HttpClient Logging Practices HttpComponents Team $Id$

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:

By implementing some simple interfaces Commons Logging can be extended to support basically any other custom logging framework. Commons Logging tries to automatically discover the logging framework to use. If it fails to select the expected one, you must configure Commons Logging by hand. Please refer to the Commons Logging documentation for more information.

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.ConsoleHandler
.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
To customize logging a custom 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.Main
Alternatively 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.