微信公众平台接入之简单任务分发器

　　微信公众号现在影响力有目共睹，所以接入其功能也是很正常的。

　　现在的应用中，有很多是基于spring的框架来做的。针对自行开发的系统，我们可以通过任意的自定义 url 来进行业务功能的映射。然而大家知道，微信的回调地址永远只有一个，但是其内部的内容则是多样的。针对不同的内容，咱们做出的响应自然也是不一样的。咱们可以通过n个if...else 区分出需要处理的业务。但是这样的代码会很不清晰，维护起来将是噩梦。所以，咱们有必要根据内容来做一个业务功能的分发，使代码能够更清晰。

　　只需要一个简单的 mapping 就可以了。

比如，我们可以配置一个微信回调地址: http://a.bc.com/xxx/wxcallback

我们需要响应两种类型的请求，一个是 get 请求，进行服务验证，一个是 post 请求，进行业务事件通知！demo 如下：

    @RequestMapping(value = "/{wxServiceType}/wxcallback", method = RequestMethod.GET, produces = "text/html")
    @ResponseBody
    public String gatewayGet(@ModelAttribute WxTokenVerifyReqModel verifyReqModel, @PathVariable(value = "wxServiceType") String wxServiceType) {
        log.info("请求token:{}", verifyReqModel);
        try {
            String reply = serverValidateService.validServerToken(verifyReqModel, WxGatewayServiceKeyEnum.xxx);
            log.info("成功返回:{}", reply);
            return reply;
        } catch (WeixinSystemException e) {
            log.warn("验证失败, code:{}, msg:{}", e.errCode, e.message);
            return "fail";
        } catch (Exception e) {
            log.error("微信校验接口异常error=", e);
            throw new RuntimeException(e);
        }
    }

    /**
     * 公众号主要消息请求入口
     *
     * @param req  请求， xml 格式
     * @param resp 响应
     * @return 按格式返回
     */
    @RequestMapping(value = "/{wxServiceType}/wxcallback", method = RequestMethod.POST, produces = "application/xml; charset=utf-8")
    @ResponseBody
    public String gatewayPost(HttpServletRequest req, HttpServletResponse resp, @PathVariable(value = "wxServiceType") String wxServiceType) throws IOException {

        try {
            // 交给内部分发器处理，返回处理结果
            Object retMessage = wxMessageHandleDispatcher.handle(req, wxServiceType);
            if (null != retMessage) {
                return retMessage.toString();
            }
        }
        catch (DocumentException | IOException e) {
            log.error("参数解析异常", e);
        } catch (Exception e) {
            log.error("其他异常,", e);
        }
        return "success";
    }

　　第一个token验证，与springmvc的普通模式一样，直接通过 ServletModelAttributeMethodProcessor 参数解析器给解析了。

　　所以,咱们只需处理 xml 的正文请求即可！即如下分发：

Object retMessage = wxMessageHandleDispatcher.handle(req, wxServiceType);

分发入口类：

@Component
public class WxMessageHandleDispatcher {

    @Resource
    private WxMessageHandlerMappingBean wxMessageHandlerMappingBean;

    /**
     * 请求编号，可用于统计当日访问量
     */
    private AtomicInteger requestSeqNum = new AtomicInteger(0);

    /**
     * 服务标识
     */
    private static final ThreadLocal<WxGatewayServiceKeyEnum> gatewayServiceKeyHolder = new ThreadLocal<>();

    /**
     * 处理微信消息响应入口
     *
     * @param request xml
     * @return 返回结果
     * @throws RuntimeException
     * @apiNote {@link WxMessageBaseReqModel}
     */
    public Object handle(HttpServletRequest request, WxGatewayServiceKeyEnum serviceKey)
            throws DocumentException, IOException, RuntimeException {
        Long startTime = System.currentTimeMillis();
        // 处理参数
        Map<String, String> parameters = extractRequestParams(request);

        // 初始化基础环境
        prepareGatewayServiceHandle(serviceKey);

        // 转换为 uri
        String handleUri = exchangeHandleUri(parameters, serviceKey);
        log.info("【微信消息处理】enter {} method, params: {}, serviceKey:{}, seqNum:{}", handleUri, JSONObject.toJSONString(parameters), serviceKey, requestSeqNum.get());

        Object retMessage = null;

        try {
            // 调用 handleMethod
            retMessage = invokeHandleMethod(parameters, handleUri);
        }
        // 业务异常，看情况捕获
        catch (WeixinSystemException e) {
            log.warn("@{} 发生业务异常:code:{}, msg:{}", handleUri, e.errCode, e.message);
            throw e;
        }
        // 其他异常
        catch (Exception e) {
            log.error("处理方法" + handleUri + " 发生异常", e);
        }
        // 最终打印
        finally {
            log.info("exit {} method, params: {}, result:{}, serviceKey:{}, seqNum:{}, cost:{}ms",
                    handleUri, JSONObject.toJSONString(parameters), retMessage, serviceKey,
                    requestSeqNum.get(), (System.currentTimeMillis() - startTime));
            finishGatewayServiceHandle();
        }

        return retMessage;
    }

    /**
     * 解析请求参数
     *
     * @param request 原始请求
     * @return k-v
     * @throws IOException
     * @throws DocumentException
     */
    private Map<String, String> extractRequestParams(HttpServletRequest request) throws IOException, DocumentException {
        Map<String, String> parameters = WechatMessageUtil.xmlToMap(request);
        String requestIp = NetworkUtil.getIpAddress(request);
        parameters.put("requestIp", requestIp);
        return parameters;
    }

    /**
     * 初始化 serviceKey, 供全局调用
     *
     * @param serviceKey gateway 传入 服务标识
     */
    private void prepareGatewayServiceHandle(WxGatewayServiceKeyEnum serviceKey) {
        requestSeqNum.incrementAndGet();
        gatewayServiceKeyHolder.set(serviceKey);
    }

    /**
     * 转换需要处理的 uri 资源请求
     *
     * @param parameters 原始参数
     * @param serviceKey serviceKey gateway 传入 服务标识
     * @return 如 /xxx/text
     */
    private String exchangeHandleUri(Map<String, String> parameters, WxGatewayServiceKeyEnum serviceKey) {
        String msgType = parameters.get("MsgType");
        String eventType = parameters.get("Event");
        String handleUri = serviceKey.getAlias() + "/" + msgType;
        if(eventType != null) {
            handleUri = handleUri + "/" + eventType;
        }
        return handleUri;
    }

    /**
     * 调用处理方法
     *
     * @param parameters 参数请求
     * @param handleUri uri
     * @return 处理结果
     * @throws NoSuchMethodException
     * @throws IllegalAccessException
     * @throws InvocationTargetException
     */
    private Object invokeHandleMethod(Map<String, String> parameters, String handleUri)
            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
        Object retMessage = "";     // 回复null会有bug

        // 获取handleMethod
        WxMessageRequestMappingInfo methodConfig = wxMessageHandlerMappingBean.getHandlerConfig(handleUri);

        if(methodConfig != null) {
            WxMessageHandleService handleService = (WxMessageHandleService) SpringContextsUtil.getBean(methodConfig.getHandlerClz());
            WxMessageBaseReqModel paramsToHandle = (WxMessageBaseReqModel) JSONObject.parseObject(JSONObject.toJSONString(parameters), methodConfig.getParamClz());
            if(StringUtils.isBlank(methodConfig.getMethodName())) {
                retMessage = handleService.handle(paramsToHandle);
            }
            else {
                String methodName = methodConfig.getMethodName();
                retMessage = MethodUtils.invokeExactMethod(handleService, methodName, paramsToHandle);
            }
        }
        else {
            log.info("【微信消息处理】no handler found for {}", handleUri);
        }
        return retMessage;
    }

    /**
     * 获取gateway 进来的 serviceKey
     *
     * @return 自拥有的 serviceKey 服务标识
     */
    public WxGatewayServiceKeyEnum getGatewayServiceKey() {
        return gatewayServiceKeyHolder.get();
    }

    /**
     * 操作完成后，重置 serviceKey
     */
    private void finishGatewayServiceHandle() {
        gatewayServiceKeyHolder.remove();
    }
}

如上分发类，主要做一主体的操作，如参数解析，uri 重新获取，实际业务方法的调用等；
所以，关键点还是在于怎么调用业务方法？
首先，看一下业务方法配置的获取：

 WxMessageHandlerMethodEnum methodConfig = wxMessageHandlerMappingBean.getHandlerConfig(handleUri);

@Component
@Slf4j
public class WxMessageHandlerMappingBean implements InitializingBean, BeanNameAware,
        ApplicationContextAware {

    /**
     * 直接匹配的mapping
     */
    private final Map<String, WxMessageRequestMappingInfo> directHandlerMappings = new ConcurrentHashMap<>();

    /**
     * 使用正则匹配的mapping
     */
    private final Map<String, WxMessageRequestMappingInfo> patternHandlerMappings = new HashMap<>();

    // spring 式的 mapping
    private final Map<WxMessageRequestMappingInfo, HandlerMethod> springPatternMethodMappings = new ConcurrentHashMap<>();

    private transient String beanName;

    private transient ApplicationContext applicationContext;

    public void setBeanName(String name) {
        this.beanName = name;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }
    /**
     * 获取处理方法配置，主要为处理类
     *     先精确匹配，不行再用正则匹配一次
     *
     * @param messageHandleUri uri,如 xxx/text
     * @return 处理类，一般需继承 {@link com.mobanker.weixin.dae.service.WxMessageHandleService}
     */
    public final WxMessageRequestMappingInfo getHandlerConfig(String messageHandleUri) {
        // 直接匹配
        WxMessageRequestMappingInfo handlerMethodConfig = directHandlerMappings.get(messageHandleUri);
        if(handlerMethodConfig != null) {
            return handlerMethodConfig;
        }
        // 正则匹配
        handlerMethodConfig = getPatternHandlerMapping(messageHandleUri);
        if(handlerMethodConfig != null) {
            return handlerMethodConfig;
        }
        return null;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        // 扫描处理方法
        initHandlerMethods();
    }

    /**
     * 正则路由注册
     *
     * @param methodConfig 路由配置
     */
    private void registerPatternHandlerMapping(WxMessageRequestMappingInfo methodConfig) {
        Pattern normalUriPattern = Pattern.compile("^[a-zA-Z0-9/\-_:\$]+$");
        if(!normalUriPattern.matcher(methodConfig.getLookup()).matches()) {
            String patternedUri = methodConfig.getLookup().replace("*", ".*");
            patternHandlerMappings.put(patternedUri, methodConfig);
        }
    }

    /**
     * 正则路由匹配
     *
     * @param messageHandleUri 如 xxx/event/(VIEW|CLICK)
     * @return 匹配到的方法或者 null
     */
    private WxMessageRequestMappingInfo getPatternHandlerMapping(String messageHandleUri) {
        for (Map.Entry<String, WxMessageRequestMappingInfo> config1 : patternHandlerMappings.entrySet()) {
            Pattern uriPattern = Pattern.compile(config1.getKey());
            if(uriPattern.matcher(messageHandleUri).matches()) {
                return config1.getValue();
            }
        }
        return null;
    }
    protected ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    /**
     * Scan beans in the ApplicationContext, detect and register handler methods.
     * @see #isWxMessageHandler(Class)
     * @see #getMappingForMethod(Method, Class)
     */
    protected void initHandlerMethods() {
        if (log.isDebugEnabled()) {
            log.debug("Looking for request mappings in application context: " + getApplicationContext());
        }

        String[] beanNames =
                getApplicationContext().getBeanNamesForType(Object.class);

        for (String beanName : beanNames) {
            if (isWxMessageHandler(getApplicationContext().getType(beanName))){
                detectHandlerMethods(beanName);
            }
        }

    }

    protected boolean isWxMessageHandler(Class<?> beanType) {
        return ((AnnotationUtils.findAnnotation(beanType, WxMessageHandler.class) != null));
    }

    /**
     * Look for handler methods in a handler.
     * @param handler the bean name of a handler or a handler instance
     */
    protected void detectHandlerMethods(final Object handler) {
        Class<?> handlerType =
                (handler instanceof String ? getApplicationContext().getType((String) handler) : handler.getClass());

        // Avoid repeated calls to getMappingForMethod which would rebuild RequestMappingInfo instances
        final Map<Method, WxMessageRequestMappingInfo> mappings = new IdentityHashMap<>();
        final Class<?> userType = ClassUtils.getUserClass(handlerType);

        Set<Method> methods = MethodIntrospector.selectMethods(userType, new ReflectionUtils.MethodFilter() {
            @Override
            public boolean matches(Method method) {
                WxMessageRequestMappingInfo mapping = getMappingForMethod(method, userType);
                if (mapping != null) {
                    mappings.put(method, mapping);
                    return true;
                }
                else {
                    return false;
                }
            }
        });

        for (Method method : methods) {
            registerHandlerMethod(handler, method, mappings.get(method));
        }
    }

    /**
     * Uses method and type-level @{@link RequestMapping} annotations to create
     * the RequestMappingInfo.
     * @return the created RequestMappingInfo, or {@code null} if the method
     * does not have a {@code @RequestMapping} annotation.
     */
    protected WxMessageRequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
        WxMessageRequestMappingInfo info = null;
        WxMessageRequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, WxMessageRequestMapping.class);
        if (methodAnnotation != null) {
            info = createRequestMappingInfo(methodAnnotation, handlerType, method);
        }
        return info;
    }

    /**
     * Created a RequestMappingInfo from a RequestMapping annotation.
     */
    protected WxMessageRequestMappingInfo createRequestMappingInfo(WxMessageRequestMapping annotation,
                                                                   Class<?> handlerType, Method method) {
        String uri = annotation.value();
        return new WxMessageRequestMappingInfo(
                uri,
                handlerType,
                method.getName(),
                method.getParameterTypes()[0],
                "auto gen"
        );
    }


    /**
     * Register a handler method and its unique mapping.
     * @param handler the bean name of the handler or the handler instance
     * @param method the method to register
     * @param mapping the mapping conditions associated with the handler method
     * @throws IllegalStateException if another method was already registered
     * under the same mapping
     */
    protected void registerHandlerMethod(Object handler, Method method, WxMessageRequestMappingInfo mapping) {
        // old gen
        this.directHandlerMappings.put(mapping.getLookup(), mapping);
        registerPatternHandlerMapping(mapping);

        // new gen
        HandlerMethod handlerMethod = createHandlerMethod(handler, method);
        springPatternMethodMappings.put(mapping, handlerMethod);

        log.info("Mapped WxMessageHandler {}", mapping);
    }


    protected HandlerMethod createHandlerMethod(Object handler, Method method) {
        HandlerMethod handlerMethod;
        if (handler instanceof String) {
            String beanName = (String) handler;
            handlerMethod = new HandlerMethod(beanName,
                    getApplicationContext().getAutowireCapableBeanFactory(), method);
        }
        else {
            handlerMethod = new HandlerMethod(handler, method);
        }
        return handlerMethod;
    }

}

handler 的注解配置如下：

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface WxMessageHandler {


    /**
     * 路由映射 url
     *
     * @return 如: xxx/text
     */
    String value() default "";

}

路由配置 requestMapping 如下：

public class WxMessageRequestMappingInfo {

    /**
     * 消息处理路由
     */
    private String lookup;

    /**
     * 处理类，调用期 handle 方法*/
    private Class<?> handlerClz;

    /**
     * 处理方法名称
     */
    private String methodName;

    /**
     * 方法参数
     */
    private Class<?> paramClz;

    /**
     * 备注
     */
    private String remark;


    public WxMessageRequestMappingInfo(String lookup, @NotNull Class<?> handlerClz, String methodName,
                                       Class<?> paramClz, String remark) {
        this.lookup = lookup;
        this.handlerClz = handlerClz;
        this.methodName = methodName;
        this.paramClz = paramClz;
        this.remark = remark;
    }

    public String getLookup() {
        return lookup;
    }

    public Class<?> getHandlerClz() {
        return handlerClz;
    }

    public String getMethodName() {
        return methodName;
    }

    public Class<?> getParamClz() {
        return paramClz;
    }

    public String getRemark() {
        return remark;
    }

    @Override
    public String toString() {
        return ""{[" + lookup + "]}" onto @" + handlerClz.getName() + "#" + methodName + " : " + remark;
    }
}

使用时，只需在类上添加注解 @WxMessageHandler 即可：

@WxMessageHandler

在方法上加上 路由注解即可： 

    @WxMessageRequestMapping(value = "xxx/event/subscribe")

如：

@WxMessageHandler
public class SxkEventPushServiceImpl implements WxEventPushHandleService {

    @WxMessageRequestMapping(value = "xxx/event/subscribe")
    @Override
    public Object subscribe(WxEventPushSubscribeReqModel reqModel) {
        System.out.println("hello, welcome.")
        return "hello, welcome.";
    }
}

　　方法配置做两件事：

　　1. 在启动时，将hander 添加的 mappings 中；

　　2. 在使用时，从mappings 中获取 handler 信息；

其实现原理与 spring 的 handlerMappings 类似！

　　这里的参数解析，只处理了第一个参数，假设方法只能使用一个参数！

　　找到处理方法后，就可以进行反射调用了！