1.示例代码

public class User {

    private String name;

    private Integer age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }
}
    @RequestMapping(value = "/test",method = RequestMethod.GET)
    public String getUpToken(User user,String name){
        User u=new User();
        return "t";
    }

2.入口分析

我们从InvocableHandlerMethod的invokeForRequest方法分析,
getMethodArgumentValues方法是我们重点想要的分析

    public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
            Object... providedArgs) throws Exception {

        Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
        if (logger.isTraceEnabled()) {
            logger.trace("Invoking '" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) +
                    "' with arguments " + Arrays.toString(args));
        }
        Object returnValue = doInvoke(args);
        if (logger.isTraceEnabled()) {
            logger.trace("Method [" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) +
                    "] returned [" + returnValue + "]");
        }
        return returnValue;
    }

3. getMethodArgumentValues

这里可以看到，对参数的解析，其实是由HandlerMethodArgumentResolver完成的

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

        MethodParameter[] parameters = getMethodParameters();
        Object[] args = new Object[parameters.length];
        for (int i = 0; i < parameters.length; i++) {
            MethodParameter parameter = parameters[i];
            parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
            args[i] = resolveProvidedArgument(parameter, providedArgs);
            if (args[i] != null) {
                continue;
            }
            if (this.argumentResolvers.supportsParameter(parameter)) {
                try {
                    args[i] = this.argumentResolvers.resolveArgument(
                            parameter, mavContainer, request, this.dataBinderFactory);
                    continue;
                }
                catch (Exception ex) {
                    if (logger.isDebugEnabled()) {
                        logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex);
                    }
                    throw ex;
                }
            }
            if (args[i] == null) {
                throw new IllegalStateException("Could not resolve method parameter at index " +
                        parameter.getParameterIndex() + " in " + parameter.getExecutable().toGenericString() +
                        ": " + getArgumentResolutionErrorMessage("No suitable resolver for", i));
            }
        }
        return args;
    }

4.HandlerMethodArgumentResolver

内置由很多Resolver组成

/**
 * Strategy interface for resolving method parameters into argument values in
 * the context of a given request.
 */
public interface HandlerMethodArgumentResolver {

    boolean supportsParameter(MethodParameter parameter);

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

}

比如如下参数
1.name由RequestParamMethodArgumentResolver负责解析
2.test由RequestParamMapMethodArgumentResolver负责解析

    @RequestMapping(value = "/test",method = RequestMethod.GET)
    public String getUpToken(String name,@RequestParam("name") String test){
        return "t";
    }

4.解析单个参数流程

    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();
                }
                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;
    }

当参数是非简单类型时,则会ServletModelAttributeMethodProcessor流程

1.首先为WebDataBinder准备参数 name是MethodParameter的名字, attribute是为参数化实例
2.WebDataBinderFactory创建WebDataBinder对象
3.执行WebDataBinder绑定ServletRequest参数流程
4.返回参数化实例attribute

5.自定义HandlerMethodArgumentResolver

基础WebMvcConfigurationSupport重写addArgumentResolvers方法

    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
       
    }

参考:
https://www.jianshu.com/p/f0a6aefa2706
SpringMVC 4.3 源码分析之 HandlerMethodArgumentResolver