    @Autowired
    private TopicGenerator cppTopicGenerator;

    @Autowired
    private TopicGenerator phpTopicGenerator;

    @Autowired
    private TopicGenerator javaTopicGenerator;

    @Bean
    public List<TopicGenerator> topicGeneratorList()
    {
        return Arrays.asList(cppTopicGenerator, phpTopicGenerator, javaTopicGenerator);
    }
}

有了这个，你的原始代码应该可以正常工作了。

Beans 可以用它们各自的 Class Name 的 camelCase 来引用。例如cppTopicGenerator 将引用 CppTopicGenerator.java 类的 bean。虽然使用@Qualifier 更清楚是一种好习惯。

Answer 2

使用限定符注释。 https://www.tutorialspoint.com/spring/spring_qualifier_annotation.htm

https://stackoverflow.com/a/40844528/4587961

那么你的 Facade 就可以拥有所有这些实现。而且您有一个方法可以根据您的条件返回特定的实现。

然后在自动装配所有依赖项后初始化列表。 https://stackoverflow.com/a/8519295/4587961

@Service // Try and play around with annotations.
public class TopicFacade {

    @Autowired
    @Qualifier("Service1")
    private final TopicService topicService1;

    //... The same stuff for other services.

    @Autowired
    @Qualifier("ServiceN")
    private final TopicService topicServiceN;

    //Initialize this in the post construct and put all your services there.
    @NonNull
    private final List<TopicGenerator> topicGenerators = new ArrayList();

    @PostConstruct
    public void initTopicGenerators() throws Exception {
        topicGenerators.add(topicService1);
        //And others.
        topicGenerators.add(topicServiceN);
    }

    public void generate(MultiValueMap<String, String> params, HttpServletResponse response) {
        for (ReportGenerator reportGenerator : reportGenerators) {
            if (reportGenerator.accept(params)) {
                File tempFile = topicService.generate(params);
                //do something else.
            }
        }
    }
}