Sensible logging for Android aim to provide no-nonsense logging frontend API that is easily extended. The goal of this library is not to be rich in features, but to provide a stable baseline for you to build on in your own projects.

Core concepts

The library consists of a few fundamental elements:

Log class

The Log class is the main interaction point of this library. Inside it you will find the familiar log statement methods such as Log.d()

Log.d("Initialising the flux capacitor", Categories.UI, Channels.CrashReporting)

Channels

Log directs the log statements to Channel implementations. Think of Channels as sinks you print your statements to. Currently, the library includes LogCatChannel and StandardOutChannel (for unit tests).

Depending on your use-case, either implement a subtype of ReleaseChannel or DebugChannel.

• DebugChannels are meant to be used during development. Additional to the log-line, it includes the following information:

data class Meta(
   val className: String,
   val simpleClassName: String,
   val functionName: String,
   val lineNumber: Int,
   val threadName: String,
   val fileName: String
)

It retrieves this data using Throwable().stackTrace. Be aware that it can have negative impact to performance, so default to only use it in debug builds.

• ReleaseChannels only include the log-line and are meant to be used in release-builds.

Channel ids

A channel has a integer identifier. You can optionally specify a channel ID in your log statement to also print to that channel.

As an example, you can log non-fatal exceptions and messages to your crash reporting service via a CrashReportingChannel. Using that you can easily log to your crash reporting service from wherever in your code.

    Log.e("Something fatal occurred", exception, 4 /*CrashReportingChannel*/)

While the channel parameter is an integer. We recommend organising your channels in one file, for auto-completeness. Like so:

typealias Channel = Int

object Channels {
    const val LogCat: Channel = LogCatChannel.ID
    const val CrashReporting: Channel = CrashReportingChannel.ID
}

// then you can autocomplete your way to the channel
Log.e("Something fatal occurred", exception, Channels.CrashReporting)

Default channels

During setup, you can mark a Channel as default. Log statements are always forwarded to default channels, meaning you don't have to specify them explicitly in your log statements.

An example where this is useful; you can mark the LogCat channel as default in a debug build, but not in a release build.

Filters

interface Filter {
    fun matches(line: Line): Boolean
}

To control what a Channel should output you pass an instance of Filter. You can combine different filters by using the infix functions and & or:

    SimpleLogLevelFilter(Level.ERROR) and SimpleCategoryFilter(Categories.UI)

would only print messages with level error and above, and of the category UI. If you don't care about filters, you can pass the AllowAllFilter to your Channel.

Formatters

interface Formatter {
    fun format(line: Line, meta: Meta?): String
}

A Channel uses a Formatter to control the format of the output. If you are directing your output to a file, we recommend using SimpleFormatter

Categories

All log statement methods inside Log allow the passing of a log category. This can be used to order your statements into high level areas of interest. Want to know what is going on with your backend? Direct your network client log statements to the Network category, and enable only that category.

Similar to channels, the category parameter is a string. Here we also recommend organising your categories in one file. Like so:

object Categories {
    const val Default = sh.vcm.sensiblelogging.util.Constants.DEFAULT_CATEGORY
    const val Analytics = Category("Analytics")
    const val Network = Category("Network")
    const val Process = Category("Process")
    const val Activity = Category("Activity")
    const val Service = Category("Service")
    const val Fragment = Category("Fragment")
    const val RxJava = Category("RxJava")
    const val FluxCapacitorFeature = Category("FluxCapacitorFeature")
    const val Push = Category("Push")
    const val UI = Category("UI")
}

Usage

Step 1

    if (BuildConfig.DEBUG) {
    // Sane defaults filter
    val categoriesFilter = Filter.categories(listOf(
        Categories.Default,
        Categories.Network,
        Categories.FluxCapacitorFeature,
        Categories.Process,
        Categories.Activity,
        Categories.Fragment
    ))
    val filterCombination = Filter.level(Level.WARN) or categoriesFilter
    val channels = Log.Setup.Configuration()
        .addLogCatChannel(filter = filterCombination, default = true)
        .create()
    Log.Setup.addChannels(channels)

    // optionally opt-in to logging out Process, Activity and Fragment lifecycle methods from the :lifecycle dependency
    registerLifecycleLoggers(
        processCategory = Categories.Process,
        activityCategory = Categories.Activity,
        fragmentCategory = Categories.Fragment
    )
}

Step 2

 // Log from your code
 // Passing "Default" as category is optional, if no category is passed, default will be used 
 // Passing "LogCat" as channel is optional, if no channel is passed, default will be used 
 Log.d("Initialising the flux capacitor", Categories.Default, Channels.LogCat)

Step 3

Build your own Channels, Filters & Formatters to solve your project needs.

For example: you can log non-fatal exceptions to your crash reporting service via a CrashReportingChannel. The CrashReportingChannel can be configured with a Filter that only pass a subset of your categories and all logged errors. Using that you can easily log to this channel from wherever in your code.

Want persisted logs? Implement a SQLiteChannel using your favourite ORM library. You can then display those statements from your debug UI. Or provide a shortcut from your app settings to dump the database to a text file that your users can email to you.

Want to control the log categories in runtime? Use the SharedPreferencesCategoryFilter with your LogCatChannel and enable updating of it from your debug UI.

Download

// in your root build.gradle
repositories {
  mavenCentral()
}

// in your app build.gradle
dependencies {
  implementation 'sh.vcm.sensiblelogging:sensible-logging:1.2.1'
  implementation 'sh.vcm.sensiblelogging:lifecycle:1.2.1'
}

Requirements

• minSdk is currently set to 16
• The base library is only dependant on the Android SDK and kotlin stdlib
• The lifecycle extensions are dependant on androidx.appcompat and androidx.lifecycle libraries

License

Copyright 2022 Volvo Cars Corporation

Licensed 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.