1.定义版本注解

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Mapping
public @interface ApiVersion {
    String value();
}

2.自定义HandlerMapping

public class CustomRequestMappingHandlerMapping extends RequestMappingHandlerMapping {

    @Override   // ①
    protected RequestCondition<ApiVesrsionCondition> getCustomTypeCondition(Class<?> handlerType) {
        ApiVersion apiVersion = AnnotationUtils.findAnnotation(handlerType, ApiVersion.class);
        return createCondition(apiVersion);
    }

    @Override  //②
    protected RequestCondition<ApiVesrsionCondition> getCustomMethodCondition(Method method) {
        ApiVersion apiVersion = AnnotationUtils.findAnnotation(method, ApiVersion.class);
        return createCondition(apiVersion);
    }
    //③  实例化RequestCondition
    private RequestCondition<ApiVesrsionCondition> createCondition(ApiVersion apiVersion) {
        return apiVersion == null ? null : new ApiVesrsionCondition(apiVersion.value());
    }

}

我们知道，光定义注解是没什么用的，重要的是我们识别到注解，做相应的事。RequestMappingHandlerMapping类是与 @RequestMapping相关的，它定义映射的规则。即满足怎样的条件则映射到那个接口上。

  ①处构建类级的映射要求，AnnotationUtils.findAnnotation根据在类上面的注解实例化一个注解类。然后构造RequestCondition。

  ②处构建类级的映射要求，AnnotationUtils.findAnnotation根据在方法上面的注解实例化一个注解类。然后构造RequestCondition。 AnnotationUtils.findAnnotation是用到Spring的工具类，根据标注的注解识别注解。很方便，比通过反射的方式来找到注解要方便。

3.自定义条件匹配

public class ApiVersionCondition implements RequestCondition<ApiVersionCondition> {

    // Header中版本号名称
    private final static String API_VERSION = "apiVersion";

    private final static String VERSION_SEPATATOR = ".";

    // 路径中版本的前缀， 这里用 /v[1-9]/的形式
    private final static String VERSION_PREFIX_PATTERN = "(\\d+)(.\\d+)*";

    private String apiVersion;

    public ApiVersionCondition(String apiVersion) {
        this.apiVersion = apiVersion;
    }

    @Override
    public ApiVersionCondition combine(ApiVersionCondition other) {
        // 采用最后定义优先原则，则方法上的定义覆盖类上面的定义
        return new ApiVersionCondition(other.getApiVersion());
    }

    @Override
    @Nullable
    public ApiVersionCondition getMatchingCondition(HttpServletRequest request) {
        String apiVersion = request.getHeader(API_VERSION);

        if (StringUtils.isBlank(apiVersion) || !apiVersion.matches(VERSION_PREFIX_PATTERN)) {
            return null;
        }

        if (convertNumber(apiVersion) == convertNumber(this.apiVersion)) {
            return this;
        }

        return null;
    }

    @Override
    public int compareTo(ApiVersionCondition other, HttpServletRequest request) {
        // 优先匹配最新的版本号
        return convertNumber(other.getApiVersion()) - convertNumber(this.apiVersion);
    }

    public String getApiVersion() {
        return apiVersion;
    }


    private int convertNumber(String version) {
        return Integer.parseInt(version.replace(VERSION_SEPATATOR, ""));
    }
}

4.自定义条件匹配

最后则是需要将我们的 HandlerMapping 注册到 Spring MVC 容器，在这里我们借助WebMvcConfigurationSupport来手动注册，如下：

@Configuration
public class WebMvcConfig extends WebMvcConfigurationSupport {

    @Override
    @Bean
    public RequestMappingHandlerMapping requestMappingHandlerMapping() {
        RequestMappingHandlerMapping handlerMapping = new CustomRequestMappingHandlerMapping();
        handlerMapping.setOrder(0);
        handlerMapping.setInterceptors(getInterceptors());
        return handlerMapping;
    }
}

测试

定义几个接口，用于区分不同的版本，如下：

    @ApiVersion("1.0.1")
    @GetMapping("/test")
    public String test1(){
        log.info("版本控制测试！");
        return "V1测试成功";
    }


    @ApiVersion("1.0.2")
    @GetMapping("/test")
    public String test2(){
        log.info("版本控制测试！");
        return "V2测试成功";
    }

启动服务，请求localhost:8080/test, Header中携带版本号1.0.1, test1执行。Header中携带版本号1.0.2, test2执行。