springboot web - 建立路由

一. 测试代码

@RestController
@RequestMapping("/book")
public class BookController {

    @PostMapping("add")
    public JsonResponse<Integer> add(@Valid @RequestBody Book book, BindingResult errors){
        //1. 对 item  数据进行验证
        StringBuffer sb = new StringBuffer();
        if (errors.hasErrors()) {
            for (ObjectError objectError : errors.getAllErrors()) {
                sb.append(objectError.getDefaultMessage());
            }
        }
        if (sb.length() > 0) {
            return JsonResponse.error(sb.toString());
        }
        int id = BookDB.add(book);
        return JsonResponse.success(id);
    }

    @GetMapping("getById")
    public JsonResponse<Book> getById(@RequestParam("id") Integer id){
        Book book = BookDB.getById(id);
        return JsonResponse.success(book);
    }

    @GetMapping("getAll")
    public JsonResponse<List<Book>> getAll(){
        List<Book> list = BookDB.getAll();
        return JsonResponse.success(list);
    }
}

在 BookController 中, 有三个方法可以访问.

/book/add -> add()

/book/getById -> getById()

/book/getAll -> getAll()

url 和 对应的名字, 是可以不一样的, 比如 我新写个方法:

@GetMapping("byWhat")
public JsonResponse<Book> getBy(){return JsonResponse.success(null);
}

此时的对应关系就是: /book/byWhat -> getBy() 方法.

这种映射, 就是一种路由关系. 通过地址路由到方法上. 

二. 建立路由

1. 配置文件配置

DispatcherServlet.properties 文件中配置了两个路由处理类:

org.springframework.web.servlet.HandlerMapping=org.`.web.servlet.handler.BeanNameUrlHandlerMapping,\
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping

2. 配置类配置

spring-boot-autoconfigure 中, 有一块专门对 web 进行配置的类, WebMvcAutoConfiguration 是其中之一

@Bean
public SimpleUrlHandlerMapping faviconHandlerMapping() {
    SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
    mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
    mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",
            faviconRequestHandler()));
    return mapping;
}

@Bean
public ResourceHttpRequestHandler faviconRequestHandler() {
    ResourceHttpRequestHandler requestHandler = new ResourceHttpRequestHandler();
    requestHandler.setLocations(resolveFaviconLocations());
    return requestHandler;
}

3. 类图

4. SimpleUrlHandlerMapping

由于 其 祖先类  ApplicationObjectSupport 实现了 ApplicationContextAware 接口, 所以在实例化后, 会调用  setApplicationContext() 方法:

@Override
public final void setApplicationContext(@Nullable ApplicationContext context) throws BeansException {
    if (context == null && !isContextRequired()) {
        // Reset internal context state.
        this.applicationContext = null;
        this.messageSourceAccessor = null;
    }
    else if (this.applicationContext == null) {
        // Initialize with passed-in context.
        if (!requiredContextClass().isInstance(context)) {
            throw new ApplicationContextException(
                    "Invalid application context: needs to be of type [" + requiredContextClass().getName() + "]");
        }
        this.applicationContext = context;
        this.messageSourceAccessor = new MessageSourceAccessor(context);
        initApplicationContext(context);
    }
    else {
        // Ignore reinitialization if same context passed in.
        if (this.applicationContext != context) {
            throw new ApplicationContextException(
                    "Cannot reinitialize with different application context: current one is [" +
                    this.applicationContext + "], passed-in one is [" + context + "]");
        }
    }
}

protected void initApplicationContext(ApplicationContext context) throws BeansException {
    initApplicationContext();
}

//空方法, 被子类重写
protected void initApplicationContext() throws BeansException {
}

SimpleUrlHandlerMapping 重写了  initApplicationContext 方法:

@Override
public void initApplicationContext() throws BeansException {
　　//此处调用了 AbstractHandlerMapping 中的方法
    super.initApplicationContext();
    registerHandlers(this.urlMap);
}

protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
    if (urlMap.isEmpty()) {
        logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
    }
    else {
        urlMap.forEach((url, handler) -> {
            // Prepend with slash if not already present.
            if (!url.startsWith("/")) {
                url = "/" + url;
            }
            // Remove whitespace from handler bean name.
            if (handler instanceof String) {
                handler = ((String) handler).trim();
            }
            registerHandler(url, handler);
        });
    }
}

在 faviconHandlerMapping() 中, 设置了 urlMap, 经过上面的方法后, 其关系为

/**/favicon.ico -> ResourceHttpRequestHandler

然后对其进行注册:

protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
    Assert.notNull(urlPath, "URL path must not be null");
    Assert.notNull(handler, "Handler object must not be null");
    Object resolvedHandler = handler;

    // Eagerly resolve handler if referencing singleton via name.
    if (!this.lazyInitHandlers && handler instanceof String) {
        String handlerName = (String) handler;
        ApplicationContext applicationContext = obtainApplicationContext();
        if (applicationContext.isSingleton(handlerName)) {
            resolvedHandler = applicationContext.getBean(handlerName);
        }
    }

    Object mappedHandler = this.handlerMap.get(urlPath);
    if (mappedHandler != null) {
        if (mappedHandler != resolvedHandler) {
            throw new IllegalStateException(
                    "Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
                    "]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
        }
    }
    else {
        if (urlPath.equals("/")) {
            if (logger.isInfoEnabled()) {
                logger.info("Root mapping to " + getHandlerDescription(handler));
            }
            setRootHandler(resolvedHandler);
        }
        else if (urlPath.equals("/*")) {
            if (logger.isInfoEnabled()) {
                logger.info("Default mapping to " + getHandlerDescription(handler));
            }
            setDefaultHandler(resolvedHandler);
        }
        else {
            this.handlerMap.put(urlPath, resolvedHandler);
            if (logger.isInfoEnabled()) {
                logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
            }
        }
    }
}

5. BeanNameUrlHandlerMapping

这个类并没有重写   initApplicationContext() 方法. 但是他的父类 AbstractDetectingUrlHandlerMapping 重写了此方法:

@Override
public void initApplicationContext() throws ApplicationContextException {
    super.initApplicationContext();
    detectHandlers();
}

protected void detectHandlers() throws BeansException {
    ApplicationContext applicationContext = obtainApplicationContext();
    if (logger.isDebugEnabled()) {
        logger.debug("Looking for URL mappings in application context: " + applicationContext);
    }
　　 //拿取容器中所有的 bean
    String[] beanNames = (this.detectHandlersInAncestorContexts ?
            BeanFactoryUtils.beanNamesForTypeIncludingAncestors(applicationContext, Object.class) :
            applicationContext.getBeanNamesForType(Object.class));

    //遍历容器中所有的 bean, 按照规则, 进行 urls 的生成工作
    // Take any bean name that we can determine URLs for.
    for (String beanName : beanNames) {
　　　　 //这个是一个抽象方法, 留给子类BeanNameUrlHandlerMapping实现的
        String[] urls = determineUrlsForHandler(beanName);
        if (!ObjectUtils.isEmpty(urls)) {
            // URL paths found: Let's consider it a handler.
            registerHandler(urls, beanName);
        }
        else {
            if (logger.isDebugEnabled()) {
                logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
            }
        }
    }
}

接着看一下  BeanNameUrlHandlerMapping 里的方法:

public class BeanNameUrlHandlerMapping extends AbstractDetectingUrlHandlerMapping {

    /**
     * Checks name and aliases of the given bean for URLs, starting with "/".
     */
    @Override
    protected String[] determineUrlsForHandler(String beanName) {
        List<String> urls = new ArrayList<>();
        if (beanName.startsWith("/")) {
            urls.add(beanName);
        }
        String[] aliases = obtainApplicationContext().getAliases(beanName);
        for (String alias : aliases) {
            if (alias.startsWith("/")) {
                urls.add(alias);
            }
        }
        return StringUtils.toStringArray(urls);
    }
}

determineUrlsForHandler 实现了父类留的坑, 此处主要是检测 beanName 或其别名 是否是以 "/" 开头的, 如果是, 则对其执行注册方法 registerHandler(与前面4里是同一个方法). 

在此例中, 并没有 beanName 是以 "/" 开头的, 所以这里并没有进行任何注册操作.

6. RequestMappingHandlerMapping

RequestMappingHandlerMapping 并不是通过 initApplicationContext() 来进行扫描触发的.

其祖先类 AbstractHandlerMethodMapping 实现了 InitializingBean 接口, 也就是说, 在属性设置后, 会调用其 afterPropertiesSet() 方法.

但是  RequestMappingHandlerMapping 重写了 afterPropertiesSet() 方法:

@Override
public void afterPropertiesSet() {
    this.config = new RequestMappingInfo.BuilderConfiguration();
    this.config.setUrlPathHelper(getUrlPathHelper());
    this.config.setPathMatcher(getPathMatcher());
    this.config.setSuffixPatternMatch(this.useSuffixPatternMatch);
    this.config.setTrailingSlashMatch(this.useTrailingSlashMatch);
    this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch);
    this.config.setContentNegotiationManager(getContentNegotiationManager());

    super.afterPropertiesSet();
}

super.afterPropertiesSet() 调用的就是 AbstractHandlerMethodMapping 的方法了.

@Override
public void afterPropertiesSet() {
    initHandlerMethods();
}

private static final String SCOPED_TARGET_NAME_PREFIX = "scopedTarget.";

protected void initHandlerMethods() {
    if (logger.isDebugEnabled()) {
        logger.debug("Looking for request mappings in application context: " + getApplicationContext());
    }
    //获取容器中所有的 beanName
    String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
            BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
            obtainApplicationContext().getBeanNamesForType(Object.class));

　　//遍历 beanName
    for (String beanName : beanNames) {
　　　　　　//判断 beanName是否以 scopedTarget. 开头
        if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
            Class<?> beanType = null;
            try {
                beanType = obtainApplicationContext().getType(beanName);
            }
            catch (Throwable ex) {
                // An unresolvable bean type, probably from a lazy bean - let's ignore it.
                if (logger.isDebugEnabled()) {
                    logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);
                }
            }
            if (beanType != null && isHandler(beanType)) {
　　　　　　　　　　//进一步处理
                detectHandlerMethods(beanName);
            }
        }
    }
    handlerMethodsInitialized(getHandlerMethods());
}

isHandler() 是一个过滤方法, 判断 bean 是否有 Controller 或 RequestMapping 注解:

@Override
protected boolean isHandler(Class<?> beanType) {
    return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
            AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}

detectHandlerMethods() 能进来的, 此例中就 bookController 了.

protected void detectHandlerMethods(final Object handler) {
    Class<?> handlerType = (handler instanceof String ?
            obtainApplicationContext().getType((String) handler) : handler.getClass());

    if (handlerType != null) {
        final Class<?> userType = ClassUtils.getUserClass(handlerType);
        Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
                (MethodIntrospector.MetadataLookup<T>) method -> {
                    try {
                        return getMappingForMethod(method, userType);
                    }
                    catch (Throwable ex) {
                        throw new IllegalStateException("Invalid mapping on handler class [" +
                                userType.getName() + "]: " + method, ex);
                    }
                });
        if (logger.isDebugEnabled()) {
            logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
        }
        methods.forEach((method, mapping) -> {
            Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
            registerHandlerMethod(handler, invocableMethod, mapping);
        });
    }
}

methods 就是 BookController 里面的那三个方法: add , getById, getAll

查找的基本思路:

1. 拿到spring容器中所有的 beanNames

2. 遍历beanNames, 进行过滤, 过滤依据: bean上是否有  Controller 或  RequestMapping 注解修饰

3. 对 bean 进行处理, 拿到他和他所有父类中的方法

4. 对这些方法进行过滤, 过滤依据为: 方法上是否有  RequestMapping 注解修饰, 并创建 RequestMappingInfo 对象 - A.

5. 为 bean 也创建 RequestMappingInfo 对象 - B. 

　　如果 B 为空(bean上没有 RequestMappingInfo注解修饰), 则跳过合并操作

　　如果B不为空, 则对 A 和 B 进行合并操作. 路径 "/book/add"也就组合出来了.

protected void registerHandlerMethod(Object handler, Method method, T mapping) {
    this.mappingRegistry.register(mapping, handler, method);
}
    
public void register(T mapping, Object handler, Method method) {
    this.readWriteLock.writeLock().lock();
    try {
        HandlerMethod handlerMethod = createHandlerMethod(handler, method);
        assertUniqueMethodMapping(handlerMethod, mapping);

        if (logger.isInfoEnabled()) {
            logger.info("Mapped \"" + mapping + "\" onto " + handlerMethod);
        }
        this.mappingLookup.put(mapping, handlerMethod);

        List<String> directUrls = getDirectUrls(mapping);
        for (String url : directUrls) {
            this.urlLookup.add(url, mapping);
        }

        String name = null;
        if (getNamingStrategy() != null) {
            name = getNamingStrategy().getName(handlerMethod, mapping);
            addMappingName(name, handlerMethod);
        }

        CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
        if (corsConfig != null) {
　　　　　　　　//如果配置了跨域, 此处还会对跨域进行记录
            this.corsLookup.put(handlerMethod, corsConfig);
        }

        this.registry.put(mapping, new MappingRegistration<>(mapping, handlerMethod, directUrls, name));
    }
    finally {
        this.readWriteLock.writeLock().unlock();
    }
}

这里的 mappingLookup 存放的是 RequestMappingInfo -> HandlerMethod

而 urlLookup 存放的是 url -> RequestMappingInfo

private final Map<T, HandlerMethod> mappingLookup = new LinkedHashMap<>();

private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<>();