一、参数解析绑定
1. 自定义绑定：不绑定某些项
@InitBinder private void initBinder(WebDataBinder dataBinder) { dataBinder.setDisallowedFields("company", "dateCreated", "lastUpdated"); }
2. 什么时候使用DataBinder
RequestMappingHandlerAdapter 的 invokeHandlerMethod 方法
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ServletWebRequest webRequest = new ServletWebRequest(request, response); //获取WebDataBinderFactory WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod); ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory); ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod); invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers); invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers); invocableMethod.setDataBinderFactory(binderFactory); invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer); ModelAndViewContainer mavContainer = new ModelAndViewContainer(); mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request)); modelFactory.initModel(webRequest, mavContainer, invocableMethod); mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect); AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response); asyncWebRequest.setTimeout(this.asyncRequestTimeout); 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 + "]"); } invocableMethod = invocableMethod.wrapConcurrentResult(result); }
//注入方法参数 invocableMethod.invokeAndHandle(webRequest, mavContainer); if (asyncManager.isConcurrentHandlingStarted()) { return null; } return getModelAndView(mavContainer, modelFactory, webRequest); }
3. RequestMappingHandlerAdapter
1. RequestMappingHandlerAdapter中两个和参数解析器相关的成员变量
private List<HandlerMethodArgumentResolver> customArgumentResolvers;
private HandlerMethodArgumentResolverComposite argumentResolvers;
2. RequestMappingHandlerAdapter实例化后，会调用afterPropertiesSet()，在这里把系统默认的解析器和我们写的自定义解析器汇总
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
3. 调用匹配的methodArgumentResolver解析数据
参数解析绑定总结
- SpringMVC初始化时，RequestMappingHandlerAdapter类会把一些默认的参数解析器添加到argumentResolvers中。当SpringMVC接收到请求后首先根据url查找对应的HandlerMethod。
- 遍历HandlerMethod的MethodParameter数组
- 根据MethodParameter的类型来查找确认使用哪个HandlerMethodArgumentResolver，遍历所有的argumentResolvers的supportsParameter(MethodParameter parameter)方法。如果返回true，则表示查找成功，当前MethodParameter，使用该HandlerMethodArgumentResolver。这里确认大多都是根据参数的注解已经参数的Type来确认。
- 解析参数，从request中解析出MethodParameter对应的参数，这里解析出来的结果都是String类型。
- 转换参数，把对应String转换成具体方法所需要的类型，这里就包括了基本类型、对象、List、Set、Map。
二、输入输出转换
1.
public interface ConverterFactory<S, R> { /** * Get the converter to convert from S to target type T, where T is also an instance of R. * @param <T> the target type * @param targetType the target type to convert to * @return A converter from S to T */ <T extends R> Converter<S, T> getConverter(Class<T> targetType); }
Spring实现ConvertFactory示例
final class StringToEnumConverterFactory implements ConverterFactory<String, Enum> { @Override public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) { Class<?> enumType = targetType; while (enumType != null && !enumType.isEnum()) { enumType = enumType.getSuperclass(); } if (enumType == null) { throw new IllegalArgumentException "The target type " + targetType.getName() + " does not refer to an enum"); } return new StringToEnum(enumType); } private class StringToEnum<T extends Enum> implements Converter<String, T> { private final Class<T> enumType; public StringToEnum(Class<T> enumType) { this.enumType = enumType; } @Override public T convert(String source) { if (source.length() == 0) { // It's an empty enum identifier: reset the enum value to null. return null; } return (T) Enum.valueOf(this.enumType, source.trim()); } } }
上面的示例不支持基数转换为枚举，改进如下：
public class StringToEnumConverterFactory implements ConverterFactory<String, Enum> { public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) { return new StringToEnumConverter(targetType); } private final class StringToEnumConverter<T extends Enum> implements Converter<String, T> { private Class<T> enumType; public StringToEnumConverter(Class<T> enumType) { this.enumType = enumType; } public T convert(String source) { try { Integer ordinal = Integer.parseInt(source);
//Enum的values是编译器加的 T[] values = (T[]) enumType.getDeclaredMethod("values", new Class[0]).invoke(null, new Object[0]); return values[ordinal]; } catch (Exception e) { } try { Method valueOf = enumType.getDeclaredMethod("valueOf", String.class); return (T) valueOf.invoke(null, source); } catch (Exception e) { } throw new IllegalStateException("非法参数值:" + source); } } }
二、json输出转换: ObjectMapper
spring提供三种不同级别的自定义方式
参考：
spring reference: how to customer ObjectMapper