AndroidChangeWifiProxy.java

package kagasu.net.wifiproxy;

import android.net.wifi.WifiConfiguration;
import android.net.wifi.WifiManager;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import java.io.BufferedOutputStream;
import java.io.DataOutputStream;
import java.io.FileOutputStream;

public class MainActivity extends AppCompatActivity {
    private WifiManager wifiManager;

    private static final int IPCONFIG_FILE_VERSION = 2;
    private static final String ipConfigFile = Environment.getDataDirectory() + "/misc/wifi/ipconfig.txt";
    private static final String sdcardIpConfigFile = Environment.getExternalStorageDirectory() + "/ipconfig.txt";
    private static final String ID_KEY = "id";
    private static final String IP_ASSIGNMENT_KEY = "ipAssignment";
    private static final String PROXY_SETTINGS_KEY = "proxySettings";
    private static final String PROXY_HOST_KEY = "proxyHost";
    private static final String PROXY_PORT_KEY = "proxyPort";
    private static final String EXCLUSION_LIST_KEY = "exclusionList";
    private static final String EOS = "eos";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Wi-Fiの状態を取得する
        wifiManager = (WifiManager)getSystemService(WIFI_SERVICE);

        // Wi-Fiが有効になっている場合、無効にする
        if(wifiManager.isWifiEnabled()) {
            wifiManager.setWifiEnabled(false);
        }

        try {
            DataOutputStream out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(sdcardIpConfigFile)));

            out.writeInt(IPCONFIG_FILE_VERSION);
            out.writeUTF(IP_ASSIGNMENT_KEY);
            out.writeUTF("DHCP");
            out.writeUTF(PROXY_SETTINGS_KEY);
            out.writeUTF("STATIC");
            out.writeUTF(PROXY_HOST_KEY);
            out.writeUTF("192.168.1.11");
            out.writeUTF(PROXY_PORT_KEY);
            out.writeInt(8008);
            out.writeUTF(EXCLUSION_LIST_KEY);
            out.writeUTF("");
            out.writeUTF(ID_KEY);
            // 任意の値に変更
            out.writeInt(0x4062a3d6);
            out.writeUTF(EOS);
            out.flush();

            Process process = Runtime.getRuntime().exec(new String[] { "su", "-c", "cp" + " " + sdcardIpConfigFile + " " + ipConfigFile});
            process.waitFor();

        }catch(Exception e)
        {
            e.printStackTrace();
        }

        // Wi-Fiを有効にする
        wifiManager.setWifiEnabled(true);
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="kagasu.net.wifiproxy">

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>