Spring Boot开发之参数处理

1 普通参数

1 注解

包括: @PathVariable、@RequestHeader、@ModelAttribute、@RequestParam、@MatrixVariable、@CookieValue、@RequestBody等

 @GetMapping("/car/{id}/owner/{username}")
    public Map<String,Object> getCar(@PathVariable("id") Integer id,
                                     @PathVariable("username") String name,
                                     @PathVariable Map<String,String> pv,
                                     @RequestHeader("User-Agent") String userAgent,
                                     @RequestHeader Map<String,String> header,
                                     @RequestParam("age") Integer age,
                                     @RequestParam("inters") List<String> inters,
                                     @RequestParam Map<String,String> params,
                                     @CookieValue("_ga") String _ga,
                                     @CookieValue("_ga") Cookie cookie){
        // xxx
    }
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2 Servlet的API

涉及类为: WebRequest、ServletRequest、MultipartRequest、 HttpSession、javax.servlet.http.PushBuilder、Principal、InputStream、Reader、HttpMethod、Locale、TimeZone、ZoneId.

@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) ||
				InputStream.class.isAssignableFrom(paramType) ||
				Reader.class.isAssignableFrom(paramType) ||
				HttpMethod.class == paramType ||
				Locale.class == paramType ||
				TimeZone.class == paramType ||
				ZoneId.class == paramType);
	}
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3 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（response）、SessionStatus、UriComponentsBuilder、ServletUriComponentsBuilder

Map<String,Object> map,  Model model, HttpServletRequest request 都是可以给request域中放数据
// request中取值 
request.getAttribute();
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4 自定义对象参数

可以自动类型转换与格式化，可以级联封装.

/**
 *     姓名：  

 *     年龄：  

 *     生日：  

 *     宠物姓名：

 *     宠物年龄：
 */
@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;

}
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2 参数处理原理

• HandlerMapping中找到能处理请求的Handler（Controller.method()）
• 为当前Handler 找一个适配器 HandlerAdapter
• 适配器执行目标方法并确定方法参数的每一个值

1 HandlerAdapter

支持方法上标注的@RequestMapping , 支持函数式编程的.

2 执行目标方法

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


mav = invokeHandlerMethod(request, response, handlerMethod); //执行目标方法


//ServletInvocableHandlerMethod
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
//获取方法的参数值
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);

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3 参数解析器

HandlerMethodArgumentResolver, 参数解析器:

确定将要执行的目标方法的每一个参数的值是什么, SpringMVC目标方法能写多少种参数类型。取决于参数解析器.

提供两个方法:

• 当前解析器是否支持解析这种参数 supportsParameter
• 支持就调用 resolveArgument

4 确定方法参数值

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		MethodParameter[] parameters = getMethodParameters();
		if (ObjectUtils.isEmpty(parameters)) {
			return EMPTY_ARGS;
		}

		Object[] args = new Object[parameters.length];
		for (int i = 0; i < parameters.length; i++) {
			MethodParameter parameter = parameters[i];
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = findProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
				continue;
			}
			if (!this.resolvers.supportsParameter(parameter)) {
				throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
			}
			try {
				args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
			}
			catch (Exception ex) {
				// Leave stack trace for later, exception may actually be resolved and handled...
				if (logger.isDebugEnabled()) {
					String exMsg = ex.getMessage();
					if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {
						logger.debug(formatArgumentError(parameter, exMsg));
					}
				}
				throw ex;
			}
		}
		return args;
	}
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遍历判断所有参数解析器

	@Nullable
	private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
		HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
		if (result == null) {
			for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {
				if (resolver.supportsParameter(parameter)) {
					result = resolver;
					this.argumentResolverCache.put(parameter, result);
					break;
				}
			}
		}
		return result;
	}
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解析参数

调用各自 HandlerMethodArgumentResolver 的 resolveArgument 方法即可
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5 目标方法执行完成

将所有的数据都放在 ModelAndViewContainer；包含要去的页面地址View。还包含Model数据。

6 处理派发结果

结果派发涉及到:

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

renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);

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

		// Expose the model object as request attributes.
		exposeModelAsRequestAttributes(model, request);

		// Expose helpers as request attributes, if any.
		exposeHelpers(request);

		// Determine the path for the request dispatcher.
		String dispatcherPath = prepareForRendering(request, response);

		// Obtain a RequestDispatcher for the target resource (typically a JSP).
		RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
		if (rd == null) {
			throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +
					"]: Check that the corresponding file exists within your web application archive!");
		}

		// If already included or response already committed, perform include, else forward.
		if (useInclude(request, response)) {
			response.setContentType(getContentType());
			if (logger.isDebugEnabled()) {
				logger.debug("Including [" + getUrl() + "]");
			}
			rd.include(request, response);
		}

		else {
			// Note: The forwarded resource is supposed to determine the content type itself.
			if (logger.isDebugEnabled()) {
				logger.debug("Forwarding to [" + getUrl() + "]");
			}
			rd.forward(request, response);
		}
	}
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暴露模型作为请求域属性: exposeModelAsRequestAttributes(model, request);

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

    // model中的所有数据遍历挨个放在请求域中
		model.forEach((name, value) -> {
			if (value != null) {
				request.setAttribute(name, value);
			}
			else {
				request.removeAttribute(name);
			}
		});
	}
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