SpringBoot与SpringMVC中参数传递的原理解析

时间:2021-09-29 16:17:14

一:普通参数与基本注解

HandlerMapping中找到能处理请求的Handler(Controller,method())
为当前Handler找一个适配器HandlerAdapter:RequestMappingHandlerAdapter

SpringBoot与SpringMVC中参数传递的原理解析

1.HandlerAdapter

SpringBoot与SpringMVC中参数传递的原理解析

0-支持方法上标注@RequestMapping
1-支持函数式编程的
xxxx

2.执行目标方法

SpringBoot与SpringMVC中参数传递的原理解析
SpringBoot与SpringMVC中参数传递的原理解析

3.参数解析器:确定要执行的目标方法每一个参数的值是什么

SpringBoot与SpringMVC中参数传递的原理解析

SpringBoot与SpringMVC中参数传递的原理解析

boolean supportsParameter(MethodParameter parameter);
Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
先判断是否支持该参数类型, 如果支持, 就调用resolveArgument解析方法

4.返回值处理器

SpringBoot与SpringMVC中参数传递的原理解析

5.挨个判断所有参数解析器哪个支持这个参数:HandlerMethodArgumentResolver: 把控着支持的方法参数类型

SpringBoot与SpringMVC中参数传递的原理解析

请求进来后, 首先从handlerMapping中查找是否有对应的映射处理, 得到映射适配器Adapter,再通过适配器,查找有哪些方法匹配请求,首先判断方法名,以及参数类型是否匹配,首先获得方法中声明的参数名字, 放到数组里,循环遍历27种解析器判断是否有支持处理对应参数名字类型的解析器,如果有的话,根据名字进行解析参数,根据名字获得域数据中的参数, 循环每个参数名字进行判断, 从而为每个参数进行赋值.

对于自定义的POJO类参数:
ServletRequestMethodArgumentResolver 这个解析器用来解析: 是通过主要是通过判断是否是简单类型得到的

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@Override
    public boolean supportsParameter(MethodParameter parameter) {
        return (parameter.hasParameterAnnotation(ModelAttribute.class) ||
                (this.annotationNotRequired && !BeanUtils.isSimpleProperty(parameter.getParameterType())));
    }
    
public static boolean isSimpleValueType(Class<?> type) {
        return (Void.class != type && void.class != type &&
                (ClassUtils.isPrimitiveOrWrapper(type) ||
                Enum.class.isAssignableFrom(type) ||
                CharSequence.class.isAssignableFrom(type) ||
                Number.class.isAssignableFrom(type) ||
                Date.class.isAssignableFrom(type) ||
                Temporal.class.isAssignableFrom(type) ||
                URI.class == type ||
                URL.class == type ||
                Locale.class == type ||
                Class.class == type));
    }
 
 
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
 
        Assert.state(mavContainer != null, "ModelAttributeMethodProcessor requires ModelAndViewContainer");
        Assert.state(binderFactory != null, "ModelAttributeMethodProcessor requires WebDataBinderFactory");
 
        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 (isBindExceptionRequired(parameter)) {
                    // No BindingResult parameter -> fail with BindException
                    throw ex;
                }
                // Otherwise, expose null/empty value and associated BindingResult
                if (parameter.getParameterType() == Optional.class) {
                    attribute = Optional.empty();
                }
                else {
                    attribute = ex.getTarget();
                }
                bindingResult = ex.getBindingResult();
            }
        }
 
        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)) {
                    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 binder =binderFactory.createBinder(webRequest,attribute,name)
WebDataBinder:web数据绑定器,将请求参数的值绑定到指定的javaBean里面
WebDataBinder 利用它里面的Converters将请求数据转成指定的数据类型,通过反射一系列操作,再次封装到javabean中

GenericConversionService:在设置每一个值的时候,找它里面所有的converter哪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(javabean—某一个类型)

SpringBoot与SpringMVC中参数传递的原理解析
SpringBoot与SpringMVC中参数传递的原理解析

未来我们可以给WebDataBinder里面放自己的Converter

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private static final class StringToNumber implements Converter<String, T> {
 
converter总接口:
@FunctionalInterface
public interface Converter<S, T> {

//自定义转换器:实现按照自己的规则给相应对象赋值

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@Override
    public void addFormatters(FormatterRegistry registry) {
            registry.addConverter(new Converter<String, Pet>() {
                @Override
                public Pet convert(String source) {
                    if (!StringUtils.isEmpty(source)){
                        Pet pet = new Pet();
                        String[] split = source.split(",");
                        pet.setName(split[0]);
                        pet.setAge(split[1]);
                        return pet;
                    }
 
                    return null;
                }
            });
    }

二:复杂参数

Map/Model(map/model里面的数据会被放在request的请求域 相当于request.setAttribute)/Errors/BindingResult/RedirectAttributes(重定向携带数据)/ServletRespons().SessionStaus.UriComponentsBuilder

6.在上面第五步目标方法执行完成后:
将所有的数据都放在ModelAdnViewContainer;包含要去的页面地址View,还包含Model数据

SpringBoot与SpringMVC中参数传递的原理解析

7.处理派发结果

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

在页面进行响应前, 进行视图渲染的时候:
exposeModelAsRequestAttributes(model, request); 该方法将model中所有参数都放在请求域数据中

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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);
        }
    }

通过循环遍历model中的所有数据放在请求域中

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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);
            }
        });
    }

不管我们在方法形参位置放 Map集合或者Molde 最终在底层源码都是同一个对象在mvcContainer容器中进行保存

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原文链接:https://blog.csdn.net/qmxqing/article/details/119141647