Andriod Log

I was thinking how to use log on Android properly, and can control it without re-compile your app. Here is what I found.

Long story for short, you should do something like this in you code (An example from AOSP LocationManagerService.java

public class LocationManagerService extends ILocationManager.Stub {
    private static final String TAG = "LocationManagerService";
    public static final boolean D = Log.isLoggable(TAG, Log.DEBUG);

    ....

    public void systemRunning() {
        synchronized (mLock) {
            if (D) Log.d(TAG, "systemRunning()");
            // fetch package manager
            mPackageManager = mContext.getPackageManager();
            ..

Then you can use log.tag.TAG to set the logging level like this adb shell setprop log.tag.LocationManagerService VERBOSE. For details, check the document here isLoggable

Why don’t wrap those if (D) Log.d(TAG, "...") to another function, so it can handle the log logic internally? You can find the reason from the comments of android.util.Log.java:

when you’re building the string to pass into Log.d, the compiler uses a StringBuilder and at least three allocations occur: the StringBuilder itself, the buffer, and the String object. Realistically, there is also another buffer allocation and copy, and even more pressure on the gc. That means that if your log message is filtered out, you might be doing significant work and incurring significant overhead.