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19
20 package org.apache.james.mime4j.storage;
21
22 import org.apache.commons.logging.Log;
23 import org.apache.commons.logging.LogFactory;
24
25 /**
26 * Allows for a default {@link StorageProvider} instance to be configured on an
27 * application level.
28 * <p>
29 * The default instance can be set by either calling
30 * {@link #setInstance(StorageProvider)} when the application starts up or by
31 * setting the system property
32 * <code>org.apache.james.mime4j.defaultStorageProvider</code> to the class
33 * name of a <code>StorageProvider</code> implementation.
34 * <p>
35 * If neither option is used or if the class instantiation fails this class
36 * provides a pre-configured default instance.
37 */
38 public class DefaultStorageProvider {
39
40 /** Value is <code>org.apache.james.mime4j.defaultStorageProvider</code> */
41 public static final String DEFAULT_STORAGE_PROVIDER_PROPERTY =
42 "org.apache.james.mime4j.defaultStorageProvider";
43
44 private static Log log = LogFactory.getLog(DefaultStorageProvider.class);
45
46 private static volatile StorageProvider instance = null;
47
48 static {
49 initialize();
50 }
51
52 private DefaultStorageProvider() {
53 }
54
55 /**
56 * Returns the default {@link StorageProvider} instance.
57 *
58 * @return the default {@link StorageProvider} instance.
59 */
60 public static StorageProvider getInstance() {
61 return instance;
62 }
63
64 /**
65 * Sets the default {@link StorageProvider} instance.
66 *
67 * @param instance
68 * the default {@link StorageProvider} instance.
69 */
70 public static void setInstance(StorageProvider instance) {
71 if (instance == null) {
72 throw new IllegalArgumentException();
73 }
74
75 DefaultStorageProvider.instance = instance;
76 }
77
78 private static void initialize() {
79 String clazz = System.getProperty(DEFAULT_STORAGE_PROVIDER_PROPERTY);
80 try {
81 if (clazz != null) {
82 instance = (StorageProvider) Class.forName(clazz).newInstance();
83 }
84 } catch (Exception e) {
85 log.warn("Unable to create or instantiate StorageProvider class '"
86 + clazz + "'. Using default instead.", e);
87 }
88
89 if (instance == null) {
90 StorageProvider backend = new TempFileStorageProvider();
91 instance = new ThresholdStorageProvider(backend, 1024);
92 }
93 }
94
95 // for unit tests only
96 static void reset() {
97 instance = null;
98 initialize();
99 }
100
101 }