Spring中的多种实现

Question

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

@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

@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.
            }
        }
    }
}

@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);
            }
        }

我得到一个错误，如:org.springframework.beans.factory.UnsatisfiedDependencyException：创建名为“topic serviceimpl”的bean时出错：通过字段“topic generators”表示的未满足的依赖项；嵌套异常为org.springframework.beans.factory.NoSuchBeanDefinitionException：没有“java.util.list ”类型的合格bean可用：至少需要一个合格的自动候选bean。依赖项注释：{@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个实现中的一个之前添加@service，代码正在工作，但这不是我想要的。）

Answer 1

可以定义list 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);
    }
}

这样，您的原始代码就可以正常工作了。

bean可以用它们各自的类名的camelCase来引用。例如，cppTopicGenerator将引用类cppTopicGenerator.java的bean。虽然使用@qualifier更清晰是一个好的做法。