springmvc的學習分析

時間 2019-12-05

原文原文鏈接

springmvc是一個servlet,controller中單獨寫處理head請求的方法，此方法能夠用來檢查服務器的狀態，由於不返回body因此比get請求更節省網絡資源。java

springmvc的servlet圖node

XXXAware在spring中表示對xxx能夠感知：若是在某個類中想要使用spring的一些東西，能夠實現xxxAware接口告訴spring,spring能夠給你送過來，接收的方法實現接口惟一的方法setxxx,好比有個類要用applicationContext，咱們只需讓它實現applicationContextAware接口，而後實現接口中惟一的方法void setApplicationContext(ApplicationContext applicationContext)就能夠了。web

EnvironmentCapable接口就是具備提供Enviroment的能力，Enviroment getEnvironment();spring

ApplicationContext服務器

Environment網絡

HttpServletBean中Enviroment使用的是Standrad_Servlet_Environment封裝了ServletContext,ServletConfig,JndiProperty,系統環境變量和系統屬性，這些都封裝到了其propertySources屬性下。mvc

ServletContextPropertySource封裝的就是ServletConfig,保存的是ServletContextapp

mandatorywebapp	英 [ˈmændətəri]ide	美 [ˈmændətɔ:ri]
adj.	強制的; 命令的; 受委託的;

受託者;

[例句]Attendance is mandatory.

務必參加。

@Override

public final void init() throws ServletException {

if (logger.isDebugEnabled()) {

logger.debug("Initializing servlet '" + getServletName() + "'");

}

// Set bean properties from init parameters.

try {

PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);

BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);

ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());

bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));

initBeanWrapper(bw);

bw.setPropertyValues(pvs, true);

}

catch (BeansException ex) {

logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);

throw ex;

}

// Let subclasses do whatever initialization they like.

initServletBean();

if (logger.isDebugEnabled()) {

logger.debug("Servlet '" + getServletName() + "' configured successfully");

}

httpServletBean的init中，首先將servlet中配置參數使用BeanWrapper設置到DispatcherServlet的相關屬性，而後調用模板方法initServletBean,子類就經過這個方法初始化。

BeanWrapper是什麼，怎麼用？

是spring提供的操做havaBean屬性的工具，使用它能夠直接修改一個對象的屬性。

FrameworkServlet

從httpServletBean中可知，FrameworkServlet的初始化入口方法應該是initServletBean

package org.springframework.web.servlet;

protected final void initServletBean() throws ServletException {

getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");

if (this.logger.isInfoEnabled()) {

this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");

}

long startTime = System.currentTimeMillis();

try {

this.webApplicationContext = initWebApplicationContext();

initFrameworkServlet();

}

catch (ServletException ex) {

this.logger.error("Context initialization failed", ex);

throw ex;

}

catch (RuntimeException ex) {

this.logger.error("Context initialization failed", ex);

throw ex;

}

if (this.logger.isInfoEnabled()) {

long elapsedTime = System.currentTimeMillis() - startTime;

this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +

elapsedTime + " ms");

}

FrameworkServlet在構建過程當中的主要做用就是初始化webApplicationContext;

protected WebApplicationContext initWebApplicationContext() {

WebApplicationContext rootContext =

WebApplicationContextUtils.getWebApplicationContext(getServletContext());

WebApplicationContext wac = null;

if (this.webApplicationContext != null) {

// A context instance was injected at construction time -> use it

wac = this.webApplicationContext;

if (wac instanceof ConfigurableWebApplicationContext) {

ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;

if (!cwac.isActive()) {

// The context has not yet been refreshed -> provide services such as

// setting the parent context, setting the application context id, etc

if (cwac.getParent() == null) {

// The context instance was injected without an explicit parent -> set

// the root application context (if any; may be null) as the parent

cwac.setParent(rootContext);

}

configureAndRefreshWebApplicationContext(cwac);

}

if (wac == null) {

// No context instance was injected at construction time -> see if one

// has been registered in the servlet context. If one exists, it is assumed

// that the parent context (if any) has already been set and that the

// user has performed any initialization such as setting the context id

wac = findWebApplicationContext();

}

if (wac == null) {

// No context instance is defined for this servlet -> create a local one

wac = createWebApplicationContext(rootContext);

}

if (!this.refreshEventReceived) {

// Either the context is not a ConfigurableApplicationContext with refresh

// support or the context injected at construction time had already been

// refreshed -> trigger initial onRefresh manually here.

onRefresh(wac);

}

if (this.publishContext) {

// Publish the context as a servlet context attribute.

String attrName = getServletContextAttributeName();

getServletContext().setAttribute(attrName, wac);

if (this.logger.isDebugEnabled()) {

this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +

"' as ServletContext attribute with name [" + attrName + "]");

}

return wac;

}

initWebApplicationContext方法作了三件事

獲取spring的根容器rootContext,

設置webApplicationContext,並根據狀況調用onRefresh方法

將webApplicationContext設置到ServletContext的attribute中

獲取spring的根容器rootContext

默認狀況下spring會將本身的容器設置成ServletContext的屬性，默認根容器的key爲 org.springframework.web.context.WebApplicationContext.ROOT,定義在org.springframework.web.context.WebApplicationContext中；

獲取根容器只須要調用ServletContext的getAtttribute:

ServletContext#getAttribute(「org.springframework.web.context.WebApplicationContext.ROOT」)

設置webApplicationContext並根據狀況調用onrefresh方法

有三種方法設置webapplicationcontext:

第一種在構造方法中已經傳遞了webApplicatioonContext參數,這時只須要一些設置便可。

第二種方法webapplicationContext已經在servletContext中了，配置servlet的時候將servletContext中的webapplicationContext的name配置到contextAttribute屬性就能夠了。

第三種方法是在前兩種方式都無效的狀況下本身建立一個,正常狀況下就是使用這種方式。在createWebApplicationcontext方法中，內部又調用了configureAndRefreshWebApplicationContext方法。

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {

if (ObjectUtils.identityToString(wac).equals(wac.getId())) {

// The application context id is still set to its original default value

// -> assign a more useful id based on available information

if (this.contextId != null) {

wac.setId(this.contextId);

}

else {

// Generate default id...

wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +

ObjectUtils.getDisplayString(getServletContext().getContextPath()) + "/" + getServletName());

}

wac.setServletContext(getServletContext());

wac.setServletConfig(getServletConfig());

wac.setNamespace(getNamespace());

wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));

// The wac environment's #initPropertySources will be called in any case when the context

// is refreshed; do it eagerly here to ensure servlet property sources are in place for

// use in any post-processing or initialization that occurs below prior to #refresh

ConfigurableEnvironment env = wac.getEnvironment();

if (env instanceof ConfigurableWebEnvironment) {

((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());

}

postProcessWebApplicationContext(wac);

applyInitializers(wac);

wac.refresh();

}

private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {

@Override

public void onApplicationEvent(ContextRefreshedEvent event) {

FrameworkServlet.this.onApplicationEvent(event);

}

public void onApplicationEvent(ContextRefreshedEvent event) {

this.refreshEventReceived = true;

onRefresh(event.getApplicationContext());

}

在接收到事件後調用一次onRefresh，並將refreshEventReceived標誌置爲true,表示已經refresh過。

上面三種方法無論哪一種，最終都會調用一次refresh方法，而且DispatcherServlet正是經過重寫這個模板來實現初始化的。

前面介紹了配置servlet時能夠設置的一些初始化參數，總結以下：

contextAttribute:在servletContext的屬性中，要作WebApplicationContext的屬性名稱

contextClass:建立webApplicationContext的類型

contextConfigLocation:Springmvc配置文件的位置

publishContext:是否將webApplicationContext設置到ServletContext的屬性。

DispatcherServlet

onRefresh方法是DispatcherServlet的入口方法，onRefresh方法調用了initStrategies,其中調用了9個初始化的方法：

package org.springframework.web.servlet

protected void onRefresh(ApplicationContext context) {

initStrategies(context);

}

初始化servlet使用的九個組件

/**

* Initialize the strategy objects that this servlet uses.

* <p>May be overridden in subclasses in order to initialize further strategy objects.

protected void initStrategies(ApplicationContext context) {

initMultipartResolver(context);

initLocaleResolver(context);

initThemeResolver(context);

initHandlerMappings(context);

initHandlerAdapters(context);

initHandlerExceptionResolvers(context);

initRequestToViewNameTranslator(context);

initViewResolvers(context);

initFlashMapManager(context);

}

爲何不把initStrategies直接寫到onRefresh中去呢？這是功能分層的緣由,onRefresh是用來刷新的,這樣寫可使邏輯更清晰一些。

private void initLocaleResolver(ApplicationContext context) {

try {

this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);

if (logger.isDebugEnabled()) {

logger.debug("Using LocaleResolver [" + this.localeResolver + "]");

}

catch (NoSuchBeanDefinitionException ex) {

// We need to use the default.

this.localeResolver = getDefaultStrategy(context, LocaleResolver.class);

if (logger.isDebugEnabled()) {

logger.debug("Unable to locate LocaleResolver with name '" + LOCALE_RESOLVER_BEAN_NAME +

"': using default [" + this.localeResolver + "]");

}

初始化分爲兩步，首先用context.getBean在容器裏面按照註冊的名稱或者類型(localeResolver名稱或者localeResolver.class類型)進行查找，因此在spring mvc的配置文件中只須要配置相應類型的組件，容器就能夠找到。若是找不到，就按照getDefaultStrategy按照類型得到默認的組件。這裏的context指的是frameworkServlet中建立的webApplicationContext,而不是servletContext,

protected <T> T getDefaultStrategy(ApplicationContext context, Class<T> strategyInterface) {

List<T> strategies = getDefaultStrategies(context, strategyInterface);

if (strategies.size() != 1) {

throw new BeanInitializationException(

"DispatcherServlet needs exactly 1 strategy for interface [" + strategyInterface.getName() + "]");

}

return strategies.get(0);

}

@SuppressWarnings("unchecked")

protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {

String key = strategyInterface.getName();

//得到須要的策略類型

String value = defaultStrategies.getProperty(key);

if (value != null) {

String[] classNames = StringUtils.commaDelimitedListToStringArray(value);

List<T> strategies = new ArrayList<T>(classNames.length);

for (String className : classNames) {

try {

Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());

Object strategy = createDefaultStrategy(context, clazz);

strategies.add((T) strategy);

}

catch (ClassNotFoundException ex) {

throw new BeanInitializationException(

"Could not find DispatcherServlet's default strategy class [" + className +

"] for interface [" + key + "]", ex);

}

catch (LinkageError err) {

throw new BeanInitializationException(

"Error loading DispatcherServlet's default strategy class [" + className +

"] for interface [" + key + "]: problem with class file or dependent class", err);

}

return strategies;

}

else {

return new LinkedList<T>();

}

classname來自classNames，classnames來自value,value來自defaultStrategy

private static final Properties defaultStrategies;

static {

// Load default strategy implementations from properties file.

// This is currently strictly internal and not meant to be customized

// by application developers.

try {

ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);

defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);

}

catch (IOException ex) {

throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());

}

DEFAULT_STRATEGIES_PATH的值是DispatcherServlet.properties中定義的

在同目錄下的properties文件

# Default implementation classes for DispatcherServlet's strategy interfaces.

# Used as fallback when no matching beans are found in the DispatcherServlet context.

# Not meant to be customized by application developers.

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\

org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\

org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\

org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\

org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\

org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

定義了八個組件，multipartResolver是沒有默認配置的，並非每一個應用都須要上傳功能，因此multioartResolver不須要默認配置。

都作了默認配置，也不是spring的推薦配置，只是在沒有配置的時候有個默認值，不至於空着，默認配置是相應類型沒有配置的時候纔會使用，如當使用<mvc:annotation-driven>後，並不會使用默認配置，由於它配置了handlerMapping.handlerAdapter和handler-ExceptionResolver,並且還作了不少別的工做。DispatcherServlet建立過程主要對9大組件進行初始化。

在spring中xml文件中經過命名空間配置的標籤時怎麼解析的

spring xml中能夠有不少命名空間配置的信息，這些命名空間配置是怎麼解析的？對於具體的一個命名空間。spring是如何找到解析他們的類的？

解析標籤的類都放在相應的META-INF目錄下的springhandlers文件中。如mvc命名空間解析設置在spring-webmvc-xxx.jar下META-INF下spring.handlers文件中，內容是

http\://www.springframework.org/schema/mvc=org.springframework.web.servlet.config.MvcNamespaceHandler

如內部將mvc:annotation-drivern的解析交給AnnotationDrivenBeanDefinitionParser

public interface NamespaceHandler {

void init();

BeanDefinition parse(Element element, ParserContext parserContext);

BeanDefinitionHolder decorate(Node source, BeanDefinitionHolder definition, ParserContext parserContext);

}

接口Namespacehandler的實現類主要有三個：NamespaceHandlerSupport,SimpleConstructorNamespaceHandler,SimplePropertyNamespaceHandler;

NamespaceHandlerSupport是NamespaceHandler的默認實現類，通常的NamespaceHandler都繼承自這個類；特殊狀況springSecurity的SecurityNamespaceHandler是直接實現的NamespaceHandler接口；SimpleConstructorNamespaceHandler用於統一對C:配置的構造方法進行解析,SimplePropertyNamespaceHandler統一對經過p:配置的參數進行解析。

public class MvcNamespaceHandler extends NamespaceHandlerSupport{}

NamespaceHandlerSupport

public abstract class NamespaceHandlerSupport implements NamespaceHandler {

/**

* Stores the {@link BeanDefinitionParser} implementations keyed by the

* local name of the {@link Element Elements} they handle.

private final Map<String, BeanDefinitionParser> parsers =

new HashMap<String, BeanDefinitionParser>();

/**

* Stores the {@link BeanDefinitionDecorator} implementations keyed by the

* local name of the {@link Element Elements} they handle.

private final Map<String, BeanDefinitionDecorator> decorators =

new HashMap<String, BeanDefinitionDecorator>();

/**

* Stores the {@link BeanDefinitionDecorator} implementations keyed by the local

* name of the {@link Attr Attrs} they handle.

private final Map<String, BeanDefinitionDecorator> attributeDecorators =

new HashMap<String, BeanDefinitionDecorator>();

/**

* Parses the supplied {@link Element} by delegating to the {@link BeanDefinitionParser} that is

* registered for that {@link Element}.

@Override

public BeanDefinition parse(Element element, ParserContext parserContext) {

return findParserForElement(element, parserContext).parse(element, parserContext);

}

/**

* Locates the {@link BeanDefinitionParser} from the register implementations using

* the local name of the supplied {@link Element}.

private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {

String localName = parserContext.getDelegate().getLocalName(element);

BeanDefinitionParser parser = this.parsers.get(localName);

if (parser == null) {

parserContext.getReaderContext().fatal(

"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);

}

return parser;

}

/**

* Decorates the supplied {@link Node} by delegating to the {@link BeanDefinitionDecorator} that

* is registered to handle that {@link Node}.

@Override

public BeanDefinitionHolder decorate(

Node node, BeanDefinitionHolder definition, ParserContext parserContext) {

return findDecoratorForNode(node, parserContext).decorate(node, definition, parserContext);

}

/**

* Locates the {@link BeanDefinitionParser} from the register implementations using

* the local name of the supplied {@link Node}. Supports both {@link Element Elements}

* and {@link Attr Attrs}.

private BeanDefinitionDecorator findDecoratorForNode(Node node, ParserContext parserContext) {

BeanDefinitionDecorator decorator = null;

String localName = parserContext.getDelegate().getLocalName(node);

if (node instanceof Element) {

decorator = this.decorators.get(localName);

}

else if (node instanceof Attr) {

decorator = this.attributeDecorators.get(localName);

}

else {

parserContext.getReaderContext().fatal(

"Cannot decorate based on Nodes of type [" + node.getClass().getName() + "]", node);

}

if (decorator == null) {

parserContext.getReaderContext().fatal("Cannot locate BeanDefinitionDecorator for " +

(node instanceof Element ? "element" : "attribute") + " [" + localName + "]", node);

}

return decorator;

}

/**

* Subclasses can call this to register the supplied {@link BeanDefinitionParser} to

* handle the specified element. The element name is the local (non-namespace qualified)

* name.

protected final void registerBeanDefinitionParser(String elementName, BeanDefinitionParser parser) {

this.parsers.put(elementName, parser);

}

/**

* Subclasses can call this to register the supplied {@link BeanDefinitionDecorator} to

* handle the specified element. The element name is the local (non-namespace qualified)

* name.

protected final void registerBeanDefinitionDecorator(String elementName, BeanDefinitionDecorator dec) {

this.decorators.put(elementName, dec);

}

/**

* Subclasses can call this to register the supplied {@link BeanDefinitionDecorator} to

* handle the specified attribute. The attribute name is the local (non-namespace qualified)

* name.

protected final void registerBeanDefinitionDecoratorForAttribute(String attrName, BeanDefinitionDecorator dec) {

this.attributeDecorators.put(attrName, dec);

}

NamespaaceHandlerSupport定義了三個處理器parsers,decorators.attributeDecorators分別用於處理解析工做，處理標籤類型，處理屬性類型的裝飾。具體的處理器由子類實現，而後註冊到NamespaceHandlerSupport上面，因此要定義一個命名空間的解析器，只須要在init中定義相應的parsers,decorators.attributeDecorators,並註冊到NamespacehandlerSupport上面。

mvc命名空間的mvcNamespaceHandler的代碼：

public class MvcNamespaceHandler extends NamespaceHandlerSupport {

@Override

public void init() {

registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());

registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());

registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());

registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());

registerBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());

registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());

registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());

registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());

registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());

registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());

registerBeanDefinitionParser("velocity-configurer", new VelocityConfigurerBeanDefinitionParser());

registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());

}

從上面代碼能夠看出解析annotation-driven的是子類解析器AnnotationDrivenBeanDefinitionParser，註冊到了NamespaceHandlerSupport的parsers上

上面主要解析了springmvc建立servlet的三個層次HttpServletBean ,FrameworkServlet,DispatcherServlet;HttpServletBean直接繼承了java中的HttpServlet,做用是將相應的servlet的配置參數設置到對應的屬性上，FrameworkServlet初始化了WebApplicationContext,DispatcherServlet初始化自身的9個組件。

spring的特色：結構簡單，實現複雜，結構簡單是頂層設計好，實現複雜是實現的功能比較多，可配置的地方也很是多。