Being a library HttpClient is not to dictate which logging framework the user has to use. Therefore HttpClient utilizes the logging interface provided by the Commons Logging package. Commons Logging provides a simple and generalized log interface to various logging packages. By using Commons Logging, HttpClient can be configured for a variety of different logging behaviours. That means the user will have to make a choice which logging framework to use. By default Commons Logging supports the following logging frameworks:
HttpClient performs two different kinds of logging: the standard context logging used within each class, and wire logging.
            Context logging contains information about the internal operation
            of HttpClient as it performs HTTP requests.  Each class has its own
            log named according to the class's fully qualified name.  For example
            the class HttpClient has a log named 
            org.apache.commons.httpclient.HttpClient.  Since all classes
            follow this convention it is possible to configure context logging for 
            all classes using the single log named org.apache.commons.httpclient.
         
The wire log is used to log all data transmitted to and from servers when executing HTTP requests. This log should only be enabled to debug problems, as it will produce an extremely large amount of log data, some of it in binary format.
            Because the content of HTTP requests is usually less important for debugging 
            than the HTTP headers, these two types of data have been separated into 
            different wire logs.  The content log is httpclient.wire.content 
            and the header log is httpclient.wire.header.
         
Commons Logging can delegate to a variety of loggers for processing the actual output. Below are configuration examples for Commons Logging, Log4j and java.util.logging.
                 Commons Logging comes with a basic logger called 
                 SimpleLog.  This logger writes all logged messages to 
                 System.err. The following examples show how to  configure 
                 Commons Logging via system properties to use SimpleLog.
              
Note: The system properties must be set before a reference to any Commons Logging class is made.
                Enable header wire + context logging - Best for Debugging
                
System.setProperty("org.apache.commons.logging.Log", "org.apache.commons.logging.impl.SimpleLog");
System.setProperty("org.apache.commons.logging.simplelog.showdatetime", "true");
System.setProperty("org.apache.commons.logging.simplelog.log.httpclient.wire.header", "debug");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.commons.httpclient", "debug");
                Enable full wire(header and content) + context logging
                
System.setProperty("org.apache.commons.logging.Log", "org.apache.commons.logging.impl.SimpleLog");
System.setProperty("org.apache.commons.logging.simplelog.showdatetime", "true");
System.setProperty("org.apache.commons.logging.simplelog.log.httpclient.wire", "debug");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.commons.httpclient", "debug");
                Enable just context logging
                
System.setProperty("org.apache.commons.logging.Log", "org.apache.commons.logging.impl.SimpleLog");
System.setProperty("org.apache.commons.logging.simplelog.showdatetime", "true");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.commons.httpclient", "debug");
The simplest way to configure Log4j is via a log4j.properties file. Log4j will automatically read and configure itself using a file named log4j.properties when it's present at the root of the application classpath. Below are some Log4j configuration examples.
Note: Log4j is not included in the HttpClient distribution.
                Enable header wire + context logging - Best for Debugging
                
log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%c] %m%n
log4j.logger.httpclient.wire.header=DEBUG
log4j.logger.org.apache.commons.httpclient=DEBUG
                Enable full wire(header and content) + context logging
                
log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%c] %m%n
log4j.logger.httpclient.wire=DEBUG
log4j.logger.org.apache.commons.httpclient=DEBUG
                Log wire to file + context logging
                
log4j.rootLogger=INFO
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%c] %m%n
log4j.appender.F=org.apache.log4j.FileAppender
log4j.appender.F.File=wire.log
log4j.appender.F.layout=org.apache.log4j.PatternLayout
log4j.appender.F.layout.ConversionPattern =%5p [%c] %m%n
log4j.logger.httpclient.wire=DEBUG, F
log4j.logger.org.apache.commons.httpclient=DEBUG, stdout
                Enable just context logging
                
log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%c] %m%n
log4j.logger.org.apache.commons.httpclient=DEBUG
Note that the default configuration for Log4J is very inefficient as it causes all the logging information to be generated but not actually sent anywhere. The Log4J manual is the best reference for how to configure Log4J. It is available at http://logging.apache.org/log4j/docs/manual.html
              Since JDK 1.4 there has been a package 
              
              java.util.logging that provides a
              logging framework similar to Log4J. By default it reads a config file from
              $JAVA_HOME/jre/lib/logging.properties which looks like this
              (comments stripped):
              
handlers=java.util.logging.ConsoleHandlerTo customize logging a custom
.level=INFO
java.util.logging.FileHandler.pattern = %h/java%u.log
java.util.logging.FileHandler.limit = 50000
java.util.logging.FileHandler.count = 1
java.util.logging.FileHandler.formatter = java.util.logging.XMLFormatter
java.util.logging.ConsoleHandler.level = INFO
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
com.xyz.foo.level = SEVERE
logging.properties file should be created
              in the project directory. The location of this file must be passed to the JVM as a
              system property. This can be done on the command line like so:
              $JAVA_HOME/java -Djava.util.logging.config.file=$HOME/myapp/logging.properties -classpath $HOME/myapp/target/classes com.myapp.MainAlternatively LogManager#readConfiguration(InputStream) can be used to pass it the desired configuration.
              Enable header wire + context logging - Best for Debugging
              
.level=INFO
handlers=java.util.logging.ConsoleHandler
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
httpclient.wire.header.level=FINEST
org.apache.commons.httpclient.level=FINEST
              Enable full wire(header and content) + context logging
              
.level=INFO
handlers=java.util.logging.ConsoleHandler
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
httpclient.wire.level=FINEST
org.apache.commons.httpclient.level=FINEST
              Enable just context logging
              
.level=INFO
handlers=java.util.logging.ConsoleHandler
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
org.apache.commons.httpclient.level=FINEST
More detailed information is available from the Java Logging documentation.