springboot版本控制

HandlerMapping通过继承InitializingBean接口在完成实例后，扫描所有的Controller和标识RequestMapping的方法，缓存这个映射对应关系。然后在应用运行的时候，根据请求的request来找到相应的handler来处理这个请求。在这里，我们添加扩展类：

• ApiVersion
• ApiVesrsionCondition
• CustomRequestMappingHandlerMapping
• WebConfig

现分别来看下这个类，首先看下ApiVersion这个注解：

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Mapping
public @interface ApiVersion {
    /**
     * 版本号
     * @return
     */
    int value();
}

这个注解用来标识某个类或者方法要处理的对应版本号，使用如下：

@Controller
@RequestMapping("/{version}/")
public class HelloController {

    @RequestMapping("hello/")
    @ApiVersion(1)
    @ResponseBody
    public String hello(HttpServletRequest request){
        System.out.println("haha1..........");

        return "hello";
    }

    @RequestMapping("hello/")
    @ApiVersion(2)
    @ResponseBody
    public String hello2(HttpServletRequest request){
        System.out.println("haha2.........");

        return "hello";
    }

    @RequestMapping("hello/")
    @ApiVersion(5)
    @ResponseBody
    public String hello5(HttpServletRequest request){
        System.out.println("haha5.........");

        return "hello";
    }
}

现在我们就可以通过 /v1/hello/, /v2/hello/, /v5/hello来分别调用版本1，2，5的管理。当然我们也要解决刚才说的两点问题，如果用户通过 /v4/hello/来访问接口，则要自动适配到 /v2/hello/，因为 v2是比v4低的版本中最新的版本。

再来看下 ApiVersionCondition 这个类。这个类就是我们自定义一个条件筛选器，让SpringMVC在原有逻辑的基本上添加一个版本号匹配的规则：

public class ApiVesrsionCondition implements RequestCondition<ApiVesrsionCondition> {

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

    private int apiVersion;

    public ApiVesrsionCondition(int apiVersion){
        this.apiVersion = apiVersion;
    }

    public ApiVesrsionCondition combine(ApiVesrsionCondition 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 ApiVesrsionCondition(other.getApiVersion());
    }

    public ApiVesrsionCondition getMatchingCondition(HttpServletRequest request) {
        Matcher m = VERSION_PREFIX_PATTERN.matcher(request.getPathInfo());
        if(m.find()){
            Integer version = Integer.valueOf(m.group(1));
            if(version >= this.apiVersion) // 如果请求的版本号大于配置版本号， 则满足
                return this;
        }
        return null;
    }

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

    public int getApiVersion() {
        return apiVersion;
    }

}

要把这个筛选规则生效的话，要扩展原胡的HandlerMapping，把这个规则设置进去生效，看下CustomRequestMappingHandlerMapping的代码：

public class CustomRequestMappingHandlerMapping extends RequestMappingHandlerMapping {

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

    @Override
    protected RequestCondition<ApiVesrsionCondition> getCustomMethodCondition(Method method) {
        ApiVersion apiVersion = AnnotationUtils.findAnnotation(method, ApiVersion.class);
        return createCondition(apiVersion);
    }

    private RequestCondition<ApiVesrsionCondition> createCondition(ApiVersion apiVersion) {
        return apiVersion == null ? null : new ApiVesrsionCondition(apiVersion.value());
    }
}

最后，得让SpringMVC加载我们定义的CustomRequestMappingHandlerMapping以覆盖原先的RequestMappingHandlerMapping, 所以要去掉前面说的<mvc:annotation-driven/>这个配置，我们通过JavaConfig的方式注入：

@Configuration
public class WebConfig extends WebMvcConfigurationSupport{

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