in src/main/java/org/apache/commons/logging/LogFactory.java [417:645]
public static LogFactory getFactory() throws LogConfigurationException {
// Identify the class loader we will be using
final ClassLoader contextClassLoader = getContextClassLoaderInternal();
// This is an odd enough situation to report about. This
// output will be a nuisance on JDK1.1, as the system
// classloader is null in that environment.
if (contextClassLoader == null && isDiagnosticsEnabled()) {
logDiagnostic("Context classloader is null.");
}
// Return any previously registered factory for this class loader
LogFactory factory = getCachedFactory(contextClassLoader);
if (factory != null) {
return factory;
}
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] LogFactory implementation requested for the first time for context classloader " +
objectId(contextClassLoader));
logHierarchy("[LOOKUP] ", contextClassLoader);
}
// Load properties file.
//
// If the properties file exists, then its contents are used as
// "attributes" on the LogFactory implementation class. One particular
// property may also control which LogFactory concrete subclass is
// used, but only if other discovery mechanisms fail..
//
// As the properties file (if it exists) will be used one way or
// another in the end we may as well look for it first.
final Properties props = getConfigurationFile(contextClassLoader, FACTORY_PROPERTIES);
// Determine whether we will be using the thread context class loader to
// load logging classes or not by checking the loaded properties file (if any).
ClassLoader baseClassLoader = contextClassLoader;
if (props != null) {
final String useTCCLStr = props.getProperty(TCCL_KEY);
// The Boolean.valueOf(useTCCLStr).booleanValue() formulation
// is required for Java 1.2 compatibility.
if ((useTCCLStr != null) && !Boolean.parseBoolean(useTCCLStr)) {
// Don't use current context classloader when locating any
// LogFactory or Log classes, just use the class that loaded
// this abstract class. When this class is deployed in a shared
// classpath of a container, it means webapps cannot deploy their
// own logging implementations. It also means that it is up to the
// implementation whether to load library-specific config files
// from the TCCL or not.
baseClassLoader = thisClassLoaderRef.get();
}
}
// Determine which concrete LogFactory subclass to use.
// First, try a global system property
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Looking for system property [" + FACTORY_PROPERTY +
"] to define the LogFactory subclass to use...");
}
try {
final String factoryClass = getSystemProperty(FACTORY_PROPERTY, null);
if (factoryClass != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Creating an instance of LogFactory class '" + factoryClass +
"' as specified by system property " + FACTORY_PROPERTY);
}
factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
} else {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] No system property [" + FACTORY_PROPERTY + "] defined.");
}
}
} catch (final SecurityException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] A security exception occurred while trying to create an" +
" instance of the custom factory class" + ": [" + trim(e.getMessage()) +
"]. Trying alternative implementations...");
}
// ignore
} catch (final RuntimeException e) {
// This is not consistent with the behavior when a bad LogFactory class is
// specified in a services file.
//
// One possible exception that can occur here is a ClassCastException when
// the specified class wasn't castable to this LogFactory type.
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] An exception occurred while trying to create an" +
" instance of the custom factory class" + ": [" +
trim(e.getMessage()) +
"] as specified by a system property.");
}
throw e;
}
// Second, try to find a service by using the JDK1.3 class
// discovery mechanism, which involves putting a file with the name
// of an interface class in the META-INF/services directory, where the
// contents of the file is a single line specifying a concrete class
// that implements the desired interface.
if (factory == null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Looking for a resource file of name [" + SERVICE_ID +
"] to define the LogFactory subclass to use...");
}
try {
final InputStream is = getResourceAsStream(contextClassLoader, SERVICE_ID);
if( is != null ) {
// This code is needed by EBCDIC and other strange systems.
// It's a fix for bugs reported in xerces
BufferedReader rd;
try {
rd = new BufferedReader(new InputStreamReader(is, "UTF-8"));
} catch (final java.io.UnsupportedEncodingException e) {
rd = new BufferedReader(new InputStreamReader(is));
}
String factoryClassName;
try {
factoryClassName = rd.readLine();
} finally {
rd.close();
}
if (factoryClassName != null && ! factoryClassName.isEmpty()) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Creating an instance of LogFactory class " +
factoryClassName +
" as specified by file '" + SERVICE_ID +
"' which was present in the path of the context classloader.");
}
factory = newFactory(factoryClassName, baseClassLoader, contextClassLoader );
}
} else {
// is == null
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] No resource file with name '" + SERVICE_ID + "' found.");
}
}
} catch (final Exception ex) {
// note: if the specified LogFactory class wasn't compatible with LogFactory
// for some reason, a ClassCastException will be caught here, and attempts will
// continue to find a compatible class.
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] A security exception occurred while trying to create an" +
" instance of the custom factory class" +
": [" + trim(ex.getMessage()) +
"]. Trying alternative implementations...");
}
// ignore
}
}
// Third try looking into the properties file read earlier (if found)
if (factory == null) {
if (props != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] Looking in properties file for entry with key '" + FACTORY_PROPERTY +
"' to define the LogFactory subclass to use...");
}
final String factoryClass = props.getProperty(FACTORY_PROPERTY);
if (factoryClass != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] Properties file specifies LogFactory subclass '" + factoryClass + "'");
}
factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
// TODO: think about whether we need to handle exceptions from newFactory
} else {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Properties file has no entry specifying LogFactory subclass.");
}
}
} else {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] No properties file available to determine" + " LogFactory subclass from..");
}
}
}
// Fourth, try the fallback implementation class
if (factory == null) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] Loading the default LogFactory implementation '" + FACTORY_DEFAULT +
"' via the same classloader that loaded this LogFactory" +
" class (ie not looking in the context classloader).");
}
// Note: unlike the above code which can try to load custom LogFactory
// implementations via the TCCL, we don't try to load the default LogFactory
// implementation via the context classloader because:
// * that can cause problems (see comments in newFactory method)
// * no-one should be customising the code of the default class
// Yes, we do give up the ability for the child to ship a newer
// version of the LogFactoryImpl class and have it used dynamically
// by an old LogFactory class in the parent, but that isn't
// necessarily a good idea anyway.
factory = newFactory(FACTORY_DEFAULT, thisClassLoaderRef.get(), contextClassLoader);
}
if (factory != null) {
/**
* Always cache using context class loader.
*/
cacheFactory(contextClassLoader, factory);
if (props != null) {
final Enumeration names = props.propertyNames();
while (names.hasMoreElements()) {
final String name = (String) names.nextElement();
final String value = props.getProperty(name);
factory.setAttribute(name, value);
}
}
}
return factory;
}