1 /*
2 * #%L
3 * settings4j
4 * ===============================================================
5 * Copyright (C) 2008 - 2015 Brabenetz Harald, Austria
6 * ===============================================================
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 * #L%
19 */
20 package org.settings4j.contentresolver;
21
22 import java.io.IOException;
23 import java.io.InputStream;
24 import java.net.URL;
25
26 import org.apache.commons.io.IOUtils;
27 import org.settings4j.ContentResolver;
28
29 /**
30 * {@link ContentResolver} implementation to read content from the Classpath.
31 * <p>
32 * Uses the default ClassLoader: typically the thread context ClassLoader see {@link #getClassLoader()}.
33 * </p>
34 * <p>
35 * Optional Path Prefix is "classpath:".
36 * </p>
37 *
38 * @author Harald.Brabenetz
39 */
40 public class ClasspathContentResolver implements ContentResolver {
41
42 /** General Logger for this Class. */
43 private static final org.slf4j.Logger LOG = org.slf4j.LoggerFactory.getLogger(ClasspathContentResolver.class);
44
45 /** Pseudo URL prefix for loading from the class path: "classpath:". */
46 public static final String CLASSPATH_URL_PREFIX = "classpath:";
47
48 @Override
49 public void addContentResolver(final ContentResolver contentResolver) {
50 throw new UnsupportedOperationException("ClasspathContentResolver cannot add other ContentResolvers");
51 }
52
53 @Override
54 public byte[] getContent(final String key) {
55 final String normalizedKey = normalizeKey(key);
56
57 InputStream is = null;
58 try {
59 is = getClassLoader().getResourceAsStream(normalizedKey);
60 if (is != null) {
61 return IOUtils.toByteArray(is);
62 }
63 // else
64 return null;
65 } catch (final IOException e) {
66 LOG.error(e.getMessage(), e);
67 return null;
68 } finally {
69 IOUtils.closeQuietly(is);
70 }
71 }
72
73 /**
74 * Method to get onlx the URL for the given Key.
75 *
76 * @param key the key (could have a 'classpath:' prefix or not)
77 * @return The {@link URL}, see {@link ClassLoader#getResource(String)}.
78 */
79 public static URL getResource(final String key) {
80 final String normalizedKey = normalizeKey(key);
81
82 return getClassLoader().getResource(normalizedKey);
83 }
84
85
86 /**
87 * Return the default ClassLoader to use: typically the thread context ClassLoader, if available; the ClassLoader that loaded the ClasspathContentResolver
88 * class will be used as fallback.
89 * <p>
90 * Call this method if you intend to use the thread context ClassLoader in a scenario where you absolutely need a non-null ClassLoader reference: for
91 * example, for class path resource loading (but not necessarily for <code>Class.forName</code>, which accepts a <code>null</code> ClassLoader reference as
92 * well).
93 * </p>
94 *
95 * @return the default ClassLoader (never <code>null</code>)
96 * @see java.lang.Thread#getContextClassLoader()
97 */
98 // SuppressWarnings PMD.UseProperClassLoader: ProperClassLoader is only a fall back solution if Thread ContextClassloder not exit.
99 @SuppressWarnings("PMD.UseProperClassLoader")
100 public static ClassLoader getClassLoader() {
101 ClassLoader cl = null;
102 try {
103 cl = Thread.currentThread().getContextClassLoader();
104 } catch (final Throwable ex) {
105 LOG.debug("Cannot access thread context ClassLoader - falling back to system class loader", ex);
106 }
107 if (cl == null) {
108 // No thread context class loader -> use class loader of this class.
109 cl = ClasspathContentResolver.class.getClassLoader();
110 }
111 return cl;
112 }
113
114 private static String normalizeKey(final String key) {
115 String normalizedKey = key;
116 if (normalizedKey.startsWith(CLASSPATH_URL_PREFIX)) {
117 normalizedKey = normalizedKey.substring(CLASSPATH_URL_PREFIX.length());
118 }
119 if (normalizedKey.startsWith("/")) {
120 normalizedKey = normalizedKey.substring(1);
121 }
122 return normalizedKey;
123 }
124 }