How to adjust microphone sensitivity while recording audio in android

As I understand you don't want any automatic adjustments, only manual from the UI. There is no built-in functionality for this in Android, instead you have to modify your data manually.

Suppose you use read (short[] audioData, int offsetInShorts, int sizeInShorts) for reading the stream. So you should just do something like this:

float gain = getGain(); // taken from the UI control, perhaps in range from 0.0 to 2.0
int numRead = read(audioData, 0, SIZE);
if (numRead > 0) {
    for (int i = 0; i < numRead; ++i) {
        audioData[i] = (short)Math.min((int)(audioData[i] * gain), (int)Short.MAX_VALUE);
    }
}

Math.min is used to prevent overflow if gain is greater than 1.

Dynamic microphone sensitivity is not a thing that the hardware or operating system is capable of as it requires analysis on the recorded sound. You should implement your own algorithm to analyze the recorded sound and adjust (amplify or decrease) the sound level on your own.

You can start by analyzing last few seconds and find a multiplier that is going to "balance" the average amplitude. The multiplier must be inversely proportional to the average amplitude to balance it.

PS: If you still want to do it, the mic levels are accessible when you have a root access, but I am still not sure -and don't think it is possible- if you can change the settings while recording. Hint: "/system/etc/snd_soc_msm" file.