SpringMVC 和SpringBoot中的注解是如何起作用的，如何实现的

SpringMVC源码解读 - HandlerMapping - RequestMappingHandlerMapping初始化

 

https://www.cnblogs.com/leftthen/p/5208404.html

 

RequestMappingHandlerMapping ,用于注解@Controller,@RequestMapping来定义controller.

 1 @Controller
 2 @RequestMapping(value = "books")
 3 public class BookController {
 4
 5     @RequestMapping(value = "/{id}")
 6     @ResponseBody
 7     public String getBook(@PathVariable("id") String id) {
 8         // ...
 9         return id;
10     }
11 }

初始化时,3个类的大致分工如下:

　　AbstractHandlerMethodMapping定义整个算法流程;

　　RequestMappingInfoHandlerMapping提供匹配条件RequestMappingInfo的解析处理;

　　RequestMappingHandlerMapping根据@RequestMapping注解生成 RequestMappingInfo,同时提供isHandler实现

整个初始化工作由AbstractHandlerMethodMapping的initHandlerMethods主导.

　　1. 使用BeanFactoryUtils扫描应用下的Object或者直接从容器中获取Object

　　2. 迭代类,分别判断isHandler判断目标类是否Handler

　　　　2.1 RequestMappingHandlerMapping.isHandler根据@Controller或@RequestMapping注解判断(有任意一个)

　　3. 对handler解析出所有需要分发的方法detectHandlerMethods

　　　　3.1 获取原始的Class<?>

　　　　3.2 使用HandlerMethodSelector.selectMethods过滤具体handler method,预留getMappingForMethod模板方法给子类

　　　　　　RequestMappingHandlerMapping.getMappingForMethod根据类,方法上的RequestMapping注解生成匹配条件RequestMappingInfo

　　　　3.3 对过滤到的每个method进行注册registerHandlerMethod

　　　　　　a, 使用createHandlerMethod封装处理器为HandlerMethod

　　　　　　b, 判断之前是否已经匹配条件对应的处理器是否冲突(相同的匹配条件只能有一个对应的处理器)

　　　　　　c, 设置匹配条件到handler method的映射关系

　　　　　　d, 从匹配条件中解析出url,并注册到urlMap(url到匹配条件的映射),这边由RequestMappingInfoHandlerMapping.getMappingPathPatterns实现

　　4. 对HandlerMethod进行初始化handlerMethodsInitialized,其实现在什么都没做

在讲初始化之前,我们先来聊聊使用到的一些概念

　　1. 映射关系,url到匹配条件RequestMappingInfo,匹配条件到HandlerMethod

　　2. 特殊的MultiValueMap,特别在value是个List

　　3. 使用到注解@Controller,@RequestMapping

　　4. 封装处理器信息的HandlerMethod

　　5. 封装各类匹配条件的RequestMappingInfo(诸如pattern,http method,request parameter等)

　　6. RequestCondition记录匹配条件

1. 进行request分发前,需要在初始化时准备好映射关系,这边AbstractHandlerMethodMapping中有两个属性保存了映射关系

// AbstractHandlerMethodMapping

1     // 匹配条件到HandlerMethod的映射
2     private final Map<T, HandlerMethod> handlerMethods = new LinkedHashMap<T, HandlerMethod>();
3     // url到匹配条件的映射
4     private final MultiValueMap<String, T> urlMap = new LinkedMultiValueMap<String, T>();

2. 这边的MultiValueMap其实挺简单,就是map的值是个list

1 public interface MultiValueMap<K, V> extends Map<K, List<V>> {
2   // ...
3 }

3. 我们再来看看这边使用到的两个注解:

// @Controller

 1     // org.springframework.stereotype.Controller
 2 @Target({ElementType.TYPE})
 3 @Retention(RetentionPolicy.RUNTIME)
 4 @Documented
 5 @Component
 6 public @interface Controller {
 7
 8     /**
 9      * The value may indicate a suggestion for a logical component name,
10      * to be turned into a Spring bean in case of an autodetected component.
11      * @return the suggested component name, if any
12      */
13     String value() default "";
14
15 }

// @RequestMapping

 1     // org.springframework.web.bind.annotation.RequestMapping
 2     @Target({ElementType.METHOD, ElementType.TYPE})
 3     @Retention(RetentionPolicy.RUNTIME)
 4     @Documented
 5     @Mapping
 6     public @interface RequestMapping {
 7
 8         /**
 9          * url路径,如/myPath/*.do
10          */
11         String[] value() default {};
12
13         /**
14          * HTTP request methods 如:GET, POST, HEAD, OPTIONS, PUT, PATCH, DELETE, TRACE.
15          */
16         RequestMethod[] method() default {};
17
18         /**
19          * requeset parameter 有3种匹配方式,是否包含某个参数,参数值相等,参数值不等于某个值,如myParam!=myValue
20          */
21         String[] params() default {};
22
23         /**
24          * request的header
25          */
26         String[] headers() default {};
27
28         /**
29          * request的content type
30          */
31         String[] consumes() default {};
32
33         /**
34          * 返回内容的content type
35          */
36         String[] produces() default {};
37
38     }
39 }

4. HandlerMethod封装了处理器相关的全部信息,如类Object,方法Method,BeanFactory,参数MethodParameter[],原始方法Method

// HandlerMethod

 1     // org.springframework.web.method.HandlerMethod
 2     private final Object bean;// 因为final不可修改,所以下面每次需要修改信息时,都需要new一个
 3
 4     private final Method method;
 5
 6     private final BeanFactory beanFactory;
 7
 8     private final MethodParameter[] parameters;
 9
10     private final Method bridgedMethod;

5. 这边匹配条件的范型只有一个实现,RequestMappingInfo.匹配条件里记录的是RequestCondition子类,用于诸如pattern,http method,request parameter等

// RequestMappingInfo

 1     // javax.servlet.http.HttpServletRequest.RequestMappingInfo
 2 public final class RequestMappingInfo implements RequestCondition<RequestMappingInfo> {
 3
 4     private final PatternsRequestCondition patternsCondition;
 5
 6     private final RequestMethodsRequestCondition methodsCondition;
 7
 8     private final ParamsRequestCondition paramsCondition;
 9
10     private final HeadersRequestCondition headersCondition;
11
12     private final ConsumesRequestCondition consumesCondition;
13
14     private final ProducesRequestCondition producesCondition;
15
16     private final RequestConditionHolder customConditionHolder;
17     // ...
18
19 }

6. 最后再简单看看RequestCondition ,这边定义了3个方法

 1 package org.springframework.web.servlet.mvc.condition;
 2     public interface RequestCondition<T> {
 3         /**
 4          * 拼接条件
 5          */
 6         T combine(T other);
 7
 8         /**
 9          * 查找匹配的条件,并返回
10          */
11         T getMatchingCondition(HttpServletRequest request);
12
13         /**
14          * 用于排序
15          */
16         int compareTo(T other, HttpServletRequest request);
17     }

看看继承体系吧,老套路,定义接口,然后模板方法实现主要逻辑,具体算法留给子类实现,还有正事要做,还是后期再细化吧.

正文

整个初始化工作由AbstractHandlerMethodMapping的initHandlerMethods主导.copy一段,省得回去比对看

　　1. 使用BeanFactoryUtils扫描应用下的Object或者直接从容器中获取Object

　　2. 迭代类,分别判断isHandler判断目标类是否Handler

　　　　2.1 RequestMappingHandlerMapping.isHandler根据@Controller或@RequestMapping注解判断(有任意一个)

　　3. 对handler解析出所有需要分发的方法detectHandlerMethods

　　　　3.1 获取原始的Class<?>

　　　　3.2 使用HandlerMethodSelector.selectMethods过滤具体handler method,预留getMappingForMethod模板方法给子类

　　　　　　RequestMappingHandlerMapping.getMappingForMethod根据类,方法上的RequestMapping注解生成匹配条件RequestMappingInfo

　　　　3.3 对过滤到的每个method进行注册registerHandlerMethod

　　　　　　a, 使用createHandlerMethod封装处理器为HandlerMethod

　　　　　　b, 判断之前是否已经匹配条件对应的处理器是否冲突(相同的匹配条件只能有一个对应的处理器)

　　　　　　c, 设置匹配条件到handler method的映射关系

　　　　　　d, 从匹配条件中解析出url,并注册到urlMap(url到匹配条件的映射),这边由RequestMappingInfoHandlerMapping.getMappingPathPatterns实现

　　4. 对HandlerMethod进行初始化handlerMethodsInitialized,其实现在什么都没做

// AbstractHandlerMethodMapping

 1 /** 这个方法哪来的,具体看备注的InitializingBean
 2      * Detects handler methods at initialization.
 3      */
 4     public void afterPropertiesSet() {
 5         initHandlerMethods();
 6     }
 7
 8     /**扫描ApplicationContext中的bean,然后筛选handler method 并注册
 9      * Scan beans in the ApplicationContext, detect and register handler methods.
10      * @see #isHandler(Class)
11      * @see #getMappingForMethod(Method, Class)
12      * @see #handlerMethodsInitialized(Map)
13      */
14     protected void initHandlerMethods() {
15         if (logger.isDebugEnabled()) {
16             logger.debug("Looking for request mappings in application context: " + getApplicationContext());
17         }
18
19         String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
20                 BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
21                 getApplicationContext().getBeanNamesForType(Object.class));
22
23         for (String beanName : beanNames) {
24             if (isHandler(getApplicationContext().getType(beanName))){
25                 detectHandlerMethods(beanName);
26             }
27         }
28         handlerMethodsInitialized(getHandlerMethods());
29     }

预留给子类实现的判断handler,实际是由RequestMappingHandlerMapping实现　　

// AbstractHandlerMethodMapping

1     /**
2      * Whether the given type is a handler with handler methods.
3      * @param beanType the type of the bean being checked
4      * @return "true" if this a handler type, "false" otherwise.
5      */
6     protected abstract boolean isHandler(Class<?> beanType);

// RequestMappingHandlerMapping

这边判断的逻辑很简单,类上使用Controller或RequestMapping其中至少一个注解就可以.

1     /**
2      * {@inheritDoc}
3      * Expects a handler to have a type-level @{@link Controller} annotation.
4      */
5     @Override
6     protected boolean isHandler(Class<?> beanType) {
7         return ((AnnotationUtils.findAnnotation(beanType, Controller.class) != null) ||
8                 (AnnotationUtils.findAnnotation(beanType, RequestMapping.class) != null));
9     }

// AbstractHandlerMethodMapping

 1     /**
 2      * Look for handler methods in a handler.
 3      * @param handler the bean name of a handler or a handler instance
 4      */
 5     protected void detectHandlerMethods(final Object handler) {
 6         Class<?> handlerType = (handler instanceof String) ?
 7                 getApplicationContext().getType((String) handler) : handler.getClass();
 8
 9         final Class<?> userType = ClassUtils.getUserClass(handlerType);
10
11         Set<Method> methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {
12             public boolean matches(Method method) {
13                 return getMappingForMethod(method, userType) != null;
14             }
15         });
16
17         for (Method method : methods) {
18             T mapping = getMappingForMethod(method, userType);
19             registerHandlerMethod(handler, method, mapping);
20         }
21     }

// AbstractHandlerMethodMapping

这边具体的实现是由RequestMappingHandlerMapping实现,根据注解生产匹配关系,这边实现类是RequestMappingInfo,就是代码有点多,慢慢看

1     /**
2      * Provide the mapping for a handler method. A method for which no
3      * mapping can be provided is not a handler method.
4      * @param method the method to provide a mapping for
5      * @param handlerType the handler type, possibly a sub-type of the method's
6      * declaring class
7      * @return the mapping, or {@code null} if the method is not mapped
8      */
9     protected abstract T getMappingForMethod(Method method, Class<?> handlerType);

// RequestMappingHandlerMapping

 1     /**
 2      * Uses method and type-level @{@link RequestMapping} annotations to create
 3      * the RequestMappingInfo.
 4      *
 5      * @return the created RequestMappingInfo, or {@code null} if the method
 6      * does not have a {@code @RequestMapping} annotation.
 7      *
 8      * @see #getCustomMethodCondition(Method)
 9      * @see #getCustomTypeCondition(Class)
10      */
11     @Override
12     protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
13         RequestMappingInfo info = null;
14         // 读取方法上的RequestMapping注解信息
15         RequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, RequestMapping.class);
16         if (methodAnnotation != null) {
17             // 读取自定义的条件,这边没有使用
18             RequestCondition<?> methodCondition = getCustomMethodCondition(method);
19             // 根据方法上的RequsetMapping注解和自定义条件,生成匹配条件.这边的匹配条件包括http method,request parameter,request header等
20             info = createRequestMappingInfo(methodAnnotation, methodCondition);
21             // 读取类上的RequestMapping注解信息
22             RequestMapping typeAnnotation = AnnotationUtils.findAnnotation(handlerType, RequestMapping.class);
23             if (typeAnnotation != null) {
24                 RequestCondition<?> typeCondition = getCustomTypeCondition(handlerType);
25                 // 生成类上的匹配条件,并合并方法上的
26                 info = createRequestMappingInfo(typeAnnotation, typeCondition).combine(info);
27             }
28         }
29         return info;
30     }

// RequestMappingHandlerMapping

 1     /**
 2      * Created a RequestMappingInfo from a RequestMapping annotation.
 3      */
 4     private RequestMappingInfo createRequestMappingInfo(RequestMapping annotation, RequestCondition<?> customCondition) {
 5         String[] patterns = resolveEmbeddedValuesInPatterns(annotation.value());
 6         return new RequestMappingInfo(
 7                 new PatternsRequestCondition(patterns, getUrlPathHelper(), getPathMatcher(),
 8                         this.useSuffixPatternMatch, this.useTrailingSlashMatch, this.fileExtensions),
 9                 new RequestMethodsRequestCondition(annotation.method()),
10                 new ParamsRequestCondition(annotation.params()),
11                 new HeadersRequestCondition(annotation.headers()),
12                 new ConsumesRequestCondition(annotation.consumes(), annotation.headers()),
13                 new ProducesRequestCondition(annotation.produces(), annotation.headers(), getContentNegotiationManager()),
14                 customCondition);
15     }
16
17     /**
18      * Resolve placeholder values in the given array of patterns.
19      * @return a new array with updated patterns
20      */
21     protected String[] resolveEmbeddedValuesInPatterns(String[] patterns) {
22         if (this.embeddedValueResolver == null) {
23             return patterns;
24         }
25         else {
26             String[] resolvedPatterns = new String[patterns.length];
27             for (int i=0; i < patterns.length; i++) {
28                 resolvedPatterns[i] = this.embeddedValueResolver.resolveStringValue(patterns[i]);
29             }
30             return resolvedPatterns;
31         }
32     }

// AbstractHandlerMethodMapping

 1 /**
 2      * Register a handler method and its unique mapping.
 3      * @param handler the bean name of the handler or the handler instance
 4      * @param method the method to register
 5      * @param mapping the mapping conditions associated with the handler method
 6      * @throws IllegalStateException if another method was already registered
 7      * under the same mapping
 8      */
 9     protected void registerHandlerMethod(Object handler, Method method, T mapping) {
10         HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);
11         HandlerMethod oldHandlerMethod = handlerMethods.get(mapping);
12         if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {
13             throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean()
14                     + "' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '"
15                     + oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");
16         }
17
18         this.handlerMethods.put(mapping, newHandlerMethod);// 匹配条件requestMappingInfo 到处理器HandlerMethod
19         if (logger.isInfoEnabled()) {
20             logger.info("Mapped \"" + mapping + "\" onto " + newHandlerMethod);
21         }
22
23         Set<String> patterns = getMappingPathPatterns(mapping);
24         for (String pattern : patterns) {
25             if (!getPathMatcher().isPattern(pattern)) {
26                 this.urlMap.add(pattern, mapping);// url到匹配条件RequestMappingInfo
27             }
28         }
29     }

// AbstractHandlerMethodMapping

 1     /**
 2      * Create the HandlerMethod instance.
 3      * @param handler either a bean name or an actual handler instance
 4      * @param method the target method
 5      * @return the created HandlerMethod
 6      */
 7     protected HandlerMethod createHandlerMethod(Object handler, Method method) {
 8         HandlerMethod handlerMethod;
 9         if (handler instanceof String) {
10             String beanName = (String) handler;
11             handlerMethod = new HandlerMethod(beanName, getApplicationContext(), method);
12         }
13         else {
14             handlerMethod = new HandlerMethod(handler, method);
15         }
16         return handlerMethod;
17     }

// AbstractHandlerMethodMapping

1     /**
2      * Extract and return the URL paths contained in a mapping.
3      */
4     protected abstract Set<String> getMappingPathPatterns(T mapping);

RequestMappingInfoHandlerMapping会实现这个模板方法

// RequestMappingInfoHandlerMapping

1     /**
2      * Get the URL path patterns associated with this {@link RequestMappingInfo}.
3      */
4     @Override
5     protected Set<String> getMappingPathPatterns(RequestMappingInfo info) {
6         return info.getPatternsCondition().getPatterns();
7     }

备注:

1. 这边的afterPropertiesSet是因为实现了InitializingBean接口

// org.springframework.beans.factory.InitializingBean

 1 /**
 2  * Interface to be implemented by beans that need to react once all their
 3  * properties have been set by a BeanFactory: for example, to perform custom
 4  * initialization, or merely to check that all mandatory properties have been set.
 5  *
 6  * <p>An alternative to implementing InitializingBean is specifying a custom
 7  * init-method, for example in an XML bean definition.
 8  * For a list of all bean lifecycle methods, see the BeanFactory javadocs.
 9  *
10  * @author Rod Johnson
11  * @see BeanNameAware
12  * @see BeanFactoryAware
13  * @see BeanFactory
14  * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
15  * @see org.springframework.context.ApplicationContextAware
16  */
17 public interface InitializingBean {
18
19     /**
20      * Invoked by a BeanFactory after it has set all bean properties supplied
21      * (and satisfied BeanFactoryAware and ApplicationContextAware).
22      * <p>This method allows the bean instance to perform initialization only
23      * possible when all bean properties have been set and to throw an
24      * exception in the event of misconfiguration.
25      * @throws Exception in the event of misconfiguration (such
26      * as failure to set an essential property) or if initialization fails.
27      */
28     void afterPropertiesSet() throws Exception;
29
30 }