我这边用一个get请求来示例。这东西知道在哪断点查看，以后遇到问题可以快速定位。
我这里的接口是 http://localhost:8082/pathVariable2/2
代码是
@GetMapping("/pathVariable2/{id}")
public String pathVariable2(@PathVariable(value = "id")
String id){
return id;
}
1.入口是httpservlet,然后到org.springframework.web.servlet.DispatcherServlet#doDispatch打断点
2.这里2个关键方法
第一是获取适配器
第二个真正用适配器解析参数
2.1适配器一共4个，一般的请求用第一个就好
2.2执行参数解析
1）org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal 一路走下去
2）org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#invokeHandlerMethod 一路走下去
520：这里是拿到所有的参数解析器：最终是遍历所有的参数解析器去解析参数的
0 = {RequestParamMethodArgumentResolver@6898}
1 = {RequestParamMapMethodArgumentResolver@6899}
2 = {PathVariableMethodArgumentResolver@6900}
3 = {PathVariableMapMethodArgumentResolver@6901}
4 = {MatrixVariableMethodArgumentResolver@6902}
5 = {MatrixVariableMapMethodArgumentResolver@6903}
6 = {ServletModelAttributeMethodProcessor@6904}
7 = {RequestResponseBodyMethodProcessor@6905}
8 = {RequestPartMethodArgumentResolver@6906}
9 = {RequestHeaderMethodArgumentResolver@6907}
10 = {RequestHeaderMapMethodArgumentResolver@6908}
11 = {ServletCookieValueMethodArgumentResolver@6909}
12 = {ExpressionValueMethodArgumentResolver@6910}
13 = {SessionAttributeMethodArgumentResolver@6911}
14 = {RequestAttributeMethodArgumentResolver@6912}
15 = {ServletRequestMethodArgumentResolver@6913}
16 = {ServletResponseMethodArgumentResolver@6914}
17 = {HttpEntityMethodProcessor@6915}
18 = {RedirectAttributesMethodArgumentResolver@6916}
19 = {ModelMethodProcessor@6917}
20 = {MapMethodProcessor@6918}
21 = {ErrorsMethodArgumentResolver@6919}
22 = {SessionStatusMethodArgumentResolver@6920}
23 = {UriComponentsBuilderMethodArgumentResolver@6921}
24 = {PrincipalMethodArgumentResolver@6922}
25 = {RequestParamMethodArgumentResolver@6923}
26 = {ServletModelAttributeMethodProcessor@6924}
所以可以分析的出，我这个接口用PathVariableMethodArgumentResolver来解析，这是后话，肯定是哪所有解析器一个个去解析的。
524：拿到所有的返回值处理器
0 = {ModelAndViewMethodReturnValueHandler@6340}
1 = {ModelMethodProcessor@6341}
2 = {ViewMethodReturnValueHandler@6342}
3 = {ResponseBodyEmitterReturnValueHandler@6343}
4 = {StreamingResponseBodyReturnValueHandler@6344}
5 = {HttpEntityMethodProcessor@6345}
6 = {HttpHeadersReturnValueHandler@6346}
7 = {CallableMethodReturnValueHandler@6347}
8 = {DeferredResultMethodReturnValueHandler@6348}
9 = {AsyncTaskMethodReturnValueHandler@6349}
10 = {ServletModelAttributeMethodProcessor@6350}
11 = {RequestResponseBodyMethodProcessor@6351}
12 = {ViewNameMethodReturnValueHandler@6352}
13 = {MapMethodProcessor@6353}
14 = {ServletModelAttributeMethodProcessor@6354}
3）继续断点，核心执行解析是553行
4）org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod#invokeAndHandle
52行真正执行目标方法，我们进去
5）继续断点org.springframework.web.method.support.InvocableHandlerMethod#invokeForRequest
56行获取参数 61行反射执行方法。所以我们得进入56行
6）org.springframework.web.method.support.InvocableHandlerMethod#getMethodArgumentValues 方法
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
//这里拿的是这个方法（到这步已经确认调用哪个方法了）所有参数，遍历去给它们设置值
MethodParameter[] parameters = this.getMethodParameters();
if (ObjectUtils.isEmpty(parameters)) {
return EMPTY_ARGS;
} else {
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) {
//判断参数解析器是否支持这种参数解析
if (!this.resolvers.supportsParameter(parameter)) {
throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
}
try {
//真正去给参数设置值
args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
} catch (Exception var10) {
if (logger.isDebugEnabled()) {
String exMsg = var10.getMessage();
if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {
logger.debug(formatArgumentError(parameter, exMsg));
}
}
throw var10;
}
}
}
return args;
}
}
6-1）判断参数解析器是否支持这种参数解析
遍历27个参数解析器，看看哪个支持。然后break掉
最终发现是PathVariableMethodArgumentResolver支持
org.springframework.web.servlet.mvc.method.annotation.PathVariableMethodArgumentResolver#supportsParameter
public boolean supportsParameter(MethodParameter parameter) {
//不是PathVariable注解的不行
if (!parameter.hasParameterAnnotation(PathVariable.class)) {
return false;
//不是map开头的可以
} else if (!Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) {
return true;
//其他情况的考虑
} else {
PathVariable pathVariable = (PathVariable)parameter.getParameterAnnotation(PathVariable.class);
return pathVariable != null && StringUtils.hasText(pathVariable.value());
}
}
6-2）真正去解析参数的值
@Nullable
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
//获取参数解析器
HandlerMethodArgumentResolver resolver = this.getArgumentResolver(parameter);
if (resolver == null) {
throw new IllegalArgumentException("Unsupported parameter type [" + parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
} else {
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
}
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
//获取参数对象
AbstractNamedValueMethodArgumentResolver.NamedValueInfo namedValueInfo = this.getNamedValueInfo(parameter);
//确认需要解析的参数名字
MethodParameter nestedParameter = parameter.nestedIfOptional();
Object resolvedName = this.resolveEmbeddedValuesAndExpressions(namedValueInfo.name);
if (resolvedName == null) {
throw new IllegalArgumentException("Specified name must not resolve to null: [" + namedValueInfo.name + "]");
} else {
//真正去解析参数的值
Object arg = this.resolveName(resolvedName.toString(), nestedParameter, webRequest);
类名是:PathVariableMethodArgumentResolver 通过它来解析
uriTemplateVars是请求头带过来的值id=2
这样最终得到参数的值是2