1.commons logging source code analysis
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
private Log loger = LogFactory.getLog(this.getClass());
Achieve 1.1getLog () method is as follows:
/**
* Convenience method to return a named logger, without the application
* having to care about factories.
*
* @param clazz Class from which a log name will be derived
* @throws LogConfigurationException if a suitable <code>Log</code>
* instance cannot be returned
*/
public static Log getLog(Class clazz) throws LogConfigurationException {
return getFactory().getInstance(clazz);
}
commons logging is to obtain the corresponding implementation class getFactory method, then for examples
Embodied 1.2getFactory (longer methods outlined under process)
1.2.1 cached data first acquires
LogFactory factory = getCachedFactory(contextClassLoader);
1.2.2 cache data is not acquired when the acquisition system is implemented as an environment variable configuration org.apache.commons.logging.LogFactory
/**
* The name (<code>org.apache.commons.logging.LogFactory</code>) of the property
* used to identify the LogFactory implementation
* class name. This can be used as a system property, or as an entry in a
* configuration properties file.
*/
public static final String FACTORY_PROPERTY = "org.apache.commons.logging.LogFactory";
String factoryClass = getSystemProperty(FACTORY_PROPERTY, null);
factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
1.2.3 obtaining META-INF / services / org.apache.commons.logging.LogFactory directory environment variables are not acquired configuration acquisition implementation class (jcl-over-slf4j is to increase the file in the package)
/**
* JDK1.3+ <a href="http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html#Service%20Provider">
* 'Service Provider' specification</a>.
*/
protected static final String SERVICE_ID =
"META-INF/services/org.apache.commons.logging.LogFactory";
final InputStream is = getResourceAsStream(contextClassLoader, SERVICE_ID);
1.2.4 Gets an instance of commons-logging.properties file configuration org.apache.commons.logging.LogFactory
public static final String FACTORY_PROPERTY = "org.apache.commons.logging.LogFactory";
String factoryClass = props.getProperty(FACTORY_PROPERTY);
factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
1.2.5 Get the default implementation class org.apache.commons.logging.impl.LogFactoryImpl
1.2.6 The implementation class to get into the cache
So far fetch the factory implementation class is over, we must get to the factory for specific log implementation class (for example, you want to use here can be used to configure org.apache.commons.logging.impl.SLF4JLogFactory to get to SLF4JLogFactory) further acquisition specific implementation class corresponding to the log
1.3 Get the logging implementation class getInstance
public Log getInstance(Class clazz) throws LogConfigurationException {
return getInstance(clazz.getName());
}
public Log getInstance(String name) throws LogConfigurationException {
Log instance = (Log) instances.get(name);
if (instance == null) {
instance = newInstance(name);
instances.put(name, instance);
}
return instance;
}
newInstance Implementation
protected Log newInstance(String name) throws LogConfigurationException {
Log instance;
try {
if (logConstructor == null) {
instance = discoverLogImplementation(name);
}
else {
Object params[] = { name };
instance = (Log) logConstructor.newInstance(params);
}
if (logMethod != null) {
Object params[] = { this };
logMethod.invoke(instance, params);
}
return instance;
} catch (LogConfigurationException lce) {
throw lce;
} catch (InvocationTargetException e) {
Throwable c = e.getTargetException();
throw new LogConfigurationException(c == null ? e : c);
} catch (Throwable t) {
handleThrowable(t);
throw new LogConfigurationException(t);
}
}
private Log discoverLogImplementation(String logCategory)
throws LogConfigurationException {
if (isDiagnosticsEnabled()) {
logDiagnostic("Discovering a Log implementation...");
}
initConfiguration();
Log result = null;
// See if the user specified the Log implementation to use
String specifiedLogClassName = findUserSpecifiedLogClassName();
if (specifiedLogClassName != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Attempting to load user-specified log class '" +
specifiedLogClassName + "'...");
}
result = createLogFromClass(specifiedLogClassName,
logCategory,
true);
if (result == null) {
StringBuffer messageBuffer = new StringBuffer("User-specified log class '");
messageBuffer.append(specifiedLogClassName);
messageBuffer.append("' cannot be found or is not useable.");
// Mistyping or misspelling names is a common fault.
// Construct a good error message, if we can
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LOG4J_LOGGER);
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_JDK14_LOGGER);
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LUMBERJACK_LOGGER);
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_SIMPLE_LOGGER);
throw new LogConfigurationException(messageBuffer.toString());
}
return result;
}
if (isDiagnosticsEnabled()) {
logDiagnostic(
"No user-specified Log implementation; performing discovery" +
" using the standard supported logging implementations...");
}
for(int i=0; i<classesToDiscover.length && result == null; ++i) {
result = createLogFromClass(classesToDiscover[i], logCategory, true);
}
if (result == null) {
throw new LogConfigurationException
("No suitable Log implementation");
}
return result;
}
Method 1.initConfiguration initial configuration
2.findUserSpecifiedLogClassName find the specified configuration file in the configuration system environment variables
3. Create specified and configured and arranged logConstructor logMethod
create implementation classes when the order is not specified implementation class 4
private static final String[] classesToDiscover = {
LOGGING_IMPL_LOG4J_LOGGER,
"org.apache.commons.logging.impl.Jdk14Logger",
"org.apache.commons.logging.impl.Jdk13LumberjackLogger",
"org.apache.commons.logging.impl.SimpleLog"
};
获取当前线程的classLoader,根据classLoader从缓存中获取LogFactroy,使用的缓存是WeakHashTable对象;如果缓存中存在，则返回，没有则进入下面流程；
读取classpath下的commons-logging.properties文件，判断其中是否设置了use_tccl属性，如果不为空则判断，该属性的值是否为false,若为false，则将baseClassLoader替换为当前类的classLoader；
接着，继续获取LogFactory对象，此步骤分为4中方式：
(1)在系统属性中查找“org.apache.commons.logging.LogFactory”属性的值，根据值生成LogFactory对象；
(2)通过资源“META-INF/services/org.apache.commons.logging.LogFactory”文件，获取的值生成LogFactory对象；
(3)通过配置文件commons-logging.properties，获取以“org.apache.commons.logging.LogFactory”为key的值，根据值生成logFactory；
(4)如果以上均不成功，则创建系统默认的日志工厂：org.apache.commons.logging.impl.LogFactoryImpl
成功获取日志工厂后，根据类名获取日志对象；
主要逻辑在discoverLogImplementation方法中：
(1)检查commons-logging.properties文件中是否存在“org.apache.commons.logging.Log”属性，若存在则创建具体的日志对象；若不存在，进行下面逻辑；
(2)遍历classesToDiscover数组，该数组存有日志具体实现类的全限定类名：org.apache.commons.logging.impl.Log4JLogger、org.apache.commons.logging.impl.Jdk14Logger、org.apache.commons.logging.impl.Jdk13LumberjackLogger、org.apache.commons.logging.impl.SimpleLog；
(3)根据数组中存着的全限定类名，按照顺序依次加载Class文件，进行实例化操作，最后返回Log实例，默认为Jdk14Logger；
Reference from: https://blog.csdn.net/u011794238/article/details/50749260
If not, please correct criticism
