TagIdGenerator


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.servlet.tags.form;
18  
19  import javax.servlet.jsp.PageContext  ;
20  
21  /**
22   * Utility class for generating '<code>id</code>' attributes values for JSP tags. Given the
23   * name of a tag (the data bound path in most cases) returns a unique ID for that name within
24   * the current {@link PageContext}. Each request for an ID for a given name will append an
25   * ever increasing counter to the name itself. For instance, given the name '<code>person.name</code>',
26   * the first request will give '<code>person.name1</code>' and the second will give
27   * '<code>person.name1</code>'. This supports the common use case where a set of radio or check buttons
28   * are generated for the same data field, with each button being a distinct tag instance.
29   *
30   * @author Rob Harrop
31   * @since 2.0
32   */
33  final class TagIdGenerator {
34  
35      /**
36       * The prefix for all {@link PageContext} attributes created by this tag.
37       */
38      private static final String   PAGE_CONTEXT_ATTRIBUTE_PREFIX = TagIdGenerator.class.getName();
39  
40      /**
41       * Cannot create externally.
42       */
43      private TagIdGenerator() {
44  
45      }
46  
47      /**
48       * Gets the next unique ID (withing the given {@link PageContext}) for the supplied name.
49       */
50      public static String   nextId(String   name, PageContext   pageContext) {
51          String   attributeName = PAGE_CONTEXT_ATTRIBUTE_PREFIX + "." + name;
52          Integer   currentCount = (Integer  ) pageContext.getAttribute(attributeName);
53          currentCount = (currentCount == null ? new Integer  (1) : new Integer  (currentCount.intValue() + 1));
54          pageContext.setAttribute(attributeName, currentCount);
55          return name + currentCount.intValue();
56      }
57  }
58
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