Display WiFi Hotspot clients by cat proc net arp

This example display WiFi Hotspot connected clients (with IP and MAC address) by Linux command "cat /proc/net/arp", using ProcessBuilder.

(You can download runnable APK from link on bottom)

Tethering OFF, as WiFi client.

Tethering ON, with no client connected.

Tethering ON, with two clients connected; Nexus 7 and Raspberry Pi + WiFi dongle.

But, after any client disconnected, the /proc/net/arp will not updated immediately; I dont know how long it will refresh. One way to update arp is turn OFF and ON tethering again.

Tested on unrooted Xiaomi Redmi 2 running Android 4.4.4.

MainActivity.java

package com.blogspot.android_er.androidlistclient;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.io.IOException;
import java.io.InputStream;

public class MainActivity extends AppCompatActivity {

 Button btnRead;
 TextView textResult;

 //String[] args = {"/system/bin/cat", "/proc/net/arp"};
 String[] args = {"cat", "/proc/net/arp"};

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 btnRead = (Button)findViewById(R.id.readclient);
 textResult = (TextView)findViewById(R.id.result);

 btnRead.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 textResult.setText(toRead());
 }
 });
 }

 private String toRead()
 {
 ProcessBuilder cmd;
 String result="";

 try{
 cmd = new ProcessBuilder(args);

 Process process = cmd.start();
 InputStream in = process.getInputStream();
 byte[] re = new byte[1024];
 while(in.read(re) != -1){
 System.out.println(new String(re));
 result = result + new String(re);
 }
 in.close();
 } catch(IOException ex){
 ex.printStackTrace();
 }
 return result;
 }
}

layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
 
 android_layout_width="match_parent"
 android_layout_height="match_parent"
 android_padding="16dp"
 android_orientation="vertical"
 tools_context="com.blogspot.android_er.androidlistclient.MainActivity">

 <TextView
 android_layout_width="wrap_content"
 android_layout_height="wrap_content"
 android_layout_gravity="center_horizontal"
 android_autoLink="web"
 android_text="http://android-er.blogspot.com/"
 android_textStyle="bold" />
 
 <Button
 android_id="@+id/readclient"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_textAllCaps="false"
 android_text="Read /proc/net/arp"/>

 <TextView
 android_id="@+id/result"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_typeface="monospace"
 android_textSize="12sp"/>
</LinearLayout>

Download runnable APK .

This example display arp in human readable format, but not for machine. Next post "Retrieve IP and MAC addresses from /proc/net/arp" get it in more machine readable.

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