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17 package org.apache.logging.log4j.util;
18
19 import java.io.IOException;
20 import java.net.URL;
21 import java.util.ArrayList;
22 import java.util.Enumeration;
23 import java.util.Iterator;
24 import java.util.List;
25 import java.util.Properties;
26
27 import org.apache.logging.log4j.Logger;
28 import org.apache.logging.log4j.spi.Provider;
29 import org.apache.logging.log4j.status.StatusLogger;
30
31
32
33
34 public final class ProviderUtil {
35
36 private static final String PROVIDER_RESOURCE = "META-INF/log4j-provider.properties";
37 private static final String API_VERSION = "Log4jAPIVersion";
38
39 private static final String[] COMPATIBLE_API_VERSIONS = {
40 "2.0.0"
41 };
42
43 private static final Logger LOGGER = StatusLogger.getLogger();
44
45 private static final List<Provider> PROVIDERS = new ArrayList<Provider>();
46
47 private ProviderUtil() {
48 }
49
50 static {
51 final ClassLoader cl = findClassLoader();
52 Enumeration<URL> enumResources = null;
53 try {
54 enumResources = cl.getResources(PROVIDER_RESOURCE);
55 } catch (final IOException e) {
56 LOGGER.fatal("Unable to locate " + PROVIDER_RESOURCE, e);
57 }
58
59 if (enumResources != null) {
60 while (enumResources.hasMoreElements()) {
61 final URL url = enumResources.nextElement();
62 Properties props;
63 try {
64 props = PropertiesUtil.loadClose(url.openStream(), url);
65 if (!validVersion(props.getProperty(API_VERSION))) {
66 continue;
67 }
68 PROVIDERS.add(new Provider(props, url));
69 } catch (final IOException ioe) {
70 LOGGER.error("Unable to open " + url.toString(), ioe);
71 }
72 }
73 }
74 }
75
76 public static Iterator<Provider> getProviders() {
77 return PROVIDERS.iterator();
78 }
79
80 public static boolean hasProviders() {
81 return PROVIDERS.size() > 0;
82 }
83
84 public static ClassLoader findClassLoader() {
85 ClassLoader cl;
86 if (System.getSecurityManager() == null) {
87 cl = Thread.currentThread().getContextClassLoader();
88 } else {
89 cl = java.security.AccessController.doPrivileged(
90 new java.security.PrivilegedAction<ClassLoader>() {
91 @Override
92 public ClassLoader run() {
93 return Thread.currentThread().getContextClassLoader();
94 }
95 }
96 );
97 }
98 if (cl == null) {
99 cl = ProviderUtil.class.getClassLoader();
100 }
101
102 return cl;
103 }
104
105 private static boolean validVersion(final String version) {
106 for (final String v : COMPATIBLE_API_VERSIONS) {
107 if (version.startsWith(v)) {
108 return true;
109 }
110 }
111 return false;
112 }
113 }