WebDataBinder


1   /*
2    * Copyright 2002-2006 the original author or authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package org.springframework.web.bind;
18  
19  import java.lang.reflect.Array  ;
20  import java.util.Iterator  ;
21  import java.util.Map  ;
22  
23  import org.springframework.beans.MutablePropertyValues;
24  import org.springframework.beans.PropertyValue;
25  import org.springframework.validation.DataBinder;
26  import org.springframework.web.multipart.MultipartFile;
27  
28  /**
29   * Special DataBinder to perform data binding from web request parameters
30   * to JavaBeans. Designed for web environments, but not dependent on the
31   * Servlet API; serves as base class for more specific DataBinder variants,
32   * such as ServletRequestDataBinder.
33   *
34   * <p>Includes support for field markers which address a common problem with
35   * HTML checkboxes and select options: detecting that a field was part of
36   * the form, but did not generate a request parameter because it was empty.
37   * A field marker allows to detect that state and reset the corresponding
38   * bean property accordingly.
39   *
40   * @author Juergen Hoeller
41   * @since 1.2
42   * @see #registerCustomEditor
43   * @see #setAllowedFields
44   * @see #setRequiredFields
45   * @see #setFieldMarkerPrefix
46   * @see ServletRequestDataBinder
47   */
48  public class WebDataBinder extends DataBinder {
49  
50      /**
51       * Default prefix that field marker parameters start with, followed by the field
52       * name: e.g. "_subscribeToNewsletter" for a field "subscribeToNewsletter".
53       * <p>Such a marker parameter indicates that the field was visible, that is,
54       * existed in the form that caused the submission. If no corresponding field
55       * value parameter was found, the field will be reset. The value of the field
56       * marker parameter does not matter in this case; an arbitrary value can be used.
57       * This is particularly useful for HTML checkboxes and select options.
58       * @see #setFieldMarkerPrefix
59       */
60      public static final String   DEFAULT_FIELD_MARKER_PREFIX = "_";
61  
62  
63      private String   fieldMarkerPrefix = DEFAULT_FIELD_MARKER_PREFIX;
64  
65      private boolean bindEmptyMultipartFiles = true;
66  
67  
68      /**
69       * Create a new WebDataBinder instance, with default object name.
70       * @param target target object to bind onto
71       * @see #DEFAULT_OBJECT_NAME
72       */
73      public WebDataBinder(Object   target) {
74          super(target);
75      }
76  
77      /**
78       * Create a new WebDataBinder instance.
79       * @param target target object to bind onto
80       * @param objectName objectName of the target object
81       */
82      public WebDataBinder(Object   target, String   objectName) {
83          super(target, objectName);
84      }
85  
86  
87      /**
88       * Specify a prefix that can be used for parameters that mark potentially
89       * empty fields, having "prefix + field" as name. Such a marker parameter is
90       * checked by existence: You can send any value for it, for example "visible".
91       * This is particularly useful for HTML checkboxes and select options.
92       * <p>Default is "_", for "_FIELD" parameters (e.g. "_subscribeToNewsletter").
93       * Set this to null if you want to turn off the empty field check completely.
94       * <p>HTML checkboxes only send a value when they're checked, so it is not
95       * possible to detect that a formerly checked box has just been unchecked,
96       * at least not with standard HTML means.
97       * <p>One way to address this is to look for a checkbox parameter value if
98       * you know that the checkbox has been visible in the form, resetting the
99       * checkbox if no value found. In Spring web MVC, this typically happens
100      * in a custom <code>onBind</code> implementation.
101      * <p>This auto-reset mechanism addresses this deficiency, provided
102      * that a marker parameter is sent for each checkbox field, like
103      * "_subscribeToNewsletter" for a "subscribeToNewsletter" field.
104      * As the marker parameter is sent in any case, the data binder can
105      * detect an empty field and automatically reset its value.
106      * @see #DEFAULT_FIELD_MARKER_PREFIX
107      * @see org.springframework.web.servlet.mvc.BaseCommandController#onBind
108      */
109     public void setFieldMarkerPrefix(String   fieldMarkerPrefix) {
110         this.fieldMarkerPrefix = fieldMarkerPrefix;
111     }
112 
113     /**
114      * Return the prefix for parameters that mark potentially empty fields.
115      */
116     public String   getFieldMarkerPrefix() {
117         return fieldMarkerPrefix;
118     }
119 
120     /**
121      * Set whether to bind empty MultipartFile parameters. Default is "true".
122      * <p>Turn this off if you want to keep an already bound MultipartFile
123      * when the user resubmits the form without choosing a different file.
124      * Else, the already bound MultipartFile will be replaced by an empty
125      * MultipartFile holder.
126      * @see org.springframework.web.multipart.MultipartFile
127      */
128     public void setBindEmptyMultipartFiles(boolean bindEmptyMultipartFiles) {
129         this.bindEmptyMultipartFiles = bindEmptyMultipartFiles;
130     }
131 
132     /**
133      * Return whether to bind empty MultipartFile parameters.
134      */
135     public boolean isBindEmptyMultipartFiles() {
136         return bindEmptyMultipartFiles;
137     }
138 
139 
140     /**
141      * This implementation performs a field marker check
142      * before delegating to the superclass binding process.
143      * @see #checkFieldMarkers
144      */
145     protected void doBind(MutablePropertyValues mpvs) {
146         checkFieldMarkers(mpvs);
147         super.doBind(mpvs);
148     }
149 
150     /**
151      * Check the given property values for field markers,
152      * i.e. for fields that start with the field marker prefix.
153      * <p>The existence of a field marker indicates that the specified
154      * field existed in the form. If the property values do not contain
155      * a corresponding field value, the field will be considered as empty
156      * and will be reset appropriately.
157      * @param mpvs the property values to be bound (can be modified)
158      * @see #getFieldMarkerPrefix
159      * @see #getEmptyValue(String, Class)
160      */
161     protected void checkFieldMarkers(MutablePropertyValues mpvs) {
162         if (getFieldMarkerPrefix() != null) {
163             String   fieldMarkerPrefix = getFieldMarkerPrefix();
164             PropertyValue[] pvArray = mpvs.getPropertyValues();
165             for (int i = 0; i < pvArray.length; i++) {
166                 PropertyValue pv = pvArray[i];
167                 if (pv.getName().startsWith(fieldMarkerPrefix)) {
168                     String   field = pv.getName().substring(fieldMarkerPrefix.length());
169                     if (getPropertyAccessor().isWritableProperty(field) && !mpvs.contains(field)) {
170                         Class   fieldType = getPropertyAccessor().getPropertyType(field);
171                         mpvs.addPropertyValue(field, getEmptyValue(field, fieldType));
172                     }
173                     mpvs.removePropertyValue(pv);
174                 }
175             }
176         }
177     }
178 
179     /**
180      * Determine an empty value for the specified field.
181      * <p>Default implementation returns <code>Boolean.FALSE</code>
182      * for boolean fields and an empty array of array types.
183      * Else, <code>null</code> is used as default.
184      * @param field the name of the field
185      * @param fieldType the type of the field
186      * @return the empty value (for most fields: null)
187      */
188     protected Object   getEmptyValue(String   field, Class   fieldType) {
189         if (fieldType != null && boolean.class.equals(fieldType) || Boolean  .class.equals(fieldType)) {
190             // Special handling of boolean property.
191             return Boolean.FALSE;
192         }
193         else if (fieldType != null && fieldType.isArray()) {
194             // Special handling of array property.
195             return Array.newInstance(fieldType.getComponentType(), 0);
196         }
197         else {
198             // Default value: try null.
199             return null;
200         }
201     }
202 
203 
204     /**
205      * Bind the multipart files contained in the given request, if any
206      * (in case of a multipart request).
207      * <p>Multipart files will only be added to the property values if they
208      * are not empty or if we're configured to bind empty multipart files too.
209      * @param multipartFiles Map of field name String to MultipartFile object
210      * @param mpvs the property values to be bound (can be modified)
211      * @see org.springframework.web.multipart.MultipartFile
212      * @see #setBindEmptyMultipartFiles
213      */
214     protected void bindMultipartFiles(Map   multipartFiles, MutablePropertyValues mpvs) {
215         for (Iterator   it = multipartFiles.entrySet().iterator(); it.hasNext();) {
216             Map.Entry   entry = (Map.Entry  ) it.next();
217             String   key = (String  ) entry.getKey();
218             MultipartFile value = (MultipartFile) entry.getValue();
219             if (isBindEmptyMultipartFiles() || !value.isEmpty()) {
220                 mpvs.addPropertyValue(key, value);
221             }
222         }
223     }
224 
225 }
226
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