Classes in this File | Line Coverage | Branch Coverage | Complexity | ||||
XPathExpressionEngine |
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1 | /* | |
2 | * Licensed to the Apache Software Foundation (ASF) under one or more | |
3 | * contributor license agreements. See the NOTICE file distributed with | |
4 | * this work for additional information regarding copyright ownership. | |
5 | * The ASF licenses this file to You under the Apache License, Version 2.0 | |
6 | * (the "License"); you may not use this file except in compliance with | |
7 | * the License. You may obtain a copy of the License at | |
8 | * | |
9 | * http://www.apache.org/licenses/LICENSE-2.0 | |
10 | * | |
11 | * Unless required by applicable law or agreed to in writing, software | |
12 | * distributed under the License is distributed on an "AS IS" BASIS, | |
13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
14 | * See the License for the specific language governing permissions and | |
15 | * limitations under the License. | |
16 | */ | |
17 | package org.apache.commons.configuration.tree.xpath; | |
18 | ||
19 | import java.util.ArrayList; | |
20 | import java.util.Collections; | |
21 | import java.util.List; | |
22 | import java.util.StringTokenizer; | |
23 | ||
24 | import org.apache.commons.configuration.tree.ConfigurationNode; | |
25 | import org.apache.commons.configuration.tree.ExpressionEngine; | |
26 | import org.apache.commons.configuration.tree.NodeAddData; | |
27 | import org.apache.commons.jxpath.JXPathContext; | |
28 | import org.apache.commons.jxpath.ri.JXPathContextReferenceImpl; | |
29 | import org.apache.commons.lang.StringUtils; | |
30 | ||
31 | /** | |
32 | * <p> | |
33 | * A specialized implementation of the <code>ExpressionEngine</code> interface | |
34 | * that is able to evaluate XPATH expressions. | |
35 | * </p> | |
36 | * <p> | |
37 | * This class makes use of <a href="http://jakarta.apache.org/commons/jxpath/"> | |
38 | * Commons JXPath</a> for handling XPath expressions and mapping them to the | |
39 | * nodes of a hierarchical configuration. This makes the rich and powerfull | |
40 | * XPATH syntax available for accessing properties from a configuration object. | |
41 | * </p> | |
42 | * <p> | |
43 | * For selecting properties arbitrary XPATH expressions can be used, which | |
44 | * select single or multiple configuration nodes. The associated | |
45 | * <code>Configuration</code> instance will directly pass the specified | |
46 | * property keys into this engine. If a key is not syntactically correct, an | |
47 | * exception will be thrown. | |
48 | * </p> | |
49 | * <p> | |
50 | * For adding new properties, this expression engine uses a specific syntax: the | |
51 | * "key" of a new property must consist of two parts that are | |
52 | * separated by whitespace: | |
53 | * <ol> | |
54 | * <li>An XPATH expression selecting a single node, to which the new element(s) | |
55 | * are to be added. This can be an arbitrary complex expression, but it must | |
56 | * select exactly one node, otherwise an exception will be thrown.</li> | |
57 | * <li>The name of the new element(s) to be added below this parent node. Here | |
58 | * either a single node name or a complete path of nodes (separated by the | |
59 | * "/" character) can be specified.</li> | |
60 | * </ol> | |
61 | * Some examples for valid keys that can be passed into the configuration's | |
62 | * <code>addProperty()</code> method follow: | |
63 | * </p> | |
64 | * <p> | |
65 | * | |
66 | * <pre> | |
67 | * "/tables/table[1] type" | |
68 | * </pre> | |
69 | * | |
70 | * </p> | |
71 | * <p> | |
72 | * This will add a new <code>type</code> node as a child of the first | |
73 | * <code>table</code> element. | |
74 | * </p> | |
75 | * <p> | |
76 | * | |
77 | * <pre> | |
78 | * "/tables/table[1] @type" | |
79 | * </pre> | |
80 | * | |
81 | * </p> | |
82 | * <p> | |
83 | * Similar to the example above, but this time a new attribute named | |
84 | * <code>type</code> will be added to the first <code>table</code> element. | |
85 | * </p> | |
86 | * <p> | |
87 | * | |
88 | * <pre> | |
89 | * "/tables table/fields/field/name" | |
90 | * </pre> | |
91 | * | |
92 | * </p> | |
93 | * <p> | |
94 | * This example shows how a complex path can be added. Parent node is the | |
95 | * <code>tables</code> element. Here a new branch consisting of the nodes | |
96 | * <code>table</code>, <code>fields</code>, <code>field</code>, and | |
97 | * <code>name</code> will be added. | |
98 | * </p> | |
99 | * | |
100 | * @since 1.3 | |
101 | * @author Oliver Heger | |
102 | * @version $Id: XPathExpressionEngine.java 439648 2006-09-02 20:42:10Z oheger $ | |
103 | */ | |
104 | 31 | public class XPathExpressionEngine implements ExpressionEngine |
105 | { | |
106 | /** Constant for the path delimiter. */ | |
107 | static final String PATH_DELIMITER = "/"; | |
108 | ||
109 | /** Constant for the attribute delimiter. */ | |
110 | static final String ATTR_DELIMITER = "@"; | |
111 | ||
112 | /** Constant for the delimiters for splitting node paths. */ | |
113 | private static final String NODE_PATH_DELIMITERS = PATH_DELIMITER | |
114 | + ATTR_DELIMITER; | |
115 | ||
116 | /** | |
117 | * Executes a query. The passed in property key is directly passed to a | |
118 | * JXPath context. | |
119 | * | |
120 | * @param root the configuration root node | |
121 | * @param key the query to be executed | |
122 | * @return a list with the nodes that are selected by the query | |
123 | */ | |
124 | public List query(ConfigurationNode root, String key) | |
125 | { | |
126 | 249 | if (StringUtils.isEmpty(key)) |
127 | { | |
128 | 81 | List result = new ArrayList(1); |
129 | 81 | result.add(root); |
130 | 81 | return result; |
131 | } | |
132 | else | |
133 | { | |
134 | 168 | JXPathContext context = createContext(root, key); |
135 | 168 | List result = context.selectNodes(key); |
136 | 168 | return (result != null) ? result : Collections.EMPTY_LIST; |
137 | } | |
138 | } | |
139 | ||
140 | /** | |
141 | * Returns a (canonic) key for the given node based on the parent's key. | |
142 | * This implementation will create an XPATH expression that selects the | |
143 | * given node (under the assumption that the passed in parent key is valid). | |
144 | * As the <code>nodeKey()</code> implementation of | |
145 | * <code>{@link org.apache.commons.configuration.tree.DefaultExpressionEngine DefaultExpressionEngine}</code> | |
146 | * this method will not return indices for nodes. So all child nodes of a | |
147 | * given parent whith the same name will have the same key. | |
148 | * | |
149 | * @param node the node for which a key is to be constructed | |
150 | * @param parentKey the key of the parent node | |
151 | * @return the key for the given node | |
152 | */ | |
153 | public String nodeKey(ConfigurationNode node, String parentKey) | |
154 | { | |
155 | 21 | if (parentKey == null) |
156 | { | |
157 | // name of the root node | |
158 | 2 | return StringUtils.EMPTY; |
159 | } | |
160 | 19 | else if (node.getName() == null) |
161 | { | |
162 | // paranoia check for undefined node names | |
163 | 1 | return parentKey; |
164 | } | |
165 | ||
166 | else | |
167 | { | |
168 | 18 | StringBuffer buf = new StringBuffer(parentKey.length() |
169 | + node.getName().length() + PATH_DELIMITER.length()); | |
170 | 18 | if (parentKey.length() > 0) |
171 | { | |
172 | 14 | buf.append(parentKey); |
173 | 14 | if (!node.isAttribute()) |
174 | { | |
175 | 13 | buf.append(PATH_DELIMITER); |
176 | } | |
177 | } | |
178 | 18 | if (node.isAttribute()) |
179 | { | |
180 | 2 | buf.append(ATTR_DELIMITER); |
181 | } | |
182 | 18 | buf.append(node.getName()); |
183 | 18 | return buf.toString(); |
184 | } | |
185 | } | |
186 | ||
187 | /** | |
188 | * Prepares an add operation for a configuration property. The expected | |
189 | * format of the passed in key is explained in the class comment. | |
190 | * | |
191 | * @param root the configuration's root node | |
192 | * @param key the key describing the target of the add operation and the | |
193 | * path of the new node | |
194 | * @return a data object to be evaluated by the calling configuration object | |
195 | */ | |
196 | public NodeAddData prepareAdd(ConfigurationNode root, String key) | |
197 | { | |
198 | 28 | if (key == null) |
199 | { | |
200 | 1 | throw new IllegalArgumentException( |
201 | "prepareAdd: key must not be null!"); | |
202 | } | |
203 | ||
204 | 27 | int index = key.length() - 1; |
205 | 438 | while (index >= 0 && !Character.isWhitespace(key.charAt(index))) |
206 | { | |
207 | 384 | index--; |
208 | } | |
209 | 27 | if (index < 0) |
210 | { | |
211 | 2 | throw new IllegalArgumentException( |
212 | "prepareAdd: Passed in key must contain a whitespace!"); | |
213 | } | |
214 | ||
215 | 25 | List nodes = query(root, key.substring(0, index).trim()); |
216 | 25 | if (nodes.size() != 1) |
217 | { | |
218 | 1 | throw new IllegalArgumentException( |
219 | "prepareAdd: key must select exactly one target node!"); | |
220 | } | |
221 | ||
222 | 24 | NodeAddData data = new NodeAddData(); |
223 | 24 | data.setParent((ConfigurationNode) nodes.get(0)); |
224 | 24 | initNodeAddData(data, key.substring(index).trim()); |
225 | 18 | return data; |
226 | } | |
227 | ||
228 | /** | |
229 | * Creates the <code>JXPathContext</code> used for executing a query. This | |
230 | * method will create a new context and ensure that it is correctly | |
231 | * initialized. | |
232 | * | |
233 | * @param root the configuration root node | |
234 | * @param key the key to be queried | |
235 | * @return the new context | |
236 | */ | |
237 | protected JXPathContext createContext(ConfigurationNode root, String key) | |
238 | { | |
239 | 169 | JXPathContext context = JXPathContext.newContext(root); |
240 | 169 | context.setLenient(true); |
241 | 169 | return context; |
242 | } | |
243 | ||
244 | /** | |
245 | * Initializes most properties of a <code>NodeAddData</code> object. This | |
246 | * method is called by <code>prepareAdd()</code> after the parent node has | |
247 | * been found. Its task is to interprete the passed in path of the new node. | |
248 | * | |
249 | * @param data the data object to initialize | |
250 | * @param path the path of the new node | |
251 | */ | |
252 | protected void initNodeAddData(NodeAddData data, String path) | |
253 | { | |
254 | 24 | String lastComponent = null; |
255 | 24 | boolean attr = false; |
256 | 24 | boolean first = true; |
257 | ||
258 | 24 | StringTokenizer tok = new StringTokenizer(path, NODE_PATH_DELIMITERS, |
259 | true); | |
260 | 122 | while (tok.hasMoreTokens()) |
261 | { | |
262 | 79 | String token = tok.nextToken(); |
263 | 79 | if (PATH_DELIMITER.equals(token)) |
264 | { | |
265 | 18 | if (attr) |
266 | { | |
267 | 1 | invalidPath(path, " contains an attribute" |
268 | + " delimiter at an unallowed position."); | |
269 | } | |
270 | 17 | if (lastComponent == null) |
271 | { | |
272 | 2 | invalidPath(path, |
273 | " contains a '/' at an unallowed position."); | |
274 | } | |
275 | 15 | data.addPathNode(lastComponent); |
276 | 15 | lastComponent = null; |
277 | } | |
278 | ||
279 | 61 | else if (ATTR_DELIMITER.equals(token)) |
280 | { | |
281 | 18 | if (attr) |
282 | { | |
283 | 1 | invalidPath(path, |
284 | " contains multiple attribute delimiters."); | |
285 | } | |
286 | 17 | if (lastComponent == null && !first) |
287 | { | |
288 | 1 | invalidPath(path, |
289 | " contains an attribute delimiter at an unallowed position."); | |
290 | } | |
291 | 16 | if (lastComponent != null) |
292 | { | |
293 | 8 | data.addPathNode(lastComponent); |
294 | } | |
295 | 16 | attr = true; |
296 | 16 | lastComponent = null; |
297 | } | |
298 | ||
299 | else | |
300 | { | |
301 | 43 | lastComponent = token; |
302 | } | |
303 | 74 | first = false; |
304 | } | |
305 | ||
306 | 19 | if (lastComponent == null) |
307 | { | |
308 | 1 | invalidPath(path, "contains no components."); |
309 | } | |
310 | 18 | data.setNewNodeName(lastComponent); |
311 | 18 | data.setAttribute(attr); |
312 | 18 | } |
313 | ||
314 | /** | |
315 | * Helper method for throwing an exception about an invalid path. | |
316 | * | |
317 | * @param path the invalid path | |
318 | * @param msg the exception message | |
319 | */ | |
320 | private void invalidPath(String path, String msg) | |
321 | { | |
322 | 6 | throw new IllegalArgumentException("Invalid node path: \"" + path |
323 | + "\" " + msg); | |
324 | } | |
325 | ||
326 | // static initializer: registers the configuration node pointer factory | |
327 | static | |
328 | 4 | { |
329 | 4 | JXPathContextReferenceImpl |
330 | .addNodePointerFactory(new ConfigurationNodePointerFactory()); | |
331 | } | |
332 | } |