SpringMVC源码解读 - HandlerMapping - AbstractDetectingUrlHandlerMapping系列初始化

AbstractDetectingUrlHandlerMapping是通过扫描方式注册Handler,收到请求时由AbstractUrlHandlerMapping的getHandlerInternal进行分发.

共有5个子类,一个抽象类.

与SimpleUrlHandlerMapping类似,通过覆写initApplicationContext,然后调用detectHandlers进行初始化.

detectHandlers通过BeanFactoryUtils扫描应用下的Object,然后预留determineUrlsForHandler给子类根据Handler生成对应的url.

注册使用的registerHandler依然由AbstractUrlHandlerMapping提供.

// AbstractDetectingUrlHandlerMapping

    /**
     * Calls the {@link #detectHandlers()} method in addition to the
     * superclass's initialization.
     */
    @Override
    public void initApplicationContext() throws ApplicationContextException {
        super.initApplicationContext();
        detectHandlers();
    }

这边一样是调用AbstractHandlerMapping的initApplicationContext初始化拦截器.

 

主角上场,detectHandlers,扫描Handlers

// AbstractDetectingUrlHandlerMapping

    /**
     * Register all handlers found in the current ApplicationContext.
     * <p>The actual URL determination for a handler is up to the concrete
     * {@link #determineUrlsForHandler(String)} implementation. A bean for
     * which no such URLs could be determined is simply not considered a handler.
     * @throws org.springframework.beans.BeansException if the handler couldn't be registered
     * @see #determineUrlsForHandler(String)
     */
    protected void detectHandlers() throws BeansException {
        if (logger.isDebugEnabled()) {
            logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
        }
        String[] beanNames = (this.detectHandlersInAncestorContexts ?
                BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
                getApplicationContext().getBeanNamesForType(Object.class));

        // Take any bean name that we can determine URLs for.
        for (String beanName : beanNames) {
            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");
                }
            }
        }
    }

这边预留的模板方法定义如下:

    /**
     * Determine the URLs for the given handler bean.
     * @param beanName the name of the candidate bean
     * @return the URLs determined for the bean,
     * or {@code null} or an empty array if none
     */
    protected abstract String[] determineUrlsForHandler(String beanName);

 

我们再来看看模板方法在BeanNameUrlHandlerMapping和AbstractControllerUrlHandlerMapping中的实现吧.

BeanNameUrlHandlerMapping非常简单,就实现了determineUrlsForHandler.

其中的alias应该是应该就是通过beanName在配置文件中配置的.

// BeanNameUrlHandlerMapping

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

 

再来看看AbstractControllerUrlHandlerMapping中的实现

　　isEligibleForMapping判断controller是否被排除在外(通过包package排除或类class排除).

　　buildUrlsForHandler由子类实现具体的url生成规则

　　isControllerType判断是否Controller的子类

　　buildUrlsForHandler预留给子类生产url的模板方法.

// AbstractControllerUrlHandlerMapping

    /**
     * This implementation delegates to {@link #buildUrlsForHandler},
     * provided that {@link #isEligibleForMapping} returns {@code true}.
     */
    @Override
    protected String[] determineUrlsForHandler(String beanName) {
        Class beanClass = getApplicationContext().getType(beanName);
        if (isEligibleForMapping(beanName, beanClass)) {
            return buildUrlsForHandler(beanName, beanClass);
        }
        else {
            return null;
        }
    }

 

 // AbstractControllerUrlHandlerMapping

    /**判断controller是否被排除在外(通过包package排除或类class排除).
     * Determine whether the specified controller is excluded from this mapping.
     * @param beanName the name of the controller bean
     * @param beanClass the concrete class of the controller bean
     * @return whether the specified class is excluded
     * @see #setExcludedPackages
     * @see #setExcludedClasses
     */
    protected boolean isEligibleForMapping(String beanName, Class beanClass) {
        if (beanClass == null) {
            if (logger.isDebugEnabled()) {
                logger.debug("Excluding controller bean '" + beanName + "' from class name mapping " +
                        "because its bean type could not be determined");
            }
            return false;
        }
        if (this.excludedClasses.contains(beanClass)) {
            if (logger.isDebugEnabled()) {
                logger.debug("Excluding controller bean '" + beanName + "' from class name mapping " +
                        "because its bean class is explicitly excluded: " + beanClass.getName());
            }
            return false;
        }
        String beanClassName = beanClass.getName();
        for (String packageName : this.excludedPackages) {
            if (beanClassName.startsWith(packageName)) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Excluding controller bean '" + beanName + "' from class name mapping " +
                            "because its bean class is defined in an excluded package: " + beanClass.getName());
                }
                return false;
            }
        }
        return isControllerType(beanClass);
    }

 

 // AbstractControllerUrlHandlerMapping

    /**
     * Determine whether the given bean class indicates a controller type
     * that is supported by this mapping strategy.
     * @param beanClass the class to introspect
     */
    protected boolean isControllerType(Class beanClass) {
        return this.predicate.isControllerType(beanClass);
    }

 

 // ControllerTypePredicate

这边提供2个api,分别判断是Controller的子类还是MultiActionController的子类.

/**
 * Internal helper class that identifies controller types.
 *
 * @author Juergen Hoeller
 * @since 2.5.3
 */
class ControllerTypePredicate {

    public boolean isControllerType(Class beanClass) {
        return Controller.class.isAssignableFrom(beanClass);
    }

    public boolean isMultiActionControllerType(Class beanClass) {
        return MultiActionController.class.isAssignableFrom(beanClass);
    }

}

 

预留生成url的模板方法

 // AbstractControllerUrlHandlerMapping

    /**
     * Abstract template method to be implemented by subclasses.
     * @param beanName the name of the bean
     * @param beanClass the type of the bean
     * @return the URLs determined for the bean
     */
    protected abstract String[] buildUrlsForHandler(String beanName, Class beanClass);

 

再来看看AbstractControllerUrlHandlerMapping的2个实现ControllerBeanNameUrlHandlerMapping和ControllerClassNameUrlHandlerMapping.

其实这两个,很简单,一个是根据beanName来生产url,一个是根据className来生产url.

 

// ControllerBeanNameUrlHandlerMapping

    @Override
    protected String[] buildUrlsForHandler(String beanName, Class beanClass) {
        List<String> urls = new ArrayList<String>();
        urls.add(generatePathMapping(beanName));
        String[] aliases = getApplicationContext().getAliases(beanName);// 也获取配置的别名
        for (String alias : aliases) {
            urls.add(generatePathMapping(alias));
        }
        return StringUtils.toStringArray(urls);
    }

 

// ControllerBeanNameUrlHandlerMapping

    /**对path添加前后缀,还有/
     * Prepends a '/' if required and appends the URL suffix to the name.
     */
    protected String generatePathMapping(String beanName) {
        String name = (beanName.startsWith("/") ? beanName : "/" + beanName);
        StringBuilder path = new StringBuilder();
        if (!name.startsWith(this.urlPrefix)) {
            path.append(this.urlPrefix);
        }
        path.append(name);
        if (!name.endsWith(this.urlSuffix)) {
            path.append(this.urlSuffix);
        }
        return path.toString();
    }

 

// ControllerClassNameUrlHandlerMapping

直接委托给generatePathMappings实现

    @Override
    protected String[] buildUrlsForHandler(String beanName, Class beanClass) {
        return generatePathMappings(beanClass);
    }

 

// ControllerClassNameUrlHandlerMapping

　　通过buildPathPrefix获取path的前缀

　　通过ClassUtils获取className,如BookController(不带包名),同时使用cglib代理的问题一并解决

　　根据大小写是否敏感,转换className(默认caseSensitive = false;)

　　isMultiActionControllerType判断Controller是否MultiActionController的子类,就是controller是否包含多个handler

    /**
     * Generate the actual URL paths for the given controller class.
     * <p>Subclasses may choose to customize the paths that are generated
     * by overriding this method.
     * @param beanClass the controller bean class to generate a mapping for
     * @return the URL path mappings for the given controller
     */
    protected String[] generatePathMappings(Class beanClass) {
        StringBuilder pathMapping = buildPathPrefix(beanClass);
        String className = ClassUtils.getShortName(beanClass);
        String path = (className.endsWith(CONTROLLER_SUFFIX) ?
                className.substring(0, className.lastIndexOf(CONTROLLER_SUFFIX)) : className);
        if (path.length() > 0) {
            if (this.caseSensitive) {
                pathMapping.append(path.substring(0, 1).toLowerCase()).append(path.substring(1));
            }
            else {
                pathMapping.append(path.toLowerCase());
            }
        }
        if (isMultiActionControllerType(beanClass)) {
            return new String[] {pathMapping.toString(), pathMapping.toString() + "/*"};
        }
        else {
            return new String[] {pathMapping.toString() + "*"};
        }
    }

 

// ControllerClassNameUrlHandlerMapping

    /**
     * Build a path prefix for the given controller bean class.
     * @param beanClass the controller bean class to generate a mapping for
     * @return the path prefix, potentially including subpackage names as path elements
     */
    private StringBuilder buildPathPrefix(Class beanClass) {
        StringBuilder pathMapping = new StringBuilder();
        if (this.pathPrefix != null) {
            pathMapping.append(this.pathPrefix);
            pathMapping.append("/");
        }
        else {
            pathMapping.append("/");
        }
        if (this.basePackage != null) {
            String packageName = ClassUtils.getPackageName(beanClass);
            if (packageName.startsWith(this.basePackage)) {
                String subPackage = packageName.substring(this.basePackage.length()).replace('.', '/');
                pathMapping.append(this.caseSensitive ? subPackage : subPackage.toLowerCase());
                pathMapping.append("/");
            }
        }
        return pathMapping;
    }

 

// AbstractControllerUrlHandlerMapping

predicate.isMultiActionControllerType具体实现看上面的ControllerTypePredicate

    /**
     * Determine whether the given bean class indicates a controller type
     * that dispatches to multiple action methods.
     * @param beanClass the class to introspect
     */
    protected boolean isMultiActionControllerType(Class beanClass) {
        return this.predicate.isMultiActionControllerType(beanClass);
    }