先看一个简单参数绑定，有如下Controller和请求,代码如下。
@Controller
@RequestMapping("/ParameterBind")
public class ParameterBindTestController {
@ResponseBody
@RequestMapping("/test1")
public String test1(int id){
System.out.println(id);
return "test1";
}
}
请求进入DispatcherServlet的doDispatch后，获取HandlerMethod。然后根据HandlerMethod来确认HandlerApapter，确认后执行HandlerAdapter的handle方法。这里确认HandlerApater为RequestMappingHandlerAdapter，在执行handlerMethod之前，需要处理参数的绑定。然后看看详细的参数绑定过程
执行HandlerAdapter的handler方法后，进入RequestMappingHandlerAdapter的invokeHandleMethod方法（line:711）
private ModelAndView invokeHandleMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
//根据handlerMethod和binderFactory创建一个ServletInvocableHandlerMethod。后续把请求直接交给ServletInvocableHandlerMethod执行。
//createRequestMappingMethod方法比较简单，把之前RequestMappingHandlerAdapter初始化的argumentResolvers和returnValueHandlers添加至ServletInvocableHandlerMethod中
ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
final WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
if (logger.isDebugEnabled()) {
logger.debug("Found concurrent result value [" + result + "]");
}
requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);
}
requestMappingMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
然后进入invokeAndHanldle方法，然后进入invokeForRequest方法，这个方法的职责是从request中解析出HandlerMethod方法所需要的参数，然后通过反射调用HandlerMethod中的method。代码如下
public final Object invokeForRequest(NativeWebRequest request,
ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//从request中解析出HandlerMethod方法所需要的参数，并返回Object[]
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
StringBuilder builder = new StringBuilder("Invoking [");
builder.append(this.getMethod().getName()).append("] method with arguments ");
builder.append(Arrays.asList(args));
logger.trace(builder.toString());
}
//通过反射执行HandleMethod中的method，方法参数为args。并返回方法执行的返回值
Object returnValue = invoke(args);
if (logger.isTraceEnabled()) {
logger.trace("Method [" + this.getMethod().getName() + "] returned [" + returnValue + "]");
}
return returnValue;
}
直接进入getMethodArgumentValues方法看看其过程，代码如下
/**
* 获取当前请求的方法参数值。
*/
private Object[] getMethodArgumentValues(
NativeWebRequest request, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//获取方法参数数组
MethodParameter[] parameters = getMethodParameters();
//创建一个参数数组，保存从request解析出的方法参数
Object[] args = new Object[parameters.length];
for (int i = 0; i < parameters.length; i++) {
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(parameterNameDiscoverer);
GenericTypeResolver.resolveParameterType(parameter, getBean().getClass());
args[i] = resolveProvidedArgument(parameter, providedArgs);
if (args[i] != null) {
continue;
}
//判断之前RequestMappingHandlerAdapter初始化的那24个HandlerMethodArgumentResolver（参数解析器），是否存在支持该参数解析的解析器
if (argumentResolvers.supportsParameter(parameter)) {
try {
args[i] = argumentResolvers.resolveArgument(parameter, mavContainer, request, dataBinderFactory);
continue;
} catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(getArgumentResolutionErrorMessage("Error resolving argument", i), ex);
}
throw ex;
}
}
if (args[i] == null) {
String msg = getArgumentResolutionErrorMessage("No suitable resolver for argument", i);
throw new IllegalStateException(msg);
}
}
return args;
}
