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/*
 * Copyright 2002-2007 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
 *
 *      http://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.
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package org.springframework.web.bind;

import java.lang.reflect.Array;
import java.util.Iterator;
import java.util.Map;

import org.springframework.beans.MutablePropertyValues;
import org.springframework.beans.PropertyValue;
import org.springframework.validation.DataBinder;
import org.springframework.web.multipart.MultipartFile;

/**
 * Special {@link DataBinder} for data binding from web request parameters
 * to JavaBean objects. Designed for web environments, but not dependent on
 * the Servlet API; serves as base class for more specific DataBinder variants,
 * such as {@link org.springframework.web.bind.ServletRequestDataBinder}.
 *
 * 

Includes support for field markers which address a common problem with * HTML checkboxes and select options: detecting that a field was part of * the form, but did not generate a request parameter because it was empty. * A field marker allows to detect that state and reset the corresponding * bean property accordingly. * * @author Juergen Hoeller * @since 1.2 * @see #registerCustomEditor * @see #setAllowedFields * @see #setRequiredFields * @see #setFieldMarkerPrefix * @see ServletRequestDataBinder */ public class WebDataBinder extends DataBinder { /** * Default prefix that field marker parameters start with, followed by the field * name: e.g. "_subscribeToNewsletter" for a field "subscribeToNewsletter". *

Such a marker parameter indicates that the field was visible, that is, * existed in the form that caused the submission. If no corresponding field * value parameter was found, the field will be reset. The value of the field * marker parameter does not matter in this case; an arbitrary value can be used. * This is particularly useful for HTML checkboxes and select options. * @see #setFieldMarkerPrefix */ public static final String DEFAULT_FIELD_MARKER_PREFIX = "_"; private String fieldMarkerPrefix = DEFAULT_FIELD_MARKER_PREFIX; private boolean bindEmptyMultipartFiles = true; /** * Create a new WebDataBinder instance, with default object name. * @param target target object to bind onto * @see #DEFAULT_OBJECT_NAME */ public WebDataBinder(Object target) { super(target); } /** * Create a new WebDataBinder instance. * @param target target object to bind onto * @param objectName objectName of the target object */ public WebDataBinder(Object target, String objectName) { super(target, objectName); } /** * Specify a prefix that can be used for parameters that mark potentially * empty fields, having "prefix + field" as name. Such a marker parameter is * checked by existence: You can send any value for it, for example "visible". * This is particularly useful for HTML checkboxes and select options. *

Default is "_", for "_FIELD" parameters (e.g. "_subscribeToNewsletter"). * Set this to null if you want to turn off the empty field check completely. *

HTML checkboxes only send a value when they're checked, so it is not * possible to detect that a formerly checked box has just been unchecked, * at least not with standard HTML means. *

One way to address this is to look for a checkbox parameter value if * you know that the checkbox has been visible in the form, resetting the * checkbox if no value found. In Spring web MVC, this typically happens * in a custom onBind implementation. *

This auto-reset mechanism addresses this deficiency, provided * that a marker parameter is sent for each checkbox field, like * "_subscribeToNewsletter" for a "subscribeToNewsletter" field. * As the marker parameter is sent in any case, the data binder can * detect an empty field and automatically reset its value. * @see #DEFAULT_FIELD_MARKER_PREFIX * @see org.springframework.web.servlet.mvc.BaseCommandController#onBind */ public void setFieldMarkerPrefix(String fieldMarkerPrefix) { this.fieldMarkerPrefix = fieldMarkerPrefix; } /** * Return the prefix for parameters that mark potentially empty fields. */ public String getFieldMarkerPrefix() { return this.fieldMarkerPrefix; } /** * Set whether to bind empty MultipartFile parameters. Default is "true". *

Turn this off if you want to keep an already bound MultipartFile * when the user resubmits the form without choosing a different file. * Else, the already bound MultipartFile will be replaced by an empty * MultipartFile holder. * @see org.springframework.web.multipart.MultipartFile */ public void setBindEmptyMultipartFiles(boolean bindEmptyMultipartFiles) { this.bindEmptyMultipartFiles = bindEmptyMultipartFiles; } /** * Return whether to bind empty MultipartFile parameters. */ public boolean isBindEmptyMultipartFiles() { return this.bindEmptyMultipartFiles; } /** * This implementation performs a field marker check * before delegating to the superclass binding process. * @see #checkFieldMarkers */ protected void doBind(MutablePropertyValues mpvs) { checkFieldMarkers(mpvs); super.doBind(mpvs); } /** * Check the given property values for field markers, * i.e. for fields that start with the field marker prefix. *

The existence of a field marker indicates that the specified * field existed in the form. If the property values do not contain * a corresponding field value, the field will be considered as empty * and will be reset appropriately. * @param mpvs the property values to be bound (can be modified) * @see #getFieldMarkerPrefix * @see #getEmptyValue(String, Class) */ protected void checkFieldMarkers(MutablePropertyValues mpvs) { if (getFieldMarkerPrefix() != null) { String fieldMarkerPrefix = getFieldMarkerPrefix(); PropertyValue[] pvArray = mpvs.getPropertyValues(); for (int i = 0; i < pvArray.length; i++) { PropertyValue pv = pvArray[i]; if (pv.getName().startsWith(fieldMarkerPrefix)) { String field = pv.getName().substring(fieldMarkerPrefix.length()); if (getPropertyAccessor().isWritableProperty(field) && !mpvs.contains(field)) { Class fieldType = getPropertyAccessor().getPropertyType(field); mpvs.addPropertyValue(field, getEmptyValue(field, fieldType)); } mpvs.removePropertyValue(pv); } } } } /** * Determine an empty value for the specified field. *

Default implementation returns Boolean.FALSE * for boolean fields and an empty array of array types. * Else, null is used as default. * @param field the name of the field * @param fieldType the type of the field * @return the empty value (for most fields: null) */ protected Object getEmptyValue(String field, Class fieldType) { if (fieldType != null && boolean.class.equals(fieldType) || Boolean.class.equals(fieldType)) { // Special handling of boolean property. return Boolean.FALSE; } else if (fieldType != null && fieldType.isArray()) { // Special handling of array property. return Array.newInstance(fieldType.getComponentType(), 0); } else { // Default value: try null. return null; } } /** * Bind the multipart files contained in the given request, if any * (in case of a multipart request). *

Multipart files will only be added to the property values if they * are not empty or if we're configured to bind empty multipart files too. * @param multipartFiles Map of field name String to MultipartFile object * @param mpvs the property values to be bound (can be modified) * @see org.springframework.web.multipart.MultipartFile * @see #setBindEmptyMultipartFiles */ protected void bindMultipartFiles(Map multipartFiles, MutablePropertyValues mpvs) { for (Iterator it = multipartFiles.entrySet().iterator(); it.hasNext();) { Map.Entry entry = (Map.Entry) it.next(); String key = (String) entry.getKey(); MultipartFile value = (MultipartFile) entry.getValue(); if (isBindEmptyMultipartFiles() || !value.isEmpty()) { mpvs.addPropertyValue(key, value); } } } }





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