SpringMVC——数据绑定流程

一、流程

Spring MVC 主框架将 ServletRequest • 对象及目标方法的入参实例传递给 WebDataBinderFactory 实例，以创建 DataBinder 实例对象2. DataBinder 调用装配在 Spring MVC 上下文中的 ConversionService 组件进行数据类型转换、数据格式化工作。将 Servlet 中的请求信息填充到入参对象中3. 调用 Validator 组件对已经绑定了请求消息的入参对象进行数据合法性校验，并最终生成数据绑定结果BindingData 对象4. Spring MVC 抽取 BindingResult 中的入参对象和校验错误对象，将它们赋给处理方法的响应入参

二、源码分析：

public class ModelAttributeMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {
    protected final Log logger = LogFactory.getLog(this.getClass());
    private final boolean annotationNotRequired;

    public ModelAttributeMethodProcessor(boolean annotationNotRequired) {
        this.annotationNotRequired = annotationNotRequired;
    }

    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(ModelAttribute.class) || this.annotationNotRequired && !BeanUtils.isSimpleProperty(parameter.getParameterType());
    }

    public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        String name = ModelFactory.getNameForParameter(parameter);
        ModelAttribute ann = (ModelAttribute)parameter.getParameterAnnotation(ModelAttribute.class);
        if (ann != null) {
            mavContainer.setBinding(name, ann.binding());
        }

        Object attribute = mavContainer.containsAttribute(name) ? mavContainer.getModel().get(name) : this.createAttribute(name, parameter, binderFactory, webRequest);
        WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
        if (binder.getTarget() != null) {
            if (!mavContainer.isBindingDisabled(name)) {
                this.bindRequestParameters(binder, webRequest);
            }

            this.validateIfApplicable(binder, parameter);
            if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {
                throw new BindException(binder.getBindingResult());
            }
        }

        Map<String, Object> bindingResultModel = binder.getBindingResult().getModel();
        mavContainer.removeAttributes(bindingResultModel);
        mavContainer.addAllAttributes(bindingResultModel);
        return binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
    }