PropertyEditor是Spring最初采用的转换策略。将会转移到Converter上。本文章主要对@InitBinder注解背后代码层面的运行过程做介绍。所以最好先熟悉它的用法然后来看通代码流程。
先看实例，controller代码如下：
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@Controller
public class FormAction{
// 这样的方法里，一般是用来注册一些PropertyEditor
@InitBinder
public void initBinder(WebDataBinder binder) throws Exception {
DateFormat df = new SimpleDateFormat("yyyy---MM---dd HH:mm:ss");
CustomDateEditor dateEditor = new CustomDateEditor(df, true);
binder.registerCustomEditor(Date.class, dateEditor);
}
@RequestMapping(value="/test/json",method=RequestMethod.GET)
@ResponseBody
public Map<String,Object> getFormData(Date date){
Map<String,Object> map=new HashMap<String,Object>();
map.put("name","lg");
map.put("age",23);
map.put("date",new Date());
return map;
}
}
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xml文件仅仅开启mvc:ananotation-driven:
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<mvc:annotation-driven />
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然后访问 http://localhost:8080/test/json?date=2014---08---3 03:34:23，便看到成功的获取到了数据。接下来源代码代码分析这一过程：
由于使用了@RequestMapping所以会选择RequestMappingHandlerAdapter来调度执行相应的方法，如下：
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/**
* Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
* if view resolution is required.
*/
private ModelAndView invokeHandleMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
//我们关注的重点重点重点重点重点重点重点重点
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
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);
}
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这里面就是整个执行过程。首先绑定请求参数到方法的参数上，然后执行方法，接下来根据方法返回的类型来选择合适的HandlerMethodReturnValueHandler来进行处理，最后要么走view路线，要么直接写入response的body中返回。
我们此时关注的重点是：如何绑定请求参数到方法的参数上的呢？
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
针对每次对该handlerMethod请求产生一个绑定工厂，由这个工厂来完成数据的绑定。
这里的handlerMethod包含了 controller对象FormAction和、test/json映射到的方法即getFormData。
然后详细看下getDataBinderFactory的实现：
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private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) throws Exception {
//这里的handlerType便是controller的类型FormAction
Class<?> handlerType = handlerMethod.getBeanType();
Set<Method> methods = this.initBinderCache.get(handlerType);
if (methods == null) {
//关注点1：找出FormAction类的所有的含有@InitBinder的方法（方法的返回类型必须为void），找到后同时缓存起来
methods = HandlerMethodSelector.selectMethods(handlerType, INIT_BINDER_METHODS);
this.initBinderCache.put(handlerType, methods);
}
List<InvocableHandlerMethod> initBinderMethods = new ArrayList<InvocableHandlerMethod>();
// Global methods first
//关注点2：再寻找出全局的初始化Binder的方法
for (Entry<ControllerAdviceBean, Set<Method>> entry : this.initBinderAdviceCache .entrySet()) {
if (entry.getKey().isApplicableToBeanType(handlerType)) {
Object bean = entry.getKey().resolveBean();
for (Method method : entry.getValue()) {
initBinderMethods.add(createInitBinderMethod(bean, method));
}
}
}
for (Method method : methods) {
Object bean = handlerMethod.getBean();
initBinderMethods.add(createInitBinderMethod(bean, method));
}
//关注点3：找到了所有的与该handlerMethod有关的初始化binder的方法，保存起来
return createDataBinderFactory(initBinderMethods);
}
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上面稍微做了些注释，然后看下详细的内容：
关注点1：就是使用过滤，过滤类为：INIT_BINDER_METHODS，如下
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/**
* MethodFilter that matches {@link InitBinder @InitBinder} methods.
*/
public static final MethodFilter INIT_BINDER_METHODS = new MethodFilter() {
@Override
public boolean matches(Method method) {
return AnnotationUtils.findAnnotation(method, InitBinder.class) != null;
}
};
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这个过滤类就是在handlerType即FormAction中过滤那些含有@InitBinder注解的方法。找到了之后就缓存起来，供下次使用。key为：handlerType，value为找到的方法。存至initBinderCache中。
关注点2：从initBinderAdviceCache中获取所有支持这个handlerType的method。这一块有待继续研究，这个initBinderAdviceCache是如何初始化来的等等。针对目前的工程来说，initBinderAdviceCache是为空的。
关注点3：遍历所有找到的和handlerType有关的method,然后封装成InvocableHandlerMethod，如下：
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for (Method method : methods) {
Object bean = handlerMethod.getBean();
initBinderMethods.add(createInitBinderMethod(bean, method));
}
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private InvocableHandlerMethod createInitBinderMethod(Object bean, Method method) {
InvocableHandlerMethod binderMethod = new InvocableHandlerMethod(bean, method);
binderMethod.setHandlerMethodArgumentResolvers(this.initBinderArgumentResolvers);
binderMethod.setDataBinderFactory(new DefaultDataBinderFactory(this.webBindingInitializer));
binderMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
return binderMethod;
}
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在封装的过程中，同时设置一些RequestMappingHandlerAdapter的一些参数进去initBinderArgumentResolvers、webBindingInitializer、parameterNameDiscoverer。
封装完所有的方法后，创建出最终的WebDataBinderFactory。如下：
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protected InitBinderDataBinderFactory createDataBinderFactory(List<InvocableHandlerMethod> binderMethods)
throws Exception {
return new ServletRequestDataBinderFactory(binderMethods, getWebBindingInitializer());
}
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getWebBindingInitializer()也是RequestMappingHandlerAdapter的webBindingInitializer参数。
至此绑定数据的工厂完成了，包含了这个handlerType的所有的PropertyEditor。这是准备工作，然后就是等待执行这个我们自己的方法getFormData执行时来完成参数的绑定过程。
绑定参数过程即getFormData的执行过程如下：
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ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);
略
requestMappingMethod.invokeAndHandle(webRequest, mavContainer);
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其中的requestMappingMethod经过了进一步的包装，已经包含刚才已经创建的绑定工厂。
执行过程如下：
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public final Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
StringBuilder sb = new StringBuilder("Invoking [");
sb.append(getBeanType().getSimpleName()).append(".");
sb.append(getMethod().getName()).append("] method with arguments ");
sb.append(Arrays.asList(args));
logger.trace(sb.toString());
}
Object returnValue = invoke(args);
if (logger.isTraceEnabled()) {
logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]");
}
return returnValue;
}
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分两大步，绑定参数和执行方法体。最重要的就是如何来绑定参数呢？
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private Object[] getMethodArgumentValues(NativeWebRequest request, 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);
GenericTypeResolver.resolveParameterType(parameter, getBean().getClass());
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.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;
}
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绑定参数又引出来另一个重要名词：HandlerMethodArgumentResolver。args[i] = this.argumentResolvers.resolveArgument(
parameter, mavContainer, request, this.dataBinderFactory);的具体内容如下：
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/**
* Iterate over registered {@link HandlerMethodArgumentResolver}s and invoke the one that supports it.
* @exception IllegalStateException if no suitable {@link HandlerMethodArgumentResolver} is found.
*/
@Override
public Object resolveArgument(
MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory)
throws Exception {
HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
Assert.notNull(resolver, "Unknown parameter type [" + parameter.getParameterType().getName() + "]");
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
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遍历所有已注册的HandlerMethodArgumentResolver，然后找出一个适合的来进行参数绑定，对于本工程来说，getFormData(Date date)的参数date默认是request params级别的，所以使用RequestParamMethodArgumentResolver来处理这一过程。处理过程如下：
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@Override
public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
Class<?> paramType = parameter.getParameterType();
NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);
Object arg = resolveName(namedValueInfo.name, parameter, webRequest);
if (arg == null) {
if (namedValueInfo.defaultValue != null) {
arg = resolveDefaultValue(namedValueInfo.defaultValue);
}
else if (namedValueInfo.required) {
handleMissingValue(namedValueInfo.name, parameter);
}
arg = handleNullValue(namedValueInfo.name, arg, paramType);
}
else if ("".equals(arg) && (namedValueInfo.defaultValue != null)) {
arg = resolveDefaultValue(namedValueInfo.defaultValue);
}
if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
arg = binder.convertIfNecessary(arg, paramType, parameter);
}
handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest);
return arg;
}
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NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);获取参数信息，就是按照@RequestParam的3个属性来收集的，即defaultValue=null、required=false、name=date,
Object arg = resolveName(namedValueInfo.name, parameter, webRequest);然后就是获取原始数据,获取过程如下：
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@Override
protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest webRequest) throws Exception {
Object arg;
HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
MultipartHttpServletRequest multipartRequest =
WebUtils.getNativeRequest(servletRequest, MultipartHttpServletRequest.class);
if (MultipartFile.class.equals(parameter.getParameterType())) {
assertIsMultipartRequest(servletRequest);
Assert.notNull(multipartRequest, "Expected MultipartHttpServletRequest: is a MultipartResolver configured?");
arg = multipartRequest.getFile(name);
}
else if (isMultipartFileCollection(parameter)) {
assertIsMultipartRequest(servletRequest);
Assert.notNull(multipartRequest, "Expected MultipartHttpServletRequest: is a MultipartResolver configured?");
arg = multipartRequest.getFiles(name);
}
else if(isMultipartFileArray(parameter)) {
assertIsMultipartRequest(servletRequest);
Assert.notNull(multipartRequest, "Expected MultipartHttpServletRequest: is a MultipartResolver configured?");
arg = multipartRequest.getFiles(name).toArray(new MultipartFile[0]);
}
else if ("javax.servlet.http.Part".equals(parameter.getParameterType().getName())) {
assertIsMultipartRequest(servletRequest);
arg = servletRequest.getPart(name);
}
else if (isPartCollection(parameter)) {
assertIsMultipartRequest(servletRequest);
arg = new ArrayList<Object>(servletRequest.getParts());
}
else if (isPartArray(parameter)) {
assertIsMultipartRequest(servletRequest);
arg = RequestPartResolver.resolvePart(servletRequest);
}
else {
arg = null;
if (multipartRequest != null) {
List<MultipartFile> files = multipartRequest.getFiles(name);
if (!files.isEmpty()) {
arg = (files.size() == 1 ? files.get(0) : files);
}
}
if (arg == null) {
//对于本工程，我们的重点在这里这里这里这里这里这里
String[] paramValues = webRequest.getParameterValues(name);
if (paramValues != null) {
arg = paramValues.length == 1 ? paramValues[0] : paramValues;
}
}
}
return arg;
}
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通过webRequest.getParameterValues(name)来获取原始的字符串。这里便有涉及到了容器如tomcat的处理过程，这一获取参数的过程在本系列的第五篇文章tomcat的获取参数中进行了详细的源码介绍，那一篇主要是介绍乱码的。本文章不再介绍，接着说，这样就可以获取到我们请求的原始字符串"2014---08---3 03:34:23"，接下来便是执行转换绑定的过程：
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if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
arg = binder.convertIfNecessary(arg, paramType, parameter);
}
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这一过程就是要寻找我们已经注册的所有的PropertyEditor来进行转换，如果还没有找到，则使用另一套转换流程，使用conversionService来进行转换。我们慢慢来看这一过程，有了binderFactory便可以创建出WebDataBinder，具体的创建过程如下：
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public final WebDataBinder createBinder(NativeWebRequest webRequest, Object target, String objectName)
throws Exception {
WebDataBinder dataBinder = createBinderInstance(target, objectName, webRequest);
if (this.initializer != null) {
this.initializer.initBinder(dataBinder, webRequest);
}
initBinder(dataBinder, webRequest);
return dataBinder;
}
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先创建出WebDataBinder，然后使用initializer的initBinder方法来初始化一些PropertyEditor，initializer的类型为我们常见的ConfigurableWebBindingInitializer即在mvc:annotation-driven时默认注册的最终设置为RequestMappingHandlerAdapter的webBindingInitializer属性值。this.initializer.initBinder(dataBinder, webRequest);过程如下：
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@Override
public void initBinder(WebDataBinder binder, WebRequest request) {
binder.setAutoGrowNestedPaths(this.autoGrowNestedPaths);
if (this.directFieldAccess) {
binder.initDirectFieldAccess();
}
if (this.messageCodesResolver != null) {
binder.setMessageCodesResolver(this.messageCodesResolver);
}
if (this.bindingErrorProcessor != null) {
binder.setBindingErrorProcessor(this.bindingErrorProcessor);
}
if (this.validator != null && binder.getTarget() != null &&
this.validator.supports(binder.getTarget().getClass())) {
binder.setValidator(this.validator);
}
if (this.conversionService != null) {
binder.setConversionService(this.conversionService);
}
if (this.propertyEditorRegistrars != null) {
for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
propertyEditorRegistrar.registerCustomEditors(binder);
}
}
}
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即设置一些我们conversionService、messageCodesResolver、validator 等，这些参数即我们在mvc:annotation中进行设置的，若无设置，采用默认的。
继续执行initBinder(dataBinder, webRequest);
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public void initBinder(WebDataBinder binder, NativeWebRequest request) throws Exception {
for (InvocableHandlerMethod binderMethod : this.binderMethods) {
if (isBinderMethodApplicable(binderMethod, binder)) {
Object returnValue = binderMethod.invokeForRequest(request, null, binder);
if (returnValue != null) {
throw new IllegalStateException("@InitBinder methods should return void: " + binderMethod);
}
}
}
}
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执行那些适合我们已经创建的WebDataBinder，怎样才叫适合的呢？看isBinderMethodApplicable(binderMethod, binder)方法
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protected boolean isBinderMethodApplicable(HandlerMethod initBinderMethod, WebDataBinder binder) {
InitBinder annot = initBinderMethod.getMethodAnnotation(InitBinder.class);
Collection<String> names = Arrays.asList(annot.value());
return (names.size() == 0 || names.contains(binder.getObjectName()));
}
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当initBinderMethod上的@InitBinder注解指定了value，该value可以是多个，当它包含了我们的方法的参数date,则这个initBinderMethod就会被执行。当@InitBinder注解没有指定value，则也会被执行。所以为了不用执行一些不必要的initBinderMethod，我们最好为这些initBinderMethod上的@InitBinder加上value限定。对于我们写的initBinder便因此开始执行了。
由binderFactory创建出来的WebDataBinder就此完成，然后才是详细的转换过程：
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public <T> T convertIfNecessary(String propertyName, Object oldValue, Object newValue,
Class<T> requiredType, TypeDescriptor typeDescriptor) throws IllegalArgumentException {
Object convertedValue = newValue;
// Custom editor for this type?
PropertyEditor editor = this.propertyEditorRegistry.findCustomEditor(requiredType, propertyName);
ConversionFailedException firstAttemptEx = null;
// No custom editor but custom ConversionService specified?
ConversionService conversionService = this.propertyEditorRegistry.getConversionService();
//略
}
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这里首先使用已注册的PropertyEditor，当仍然没有找到时才使用ConversionService。对于本工程来说，由于已经手动注册了对于Date的转换的PropertyEditor即CustomDateEditor，然后便会执行CustomDateEditor的具体的转换过程。至此，大体过程就算是完了。
时间： 2024-10-21 15:33:39
