# 精尽 Spring MVC 源码解析 —— HandlerAdapter 组件（一）之 HandlerAdapter

# 1. 概述

本文，我们来分享 HandlerMapping 组件。在 [《精尽 Spring MVC 源码分析 —— 组件一览》](http://svip.iocoder.cn/Spring-MVC/Components-intro) 中，我们对它已经做了介绍：

`org.springframework.web.servlet.HandlerAdapter` ，处理器适配器接口。代码如下：

```
// HandlerAdapter.java

public interface HandlerAdapter {

    /**
     * 是否支持该处理器
     */
    boolean supports(Object handler);

    /**
     * 执行处理器，返回 ModelAndView 结果
     */
    @Nullable
    ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

    /**
     * 返回请求的最新更新时间。
     *
     * 如果不支持该操作，则返回 -1 即可
     */
    long getLastModified(HttpServletRequest request, Object handler);

}
```

- 因为，处理器 `handler` 的类型是 Object 类型，需要有一个调用者来实现 `handler` 是怎么被使用，怎么被执行。而 HandlerAdapter 的用途就在于此。可能如果接口名改成 HandlerInvoker ，笔者觉得会更好理解。

# 2. HandlerAdapter

HandlerAdapter 的子类比较多，整体类图如下：[![HandlerAdapter 类图](14-Spring MVC 源码解析-HandlerAdapter 组件（一）之 HandlerAdapter.assets/01.png)](http://static.iocoder.cn/images/Spring/2022-03-20/01.png)HandlerAdapter 类图

- 左边的 AbstractHandlerMethodAdapter 和 RequestMappingHandlerAdapter 相对复杂
- 右边的 SimpleServletHandlerAdapter、HttpRequestHandlerAdapter、SimpleControllerHandlerAdapter 相对简单

那么，我们从~~难的~~简单的开始。哈哈哈哈。

# 3. SimpleControllerHandlerAdapter

`org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter` ，实现 HandlerAdapter 接口，基于 `org.springframework.web.servlet.mvc.Controller` 的 HandlerAdapter 实现类。代码如下：

```
// SimpleControllerHandlerAdapter.java

public class SimpleControllerHandlerAdapter implements HandlerAdapter {

    @Override
    public boolean supports(Object handler) {
        // <1> 判断是 Controller 类型
        return (handler instanceof Controller);
    }

    @Override
    @Nullable
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        // <2> Controller 类型的调用
        return ((Controller) handler).handleRequest(request, response);
    }

    @Override
    public long getLastModified(HttpServletRequest request, Object handler) {
        // 处理器实现了 LastModified 接口的情况下
        if (handler instanceof LastModified) {
            return ((LastModified) handler).getLastModified(request);
        }
        return -1L;
    }

}
```

- `<1>` 处，判断处理器 `handler` 是 Controller 类型。注意，不是 `@Controller` 注解。
- `<2>` 处，调用 `Controller#handleRequest(HttpServletRequest request, HttpServletResponse response)` 方法，Controller 类型的调用。

# 4. HttpRequestHandlerAdapter

`org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter` ，实现 HandlerAdapter 接口，基于 `org.springframework.web.HttpRequestHandler` 的 HandlerAdapter 实现类。代码如下：

```
// HttpRequestHandlerAdapter.java

public class HttpRequestHandlerAdapter implements HandlerAdapter {

    @Override
    public boolean supports(Object handler) {
        // 判断是 HttpRequestHandler 类型
        return (handler instanceof HttpRequestHandler);
    }

    @Override
    @Nullable
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        // HttpRequestHandler 类型的调用
        ((HttpRequestHandler) handler).handleRequest(request, response);
        return null;
    }

    @Override
    public long getLastModified(HttpServletRequest request, Object handler) {
        // 处理器实现了 LastModified 接口的情况下
        if (handler instanceof LastModified) {
            return ((LastModified) handler).getLastModified(request);
        }
        return -1L;
    }

}
```

- 和 [「3. SimpleControllerHandlerAdapter」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 类似。

# 5. SimpleServletHandlerAdapter

`org.springframework.web.servlet.handler.SimpleServletHandlerAdapter` ，实现 HandlerAdapter 接口，基于 `javax.servlet.Servlet` 的 HandlerAdapter 实现类。代码如下：

```
// SimpleServletHandlerAdapter.java

public class SimpleServletHandlerAdapter implements HandlerAdapter {

    @Override
    public boolean supports(Object handler) {
        // 判断是 Servlet 类型
        return (handler instanceof Servlet);
    }

    @Override
    @Nullable
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        // Servlet 类型的调用
        ((Servlet) handler).service(request, response);
        return null;
    }

    @Override
    public long getLastModified(HttpServletRequest request, Object handler) {
        return -1;
    }

}
```

# 6. AbstractHandlerMethodAdapter

`org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter` ，实现 HandlerAdapter、Ordered 接口，继承 WebContentGenerator 抽象类，基于 `org.springframework.web.method.HandlerMethod` 的 HandlerMethodAdapter 抽象类。

为什么要有这层抽象？让我们回过头看看 [《精尽 Spring MVC 源码解析 —— HandlerMapping 组件（三）之 AbstractHandlerMethodMapping》](http://svip.iocoder.cn/Spring-MVC/HandlerMapping-3-AbstractHandlerMethodMapping) 就会明白：

- AbstractHandlerMethodMapping 对应 [「6. AbstractHandlerMethodAdapter」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。
- RequestMappingInfoHandlerMapping 对应 [「7. RequestMappingHandlerAdapter」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。

## 6.1 构造方法

```
// AbstractHandlerMethodAdapter.java

private int order = Ordered.LOWEST_PRECEDENCE;

public AbstractHandlerMethodAdapter() {
    // no restriction of HTTP methods by default
    // 调用 WebContentGenerator 类的构造方法
    // 参数 restrictDefaultSupportedMethods 参数为 false ，表示不需要严格校验 HttpMethod
    super(false);
}
```

## 6.2 supports

实现 `#supports(Object handler)` 方法，支持 HandlerMethod 类型的处理器。代码如下：

```
// AbstractHandlerMethodAdapter.java

@Override
public final boolean supports(Object handler) {
	return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
```

- 其中，`#supportsInternal(HandlerMethod handlerMethod)` 方法，由子类实现。代码如下：

  ```
  // AbstractHandlerMethodAdapter.java
  
  /**
   * Given a handler method, return whether or not this adapter can support it.
   * @param handlerMethod the handler method to check
   * @return whether or not this adapter can adapt the given method
   */
  protected abstract boolean supportsInternal(HandlerMethod handlerMethod);
  ```

  - 关于 RequestMappingHandlerAdapter 类对该方法的实现，见 [「7.3 supportsInternal」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。

## 6.3 handle

实现 `#handle(HttpServletRequest request, HttpServletResponse response, Object handler)` 方法，处理器请求。代码如下：

```
// AbstractHandlerMethodAdapter.java

@Override
@Nullable
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
		throws Exception {
	return handleInternal(request, response, (HandlerMethod) handler);
}

/**
 * Use the given handler method to handle the request.
 * @param request current HTTP request
 * @param response current HTTP response
 * @param handlerMethod handler method to use. This object must have previously been passed to the
 * {@link #supportsInternal(HandlerMethod)} this interface, which must have returned {@code true}.
 * @return a ModelAndView object with the name of the view and the required model data,
 * or {@code null} if the request has been handled directly
 * @throws Exception in case of errors
 */
@Nullable
protected abstract ModelAndView handleInternal(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception;
```

- 其中，`#handleInternal(...)` 抽象方法，将 `handler` 参数是 HandlerMethod 类型。关于 RequestMappingHandlerAdapter 类对该方法的实现，见 [「7.5 handleInternal」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。

## 6.4 getLastModified

`#getLastModified(HttpServletRequest request, Object handler)` 方法，获得最后更新时间。代码如下：

```
// AbstractHandlerMethodAdapter.java

@Override
public final long getLastModified(HttpServletRequest request, Object handler) {
	return getLastModifiedInternal(request, (HandlerMethod) handler);
}

/**
 * Same contract as for {@link javax.servlet.http.HttpServlet#getLastModified(HttpServletRequest)}.
 * @param request current HTTP request
 * @param handlerMethod handler method to use
 * @return the lastModified value for the given handler
 */
protected abstract long getLastModifiedInternal(HttpServletRequest request, HandlerMethod handlerMethod);
```

- 套路同 [「6.3 handle」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。

# 7. RequestMappingHandlerAdapter

`org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter` ，实现 BeanFactoryAware、InitializingBean 接口，继承 AbstractHandlerMethodAdapter 抽象类，基于 `@RequestMapping` 注解的 HandlerMethod 的 HandlerMethodAdapter 实现类。

## 7.1 构造方法

```
// RequestMappingHandlerAdapter.java

/**
 * MethodFilter that matches {@link InitBinder @InitBinder} methods.
 */
public static final MethodFilter INIT_BINDER_METHODS = method ->
		AnnotatedElementUtils.hasAnnotation(method, InitBinder.class);

/**
 * MethodFilter that matches {@link ModelAttribute @ModelAttribute} methods.
 */
public static final MethodFilter MODEL_ATTRIBUTE_METHODS = method ->
		(!AnnotatedElementUtils.hasAnnotation(method, RequestMapping.class) &&
				AnnotatedElementUtils.hasAnnotation(method, ModelAttribute.class));

@Nullable
private List<HandlerMethodArgumentResolver> customArgumentResolvers;

@Nullable
private HandlerMethodArgumentResolverComposite argumentResolvers;

@Nullable
private HandlerMethodArgumentResolverComposite initBinderArgumentResolvers;

@Nullable
private List<HandlerMethodReturnValueHandler> customReturnValueHandlers;

@Nullable
private HandlerMethodReturnValueHandlerComposite returnValueHandlers;

@Nullable
private List<ModelAndViewResolver> modelAndViewResolvers;

private ContentNegotiationManager contentNegotiationManager = new ContentNegotiationManager();

private List<HttpMessageConverter<?>> messageConverters;

private List<Object> requestResponseBodyAdvice = new ArrayList<>();

@Nullable
private WebBindingInitializer webBindingInitializer;

private AsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor("MvcAsync");

@Nullable
private Long asyncRequestTimeout;

private CallableProcessingInterceptor[] callableInterceptors = new CallableProcessingInterceptor[0];

private DeferredResultProcessingInterceptor[] deferredResultInterceptors = new DeferredResultProcessingInterceptor[0];

private ReactiveAdapterRegistry reactiveAdapterRegistry = ReactiveAdapterRegistry.getSharedInstance();

private boolean ignoreDefaultModelOnRedirect = false;

private int cacheSecondsForSessionAttributeHandlers = 0;

/**
 * 是否对相同 Session 加锁
 */
private boolean synchronizeOnSession = false;

private SessionAttributeStore sessionAttributeStore = new DefaultSessionAttributeStore();

private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();

@Nullable
private ConfigurableBeanFactory beanFactory;

// ========== 缓存 ==========

private final Map<Class<?>, SessionAttributesHandler> sessionAttributesHandlerCache = new ConcurrentHashMap<>(64);

private final Map<Class<?>, Set<Method>> initBinderCache = new ConcurrentHashMap<>(64);

private final Map<ControllerAdviceBean, Set<Method>> initBinderAdviceCache = new LinkedHashMap<>();

private final Map<Class<?>, Set<Method>> modelAttributeCache = new ConcurrentHashMap<>(64);

private final Map<ControllerAdviceBean, Set<Method>> modelAttributeAdviceCache = new LinkedHashMap<>();
	
public RequestMappingHandlerAdapter() {
	// 初始化 messageConverters
	StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
	stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316

	this.messageConverters = new ArrayList<>(4);
	this.messageConverters.add(new ByteArrayHttpMessageConverter());
	this.messageConverters.add(stringHttpMessageConverter);
	try {
		this.messageConverters.add(new SourceHttpMessageConverter<>());
	} catch (Error err) {
		// Ignore when no TransformerFactory implementation is available
	}
	this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
}
```

- 属性比较多，先不着急看，有个印象即可。
- 另外，也是因为属性多，所以 RequestMappingHandlerAdapter 有大量的 setting 方法。

## 7.2 afterPropertiesSet

> 艿艿：这里我们会看到大量的 RequestMappingHandlerAdapter 的属性初始化。😈 当然，本小节还是不细讲。哈哈哈哈。

`#afterPropertiesSet()` 方法，进一步初始化 RequestMappingHandlerAdapter 。代码如下：

```
// RequestMappingHandlerAdapter.java

@Override
public void afterPropertiesSet() {
	// Do this first, it may add ResponseBody advice beans
	// <1> 初始化 ControllerAdvice 相关
	initControllerAdviceCache();

	// <2> 初始化 argumentResolvers 属性
	if (this.argumentResolvers == null) {
		List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
		this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
	}
	// <3> 初始化 initBinderArgumentResolvers 属性
	if (this.initBinderArgumentResolvers == null) {
		List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
		this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
	}
	// <4> 初始化 returnValueHandlers 属性
	if (this.returnValueHandlers == null) {
		List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
		this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
	}
}
```

- `<1>` 处，调用 `#initControllerAdviceCache()` 方法，初始化 ControllerAdvice 相关。详细解析，见 [「7.2.1 initControllerAdviceCache」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。
- `<2>` 处，初始化 `argumentResolvers` 属性。其中，`#getDefaultArgumentResolvers()` 方法，获得默认的 HandlerMethodArgumentResolver 数组。详细解析，见 [「7.2.2 getDefaultArgumentResolvers」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。
- `<3>` 处，初始化 `initBinderArgumentResolvers` 属性。其中，`#getDefaultInitBinderArgumentResolvers()` 方法，获得默认的 HandlerMethodArgumentResolver 数组。详细解析，见 [「7.2.3 getDefaultInitBinderArgumentResolvers」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。
- `<4>` 处，初始化 `returnValueHandlers` 属性。其中，`#getDefaultReturnValueHandlers()` 方法，获得默认的 HandlerMethodReturnValueHandler 数组。详细解析，见 [「7.2.4 getDefaultReturnValueHandlers」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。

### 7.2.1 initControllerAdviceCache

`#initControllerAdviceCache()` 方法，初始化 ControllerAdvice 相关。代码如下：

```
// RequestMappingHandlerAdapter.java

private void initControllerAdviceCache() {
	if (getApplicationContext() == null) {
		return;
	}

	// <1> 扫描 @ControllerAdvice 注解的 Bean 们，并将进行排序
	List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
	AnnotationAwareOrderComparator.sort(adviceBeans);

	List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();

	// <2> 遍历 ControllerAdviceBean 数组
	for (ControllerAdviceBean adviceBean : adviceBeans) {
		Class<?> beanType = adviceBean.getBeanType();
		if (beanType == null) {
			throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
		}
		// <2.1> 扫描有 @ModelAttribute ，无 @RequestMapping 注解的方法，添加到 modelAttributeAdviceCache 中
		Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
		if (!attrMethods.isEmpty()) {
			this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
		}
		// <2.2> 扫描有 @InitBinder 注解的方法，添加到 initBinderAdviceCache 中
		Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS);
		if (!binderMethods.isEmpty()) {
			this.initBinderAdviceCache.put(adviceBean, binderMethods);
		}
		// <2.3> 如果是 RequestBodyAdvice 或 ResponseBodyAdvice 的子类，添加到 requestResponseBodyAdviceBeans 中
		if (RequestBodyAdvice.class.isAssignableFrom(beanType)) {
			requestResponseBodyAdviceBeans.add(adviceBean);
		}
		if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
			requestResponseBodyAdviceBeans.add(adviceBean);
		}
	}

	// <2.3> 将 requestResponseBodyAdviceBeans 添加到 this.requestResponseBodyAdvice 属性种
	if (!requestResponseBodyAdviceBeans.isEmpty()) {
		this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
	}

	// 打印日志
	if (logger.isDebugEnabled()) {
		int modelSize = this.modelAttributeAdviceCache.size();
		int binderSize = this.initBinderAdviceCache.size();
		int reqCount = getBodyAdviceCount(RequestBodyAdvice.class);
		int resCount = getBodyAdviceCount(ResponseBodyAdvice.class);
		if (modelSize == 0 && binderSize == 0 && reqCount == 0 && resCount == 0) {
			logger.debug("ControllerAdvice beans: none");
		} else {
			logger.debug("ControllerAdvice beans: " + modelSize + " @ModelAttribute, " + binderSize +
					" @InitBinder, " + reqCount + " RequestBodyAdvice, " + resCount + ", ResponseBodyAdvice");
		}
	}
}
```

- `<1>` 处，调用 `ControllerAdviceBean#findAnnotatedBeans(ApplicationContext context)` 方法，扫描 `@ControllerAdvice` 注解的 Bean 们，并将进行排序。可能有胖友不熟悉这个注解，可以看看 [《Spring 3.2 新注解 @ControllerAdvice》](http://jinnianshilongnian.iteye.com/blog/1866350) 。
- `<2>` 处，遍历 ControllerAdviceBean 数组。
- `<2.1>` 处，扫描有 `@ModelAttribute` ，无 `@RequestMapping` 注解的方法，添加到 `modelAttributeAdviceCache` 中。
- `<2.2>` 处，扫描有 `@InitBinder` 注解的方法，添加到 `initBinderAdviceCache` 中。
- `<2.3>` 处，如果是 RequestBodyAdvice 或 ResponseBodyAdvice 的子类，添加到 `requestResponseBodyAdviceBeans` 中。

### 7.2.2 getDefaultArgumentResolvers

`#getDefaultArgumentResolvers()` 方法，获得默认的 HandlerMethodArgumentResolver 数组。见 [传送门](https://github.com/spring-projects/spring-framework/blob/master/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapter.java#L637-L682) 。

### 7.2.3 getDefaultInitBinderArgumentResolvers

`#getDefaultInitBinderArgumentResolvers()` 方法，获得默认的 HandlerMethodArgumentResolver 数组。见 [传送门](https://github.com/spring-projects/spring-framework/blob/master/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapter.java#L684-L715) 。

### 7.2.4 getDefaultReturnValueHandlers

`#getDefaultReturnValueHandlers()` 方法，获得默认的 HandlerMethodReturnValueHandler 数组。见 [传送门](https://github.com/spring-projects/spring-framework/blob/master/spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapter.java#L717-L761) 。

## 7.3 supportsInternal

实现 `#supportsInternal()` 接口，默认返回 `true` 。代码如下：

```
// RequestMappingHandlerAdapter.java

/**
 * Always return {@code true} since any method argument and return value
 * type will be processed in some way. A method argument not recognized
 * by any HandlerMethodArgumentResolver is interpreted as a request parameter
 * if it is a simple type, or as a model attribute otherwise. A return value
 * not recognized by any HandlerMethodReturnValueHandler will be interpreted
 * as a model attribute.
 */
@Override
protected boolean supportsInternal(HandlerMethod handlerMethod) {
	return true;
}
```

## 7.4 getLastModifiedInternal

实现 `#getLastModifiedInternal()` 方法，默认返回 `-1` 。代码如下：

```
// RequestMappingHandlerAdapter.java

/**
 * This implementation always returns -1. An {@code @RequestMapping} method can
 * calculate the lastModified value, call {@link WebRequest#checkNotModified(long)},
 * and return {@code null} if the result of that call is {@code true}.
 */
@Override
protected long getLastModifiedInternal(HttpServletRequest request, HandlerMethod handlerMethod) {
	return -1;
}
```

## 7.5 handleInternal

实现 `#handleInternal(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod)` 方法，处理请求。代码如下：

```
// RequestMappingHandlerAdapter.java

@Override
protected ModelAndView handleInternal(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
    // 处理结果 ModelAndView 对象
    ModelAndView mav;

    // <1> 校验请求
    checkRequest(request);

	// Execute invokeHandlerMethod in synchronized block if required.
	// <2> 调用 HandlerMethod 方法
	if (this.synchronizeOnSession) { // 同步相同 Session 的逻辑
		HttpSession session = request.getSession(false);
		if (session != null) {
			Object mutex = WebUtils.getSessionMutex(session);
			synchronized (mutex) {
				mav = invokeHandlerMethod(request, response, handlerMethod);
			}
		} else {
			// No HttpSession available -> no mutex necessary
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}
	} else {
		// No synchronization on session demanded at all...
		mav = invokeHandlerMethod(request, response, handlerMethod);
	}

	// <3> TODO WebContentGenerator
	if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
		if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
			applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
		} else {
			prepareResponse(response);
		}
	}

	return mav;
}
```

- `<1>` 处，调用父类 WebContentGenerator 的 `#checkRequest(ttpServletRequest request)` 方法，校验请求是否合法。代码如下：

  ```
  // WebContentGenerator.java
  
  protected final void checkRequest(HttpServletRequest request) throws ServletException {
  	// Check whether we should support the request method.
  	String method = request.getMethod();
  	if (this.supportedMethods != null && !this.supportedMethods.contains(method)) {
  		throw new HttpRequestMethodNotSupportedException(method, this.supportedMethods);
  	}
  
  	// Check whether a session is required.
  	if (this.requireSession && request.getSession(false) == null) {
  		throw new HttpSessionRequiredException("Pre-existing session required but none found");
  	}
  }
  ```

  - 主要是 **HttpMethod 的类型**和**是否有 Session** 的校验。

- `<2>` 处，调用 `#invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod)` 方法，调用 HandlerMethod 方法。详细解析，见 [「7.5.1 invokeHandlerMethod」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 。

  - 在 `<2>` 中，有一个通过 `synchronizeOnSession` 属性，控制是否**同步相同 Session** 的逻辑，还是蛮有趣的。其中 `WebUtils#getSessionMutex(session)` 方法，获得用来锁的对象。代码如下：

    ```
    // WebUtils.java
    	
    public static Object getSessionMutex(HttpSession session) {
    	Assert.notNull(session, "Session must not be null");
    	Object mutex = session.getAttribute(SESSION_MUTEX_ATTRIBUTE);
    	if (mutex == null) {
    		mutex = session;
    	}
    	return mutex;
    }
    ```

    - 当然，因为锁是通过 `synchronized` 是 JVM 进程级，所以在分布式环境下，无法达到**同步相同 Session** 的功能。默认情况下，`synchronizeOnSession` 为 `false` 。

- `<3>` 处，TODO 1015 WebContentGenerator

### 7.5.1 invokeHandlerMethod

`#invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod)` 方法，调用 HandlerMethod 方法。代码如下：

```
// RequestMappingHandlerAdapter.java

/**
 * Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
 * if view resolution is required.
 * @since 4.2
 * @see #createInvocableHandlerMethod(HandlerMethod)
 */
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
        HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

    // <1> 创建 ServletWebRequest 对象
    ServletWebRequest webRequest = new ServletWebRequest(request, response);
    try {
        // <2> 创建 WebDataBinderFactory 对象
        WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
        // <3> 创建 ModelFactory 对象
        ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

        // <4> 创建 ServletInvocableHandlerMethod 对象，并设置其相关属性
        ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
        if (this.argumentResolvers != null) {
            invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
        }
        if (this.returnValueHandlers != null) {
            invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
        }
        invocableMethod.setDataBinderFactory(binderFactory);
        invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);

        // <5> 创建 ModelAndViewContainer 对象，并初始其相关属性
        ModelAndViewContainer mavContainer = new ModelAndViewContainer();
        mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
        modelFactory.initModel(webRequest, mavContainer, invocableMethod);
        mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

        // <6> TODO 芋艿 1003 async
        AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
        asyncWebRequest.setTimeout(this.asyncRequestTimeout);

        // <7> TODO 芋艿 1003 async
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        asyncManager.setTaskExecutor(this.taskExecutor);
        asyncManager.setAsyncWebRequest(asyncWebRequest);
        asyncManager.registerCallableInterceptors(this.callableInterceptors);
        asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

        // <8> TODO 芋艿 1003 async
        if (asyncManager.hasConcurrentResult()) {
            Object result = asyncManager.getConcurrentResult();
            mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
            asyncManager.clearConcurrentResult();
            LogFormatUtils.traceDebug(logger, traceOn -> {
                String formatted = LogFormatUtils.formatValue(result, !traceOn);
                return "Resume with async result [" + formatted + "]";
            });
            invocableMethod = invocableMethod.wrapConcurrentResult(result);
        }

        // <9> 执行调用
        invocableMethod.invokeAndHandle(webRequest, mavContainer);

        // <10> TODO 芋艿 1003 async
        if (asyncManager.isConcurrentHandlingStarted()) {
            return null;
        }

        // <11> 获得 ModelAndView 对象
        return getModelAndView(mavContainer, modelFactory, webRequest);
    } finally {
        // <12> 标记请求完成
        webRequest.requestCompleted();
    }
}
```

- 因为，Spring MVC 提供了大量的特性，所以涉及的组件会不少。😈 我们主要先梳理好主流程，所以涉及的组件，还是先不详细解析。我们的目的是，看到怎么调用 HandlerMethod 方法的，即调用 Controller 的 `@RequestMapping` 注解的方法。

- `<1>` 处，创建 ServletWebRequest 对象。

- `<2>` 处，调用 `#getDataBinderFactory(HandlerMethod handlerMethod)` 方法，创建 WebDataBinderFactory 对象。TODO 1016 WebDataBinderFactory

- `<3>` 处，调用 `#getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory)` 方法，创建 ModelFactory 对象。TODO 1017 ModelFactory

- `<4>` 处，调用 `#createInvocableHandlerMethod(HandlerMethod handlerMethod)` 方法，创建 ServletInvocableHandlerMethod 对象，然后设置其属性。本文会对 ServletInvocableHandlerMethod 做简单的解析。当然，详细的解析，胖友可以后续看看 [《精尽 Spring MVC 源码解析 —— HandlerAdapter 组件（二）之 ServletInvocableHandlerMethod》](http://svip.iocoder.cn/Spring-MVC/HandlerAdapter-2-ServletInvocableHandlerMethod) 一文。

- `<5>` 处，创建 ModelAndViewContainer 对象，并初始其相关属性。TODO 1019 ModelAndViewContainer

- `<6>` 处，TODO 芋艿 1003 async

- `<7>` 处，TODO 芋艿 1003 async

- `<8>` 处，TODO 芋艿 1003 async

- 【关键】`<9>` 处，调用 `ServletInvocableHandlerMethod#invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs)` 方法，执行调用。代码如下：

  ```
  // ServletInvocableHandlerMethod.java
  
  /**
   * Invoke the method and handle the return value through one of the
   * configured {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
   * @param webRequest the current request
   * @param mavContainer the ModelAndViewContainer for this request
   * @param providedArgs "given" arguments matched by type (not resolved)
   */
  public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
  		Object... providedArgs) throws Exception {
  	// <x> 执行调用
  	Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
  	// 设置响应状态码
  	setResponseStatus(webRequest);
  
  	// 设置 ModelAndViewContainer 为请求已处理，返回
  	if (returnValue == null) { // 返回 null
  		if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
  			mavContainer.setRequestHandled(true);
  			return;
  		}
  	} else if (StringUtils.hasText(getResponseStatusReason())) { // 有 responseStatusReason
  		mavContainer.setRequestHandled(true);
  		return;
  	}
  
  	// 设置 ModelAndViewContainer 为请求未处理
  	mavContainer.setRequestHandled(false);
  	Assert.state(this.returnValueHandlers != null, "No return value handlers");
  	// 处理器返回值
  	try {
  		this.returnValueHandlers.handleReturnValue(
  				returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
  	} catch (Exception ex) {
  		if (logger.isTraceEnabled()) {
  			logger.trace(formatErrorForReturnValue(returnValue), ex);
  		}
  		throw ex;
  	}
  }
  ```

  - 在 `<x>` 处，调用父类 InvocableHandlerMethod 的 `#invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs)` 方法，执行调用。代码如下：

    ```
    // InvocableHandlerMethod.java
    
    @Nullable
    public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
    		Object... providedArgs) throws Exception {
    	// <y> 解析参数
    	Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
    	if (logger.isTraceEnabled()) {
    		logger.trace("Arguments: " + Arrays.toString(args));
    	}
    	// 执行调用
    	return doInvoke(args);
    }
    
    protected Object doInvoke(Object... args) throws Exception {
    	// <z1> 设置方法为可访问
    	ReflectionUtils.makeAccessible(getBridgedMethod());
    	try {
    	    // <z2> 执行调用
    		return getBridgedMethod().invoke(getBean(), args);
    	} catch (IllegalArgumentException ex) {
    		assertTargetBean(getBridgedMethod(), getBean(), args);
    		String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
    		throw new IllegalStateException(formatInvokeError(text, args), ex);
    	} catch (InvocationTargetException ex) {
    		// Unwrap for HandlerExceptionResolvers ...
    		Throwable targetException = ex.getTargetException();
    		if (targetException instanceof RuntimeException) {
    			throw (RuntimeException) targetException;
    		} else if (targetException instanceof Error) {
    			throw (Error) targetException;
    		} else if (targetException instanceof Exception) {
    			throw (Exception) targetException;
    		} else {
    			throw new IllegalStateException(formatInvokeError("Invocation failure", args), targetException);
    		}
    	}
    }
    ```

    - `<y>` 处，调用 `#getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs)` 方法，解析方法的参数值们。
    - `<z1>` 处，设置方法为可访问。
    - `<z2>` 处，反射调用 `@RequestMapping` 注解的方法。😈 有一点忘记提了，InvocableHandlerMethod 是 HandlerMethod 的子类，所以通过 HandlerMethod 的 `#getBridgedMethod()` 方法，可以获得对应的 `@RequestMapping` 注解的方法。

- `<10>` 处，TODO 芋艿 1003 async

- `<11>` 处，调用 `#getModelAndView(ModelAndViewContainer mavContainer, ModelFactory modelFactory, NativeWebRequest webRequest)` 方法，获得 ModelAndView 对象。代码如下：

  ```
  // RequestMappingHandlerAdapter.java
  
  @Nullable
  private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
          ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
      // <1> TODO 1017 ModelFactory
      modelFactory.updateModel(webRequest, mavContainer);
  
      // 情况一，如果 mavContainer 已处理，则返回“空”的 ModelAndView 对象。
      if (mavContainer.isRequestHandled()) {
          return null;
      }
  
      // 情况二，如果 mavContainer 未处，则基于 `mavContainer` 生成 ModelAndView 对象
      ModelMap model = mavContainer.getModel();
      // 创建 ModelAndView 对象，并设置相关属性
      ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
      if (!mavContainer.isViewReference()) {
          mav.setView((View) mavContainer.getView());
      }
      // TODO 1004 flashMapManager
      if (model instanceof RedirectAttributes) {
          Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
          HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
          if (request != null) {
              RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
          }
      }
      return mav;
  }
  ```

  - `<1>` 处，TODO 1017 ModelFactory
  - `<2>` 处，情况一，如果 mavContainer 已处理，则返回“空”的 ModelAndView 对象。
  - `<3>` 处，情况二，如果 mavContainer 未处，则基于 `mavContainer` 生成 ModelAndView 对象。
  - 😈 这个方法，涉及后续文章的内容，胖友可以先跳过，后续在回来理解。

- `<12>` 处，标记请求完成。

# 666. 彩蛋

😈 头疼，HandlerAdapter 的处理过程，涉及的组件较多。后续的文章，我们慢慢一个一个梳理。

还是那句老话，先整体，后局部，一点一点慢慢来。

参考和推荐如下文章：

- 韩路彪 [《看透 Spring MVC：源代码分析与实践》](https://item.jd.com/11807414.html) 的 [「第13章 HandlerAdapter」](https://svip.iocoder.cn/Spring-MVC/HandlerAdapter-1-HandlerAdapter/#) 小节