spring源码分析之freemarker整合
Posted dz11
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FreeMarker是一款模板引擎： 即一种基于模板和要改变的数据， 并用来生成输出文本（html网页、电子邮件、配置文件、源代码等）的通用工具。 它不是面向最终用户的，而是一个Java类库，是一款程序员可以嵌入他们所开发产品的组件。
FreeMarker是免费的，基于Apache许可证2.0版本发布。其模板编写为FreeMarker Template Language（FTL），属于简单、专用的语言。需要准备数据在真实编程语言中来显示，比如数据库查询和业务运算， 之后模板显示已经准备好的数据。在模板中，主要用于如何展现数据， 而在模板之外注意于要展示什么数据。
1.定义(准备工作)
freemarker整合需要定义FreeMarkerViewResolver
package com.jverstry.Configuration; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.ViewResolver; import org.springframework.web.servlet.config.annotation.EnableWebMvc; import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter; import org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer; import org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver; @EnableWebMvc @Configuration @ComponentScan(basePackages = "com.jverstry") public class WebConfig extends WebMvcConfigurerAdapter { @Bean public ViewResolver getViewResolver() { FreeMarkerViewResolver resolver = new FreeMarkerViewResolver(); resolver.setCache(false); // resolver.setPrefix(""); resolver.setSuffix(".ftl"); return resolver; } @Bean public FreeMarkerConfigurer getFreemarkerConfig() { FreeMarkerConfigurer result = new FreeMarkerConfigurer(); result.setTemplateLoaderPath("WEB-INF/pages/"); return result; } }
在web.xml定义：
<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <context-param> <param-name>contextClass</param-name> <param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext</param-value> </context-param> <context-param> <param-name>contextConfigLocation</param-name> <param-value>com.jverstry.Configuration</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <servlet> <servlet-name>MyServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value></param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>MyServlet</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file></welcome-file> </welcome-file-list> </web-app>
注意：上面的contextclass定义在FrameworkServlet中，contextclass设置了一个自定义的context类，且必须是WebApplicationContext的实现。
/** * Set a custom context class. This class must be of type * {@link org.springframework.web.context.WebApplicationContext}. * <p>When using the default FrameworkServlet implementation, * the context class must also implement the * {@link org.springframework.web.context.ConfigurableWebApplicationContext} * interface. * @see #createWebApplicationContext */ public void setContextClass(Class<?> contextClass) { this.contextClass = contextClass; }
可以看出，在dispatcherServlet时定义了bean：
FreeMarkerViewResolver、
FreeMarkerConfigurer
那么在DispatcherServlet中是如何识别的呢？
/** * Initialize the ViewResolvers used by this class. * <p>If no ViewResolver beans are defined in the BeanFactory for this * namespace, we default to InternalResourceViewResolver. */ private void initViewResolvers(ApplicationContext context) { this.viewResolvers = null; if (this.detectAllViewResolvers) { // Find all ViewResolvers in the ApplicationContext, including ancestor contexts. Map<String, ViewResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false); if (!matchingBeans.isEmpty()) { this.viewResolvers = new ArrayList<ViewResolver>(matchingBeans.values()); // We keep ViewResolvers in sorted order. OrderComparator.sort(this.viewResolvers); } } else { try { ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class); this.viewResolvers = Collections.singletonList(vr); } catch (NoSuchBeanDefinitionException ex) { // Ignore, we‘ll add a default ViewResolver later. } } // Ensure we have at least one ViewResolver, by registering // a default ViewResolver if no other resolvers are found. if (this.viewResolvers == null) { this.viewResolvers = getDefaultStrategies(context, ViewResolver.class); if (logger.isDebugEnabled()) { logger.debug("No ViewResolvers found in servlet ‘" + getServletName() + "‘: using default"); } } }
然后FreeMarkerViewResolver设置FreeMarkerView
public FreeMarkerViewResolver() { setViewClass(requiredViewClass()); } /** * Requires {@link FreeMarkerView}. */ @Override protected Class<?> requiredViewClass() { return FreeMarkerView.class; }
FreeMarkerView在初始化时查找
FreeMarkerConfigurer 的bean
/** * Invoked on startup. Looks for a single FreeMarkerConfig bean to * find the relevant Configuration for this factory. * <p>Checks that the template for the default Locale can be found: * FreeMarker will check non-Locale-specific templates if a * locale-specific one is not found. * @see freemarker.cache.TemplateCache#getTemplate */ @Override protected void initServletContext(ServletContext servletContext) throws BeansException { if (getConfiguration() != null) { this.taglibFactory = new TaglibFactory(servletContext); } else { FreeMarkerConfig config = autodetectConfiguration(); setConfiguration(config.getConfiguration()); this.taglibFactory = config.getTaglibFactory(); } GenericServlet servlet = new GenericServletAdapter(); try { servlet.init(new DelegatingServletConfig()); } catch (ServletException ex) { throw new BeanInitializationException("Initialization of GenericServlet adapter failed", ex); } this.servletContextHashModel = new ServletContextHashModel(servlet, getObjectWrapper()); }
自动检测
/** * Autodetect a {@link FreeMarkerConfig} object via the ApplicationContext. * @return the Configuration instance to use for FreeMarkerViews * @throws BeansException if no Configuration instance could be found * @see #getApplicationContext * @see #setConfiguration */ protected FreeMarkerConfig autodetectConfiguration() throws BeansException { try { return BeanFactoryUtils.beanOfTypeIncludingAncestors( getApplicationContext(), FreeMarkerConfig.class, true, false); } catch (NoSuchBeanDefinitionException ex) { throw new ApplicationContextException( "Must define a single FreeMarkerConfig bean in this web application context " + "(may be inherited): FreeMarkerConfigurer is the usual implementation. " + "This bean may be given any name.", ex); } }
2. 渲染视图整个过程
DispatcherServlet开始
/** * Render the given ModelAndView. * <p>This is the last stage in handling a request. It may involve resolving the view by name. * @param mv the ModelAndView to render * @param request current HTTP servlet request * @param response current HTTP servlet response * @throws ServletException if view is missing or cannot be resolved * @throws Exception if there‘s a problem rendering the view */ protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception { // Determine locale for request and apply it to the response. Locale locale = this.localeResolver.resolveLocale(request); response.setLocale(locale); View view; if (mv.isReference()) { // We need to resolve the view name. view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request); if (view == null) { throw new ServletException("Could not resolve view with name ‘" + mv.getViewName() + "‘ in servlet with name ‘" + getServletName() + "‘"); } } else { // No need to lookup: the ModelAndView object contains the actual View object. view = mv.getView(); if (view == null) { throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " + "View object in servlet with name ‘" + getServletName() + "‘"); } } // Delegate to the View object for rendering. if (logger.isDebugEnabled()) { logger.debug("Rendering view [" + view + "] in DispatcherServlet with name ‘" + getServletName() + "‘"); } try { view.render(mv.getModelInternal(), request, response); } catch (Exception ex) { if (logger.isDebugEnabled()) { logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name ‘" + getServletName() + "‘", ex); } throw ex; } }
2.1 创建视图View
如红色1所示，调用DispatcherServlet的
resolveViewName方法
/** * Resolve the given view name into a View object (to be rendered). * <p>The default implementations asks all ViewResolvers of this dispatcher. * Can be overridden for custom resolution strategies, potentially based on * specific model attributes or request parameters. * @param viewName the name of the view to resolve * @param model the model to be passed to the view * @param locale the current locale * @param request current HTTP servlet request * @return the View object, or {@code null} if none found * @throws Exception if the view cannot be resolved * (typically in case of problems creating an actual View object) * @see ViewResolver#resolveViewName */ protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale, HttpServletRequest request) throws Exception { for (ViewResolver viewResolver : this.viewResolvers) { View view = viewResolver.resolveViewName(viewName, locale); if (view != null) { return view; } } return null; }
然后调用各种的ReviewResolver来解析视图AbstractCachingViewResolver
@Override public View resolveViewName(String viewName, Locale locale) throws Exception { if (!isCache()) { return createView(viewName, locale); } else { Object cacheKey = getCacheKey(viewName, locale); View view = this.viewAccessCache.get(cacheKey); if (view == null) { synchronized (this.viewCreationCache) { view = this.viewCreationCache.get(cacheKey); if (view == null) { // Ask the subclass to create the View object. view = createView(viewName, locale); if (view == null && this.cacheUnresolved) { view = UNRESOLVED_VIEW; } if (view != null) { this.viewAccessCache.put(cacheKey, view); this.viewCreationCache.put(cacheKey, view); if (logger.isTraceEnabled()) { logger.trace("Cached view [" + cacheKey + "]"); } } } } } return (view != UNRESOLVED_VIEW ? view : null); } }
调用子类UrlBasedViewResolver来创建view对象
/** * Overridden to implement check for "redirect:" prefix. * <p>Not possible in {@code loadView}, since overridden * {@code loadView} versions in subclasses might rely on the * superclass always creating instances of the required view class. * @see #loadView * @see #requiredViewClass */ @Override protected View createView(String viewName, Locale locale) throws Exception { // If this resolver is not supposed to handle the given view, // return null to pass on to the next resolver in the chain. if (!canHandle(viewName, locale)) { return null; } // Check for special "redirect:" prefix. if (viewName.startsWith(REDIRECT_URL_PREFIX)) { String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length()); RedirectView view = new RedirectView(redirectUrl, isRedirectContextRelative(), isRedirectHttp10Compatible()); return applyLifecycleMethods(viewName, view); } // Check for special "forward:" prefix. if (viewName.startsWith(FORWARD_URL_PREFIX)) { String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length()); return new InternalResourceView(forwardUrl); } // Else fall back to superclass implementation: calling loadView. return super.createView(viewName, locale); }
若前缀是redirect:或者forward:则跳入相应的逻辑进行处理，否则使用父逻辑
/** * Create the actual View object. * <p>The default implementation delegates to {@link #loadView}. * This can be overridden to resolve certain view names in a special fashion, * before delegating to the actual {@code loadView} implementation * provided by the subclass. * @param viewName the name of the view to retrieve * @param locale the Locale to retrieve the view for * @return the View instance, or {@code null} if not found * (optional, to allow for ViewResolver chaining) * @throws Exception if the view couldn‘t be resolved * @see #loadView */ protected View createView(String viewName, Locale locale) throws Exception { return loadView(viewName, locale); } /** * Delegates to {@code buildView} for creating a new instance of the * specified view class, and applies the following Spring lifecycle methods * (as supported by the generic Spring bean factory): * <ul> * <li>ApplicationContextAware‘s {@code setApplicationContext} * <li>InitializingBean‘s {@code afterPropertiesSet} * </ul> * @param viewName the name of the view to retrieve * @return the View instance * @throws Exception if the view couldn‘t be resolved * @see #buildView(String) * @see org.springframework.context.ApplicationContextAware#setApplicationContext * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet */ @Override protected View loadView(String viewName, Locale locale) throws Exception { AbstractUrlBasedView view = buildView(viewName); View result = applyLifecycleMethods(viewName, view); return (view.checkResource(locale) ? result : null); }
2.2 渲染视图
如DispatchServlet红色部分2所示，调用View的render方法
void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception;
具体实现由AbstractView来做
/** * Prepares the view given the specified model, merging it with static * attributes and a RequestContext attribute, if necessary. * Delegates to renderMergedOutputModel for the actual rendering. * @see #renderMergedOutputModel */ @Override public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception { if (logger.isTraceEnabled()) { logger.trace("Rendering view with name ‘" + this.beanName + "‘ with model " + model + " and static attributes " + this.staticAttributes); } Map<String, Object> mergedModel = createMergedOutputModel(model, request, response); prepareResponse(request, response); renderMergedOutputModel(mergedModel, request, response); }
调用子类AbstractTemplateView实现上述红色部分
@Override protected final void renderMergedOutputModel( Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception { if (this.exposeRequestAttributes) { for (Enumeration<String> en = request.getAttributeNames(); en.hasMoreElements();) { String attribute = en.nextElement(); if (model.containsKey(attribute) && !this.allowRequestOverride) { throw new ServletException("Cannot expose request attribute ‘" + attribute + "‘ because of an existing model object of the same name"); } Object attributeValue = request.getAttribute(attribute); if (logger.isDebugEnabled()) { logger.debug("Exposing request attribute ‘" + attribute + "‘ with value [" + attributeValue + "] to model"); } model.put(attribute, attributeValue); } } if (this.exposeSessionAttributes) { HttpSession session = request.getSession(false); if (session != null) { for (Enumeration<String> en = session.getAttributeNames(); en.hasMoreElements();) { String attribute = en.nextElement(); if (model.containsKey(attribute) && !this.allowSessionOverride) { throw new ServletException("Cannot expose session attribute ‘" + attribute + "‘ because of an existing model object of the same name"); } Object attributeValue = session.getAttribute(attribute); if (logger.isDebugEnabled()) { logger.debug("Exposing session attribute ‘" + attribute + "‘ with value [" + attributeValue + "] to model"); } model.put(attribute, attributeValue); } } } if (this.exposeSpringMacroHelpers) { if (model.containsKey(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE)) { throw new ServletException( "Cannot expose bind macro helper ‘" + SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE + "‘ because of an existing model object of the same name"); } // Expose RequestContext instance for Spring macros. model.put(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE, new RequestContext(request, response, getServletContext(), model)); } applyContentType(response); renderMergedTemplateModel(model, request, response); }
再调用子类FreeMarkerView实现
/** * Process the model map by merging it with the FreeMarker template. * Output is directed to the servlet response. * <p>This method can be overridden if custom behavior is needed. */ @Override protected void renderMergedTemplateModel( Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception { exposeHelpers(model, request); doRender(model, request, response); }
然后调用doRender方法
/** * Render the FreeMarker view to the given response, using the given model * map which contains the complete template model to use. * <p>The default implementation renders the template specified by the "url" * bean property, retrieved via {@code getTemplate}. It delegates to the * {@code processTemplate} method to merge the template instance with * the given template model. * <p>Adds the standard Freemarker hash models to the model: request parameters, * request, session and application (ServletContext), as well as the JSP tag * library hash model. * <p>Can be overridden to customize the behavior, for example to render * multiple templates into a single view. * @param model the model to use for rendering * @param request current HTTP request * @param response current servlet response * @throws IOException if the template file could not be retrieved * @throws Exception if rendering failed * @see #setUrl * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale * @see #getTemplate(java.util.Locale) * @see #processTemplate * @see freemarker.ext.servlet.FreemarkerServlet */ protected void doRender(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception { // Expose model to JSP tags (as request attributes). exposeModelAsRequestAttributes(model, request); // Expose all standard FreeMarker hash models. SimpleHash fmModel = buildTemplateModel(model, request, response); if (logger.isDebugEnabled()) { logger.debug("Rendering FreeMarker template [" + getUrl() + "] in FreeMarkerView ‘" + getBeanName() + "‘"); } // Grab the locale-specific version of the template. Locale locale = RequestContextUtils.getLocale(request); processTemplate(getTemplate(locale), fmModel, response); }
继续处理模板
/** * Process the FreeMarker template to the servlet response. * <p>Can be overridden to customize the behavior. * @param template the template to process * @param model the model for the template * @param response servlet response (use this to get the OutputStream or Writer) * @throws IOException if the template file could not be retrieved * @throws TemplateException if thrown by FreeMarker * @see freemarker.template.Template#process(Object, java.io.Writer) */ protected void processTemplate(Template template, SimpleHash model, HttpServletResponse response) throws IOException, TemplateException { template.process(model, response.getWriter()); }
调用freemarker jar中的freemarker.template.Template类的process方法
此过程超出spring的范围，故略去不述。
3. 小结
1.spring和freemarker的整合，需要定义两个bean：FreeMarkerViewResolver、FreeMarkerConfigurer。
2.spring在Dispatcher中定义了视图渲染的过程:创建视图，然后利用Freemarker本身提供的Template方法来处理。
处理过程中以Mode、request、response为参数。
4. 附录：依赖包
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.jverstry</groupId> <artifactId>spring-freemarker-integration</artifactId> <packaging>war</packaging> <version>1.0.0</version> <name>Spring-FreeMarker-Integration</name> <properties> <java-version>1.6</java-version> <spring.version>3.1.2.RELEASE</spring.version> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <!-- Spring --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>${spring.version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>${spring.version}</version> </dependency> <dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> <version>2.5</version> <scope>provided</scope> </dependency> <!-- FreeMarker --> <dependency> <groupId>org.freemarker</groupId> <artifactId>freemarker</artifactId> <version>2.3.19</version> </dependency> <!-- CGLIB, only required and used for @Configuration usage --> <dependency> <groupId>cglib</groupId> <artifactId>cglib-nodep</artifactId> <version>2.2</version> </dependency> <!-- @Inject --> <dependency> <groupId>javax.inject</groupId> <artifactId>javax.inject</artifactId> <version>1</version> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>${java-version}</source> <target>${java-version}</target> <encoding>${project.build.sourceEncoding}</encoding> </configuration> </plugin> <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>tomcat-maven-plugin</artifactId> <version>1.1</version> <configuration> <port>8282</port> </configuration> </plugin> </plugins> </build> </project>
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