在進入DispatcherServlet的時候，spring容器會得到一個HttpServletRequest物件，但是我們在使用controller層方法時，經常會使用RequestBody，RequestHeader等註解將該物件封裝成更便於操作的物件型別。那麼在我們使用RequestBody等註解的時候，中間經歷了怎樣的轉換邏輯。今天就來解析一下。
引數解析邏輯
首先找到程式碼封裝的位置，進入InvocableHandlerMethod的invokeForRequest方法(呼叫鏈可以自行找一下，idea的debug功能很方便)。
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//這行就是獲取引數的邏輯
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
logger.trace("Arguments: " + Arrays.toString(args));
}
//執行controller方法
return doInvoke(args);
}
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
MethodParameter[] parameters = getMethodParameters();
Object[] args = new Object[parameters.length];
...
if (this.argumentResolvers.supportsParameter(parameter)) {
try {
//逐個解析方法引數
args[i] = this.argumentResolvers.resolveArgument(
parameter, mavContainer, request, this.dataBinderFactory);
continue;
}
...
return args;
}
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
//獲取對應的引數解析器
HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
if (resolver == null) {
throw new IllegalArgumentException("Unknown parameter type [" + parameter.getParameterType().getName() + "]");
}
//執行解析邏輯
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
if (result == null) {
for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) {
//遍歷解析器，supportsParameter方法返回true就可以
if (methodArgumentResolver.supportsParameter(parameter)) {
result = methodArgumentResolver;
this.argumentResolverCache.put(parameter, result);
break;
}
}
}
return result;
}
複製程式碼整個解析的邏輯還比較清晰:
- 獲取方法需要的引數型別，逐個解析
- 呼叫解析器的supportsParameter方法，判斷是否支援引數型別
- 呼叫解析器的resolveArgument方法，解析引數
引數解析示範
在這個就以最常用的RequestHeader,和RequestBody來分析一下解析的流程。
首先是RequestHeader
RequestHeader 對應的解析器為RequestHeaderMethodArgumentResolver。
先檢視supportsParameter方法:
public boolean supportsParameter(MethodParameter parameter) {
//判斷引數是否為RequestHeader註解標記，並且型別不為map
return (parameter.hasParameterAnnotation(RequestHeader.class) &&
!Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType()));
}
複製程式碼接下來檢視resolveArgument方法，這個方法在他的父類中:
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
//獲取註解資訊
NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);
MethodParameter nestedParameter = parameter.nestedIfOptional();
//獲取header的name
Object resolvedName = resolveStringValue(namedValueInfo.name);
if (resolvedName == null) {
...
}
//通過name查詢
Object arg = resolveName(resolvedName.toString(), nestedParameter, webRequest);
if (arg == null) {
...
}
if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
try {
//處理型別轉換之類的問題
arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter);
}
...
}
handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest);
return arg;
}
複製程式碼邏輯很清晰，關鍵程式碼就在resolveName方法裡了，進入該方法:
protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {
String[] headerValues = request.getHeaderValues(name);
if (headerValues != null) {
return (headerValues.length == 1 ? headerValues[0] : headerValues);
}
else {
return null;
}
}
複製程式碼這邊就可以清晰的看到獲取的過程了。
接下來看看RequestBody
RequestBody註解對應的解析器為RequestResponseBodyMethodProcessor
首先還是檢視supportsParameter方法:
public boolean supportsParameter(MethodParameter parameter) {
//判斷是否有RequestBody註解
return parameter.hasParameterAnnotation(RequestBody.class);
}
複製程式碼接下來檢視resolveArgument方法:
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
parameter = parameter.nestedIfOptional();
//解析傳入請求的請求體
Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());
String name = Conventions.getVariableNameForParameter(parameter);
if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
if (arg != null) {
//如果有需要的話校驗相關引數
validateIfApplicable(binder, parameter);
...
}
...
}
return adaptArgumentIfNecessary(arg, parameter);
}
複製程式碼首先解析請求體，其次校驗結果，這樣就是我們拿到的RequestBody物件了。這個地方解析和校驗相關的邏輯，我們是可以做點文章的具體可以檢視:SpringBoot踩坑日記-一個非空校驗引發的bug
講到這兒可以發現引數解析的邏輯大同小異，那麼springboot到底內建了多少解析器呢？
在DispatcherServlet中，根據mapping獲取到了相應的方法後，還需要找到相應的HandlerAdapter去執行。當我們使用RequestMapping註解時，使用的就是RequestMappingHandlerAdapter這個類。檢視該類的afterPropertiesSet方法()。
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
//獲取解析器的方法就在這裡
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
...
}
private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();
// Annotation-based argument resolution
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
resolvers.add(new RequestParamMapMethodArgumentResolver());
resolvers.add(new PathVariableMethodArgumentResolver());
resolvers.add(new PathVariableMapMethodArgumentResolver());
resolvers.add(new MatrixVariableMethodArgumentResolver());
resolvers.add(new MatrixVariableMapMethodArgumentResolver());
resolvers.add(new ServletModelAttributeMethodProcessor(false));
resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));
resolvers.add(new RequestHeaderMapMethodArgumentResolver());
resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new SessionAttributeMethodArgumentResolver());
resolvers.add(new RequestAttributeMethodArgumentResolver());
// Type-based argument resolution
resolvers.add(new ServletRequestMethodArgumentResolver());
resolvers.add(new ServletResponseMethodArgumentResolver());
resolvers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RedirectAttributesMethodArgumentResolver());
resolvers.add(new ModelMethodProcessor());
resolvers.add(new MapMethodProcessor());
resolvers.add(new ErrorsMethodArgumentResolver());
resolvers.add(new SessionStatusMethodArgumentResolver());
resolvers.add(new UriComponentsBuilderMethodArgumentResolver());
// Custom arguments
if (getCustomArgumentResolvers() != null) {
resolvers.addAll(getCustomArgumentResolvers());
}
// Catch-all
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
resolvers.add(new ServletModelAttributeMethodProcessor(true));
return resolvers;
}
複製程式碼在getDefaultArgumentResolvers方法中，我們可以看到springboot內建了很多的引數解析器。我們上面說到的RequestResponseBodyMethodProcessor，RequestHeaderMethodArgumentResolver就是在這邊注入進容器的。