一、基于注解的方式使用Spring MVC
使用@RequestMapping,@Controller，@ResponseBody
@RestController
public class HelloController {
@RequestMapping("hello")
public String hello (){
return "Hello Spring MVC";
}
}二、如何进行注解开发的配置
基于XML进行配置
<?xml version="1.0" encoding="UTF-8"?>
<beans>
<mvc:annotation-driven/>
<beans>基于@EnableWebMvc注解实现自动配置
基于SpringBoot中的自动配置
WebMvcAutoConfiguration
@Configuration
@EnableWebMvc
public class WebMvcConfig{
}三、配置原理
<mvc:annotation-driven/>原理
添加此标签后，Spring使用自定义的Bean定义解析器AnnotationDrivenBeanDefinitionParser加载了几个比较几个重要的Bean定义，主要是一些围绕HandlerMethod进行处理的基础组件对象
RequestHandlerMapping
根据请求映射找出对应的HandlerMethod进行处理RequestMappingHandlerAdapter
执行HandlerMethodChain进入到目标方法
AnnotationDrivenBeanDefinitionParser做了什么？
public class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
Object source = parserContext.extractSource(element);
CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
parserContext.pushContainingComponent(compDefinition);
RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, parserContext);
// 注册RequestMappingHandlerMapping，用于处理@RequestMaping注解的方法请求映射为HandlerMethod
RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
handlerMappingDef.setSource(source);
handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
handlerMappingDef.getPropertyValues().add("order", 0);
handlerMappingDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
String methodMappingName = parserContext.getReaderContext().registerWithGeneratedName(handlerMappingDef);
if (element.hasAttribute("enable-matrix-variables")) {
Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enable-matrix-variables"));
handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
}
else if (element.hasAttribute("enableMatrixVariables")) {
Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enableMatrixVariables"));
handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
}
configurePathMatchingProperties(handlerMappingDef, element, parserContext);
RuntimeBeanReference conversionService = getConversionService(element, source, parserContext);
RuntimeBeanReference validator = getValidator(element, source, parserContext);
RuntimeBeanReference messageCodesResolver = getMessageCodesResolver(element);
RootBeanDefinition bindingDef = new RootBeanDefinition(ConfigurableWebBindingInitializer.class);
bindingDef.setSource(source);
bindingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
bindingDef.getPropertyValues().add("conversionService", conversionService);
bindingDef.getPropertyValues().add("validator", validator);
bindingDef.getPropertyValues().add("messageCodesResolver", messageCodesResolver);
ManagedList<?> messageConverters = getMessageConverters(element, source, parserContext);
ManagedList<?> argumentResolvers = getArgumentResolvers(element, parserContext);
ManagedList<?> returnValueHandlers = getReturnValueHandlers(element, parserContext);
String asyncTimeout = getAsyncTimeout(element);
RuntimeBeanReference asyncExecutor = getAsyncExecutor(element);
ManagedList<?> callableInterceptors = getCallableInterceptors(element, source, parserContext);
ManagedList<?> deferredResultInterceptors = getDeferredResultInterceptors(element, source, parserContext);
// 注册RequestMappingHandlerAdapter,用于适配处理HandlerMethod
RootBeanDefinition handlerAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);
handlerAdapterDef.setSource(source);
handlerAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
handlerAdapterDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
handlerAdapterDef.getPropertyValues().add("webBindingInitializer", bindingDef);
handlerAdapterDef.getPropertyValues().add("messageConverters", messageConverters);
addResponseBodyAdvice(handlerAdapterDef);
if (element.hasAttribute("ignore-default-model-on-redirect")) {
Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignore-default-model-on-redirect"));
handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
}
else if (element.hasAttribute("ignoreDefaultModelOnRedirect")) {
// "ignoreDefaultModelOnRedirect" spelling is deprecated
Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignoreDefaultModelOnRedirect"));
handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
}
if (argumentResolvers != null) {
handlerAdapterDef.getPropertyValues().add("customArgumentResolvers", argumentResolvers);
}
if (returnValueHandlers != null) {
handlerAdapterDef.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);
}
if (asyncTimeout != null) {
handlerAdapterDef.getPropertyValues().add("asyncRequestTimeout", asyncTimeout);
}
if (asyncExecutor != null) {
handlerAdapterDef.getPropertyValues().add("taskExecutor", asyncExecutor);
}
handlerAdapterDef.getPropertyValues().add("callableInterceptors", callableInterceptors);
handlerAdapterDef.getPropertyValues().add("deferredResultInterceptors", deferredResultInterceptors);
String handlerAdapterName = parserContext.getReaderContext().registerWithGeneratedName(handlerAdapterDef);
String uriCompContribName = MvcUriComponentsBuilder.MVC_URI_COMPONENTS_CONTRIBUTOR_BEAN_NAME;
RootBeanDefinition uriCompContribDef = new RootBeanDefinition(CompositeUriComponentsContributorFactoryBean.class);
uriCompContribDef.setSource(source);
uriCompContribDef.getPropertyValues().addPropertyValue("handlerAdapter", handlerAdapterDef);
uriCompContribDef.getPropertyValues().addPropertyValue("conversionService", conversionService);
parserContext.getReaderContext().getRegistry().registerBeanDefinition(uriCompContribName, uriCompContribDef);
RootBeanDefinition csInterceptorDef = new RootBeanDefinition(ConversionServiceExposingInterceptor.class);
csInterceptorDef.setSource(source);
csInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, conversionService);
RootBeanDefinition mappedCsInterceptorDef = new RootBeanDefinition(MappedInterceptor.class);
mappedCsInterceptorDef.setSource(source);
mappedCsInterceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, (Object) null);
mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(1, csInterceptorDef);
String mappedInterceptorName = parserContext.getReaderContext().registerWithGeneratedName(mappedCsInterceptorDef);
RootBeanDefinition exceptionHandlerExceptionResolver = new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);
exceptionHandlerExceptionResolver.setSource(source);
exceptionHandlerExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
exceptionHandlerExceptionResolver.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
exceptionHandlerExceptionResolver.getPropertyValues().add("messageConverters", messageConverters);
exceptionHandlerExceptionResolver.getPropertyValues().add("order", 0);
addResponseBodyAdvice(exceptionHandlerExceptionResolver);
String methodExceptionResolverName =
parserContext.getReaderContext().registerWithGeneratedName(exceptionHandlerExceptionResolver);
RootBeanDefinition responseStatusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);
responseStatusExceptionResolver.setSource(source);
responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
responseStatusExceptionResolver.getPropertyValues().add("order", 1);
String responseStatusExceptionResolverName =
parserContext.getReaderContext().registerWithGeneratedName(responseStatusExceptionResolver);
// 注册默认的异常处理解析器
RootBeanDefinition defaultExceptionResolver = new RootBeanDefinition(DefaultHandlerExceptionResolver.class);
defaultExceptionResolver.setSource(source);
defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
defaultExceptionResolver.getPropertyValues().add("order", 2);
String defaultExceptionResolverName =
parserContext.getReaderContext().registerWithGeneratedName(defaultExceptionResolver);
parserContext.registerComponent(new BeanComponentDefinition(handlerMappingDef, methodMappingName));
parserContext.registerComponent(new BeanComponentDefinition(handlerAdapterDef, handlerAdapterName));
parserContext.registerComponent(new BeanComponentDefinition(uriCompContribDef, uriCompContribName));
parserContext.registerComponent(new BeanComponentDefinition(exceptionHandlerExceptionResolver, methodExceptionResolverName));
parserContext.registerComponent(new BeanComponentDefinition(responseStatusExceptionResolver, responseStatusExceptionResolverName));
parserContext.registerComponent(new BeanComponentDefinition(defaultExceptionResolver, defaultExceptionResolverName));
parserContext.registerComponent(new BeanComponentDefinition(mappedCsInterceptorDef, mappedInterceptorName));
// Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"
MvcNamespaceUtils.registerDefaultComponents(parserContext, source);
parserContext.popAndRegisterContainingComponent();
return null;
}
}AnnotationDrivenBeanDefinitionParser在哪里被注册？
public class MvcNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
......
}
}MvcNamespaceHandler在哪里被注册？
作用： 简单来说NamespaceHandler的作用就是处理自定义标签的，例如<mvc:annotation-driven>，每一个自定义标签都必须隶属于一个namespace下
NamespaceHandler被定义META-INF/spring.handles文件，MvcNamespaceHandler也不例外。
http\://www.springframework.org/schema/mvc=org.springframework.web.servlet.config.MvcNamespaceHandler具体的解析过程
// 解析自定义标签
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
// 根据标签拿到其namespaceUri
String namespaceUri = getNamespaceURI(ele);
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
// 使用Parser来解析标签，上面我们说过的AnnotationDrivenBeanDefinitionParser就是其一
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}public static final String DEFAULT_HANDLER_MAPPINGS_LOCATION = "META-INF/spring.handlers";
private final String handlerMappingsLocation;
// 解析获得能处理该namespace下标签的命名空间处理器
public NamespaceHandler resolve(String namespaceUri) {
Map<String, Object> handlerMappings = getHandlerMappings();
// 根据给定的namespaceUri找到对应的NamespaceHandler
Object handlerOrClassName = handlerMappings.get(namespaceUri);
if (handlerOrClassName == null) {
return null;
}
else if (handlerOrClassName instanceof NamespaceHandler) {
return (NamespaceHandler) handlerOrClassName;
}
else {
String className = (String) handlerOrClassName;
try {
Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
"] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
}
NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
namespaceHandler.init();
handlerMappings.put(namespaceUri, namespaceHandler);
return namespaceHandler;
}
catch (ClassNotFoundException ex) {
throw new FatalBeanException("NamespaceHandler class [" + className + "] for namespace [" +
namespaceUri + "] not found", ex);
}
catch (LinkageError err) {
throw new FatalBeanException("Invalid NamespaceHandler class [" + className + "] for namespace [" +
namespaceUri + "]: problem with handler class file or dependent class", err);
}
}
}
private Map<String, Object> getHandlerMappings() {
if (this.handlerMappings == null) {
synchronized (this) {
if (this.handlerMappings == null) {
try {
// 加载所有的spring.handlers文件内容为Properties对象
Properties mappings =
PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
if (logger.isDebugEnabled()) {
logger.debug("Loaded NamespaceHandler mappings: " + mappings);
}
Map<String, Object> handlerMappings = new ConcurrentHashMap<String, Object>(mappings.size());
CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
this.handlerMappings = handlerMappings;
}
catch (IOException ex) {
throw new IllegalStateException(
"Unable to load NamespaceHandler mappings from location [" + this.handlerMappingsLocation + "]", ex);
}
}
}
}
return this.handlerMappings;
} at org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver.resolve(DefaultNamespaceHandlerResolver.java:114)
at org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1419)
at org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1414)
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:189)
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:143)
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.registerBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:110)
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.registerBeanDefinitions(XmlBeanDefinitionReader.java:508)
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:391)
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:335)
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:303)
at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:180)
at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:216)
at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:187)
at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:125)
at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:94)
at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:129)
at org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:537)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:452)
// 通过打印堆栈信息，我们知道处理自定义标签的步骤发生在spring容器的启动过程中，即refresh->obtainFreshBeanFactory->loadBeanDefinitions
// refresh()是构建IOC容器的最核心代码，obtainFreshBeanFactory()加载xml中定义bean，转换为抽象世界中的BeanDefinitionNamespace在XML中的含义
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3school.com.cn"
xmlns="http://www.w3school.com.cn"
elementFormDefault="qualified">
...
...
</xs:schema>(1)xmlns:xs="http://www.w3.org/2001/XMLSchema":表明schema中用到的元素和数据类型出自此命名空间,同时规定来自此命名空间的元素和数据都要使用前序xs.
(2)targetNamespace="http://www.w3school.com.cn":显示 schema 中用到的元素和数据类型来自此命名空间.
(3)elementFormDefault="qualified":指出任何xml实例文档所使用的且在此schema中声明过的元素必须被命名空间限定.
@EnableWebMvc原理
使用@EnableWebMvc的作用大体上是与<annotation-driven>标签的作用一致。具体可以看WebMvcConfigurationSupport源码
四、请求处理原理
重要对象含义
- HandlerMapping
作用是根据request请求找到对应的Handler处理器以及Interceptor拦截器，并将它们封装在HandlerExecutionChain对象中 - RequestMappingInfo
存储@RequestMapping注解中保存的信息，作用类似于TransactionInfo，存储@Transactional注解信息
- HandlerMapping
初始化请求映射
映射存储在
// RequestMapping->HandlerMethod
private final Map<T, HandlerMethod> handlerMethods = new LinkedHashMap<T, HandlerMethod>();初始化映射的方法AbstractHandlerMethodMapping.initHandlerMethods()
@Override
public void afterPropertiesSet() {
initHandlerMethods();
}protected void initHandlerMethods() {
if (logger.isDebugEnabled()) {
logger.debug("Looking for request mappings in application context: " + getApplicationContext());
}
// 获得IOC容器中的所有对象
String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
getApplicationContext().getBeanNamesForType(Object.class));
for (String beanName : beanNames) {
// 提取标注有@Controller或@RequestMapping的对象
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX) &&
isHandler(getApplicationContext().getType(beanName))){
// 提取所有标注有@RequestMapping的方法，并注册到handlerMethods 中
detectHandlerMethods(beanName);
}
}
handlerMethodsInitialized(getHandlerMethods());
}
protected boolean isHandler(Class<?> beanType) {
return ((AnnotationUtils.findAnnotation(beanType, Controller.class) != null) ||
(AnnotationUtils.findAnnotation(beanType, RequestMapping.class) != null));
}
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, T> mappings = new IdentityHashMap<Method, T>();
final Class<?> userType = ClassUtils.getUserClass(handlerType);
// 遍历对象筛选标注有@RequestMaping注解的方法
Set<Method> methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {
@Override
public boolean matches(Method method) {
// 将@RequestMapping注解标注的信息抽象为@RequestMappingInfo对象
T mapping = getMappingForMethod(method, userType);
if (mapping != null) {
mappings.put(method, mapping);
return true;
}
else {
return false;
}
}
});
// 注册请求映射
for (Method method : methods) {
registerHandlerMethod(handler, method, mappings.get(method));
}
}请求原理
- 根据HttpRequest请求构建对应的RequestMappingInfo对象。
- 遍历handlerMethods映射找到对应的处理器方法。
- 根据RequestMappingHandlerAdaptor执行目标方法。
上面三步只是简化总结出了请求映射原理，更深一步的请求处理原理还请阅读DispatcherServlet.doDispatch()方法源码。
java
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