Disable Lumberjack and Log4j 1.x and document it (#182)

This PR removes Lumberjack and Log4j 1.x for the automatic logging
backend discovery procedure.

The updated procedure is documented in the guide.

This closes LOGGING-173 and LOGGING-188.

src/changes/changes.xml

@@ -52,6 +52,12 @@ The <action> type attribute can be add,update,fix,remove.
       <action dev="ggregory" type="add" due-to="Piotr P. Karwasz">
         Deprecate org.apache.commons.logging.impl.WeakHashtable without replacement.
       </action>
+      <action issue="LOGGING-188" dev="pkarwasz" type="add" due-to="Piotr P. Karwasz">
+        Deprecate and disable `Jdk13LumberjackLogger` and `Log4JLogger`.
+      </action>
+      <action issue="LOGGING-173" dev="pkarwasz" type="add" due-to="SingingBush">
+        Deprecate and disable `AvalonLogger` and `LogKitLogger`.
+      </action>
       <!-- FIX -->
       <action issue="LOGGING-165" dev="britter" type="add">
         Add Automatic-Module-Name Manifest Header for Java 9 compatibility.

src/main/java/org/apache/commons/logging/impl/LogFactoryImpl.java

@@ -150,10 +150,8 @@ public class LogFactoryImpl extends LogFactory {
      * but broken/unusable for some reason.
      */
     private static final String[] classesToDiscover = {
-            LOGGING_IMPL_LOG4J_LOGGER,
+            LOGGING_IMPL_JDK14_LOGGER,
-            "org.apache.commons.logging.impl.Jdk14Logger",
+            LOGGING_IMPL_SIMPLE_LOGGER
-            "org.apache.commons.logging.impl.Jdk13LumberjackLogger",
-            "org.apache.commons.logging.impl.SimpleLog"
     };
 
     /**

src/site/xdoc/guide.xml

@@ -95,15 +95,19 @@ It provides the middleware/tooling developer with a simple
 logging abstraction, that allows the user (application developer) to plug in
 a specific logging implementation.
         </p>
-<p>JCL provides thin-wrapper <code>Log</code> implementations for
+        <p>
-other logging tools, including
+          JCL provides thin-wrapper <code>Log</code> implementations for other logging APIs and backends, including
-<a href="https//logging.apache.org/log4j/docs/index.html">Log4J</a>,
+          <a href="https://logging.apache.org/log4j/2.x/manual/api-separation">Log4j API</a>,
-<a href="https//avalon.apache.org/logkit/index.html">Avalon LogKit</a>
+          <a href="https://www.slf4j.org">SLF4J</a> and <code>java.util.logging</code>.
-(the Avalon Framework's logging infrastructure),
-JDK 1.4, and an implementation of JDK 1.4 logging APIs (JSR-47) for pre-1.4
-systems.
-The interface maps closely to Log4J and LogKit.
         </p>
+
+        <p>
+          <strong>Warning:</strong> implementations for older logging backends such as
+          <a href="https//logging.apache.org/log4j/1.2/">Log4j 1.2</a>,
+          <a href="https//avalon.apache.org">Avalon LogKit</a> and
+          <a href="https://javalogging.sourceforge.net">Lumberjack</a> are also provided, although they are disabled by default.
+        </p>
+
         <p>
 Familiarity with high-level details of the relevant Logging implementations is presumed.
         </p>
@@ -134,25 +138,38 @@ JCL's discovery process).
 There are two base abstractions used by JCL: <code>Log</code>
 (the basic logger) and <code>LogFactory</code> (which knows how to create <code>Log</code>
 instances). Specifying a particular Log implementation is very useful (whether that is
-one provided by commons-logging or a user-defined one). Specifying a 
+one provided by Commons Logging or a user-defined one). Specifying a
-<code>LogFactory</code> implementation other than the default is a subject for
+<code>LogFactory</code> implementation explicitly is a subject for
 advanced users only, so will not be addressed here.
             </p>
             <p>
-The default <code>LogFactory</code> implementation uses the following discovery process
+              JCL provides three standard log factories:
+            </p>
+            <ol>
+              <li>if <a href="https://logging.apache.org/log4j/2.x/manual/api-separation">Log4j API</a>
+                  is present on the classpath and it is not redirected to SLF4J, then <code>Log4jApiLogFactory</code>
+                  is used. This factory redirects all output to Log4j API.</li>
+              <li>otherwise if <a href="https://www.slf4j.org">SLF4J</a> is presend on the classpath,
+                  then <code>Slf4jLogFactory</code> is used. This factory redirects all output to SLF4J.</li>
+              <li>otherwise the legacy <code>LogFactoryImpl</code> is used.</li>
+            </ol>
+            <p>
+The legacy <code>LogFactory</code> implementation uses the following discovery process
 to determine what type of <code>Log</code> implementation it should use
 (the process terminates when the first positive match - in order - is found):
             </p>
 
             <ol>
                 <li>
+                    <p>
 Look for a configuration attribute of this factory named
 <code>org.apache.commons.logging.Log</code> (for backwards compatibility to
 pre-1.0 versions of this API, an attribute
 <code>org.apache.commons.logging.log</code> is also consulted).
+                    </p>
                     <p>
 Configuration attributes can be set explicitly by java code, but they are more
-commonly set by placing a file named commons-logging.properties in the classpath.
+commonly set by placing a file named <code>commons-logging.properties</code> in the classpath.
 When such a file exists, every entry in the properties file becomes an "attribute"
 of the LogFactory. When there is more than one such file in the classpath, releases
 of commons-logging prior to 1.1 simply use the first one found. From release 1.1,
@@ -161,7 +178,7 @@ the highest priority is used (no priority definition implies priority of zero).
 When multiple files have the same priority, the first one found is used.
                     </p>
                     <p>
-Defining this property in a commons-logging.properties file is the recommended
+                      Defining this property in a <code>commons-logging.properties</code> file is the recommended
 way of explicitly selecting a Log implementation.
                     </p>
                 </li>
@@ -172,12 +189,7 @@ compatibility to pre-1.0 versions of this API, a system property
 <code>org.apache.commons.logging.log</code> is also consulted).
                 </li>
                 <li>
-If the Log4J logging system is available in the application
+If the <code>java.logging</code> module is available, use
-class path, use the corresponding wrapper class
-(<a href="https//commons.apache.org/logging/apidocs/org/apache/commons/logging/impl/Log4JLogger.html">Log4JLogger</a>).
-            </li>
-                <li>
-If the application is executing on a JDK 1.4 system, use
 the corresponding wrapper class
 (<a href="https//commons.apache.org/logging/apidocs/org/apache/commons/logging/impl/Jdk14Logger.html">Jdk14Logger</a>).
                 </li>
@@ -213,66 +225,6 @@ be required in the application. JCL simply forwards logging method calls to the
 implementation. When writing library code this issue is of course not relevant as the calling application
 is responsible for handling such issues.
         </p>
-            <subsection name='Configuring Log4J'>
-                <p>
-Log4J is a very commonly used logging implementation (as well as being the JCL primary default), 
-so a <i>few</i> details are presented herein to get the developer/integrator going.
-Please see the <a href='https//logging.apache.org/log4j/docs/index.html'>Log4J Home</a> for more details
-on Log4J and it's configuration.
-            </p>
-                <p>
-Configure Log4J using system properties and/or a properties file:
-            </p>
-                <ul>
-                    <li>
-<strong>log4j.configuration=<em>log4j.properties</em></strong>
-Use this system property to specify the name of a Log4J configuration file.
-If not specified, the default configuration file is <i>log4j.properties</i>.
-                </li>
-                    <li>
-<strong>log4j.rootCategory=<i>priority</i> [, <i>appender</i>]*</strong>
-                </li>
-Set the default (root) logger priority.
-                    <li>
-<strong>log4j.logger.<i>logger.name</i>=<i>priority</i></strong>
-Set the priority for the named logger
-and all loggers hierarchically lower than, or below, the
-named logger.
-<i>logger.name</i> corresponds to the parameter of
-<code>LogFactory.getLog(<i>logger.name</i>)</code>,
-used to create the logger instance.  Priorities are:
-<code>DEBUG</code>,
-<code>INFO</code>,
-<code>WARN</code>,
-<code>ERROR</code>,
-or <code>FATAL</code>.
-<br/>
-Log4J understands hierarchical names,
-enabling control by package or high-level qualifiers:
-<code>log4j.logger.org.apache.component=DEBUG</code>
-will enable debug messages for all classes in both
-<code>org.apache.component</code>
-and
-<code>org.apache.component.sub</code>.
-Likewise, setting
-<code>log4j.logger.org.apache.component=DEBUG</code>
-will enable debug message for all 'component' classes,
-but not for other Apache projects.
-                </li>
-                    <li>
-<strong>log4j.appender.<i>appender</i>.Threshold=<i>priority</i></strong>
-                </li>
-Log4J <i>appenders</i> correspond to different output devices:
-console, files, sockets, and others.
-If appender's <i>threshold</i>
-is less than or equal to the message priority then
-the message is written by that appender.
-This allows different levels of detail to be appear
-at different log destinations.
-For example: one can capture DEBUG (and higher) level information in a logfile,
-while limiting console output to INFO (and higher).
-            </ul>
-        </subsection>
     </subsection>
 </section>
     <section name='Developing With JCL'>

src/test/java/org/apache/commons/logging/log4j/log4j12/ApiClasspathStandardTestCase.java

@@ -19,6 +19,9 @@ package org.apache.commons.logging.log4j.log4j12;
 
 import org.apache.commons.logging.PathableClassLoader;
 import org.apache.commons.logging.PathableTestSuite;
+import org.apache.commons.logging.impl.Log4JLogger;
+import org.apache.commons.logging.impl.Log4jApiLogFactory;
+import org.apache.commons.logging.impl.LogFactoryImpl;
 
 import junit.framework.Test;
 import junit.framework.TestCase;
@@ -36,6 +39,8 @@ public class ApiClasspathStandardTestCase extends TestCase {
      * Return the tests included in this test suite.
      */
     public static Test suite() throws Exception {
+        // Ensure Log4JLogger is used
+        System.setProperty(LogFactoryImpl.LOG_PROPERTY, Log4JLogger.class.getName());
         final PathableClassLoader parent = new PathableClassLoader(null);
         parent.useExplicitLoader("junit.", Test.class.getClassLoader());
         parent.addLogicalLib("commons-logging-api");

src/test/java/org/apache/commons/logging/log4j/log4j12/AppClasspathStandardTestCase.java

@@ -19,6 +19,8 @@ package org.apache.commons.logging.log4j.log4j12;
 
 import org.apache.commons.logging.PathableClassLoader;
 import org.apache.commons.logging.PathableTestSuite;
+import org.apache.commons.logging.impl.Log4JLogger;
+import org.apache.commons.logging.impl.LogFactoryImpl;
 
 import junit.framework.Test;
 import junit.framework.TestCase;
@@ -34,6 +36,8 @@ public class AppClasspathStandardTestCase extends TestCase {
      * Return the tests included in this test suite.
      */
     public static Test suite() throws Exception {
+        // Ensure Log4JLogger is used
+        System.setProperty(LogFactoryImpl.LOG_PROPERTY, Log4JLogger.class.getName());
         final PathableClassLoader loader = new PathableClassLoader(null);
         loader.useExplicitLoader("junit.", Test.class.getClassLoader());
         loader.addLogicalLib("testclasses");

src/test/java/org/apache/commons/logging/log4j/log4j12/ChildClasspathStandardTestCase.java

@@ -19,6 +19,8 @@ package org.apache.commons.logging.log4j.log4j12;
 
 import org.apache.commons.logging.PathableClassLoader;
 import org.apache.commons.logging.PathableTestSuite;
+import org.apache.commons.logging.impl.Log4JLogger;
+import org.apache.commons.logging.impl.LogFactoryImpl;
 
 import junit.framework.Test;
 import junit.framework.TestCase;
@@ -35,6 +37,8 @@ public class ChildClasspathStandardTestCase extends TestCase {
      * Return the tests included in this test suite.
      */
     public static Test suite() throws Exception {
+        // Ensure Log4JLogger is used
+        System.setProperty(LogFactoryImpl.LOG_PROPERTY, Log4JLogger.class.getName());
         final PathableClassLoader parent = new PathableClassLoader(null);
         parent.useExplicitLoader("junit.", Test.class.getClassLoader());
 

src/test/java/org/apache/commons/logging/log4j/log4j12/ParentClasspathStandardTestCase.java

@@ -19,6 +19,8 @@ package org.apache.commons.logging.log4j.log4j12;
 
 import org.apache.commons.logging.PathableClassLoader;
 import org.apache.commons.logging.PathableTestSuite;
+import org.apache.commons.logging.impl.Log4JLogger;
+import org.apache.commons.logging.impl.LogFactoryImpl;
 
 import junit.framework.Test;
 import junit.framework.TestCase;
@@ -34,6 +36,8 @@ public class ParentClasspathStandardTestCase extends TestCase {
      * Return the tests included in this test suite.
      */
     public static Test suite() throws Exception {
+        // Ensure Log4JLogger is used
+        System.setProperty(LogFactoryImpl.LOG_PROPERTY, Log4JLogger.class.getName());
         final PathableClassLoader parent = new PathableClassLoader(null);
         parent.useExplicitLoader("junit.", Test.class.getClassLoader());
         parent.addLogicalLib("commons-logging");