Lombok @CustomLog for Android's Log.* logging system

AndroidLogger.java

package com.example.log;

import android.util.Log;
import com.example.BuildConfig;
import com.google.common.io.ByteStreams;
import java.io.PrintStream;

public class AndroidLogger extends PrintStream {

    private final String mLogtag;

    AndroidLogger(final String name) {

        super(ByteStreams.nullOutputStream());
        mLogtag = getLogtag(name);
    }

    private String getLogtag(final String name) {

        String tagBase = BuildConfig.LOGTAG_PREFIX + name;
        if (tagBase.length() <= 23) {

            return tagBase;
        }

        return tagBase.substring(0, 22) + "+";
    }

    public void d(String m) {

        if (BuildConfig.DEBUG) {

            Log.d(mLogtag, m);
        }
    }

    public void i(String m) {

        Log.i(mLogtag, m);
    }
    
    public void e(String m, Throwable tr) {

        Log.e(mLogtag, m, tr);
    }

    public void e(String m) {

        Log.e(mLogtag, m);
    }

    @Override
    public void println(String m) {

        d(m);
    }
}

AndroidLoggerFactory.java

package com.example.log;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

public class AndroidLoggerFactory {

    private static final ConcurrentMap<Class<?>, AndroidLogger> sLoggerMap = new ConcurrentHashMap<>();;

    /**
     * This is adapted from http://www.slf4j.org/apidocs/src-html/org/slf4j/simple/SimpleLoggerFactory.html
     */
    public static AndroidLogger getLogger(final Class<?> type) {

        AndroidLogger logger = sLoggerMap.get(type);
        if (logger != null) {

            return logger;
        }

        AndroidLogger newLogger = new AndroidLogger(type.getSimpleName());
        AndroidLogger oldLogger = sLoggerMap.putIfAbsent(type, newLogger);

        return oldLogger == null ? newLogger : oldLogger;
    }
}

build.gradle

android {

    buildTypes {

        buildTypes.each {

            // A prefix that helps us filter to our own log messages in Android Studio's Logcat viewer.
            it.buildConfigField 'String', 'LOGTAG_PREFIX', '"ABC/"'
        }
    }
}
        
dependencies {

    implementation "com.google.guava:guava:29.0-android"
}

logcat.txt

# This is how a log message, triggered as:
# @CustomLog
# public class LoginActivity {
# 
#     @Override
#     void onLoginSuccess() {
# 
#         log.d("User Login succeeded");
#     }
# }
# Will look like in logcat.

2020-09-15 19:51:59.902 16387-16387/com.example.app D/ABC/LoginActivity: User Login succeeded

Note that the Lombok-introduced static variable, log, can be passed to any method that needs a PrintStream. So instead of a method doing:

void foo() {

    System.err.println("Some stuff");
}

You can write it as:

void foo(PrintStream stream) {

    stream.println("Some stuff");
}

Then, from Android you can call this method as foo(log) and from elsewhere, as foo(System.err).

lombok.config

lombok.log.custom.declaration = com.example.log.AndroidLogger com.example.log.log.AndroidLoggerFactory.getLogger(TYPE)