SpringBootWeb开发-2-3

lamirs2023年1月23日大约 10 分钟

上一级页面：ssm-spring-boot速成学习索引

前言

33、请求处理-【源码分析】-Servlet API参数解析原理

WebRequest
ServletRequest
MultipartRequest
HttpSession
javax.servlet.http.PushBuilder
Principal
InputStream
Reader
HttpMethod
Locale
TimeZone
ZoneId

通过上一节的调试方法得到：

ServletRequestMethodArgumentResolver用来处理以上的参数

public class ServletRequestMethodArgumentResolver implements HandlerMethodArgumentResolver {

	@Nullable
	private static Class<?> pushBuilder;

	static {
		try {
			pushBuilder = ClassUtils.forName("javax.servlet.http.PushBuilder",
					ServletRequestMethodArgumentResolver.class.getClassLoader());
		}
		catch (ClassNotFoundException ex) {
			// Servlet 4.0 PushBuilder not found - not supported for injection
			pushBuilder = null;
		}
	}


	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		Class<?> paramType = parameter.getParameterType();
		return (WebRequest.class.isAssignableFrom(paramType) ||
				ServletRequest.class.isAssignableFrom(paramType) ||
				MultipartRequest.class.isAssignableFrom(paramType) ||
				HttpSession.class.isAssignableFrom(paramType) ||
				(pushBuilder != null && pushBuilder.isAssignableFrom(paramType)) ||
				(Principal.class.isAssignableFrom(paramType) && !parameter.hasParameterAnnotations()) ||
				InputStream.class.isAssignableFrom(paramType) ||
				Reader.class.isAssignableFrom(paramType) ||
				HttpMethod.class == paramType ||
				Locale.class == paramType ||
				TimeZone.class == paramType ||
				ZoneId.class == paramType);
	}

	@Override
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Class<?> paramType = parameter.getParameterType();

		// WebRequest / NativeWebRequest / ServletWebRequest
		if (WebRequest.class.isAssignableFrom(paramType)) {
			if (!paramType.isInstance(webRequest)) {
				throw new IllegalStateException(
						"Current request is not of type [" + paramType.getName() + "]: " + webRequest);
			}
			return webRequest;
		}

		// ServletRequest / HttpServletRequest / MultipartRequest / MultipartHttpServletRequest
		if (ServletRequest.class.isAssignableFrom(paramType) || MultipartRequest.class.isAssignableFrom(paramType)) {
			return resolveNativeRequest(webRequest, paramType);
		}

		// HttpServletRequest required for all further argument types
		return resolveArgument(paramType, resolveNativeRequest(webRequest, HttpServletRequest.class));
	}

	private <T> T resolveNativeRequest(NativeWebRequest webRequest, Class<T> requiredType) {
		T nativeRequest = webRequest.getNativeRequest(requiredType);
		if (nativeRequest == null) {
			throw new IllegalStateException(
					"Current request is not of type [" + requiredType.getName() + "]: " + webRequest);
		}
		return nativeRequest;
	}

	@Nullable
	private Object resolveArgument(Class<?> paramType, HttpServletRequest request) throws IOException {
		if (HttpSession.class.isAssignableFrom(paramType)) {
			HttpSession session = request.getSession();
			if (session != null && !paramType.isInstance(session)) {
				throw new IllegalStateException(
						"Current session is not of type [" + paramType.getName() + "]: " + session);
			}
			return session;
		}
		else if (pushBuilder != null && pushBuilder.isAssignableFrom(paramType)) {
			return PushBuilderDelegate.resolvePushBuilder(request, paramType);
		}
		else if (InputStream.class.isAssignableFrom(paramType)) {
			InputStream inputStream = request.getInputStream();
			if (inputStream != null && !paramType.isInstance(inputStream)) {
				throw new IllegalStateException(
						"Request input stream is not of type [" + paramType.getName() + "]: " + inputStream);
			}
			return inputStream;
		}
		else if (Reader.class.isAssignableFrom(paramType)) {
			Reader reader = request.getReader();
			if (reader != null && !paramType.isInstance(reader)) {
				throw new IllegalStateException(
						"Request body reader is not of type [" + paramType.getName() + "]: " + reader);
			}
			return reader;
		}
		else if (Principal.class.isAssignableFrom(paramType)) {
			Principal userPrincipal = request.getUserPrincipal();
			if (userPrincipal != null && !paramType.isInstance(userPrincipal)) {
				throw new IllegalStateException(
						"Current user principal is not of type [" + paramType.getName() + "]: " + userPrincipal);
			}
			return userPrincipal;
		}
		else if (HttpMethod.class == paramType) {
			return HttpMethod.resolve(request.getMethod());
		}
		else if (Locale.class == paramType) {
			return RequestContextUtils.getLocale(request);
		}
		else if (TimeZone.class == paramType) {
			TimeZone timeZone = RequestContextUtils.getTimeZone(request);
			return (timeZone != null ? timeZone : TimeZone.getDefault());
		}
		else if (ZoneId.class == paramType) {
			TimeZone timeZone = RequestContextUtils.getTimeZone(request);
			return (timeZone != null ? timeZone.toZoneId() : ZoneId.systemDefault());
		}

		// Should never happen...
		throw new UnsupportedOperationException("Unknown parameter type: " + paramType.getName());
	}


	/**
	 * Inner class to avoid a hard dependency on Servlet API 4.0 at runtime.
	 */
	private static class PushBuilderDelegate {

		@Nullable
		public static Object resolvePushBuilder(HttpServletRequest request, Class<?> paramType) {
			PushBuilder pushBuilder = request.newPushBuilder();
			if (pushBuilder != null && !paramType.isInstance(pushBuilder)) {
				throw new IllegalStateException(
						"Current push builder is not of type [" + paramType.getName() + "]: " + pushBuilder);
			}
			return pushBuilder;

		}
	}
}

用例：

@Controller
public class RequestController {

    @GetMapping("/goto")
    public String goToPage(HttpServletRequest request){

        request.setAttribute("msg","成功了...");
        request.setAttribute("code",200);
        return "forward:/success";  //转发到  /success请求
    }
}

34、请求处理-【源码分析】-Model、Map原理

复杂参数：

Map
Model（map、model里面的数据会被放在request的请求域 request.setAttribute）
Errors/BindingResult
RedirectAttributes（重定向携带数据）
ServletResponse（响应response）
SessionStatus
UriComponentsBuilder
ServletUriComponentsBuilder

用例：

@GetMapping("/params")
public String testParam(Map<String,Object> map,
                        Model model,
                        HttpServletRequest request,
                        HttpServletResponse response){
    //下面三位都是可以给request域中放数据
    map.put("hello","world666");
    model.addAttribute("world","hello666");
    request.setAttribute("message","HelloWorld");

    Cookie cookie = new Cookie("c1","v1");
    response.addCookie(cookie);
    return "forward:/success";
}

@ResponseBody
@GetMapping("/success")
public Map success(@RequestAttribute(value = "msg",required = false) String msg,
                   @RequestAttribute(value = "code",required = false)Integer code,
                   HttpServletRequest request){
    Object msg1 = request.getAttribute("msg");

    Map<String,Object> map = new HashMap<>();
    Object hello = request.getAttribute("hello");//得出testParam方法赋予的值 world666
    Object world = request.getAttribute("world");//得出testParam方法赋予的值 hello666
    Object message = request.getAttribute("message");//得出testParam方法赋予的值 HelloWorld

    map.put("reqMethod_msg",msg1);
    map.put("annotation_msg",msg);
    map.put("hello",hello);
    map.put("world",world);
    map.put("message",message);

    return map;
}

Map<String,Object> map
Model model
HttpServletRequest request

上面三位都是可以给request域中放数据，用request.getAttribute()获取

接下来我们看看，Map<String,Object> map与Model model用什么参数处理器。

`Map<String,Object> map`参数用`MapMethodProcessor`处理：

public class MapMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return (Map.class.isAssignableFrom(parameter.getParameterType()) &&
				parameter.getParameterAnnotations().length == 0);
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
		return mavContainer.getModel();
	}
    
    ...
    
}

注意到

return mavContainer.getModel();

mavContainer.getModel()如下：

public class ModelAndViewContainer {

    ...

	private final ModelMap defaultModel = new BindingAwareModelMap();

	@Nullable
	private ModelMap redirectModel;

    ...

	public ModelMap getModel() {
		if (useDefaultModel()) {
			return this.defaultModel;
		}
		else {
			if (this.redirectModel == null) {
				this.redirectModel = new ModelMap();
			}
			return this.redirectModel;
		}
	}
    
    private boolean useDefaultModel() {
		return (!this.redirectModelScenario || (this.redirectModel == null && !this.ignoreDefaultModelOnRedirect));
	}
    ...
    
}

注意到

		if (useDefaultModel()) {
			return this.defaultModel;
		}

查看this.defaultModel的类型是BindingAwareModelMap，进一步探究发现底层是

public class ExtendedModelMap extends ModelMap implements Model {
//..
}

即BindingAwareModelMap既是Model也是Map

`Model model`用`ModelMethodProcessor`处理：

public class ModelMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return Model.class.isAssignableFrom(parameter.getParameterType());
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
		return mavContainer.getModel();
	}
    ...
}

也是return mavContainer.getModel();。这里跟MapMethodProcessor方法内的处理办法一致。

最终也是使用BindingAwareModelMap类型，BindingAwareModelMap既是Model也是Map

查看BindingAwareModelMap的继承链：

![Pasted image 20230125175143.png](https://webdav-1309345210.file.myqcloud.com/images/Pasted image 20230125175143.png)

来到InvocableHandlerMethod类的getMethodArgumentValues方法

查看args，可以看到Map和Model实际上是用同一个对象来处理的

![Pasted image 20230125175559.png](https://webdav-1309345210.file.myqcloud.com/images/Pasted image 20230125175559.png)

一直“恢复程序执行”，直到来到ServletInvocableHandlerMethod#invokeAndHandle方法

查看mavContatiner的值，可以看到Map和Model实际上是用同一个对象来处理的，处理结果是图中的“hello”和"world"

![Pasted image 20230125180305.png](https://webdav-1309345210.file.myqcloud.com/images/Pasted image 20230125180305.png)

目标方法执行完成

目标方法执行完成，将所有的数据都放在ModelAndViewContainer(mavContaioner).

mavContainer包含要去的地址url，还包含Model的数据

![Pasted image 20230125182100.png](https://webdav-1309345210.file.myqcloud.com/images/Pasted image 20230125182100.png)

将数据填充到Model And View

步入getModelAndView方法

这个方法首先更新Model数据，

![Pasted image 20230125182233.png](https://webdav-1309345210.file.myqcloud.com/images/Pasted image 20230125182233.png)

然后将数据填充到ModelAndView

private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,  
      ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {  
  
//...
	// 注意这句
   ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());

如果你的数据是重定向到新网页的，这个方法还会帮你把数据绑定到新网页的请求上下文（RequestContex），以完成旧网页request携带的内容转移到新网页request上。

@Nullable  
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,  
      ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {  
  
// ...
	// 注意这里
   if (model instanceof RedirectAttributes redirectAttributes) {  
      Map<String, ?> flashAttributes = redirectAttributes.getFlashAttributes();  
      HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);  
      if (request != null) {  
         RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);  
      }  
   }

定位`processDispatchResult`方法

步出，回到org.springframework.web.servlet.DispatcherServlet#doDispatch，即DispatcherServlet类的doDispatch方法，

后文全部参照这种类#方法的表示形式

  
// Actually invoke the handler.  
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());  
  
//...
mappedHandler.applyPostHandle(processedRequest, response, mv);

// ...
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

现在ha.handle执行完成

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

方法继续往下执行，来到核心语句，这里执行拦截器的，后文会进行解析

mappedHandler.applyPostHandle(processedRequest, response, mv);

继续步过，来到核心语句，处理分发结果。这是下一小节的解析重点。

processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

如何获取`Map<String,Object> map`与`Model model`的值

看看Map<String,Object> map与Model model值是如何做到用request.getAttribute()获取的。

根据上一小节的内容，所有的数据都放在 ModelAndView ，它包含要去的页面地址View，还包含Model数据。

回顾上一小节的末尾，先看ModelAndView接下来是如何处理的？

public class DispatcherServlet extends FrameworkServlet {
    
    ...
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		...

		try {
			ModelAndView mv = null;
            
            ...

			// Actually invoke the handler.
			mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
            
            ...
            
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			catch (Throwable err) {
				// As of 4.3, we're processing Errors thrown from handler methods as well,
				// making them available for @ExceptionHandler methods and other scenarios.
				dispatchException = new NestedServletException("Handler dispatch failed", err);
			}
        	//处理分发结果
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
        ...

	}

它包含这三个核心语句

  
// Actually invoke the handler.  
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());  
  
//...
mappedHandler.applyPostHandle(processedRequest, response, mv);

// ...
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

步入processDispatchResult方法，方法首先获取view的name，然后对view进行render，

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,  
      @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,  
      @Nullable Exception exception) throws Exception {  
  
// ...
   // Did the handler return a view to render?  
   if (mv != null && !mv.wasCleared()) {  
      render(mv, request, response);  
      if (errorView) {  
         WebUtils.clearErrorRequestAttributes(request);  
      }  
   }

其中的核心语句：

render(mv, request, response);

步入render方法

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {  
// ...
  
   View view;  
   String viewName = mv.getViewName();  
   if (viewName != null) {  
      // We need to resolve the view name.  
      view = resolveViewName(viewName, mv.getModelInternal(), locale, request);  
      if (view == null) {  
         throw new ServletException("Could not resolve view with name '" + mv.getViewName() +  
               "' in servlet with name '" + getServletName() + "'");  
      }  
   }  
   //...
}

注意到核心语句：

// We need to resolve the view name.  
view = resolveViewName(viewName, mv.getModelInternal(), locale, request);

resolveViewName方法进入视图解析器的流程，以后会分析。

继续看render方法的后半段：

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {  

// ...
try {  
   if (mv.getStatus() != null) {  
      request.setAttribute(View.RESPONSE_STATUS_ATTRIBUTE, mv.getStatus());  
      response.setStatus(mv.getStatus().value());  
   }  
   view.render(mv.getModelInternal(), request, response);  
}

// ...
}

注意到核心语句

view.render(mv.getModelInternal(), request, response);

步入view.render方法，来到InternalResourceView#render方法

这里的view属为InternalResourceView类。

public class InternalResourceView extends AbstractUrlBasedView {
    
 	@Override//该方法在AbstractView，AbstractUrlBasedView继承了AbstractView
	public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		
        //...
        
		Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
		prepareResponse(request, response);
        
        //核心语句
		renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
	}

注意到核心语句：

// 创建一个要合并的输出Model
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
		prepareResponse(request, response);
//...
// 核心语句
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);

步入createMergedOutputModel方法，这个方法将Model数据转移到转移到mergedModel(即HashMap中)

protected Map<String, Object> createMergedOutputModel(@Nullable Map<String, ?> model,  
      HttpServletRequest request, HttpServletResponse response) {
// ...

// 把model里的数据全部放进mergedModel，转移到HashMap中
if (model != null) {  
   mergedModel.putAll(model);  
}

//...

}

步出，回到InternalResourceView#render方法，核心语句如下：

// 创建一个要合并的输出Model
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
		prepareResponse(request, response);
//...
// 核心语句
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);

注意到核心语句:

// 核心语句
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);

步入renderMergedOutputModel方法

    @Override
	protected void renderMergedOutputModel(
			Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

		// Expose the model object as request attributes.
        // 暴露模型作为请求域属性
		exposeModelAsRequestAttributes(model, request);//<---重点
		//...
	}

注意到核心语句：

// Expose the model object as request attributes.
// 暴露模型作为请求域属性
exposeModelAsRequestAttributes(model, request);//<---重点

步入exposeModelAsRequestAttributes方法，方法遍历Model中的所有数据，将数据放在request域中

    protected void exposeModelAsRequestAttributes(Map<String, Object> model,
			HttpServletRequest request) throws Exception {

		model.forEach((name, value) -> {
			if (value != null) {
				request.setAttribute(name, value);
			}
			else {
				request.removeAttribute(name);
			}
		});
	}
    
}

exposeModelAsRequestAttributes方法看出，

Map<String,Object> map，Model model这两种类型数据可以给request域中放数据，
- 这个操作是在渲染view（view.render()）时进行的，
- 跳转操作发生在这之后
使用数据时，用request.getAttribute()获取。

exposeModelAsRequestAttributes方法是业务逻辑的最底层了，再往下是工具类。

该方法的继承关系如下：

![Pasted image 20230125200905.png](https://webdav-1309345210.file.myqcloud.com/images/Pasted image 20230125200905.png)

35、请求处理-【源码分析】-自定义参数绑定原理

假设有下面的场景

@RestController
public class ParameterTestController {

    /**
     * 数据绑定：页面提交的请求数据（GET、POST）都可以和对象属性进行绑定
     * @param person
     * @return
     */
    @PostMapping("/saveuser")
    public Person saveuser(Person person){
        return person;
    }
}

/**
 *     姓名： <input name="userName"/> <br/>
 *     年龄： <input name="age"/> <br/>
 *     生日： <input name="birth"/> <br/>
 *     宠物姓名：<input name="pet.name"/><br/>
 *     宠物年龄：<input name="pet.age"/>
 */
@Data
public class Person {
    
    private String userName;
    private Integer age;
    private Date birth;
    private Pet pet;
    
}

@Data
public class Pet {

    private String name;
    private String age;

}

封装过程用到ServletModelAttributeMethodProcessor

public class ServletModelAttributeMethodProcessor extends ModelAttributeMethodProcessor {
	
    @Override//本方法在ModelAttributeMethodProcessor类，
	public boolean supportsParameter(MethodParameter parameter) {
		return (parameter.hasParameterAnnotation(ModelAttribute.class) ||
				(this.annotationNotRequired && !BeanUtils.isSimpleProperty(parameter.getParameterType())));
	}

	@Override
	@Nullable//本方法在ModelAttributeMethodProcessor类，
	public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		...

		String name = ModelFactory.getNameForParameter(parameter);
		ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class);
		if (ann != null) {
			mavContainer.setBinding(name, ann.binding());
		}

		Object attribute = null;
		BindingResult bindingResult = null;

		if (mavContainer.containsAttribute(name)) {
			attribute = mavContainer.getModel().get(name);
		}
		else {
			// Create attribute instance
			try {
				attribute = createAttribute(name, parameter, binderFactory, webRequest);
			}
			catch (BindException ex) {
				...
			}
		}

		if (bindingResult == null) {
			// Bean property binding and validation;
			// skipped in case of binding failure on construction.
			WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
			if (binder.getTarget() != null) {
				if (!mavContainer.isBindingDisabled(name)) {
                    //web数据绑定器，将请求参数的值绑定到指定的JavaBean里面**
					bindRequestParameters(binder, webRequest);
				}
				validateIfApplicable(binder, parameter);
				if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
					throw new BindException(binder.getBindingResult());
				}
			}
			// Value type adaptation, also covering java.util.Optional
			if (!parameter.getParameterType().isInstance(attribute)) {
				attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
			}
			bindingResult = binder.getBindingResult();
		}

		// Add resolved attribute and BindingResult at the end of the model
		Map<String, Object> bindingResultModel = bindingResult.getModel();
		mavContainer.removeAttributes(bindingResultModel);
		mavContainer.addAllAttributes(bindingResultModel);

		return attribute;
	}
}

WebDataBinder 利用它里面的 Converters 将请求数据转成指定的数据类型。再次封装到JavaBean中

在过程当中，用到GenericConversionService：在设置每一个值的时候，找它里面的所有converter那个可以将这个数据类型（request带来参数的字符串）转换到指定的类型

36、请求处理-【源码分析】-自定义Converter原理

未来我们可以给WebDataBinder里面放自己的Converter；

下面演示将字符串“啊猫,3”转换成Pet对象。

    //1、WebMvcConfigurer定制化SpringMVC的功能
    @Bean
    public WebMvcConfigurer webMvcConfigurer(){
        return new WebMvcConfigurer() {

            @Override
            public void addFormatters(FormatterRegistry registry) {
                registry.addConverter(new Converter<String, Pet>() {

                    @Override
                    public Pet convert(String source) {
                        // 啊猫,3
                        if(!StringUtils.isEmpty(source)){
                            Pet pet = new Pet();
                            String[] split = source.split(",");
                            pet.setName(split[0]);
                            pet.setAge(Integer.parseInt(split[1]));
                            return pet;
                        }
                        return null;
                    }
                });
            }
        };
    }

SpringBootWeb开发-3

spring-boot-web-开发-3