Java tutorial
/* * Copyright 2002-2017 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.web.servlet.mvc.method.annotation; import java.util.Collections; import java.util.Map; import javax.servlet.ServletRequest; import org.springframework.core.MethodParameter; import org.springframework.core.convert.ConversionService; import org.springframework.core.convert.TypeDescriptor; import org.springframework.core.convert.converter.Converter; import org.springframework.lang.Nullable; import org.springframework.util.Assert; import org.springframework.util.StringUtils; import org.springframework.validation.DataBinder; import org.springframework.web.bind.ServletRequestDataBinder; import org.springframework.web.bind.WebDataBinder; import org.springframework.web.bind.support.WebDataBinderFactory; import org.springframework.web.context.request.NativeWebRequest; import org.springframework.web.context.request.RequestAttributes; import org.springframework.web.method.annotation.ModelAttributeMethodProcessor; import org.springframework.web.servlet.HandlerMapping; /** * A Servlet-specific {@link ModelAttributeMethodProcessor} that applies data * binding through a WebDataBinder of type {@link ServletRequestDataBinder}. * * <p>Also adds a fall-back strategy to instantiate the model attribute from a * URI template variable or from a request parameter if the name matches the * model attribute name and there is an appropriate type conversion strategy. * * @author Rossen Stoyanchev * @author Juergen Hoeller * @since 3.1 */ public class ServletModelAttributeMethodProcessor extends ModelAttributeMethodProcessor { /** * Class constructor. * @param annotationNotRequired if "true", non-simple method arguments and * return values are considered model attributes with or without a * {@code @ModelAttribute} annotation */ public ServletModelAttributeMethodProcessor(boolean annotationNotRequired) { super(annotationNotRequired); } /** * Instantiate the model attribute from a URI template variable or from a * request parameter if the name matches to the model attribute name and * if there is an appropriate type conversion strategy. If none of these * are true delegate back to the base class. * @see #createAttributeFromRequestValue */ @Override protected final Object createAttribute(String attributeName, MethodParameter parameter, WebDataBinderFactory binderFactory, NativeWebRequest request) throws Exception { String value = getRequestValueForAttribute(attributeName, request); if (value != null) { Object attribute = createAttributeFromRequestValue(value, attributeName, parameter, binderFactory, request); if (attribute != null) { return attribute; } } return super.createAttribute(attributeName, parameter, binderFactory, request); } /** * Obtain a value from the request that may be used to instantiate the * model attribute through type conversion from String to the target type. * <p>The default implementation looks for the attribute name to match * a URI variable first and then a request parameter. * @param attributeName the model attribute name * @param request the current request * @return the request value to try to convert, or {@code null} if none */ @Nullable protected String getRequestValueForAttribute(String attributeName, NativeWebRequest request) { Map<String, String> variables = getUriTemplateVariables(request); String variableValue = variables.get(attributeName); if (StringUtils.hasText(variableValue)) { return variableValue; } String parameterValue = request.getParameter(attributeName); if (StringUtils.hasText(parameterValue)) { return parameterValue; } return null; } @SuppressWarnings("unchecked") protected final Map<String, String> getUriTemplateVariables(NativeWebRequest request) { Map<String, String> variables = (Map<String, String>) request .getAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST); return (variables != null ? variables : Collections.emptyMap()); } /** * Create a model attribute from a String request value (e.g. URI template * variable, request parameter) using type conversion. * <p>The default implementation converts only if there a registered * {@link Converter} that can perform the conversion. * @param sourceValue the source value to create the model attribute from * @param attributeName the name of the attribute (never {@code null}) * @param parameter the method parameter * @param binderFactory for creating WebDataBinder instance * @param request the current request * @return the created model attribute, or {@code null} if no suitable * conversion found */ @Nullable protected Object createAttributeFromRequestValue(String sourceValue, String attributeName, MethodParameter parameter, WebDataBinderFactory binderFactory, NativeWebRequest request) throws Exception { DataBinder binder = binderFactory.createBinder(request, null, attributeName); ConversionService conversionService = binder.getConversionService(); if (conversionService != null) { TypeDescriptor source = TypeDescriptor.valueOf(String.class); TypeDescriptor target = new TypeDescriptor(parameter); if (conversionService.canConvert(source, target)) { return binder.convertIfNecessary(sourceValue, parameter.getParameterType(), parameter); } } return null; } /** * This implementation downcasts {@link WebDataBinder} to * {@link ServletRequestDataBinder} before binding. * @see ServletRequestDataBinderFactory */ @Override protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) { ServletRequest servletRequest = request.getNativeRequest(ServletRequest.class); Assert.state(servletRequest != null, "No ServletRequest"); ServletRequestDataBinder servletBinder = (ServletRequestDataBinder) binder; servletBinder.bind(servletRequest); } }