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November 22, 2013 06:02
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Commons-Loggin日志门面查找日志框架的过程
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/* | |
* Licensed to the Apache Software Foundation (ASF) under one or more | |
* contributor license agreements. See the NOTICE file distributed with | |
* this work for additional information regarding copyright ownership. | |
* The ASF licenses this file to You under the Apache License, Version 2.0 | |
* (the "License"); you may not use this file except in compliance with | |
* the License. You may obtain a copy of the License at | |
* | |
* http://www.apache.org/licenses/LICENSE-2.0 | |
* | |
* Unless required by applicable law or agreed to in writing, software | |
* distributed under the License is distributed on an "AS IS" BASIS, | |
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
* See the License for the specific language governing permissions and | |
* limitations under the License. | |
*/ | |
package org.apache.commons.logging; | |
import java.lang.reflect.Constructor; | |
import java.util.Hashtable; | |
import org.apache.commons.logging.impl.NoOpLog; | |
/** | |
* <p>Factory for creating {@link Log} instances. Applications should call | |
* the <code>makeNewLogInstance()</code> method to instantiate new instances | |
* of the configured {@link Log} implementation class.</p> | |
* | |
* <p>By default, calling <code>getInstance()</code> will use the following | |
* algorithm:</p> | |
* <ul> | |
* <li>If Log4J is available, return an instance of | |
* <code>org.apache.commons.logging.impl.Log4JLogger</code>.</li> | |
* <li>If JDK 1.4 or later is available, return an instance of | |
* <code>org.apache.commons.logging.impl.Jdk14Logger</code>.</li> | |
* <li>Otherwise, return an instance of | |
* <code>org.apache.commons.logging.impl.NoOpLog</code>.</li> | |
* </ul> | |
* | |
* <p>You can change the default behavior in one of two ways:</p> | |
* <ul> | |
* <li>On the startup command line, set the system property | |
* <code>org.apache.commons.logging.log</code> to the name of the | |
* <code>org.apache.commons.logging.Log</code> implementation class | |
* you want to use.</li> | |
* <li>At runtime, call <code>LogSource.setLogImplementation()</code>.</li> | |
* </ul> | |
* | |
* @deprecated Use {@link LogFactory} instead - The default factory | |
* implementation performs exactly the same algorithm as this class did | |
* | |
* @author Rod Waldhoff | |
* @version $Id: LogSource.java 424107 2006-07-20 23:15:42Z skitching $ | |
*/ | |
public class LogSource { | |
// ------------------------------------------------------- Class Attributes | |
static protected Hashtable logs = new Hashtable(); | |
/** Is log4j available (in the current classpath) */ | |
static protected boolean log4jIsAvailable = false; | |
/** Is JDK 1.4 logging available */ | |
static protected boolean jdk14IsAvailable = false; | |
/** Constructor for current log class */ | |
static protected Constructor logImplctor = null; | |
// ----------------------------------------------------- Class Initializers | |
static { | |
// Is Log4J Available? | |
try { | |
if (null != Class.forName("org.apache.log4j.Logger")) { | |
log4jIsAvailable = true; | |
} else { | |
log4jIsAvailable = false; | |
} | |
} catch (Throwable t) { | |
log4jIsAvailable = false; | |
} | |
// Is JDK 1.4 Logging Available? | |
try { | |
if ((null != Class.forName("java.util.logging.Logger")) && | |
(null != Class.forName("org.apache.commons.logging.impl.Jdk14Logger"))) { | |
jdk14IsAvailable = true; | |
} else { | |
jdk14IsAvailable = false; | |
} | |
} catch (Throwable t) { | |
jdk14IsAvailable = false; | |
} | |
// Set the default Log implementation | |
String name = null; | |
try { | |
name = System.getProperty("org.apache.commons.logging.log"); | |
if (name == null) { | |
name = System.getProperty("org.apache.commons.logging.Log"); | |
} | |
} catch (Throwable t) { | |
} | |
if (name != null) { | |
try { | |
setLogImplementation(name); | |
} catch (Throwable t) { | |
try { | |
setLogImplementation | |
("org.apache.commons.logging.impl.NoOpLog"); | |
} catch (Throwable u) { | |
; | |
} | |
} | |
} else { | |
try { | |
if (log4jIsAvailable) { | |
setLogImplementation | |
("org.apache.commons.logging.impl.Log4JLogger"); | |
} else if (jdk14IsAvailable) { | |
setLogImplementation | |
("org.apache.commons.logging.impl.Jdk14Logger"); | |
} else { | |
setLogImplementation | |
("org.apache.commons.logging.impl.NoOpLog"); | |
} | |
} catch (Throwable t) { | |
try { | |
setLogImplementation | |
("org.apache.commons.logging.impl.NoOpLog"); | |
} catch (Throwable u) { | |
; | |
} | |
} | |
} | |
} | |
// ------------------------------------------------------------ Constructor | |
/** Don't allow others to create instances */ | |
private LogSource() { | |
} | |
// ---------------------------------------------------------- Class Methods | |
/** | |
* Set the log implementation/log implementation factory | |
* by the name of the class. The given class | |
* must implement {@link Log}, and provide a constructor that | |
* takes a single {@link String} argument (containing the name | |
* of the log). | |
*/ | |
static public void setLogImplementation(String classname) throws | |
LinkageError, ExceptionInInitializerError, | |
NoSuchMethodException, SecurityException, | |
ClassNotFoundException { | |
try { | |
Class logclass = Class.forName(classname); | |
Class[] argtypes = new Class[1]; | |
argtypes[0] = "".getClass(); | |
logImplctor = logclass.getConstructor(argtypes); | |
} catch (Throwable t) { | |
logImplctor = null; | |
} | |
} | |
/** | |
* Set the log implementation/log implementation factory | |
* by class. The given class must implement {@link Log}, | |
* and provide a constructor that takes a single {@link String} | |
* argument (containing the name of the log). | |
*/ | |
static public void setLogImplementation(Class logclass) throws | |
LinkageError, ExceptionInInitializerError, | |
NoSuchMethodException, SecurityException { | |
Class[] argtypes = new Class[1]; | |
argtypes[0] = "".getClass(); | |
logImplctor = logclass.getConstructor(argtypes); | |
} | |
/** Get a <code>Log</code> instance by class name */ | |
static public Log getInstance(String name) { | |
Log log = (Log) (logs.get(name)); | |
if (null == log) { | |
log = makeNewLogInstance(name); | |
logs.put(name, log); | |
} | |
return log; | |
} | |
/** Get a <code>Log</code> instance by class */ | |
static public Log getInstance(Class clazz) { | |
return getInstance(clazz.getName()); | |
} | |
/** | |
* Create a new {@link Log} implementation, based | |
* on the given <i>name</i>. | |
* <p> | |
* The specific {@link Log} implementation returned | |
* is determined by the value of the | |
* <tt>org.apache.commons.logging.log</tt> property. | |
* The value of <tt>org.apache.commons.logging.log</tt> may be set to | |
* the fully specified name of a class that implements | |
* the {@link Log} interface. This class must also | |
* have a public constructor that takes a single | |
* {@link String} argument (containing the <i>name</i> | |
* of the {@link Log} to be constructed. | |
* <p> | |
* When <tt>org.apache.commons.logging.log</tt> is not set, | |
* or when no corresponding class can be found, | |
* this method will return a Log4JLogger | |
* if the log4j Logger class is | |
* available in the {@link LogSource}'s classpath, or a | |
* Jdk14Logger if we are on a JDK 1.4 or later system, or | |
* NoOpLog if neither of the above conditions is true. | |
* | |
* @param name the log name (or category) | |
*/ | |
static public Log makeNewLogInstance(String name) { | |
Log log = null; | |
try { | |
Object[] args = new Object[1]; | |
args[0] = name; | |
log = (Log) (logImplctor.newInstance(args)); | |
} catch (Throwable t) { | |
log = null; | |
} | |
if (null == log) { | |
log = new NoOpLog(name); | |
} | |
return log; | |
} | |
/** | |
* Returns a {@link String} array containing the names of | |
* all logs known to me. | |
*/ | |
static public String[] getLogNames() { | |
return (String[]) (logs.keySet().toArray(new String[logs.size()])); | |
} | |
} |
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