View Javadoc

1   /*
2    * Copyright 2005-2010 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.xml.transform;
18  
19  import javax.xml.transform.Result;
20  import javax.xml.transform.Source;
21  import javax.xml.transform.Transformer;
22  import javax.xml.transform.TransformerConfigurationException;
23  import javax.xml.transform.TransformerException;
24  import javax.xml.transform.TransformerFactory;
25  import javax.xml.transform.TransformerFactoryConfigurationError;
26  
27  import org.springframework.util.Assert;
28  
29  /**
30   * Helper class for [email protected] Transformer} usage. Provides [email protected] #createTransformer()} and [email protected] #transform(Source,
31   * Result)}.
32   *
33   * @author Arjen Poutsma
34   * @since 3.0
35   */
36  public class TransformerHelper {
37  
38      private volatile TransformerFactory transformerFactory;
39  
40      private Class<? extends TransformerFactory> transformerFactoryClass;
41  
42      /**
43       * Initializes a new instance of the [email protected] TransformerHelper}.
44       */
45      public TransformerHelper() {
46      }
47  
48      /**
49       * Initializes a new instance of the [email protected] TransformerHelper} with the specified [email protected] TransformerFactory}.
50       */
51      public TransformerHelper(TransformerFactory transformerFactory) {
52          this.transformerFactory = transformerFactory;
53      }
54  
55      /**
56       * Initializes a new instance of the [email protected] TransformerHelper} with the specified [email protected] TransformerFactory} class.
57       */
58      public TransformerHelper(Class<? extends TransformerFactory> transformerFactoryClass) {
59          setTransformerFactoryClass(transformerFactoryClass);
60      }
61  
62      /**
63       * Specify the [email protected] TransformerFactory} class to use.
64       */
65      public void setTransformerFactoryClass(Class<? extends TransformerFactory> transformerFactoryClass) {
66          Assert.isAssignable(TransformerFactory.class, transformerFactoryClass);
67          this.transformerFactoryClass = transformerFactoryClass;
68      }
69  
70      /**
71       * Instantiate a new TransformerFactory.
72       * <p/>
73       * The default implementation simply calls [email protected] TransformerFactory#newInstance()}. If a [email protected]
74       * #setTransformerFactoryClass transformerFactoryClass} has been specified explicitly, the default constructor of
75       * the specified class will be called instead.
76       * <p/>
77       * Can be overridden in subclasses.
78       *
79       * @param transformerFactoryClass the specified factory class (if any)
80       * @return the new TransactionFactory instance
81       * @see #setTransformerFactoryClass
82       * @see #getTransformerFactory()
83       */
84      protected TransformerFactory newTransformerFactory(Class<? extends TransformerFactory> transformerFactoryClass) {
85          if (transformerFactoryClass != null) {
86              try {
87                  return transformerFactoryClass.newInstance();
88              }
89              catch (Exception ex) {
90                  throw new TransformerFactoryConfigurationError(ex,
91                          "Could not instantiate TransformerFactory [" + transformerFactoryClass + "]");
92              }
93          }
94          else {
95              return TransformerFactory.newInstance();
96          }
97      }
98  
99      /**
100      * Returns the [email protected] TransformerFactory}.
101      *
102      * @return the transformer factory
103      */
104     public TransformerFactory getTransformerFactory() {
105         TransformerFactory result = transformerFactory;
106         if (result == null) {
107             synchronized (this) {
108                 result = transformerFactory;
109                 if (result == null) {
110                     transformerFactory = result = newTransformerFactory(transformerFactoryClass);
111                 }
112             }
113         }
114         return result;
115     }
116 
117     /**
118      * Creates a new [email protected] Transformer}. Must be called per thread, as transformers are not thread-safe.
119      *
120      * @return the created transformer
121      * @throws TransformerConfigurationException
122      *          if thrown by JAXP methods
123      */
124     public Transformer createTransformer() throws TransformerConfigurationException {
125         return getTransformerFactory().newTransformer();
126     }
127 
128     /**
129      * Transforms the given [email protected] Source} to the given [email protected] Result}. Creates a new [email protected] Transformer} for every
130      * call, as transformers are not thread-safe.
131      *
132      * @param source the source to transform from
133      * @param result the result to transform to
134      * @throws TransformerException if thrown by JAXP methods
135      */
136     public void transform(Source source, Result result) throws TransformerException {
137         Transformer transformer = createTransformer();
138         transformer.transform(source, result);
139     }
140 
141 }