1 /*
2 * Copyright 2011-2013 smartics, Kronseder & Reiner GmbH
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 package de.smartics.util.lang.classpath;
17
18 import java.util.Iterator;
19 import java.util.ServiceConfigurationError;
20 import java.util.ServiceLoader;
21 import java.util.logging.Logger;
22
23 /**
24 * A factory to create instances of {@link ClassPathListing}.
25 */
26 public final class ClassPathListingFactory
27 {
28 // ********************************* Fields *********************************
29
30 // --- constants ------------------------------------------------------------
31
32 /**
33 * Reference to the logger for this class.
34 */
35 private static final Logger LOG = Logger
36 .getLogger(ClassPathListingFactory.class.getName());
37
38 // --- members --------------------------------------------------------------
39
40 // ****************************** Initializer *******************************
41
42 // ****************************** Constructors ******************************
43
44 // ****************************** Inner Classes *****************************
45
46 // ********************************* Methods ********************************
47
48 // --- init -----------------------------------------------------------------
49
50 // --- get&set --------------------------------------------------------------
51
52 // --- business -------------------------------------------------------------
53
54 /**
55 * Creates an instance of {@link ClassPathListing} using the configuration of
56 * the service in <code>META-INF/services</code>.
57 *
58 * @return instance of {@link ClassPathListing}.
59 */
60 public ClassPathListing create()
61 {
62 final Iterator<ClassPathListing> iterator =
63 ServiceLoader.load(ClassPathListing.class).iterator();
64
65 final StringBuilder buffer = new StringBuilder(64);
66 ClassPathListing instance = null;
67 while (iterator.hasNext())
68 {
69 try
70 {
71 if (instance != null)
72 {
73 final String implementation = iterator.next().getClass().getName();
74 buffer.append("\nDuplicated implementation rejected: "
75 + implementation);
76 continue;
77 }
78
79 instance = iterator.next();
80 }
81 catch (final ServiceConfigurationError e)
82 {
83 buffer.append("\nError encountered: ").append(e.getMessage());
84 }
85 }
86
87 if (buffer.length() > 0)
88 {
89 LOG.warning("Problems encountered while fetching implementations of '"
90 + ClassPathListing.class.getName() + "':" + buffer);
91 }
92
93 if (instance == null)
94 {
95 throw new IllegalStateException(
96 "Cannot create instance of implementation of '"
97 + ClassPathListing.class.getName() + "'.");
98 }
99
100 return instance;
101 }
102
103 // --- object basics --------------------------------------------------------
104
105 }