Android is a Linux-based operating system designed primarily for touchscreen mobile devices such as smartphones and tablet computers, developed by Google in conjunction with the Open Handset Alliance. The Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language. Apache log4j is a logging library for Java and an Apache Software Foundation Project and developed by a dedicated team of Committers of the Apache Software Foundation. Here we will explain how to integrate Log4J in Android based Java applications.
Step 1
Download Log4J library from http://logging.apache.org/log4j/1.2/download.html
Step 2
Configuring Log4J library the normal way - using XML configuration file - can't be used in Android based Java application as the configuration classes of Log4J use beans from the package "java.beans" (e.g. PropertyDescriptor). Not all classes of this package are supported in Android, so using Log4J directly in Android Java application will case exceptions like the following one to be thrown:
11-23 09:44:56.947: D/dalvikvm(1585): GC_FOR_MALLOC freed 3278 objects / 311568 bytes in 31ms
rejecting opcode 0x21 at 0x000a
rejected Lorg/apache/log4j/config/PropertySetter;.getPropertyDescriptor
(Ljava/lang/String;)Ljava/beans/PropertyDescriptor;
Verifier rejected class Lorg/apache/log4j/config/PropertySetter;
Exception Ljava/lang/VerifyError; thrown during Lorg/apache/log4j/LogManager;.
Shutting down VM
threadid=1: thread exiting with uncaught exception (group=0x400259f8)
FATAL EXCEPTION: main
java.lang.ExceptionInInitializerError
at org.slf4j.impl.Log4jLoggerFactory.getLogger(Log4jLoggerFactory.java:64)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:253)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:265)
...
Caused by: java.lang.VerifyError: org.apache.log4j.config.PropertySetter
at org.apache.log4j.PropertyConfigurator.parseAppender(PropertyConfigurator.java:772)
at org.apache.log4j.PropertyConfigurator.parseCategory(PropertyConfigurator.java:735)
at org.apache.log4j.PropertyConfigurator.configureRootCategory(PropertyConfigurator.java:615)
at org.apache.log4j.PropertyConfigurator.doConfigure(PropertyConfigurator.java:502)
at org.apache.log4j.PropertyConfigurator.doConfigure(PropertyConfigurator.java:547)
at org.apache.log4j.helpers.OptionConverter.selectAndConfigure(OptionConverter.java:483)
at org.apache.log4j.LogManager.(LogManager.java:127)
... 20 more
There is a project called android-logging-log4j, which provides a convenient way to configure the log4j system properly.
Download "Android Logging Log4J" library from http://code.google.com/p/android-logging-log4j/downloads/list
Step 3
Add Both libraries "log4j" and "android-logging-log4j" to your application libraries
Step 4
In order to log to a file on the external storage, the following permission needs to be placed in AndroidManifest.xml
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<uses-permission android:name = "android.permission.WRITE_EXTERNAL_STORAGE" />
Step 5
In your application Main class:
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package com.android.myapp ;
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import java.io.File ;
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import org.apache.log4j.Level ;
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import org.apache.log4j.Logger ;
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import android.app.Application ;
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import android.os.Environment ;
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import de.mindpipe.android.logging.log4j.LogConfigurator ;
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public class MyApplication extends Application {
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@Override
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public void onCreate ( ) {
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super . onCreate ( ) ;
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LogConfigurator logConfigurator = new LogConfigurator ( ) ;
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logConfigurator.
setFileName ( Environment .
getExternalStorageDirectory ( ) -
+ File .
separator + "MyApp" + File .
separator + "logs" -
+ File .
separator + "log4j.txt" ) ; -
logConfigurator. setRootLevel ( Level. DEBUG ) ;
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logConfigurator. setLevel ( "org.apache" , Level. ERROR ) ;
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logConfigurator. setFilePattern ( "%d %-5p [%c{2}]-[%L] %m%n" ) ;
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logConfigurator. setMaxFileSize ( 1024 * 1024 * 5 ) ;
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logConfigurator. setImmediateFlush ( true ) ;
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logConfigurator. configure ( ) ;
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Logger log = Logger. getLogger ( MyApplication. class ) ;
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log. info ( "My Application Created" ) ;
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}
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}
Now you will have log4j configured to log to Path: (Environment.getExternalStorageDirectory() + File.separator + "MyApp" + File.separator + "logs" + File.separator + "log4j.txt") with DEBUG level and ERROR lever for "org.apache" package with file pattern "%d %-5p [%c{2}]-[%L] %m%n" and other configuration parameters