Arduino Web Server FULLY CODE

 #include <WiFi.h>
#include <WebServer.h>

//http://192.168.1.10/send?char=B

const char* ssid = "CapiBara";
const char* password = "77779999";
String  gtw = "192.168.1.1";

WebServer server(80);

String lastReceivedFromAndroid = "";
String charToSendToAndroid = "Z";

void handleSend() {
  if (server.hasArg("char")) {
    lastReceivedFromAndroid = server.arg("char");
    Serial.println("Received from Android: " + lastReceivedFromAndroid);

    // Contoh: ubah respons
    if (lastReceivedFromAndroid == "A") {charToSendToAndroid = "X";}
    else if (lastReceivedFromAndroid == "B") {charToSendToAndroid = "Y";}
    else if (lastReceivedFromAndroid == "C") {charToSendToAndroid = "Z";}
    else{charToSendToAndroid = "@"+lastReceivedFromAndroid+"#";}

    server.send(200, "text/plain", "OK");
  } else {
    server.send(400, "text/plain", "Missing char param");
  }
}

void handleStatus() {
  server.send(200, "text/plain", charToSendToAndroid);
  Serial.println("Sent to Android: " + charToSendToAndroid);
}

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);

  Serial.print("Connecting");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("\nConnected to WiFi. IP: ");
  Serial.println(WiFi.localIP());
  gtw= WiFi.gatewayIP().toString();
  Serial.print("Gateway (Access Point IP): ");
  Serial.println(gtw);

  server.on("/send", handleSend);
  server.on("/status", handleStatus);
  server.begin();
}

void loop() {
  server.handleClient();
}

=======

UJI:http://192.168.1.10/send?char=B

Respon: http://192.168.1.10/status

package com.appsensor.geminillmjava;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class WebServerAA extends AppCompatActivity {
    //http://192.168.1.10/send?char=B
    private TextView txtheader;
    private EditText etQuestion;
    private Button btnSubmit;
    private TextView tvAnswer;

    String IP="http://192.168.1.3/";
    private final android.os.Handler handler = new android.os.Handler();
    private final int POLLING_INTERVAL = 2000; // tiap 2 detik
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.geminillm);

        setTitle("WebServer Android Arduino");
        txtheader = findViewById(R.id.tvTitle);
        txtheader.setText("Aplikasi RX / TX Pesan AA");

        etQuestion = findViewById(R.id.etQuestion);
        etQuestion.setText(IP+"A");
        btnSubmit = findViewById(R.id.btnSubmit);
        btnSubmit.setText("Sent WebServer");
        tvAnswer = findViewById(R.id.tvAnswer);
        tvAnswer.setText("");

        btnSubmit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String question = etQuestion.getText().toString().trim();
                if (!question.isEmpty()) {
                    String[]parts=question.split("/");
                    if(parts.length>1) {
                        IP = parts[0];
                        String message = parts[parts.length - 1];
                        sendCharToESP32(message);
                    }
                    else{
                        Toast.makeText(WebServerAA.this, "Gunakan Pola IP/PESAN, \nmisal: http://192.168.1.3/", Toast.LENGTH_SHORT).show();
                    }
                } else {
                    Toast.makeText(WebServerAA.this, "Pesan tidak boleh kosong!", Toast.LENGTH_SHORT).show();
                }
            }
        });

        tvAnswer.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
             getCharFromESP32();
            }
        });
        startAutoPolling();
    }


    private final Runnable pollingRunnable = new Runnable() {
        @Override
        public void run() {
            getCharFromESP32(); // Panggil fungsi yang sudah ada
            handler.postDelayed(this, POLLING_INTERVAL); // Jadwalkan lagi
        }
    };

    private void startAutoPolling() {
        handler.postDelayed(pollingRunnable, POLLING_INTERVAL);
    }

    private void stopAutoPolling() {
        handler.removeCallbacks(pollingRunnable);
    }
    @Override
    protected void onPause() {
        super.onPause();
        stopAutoPolling();
    }
    @Override
    protected void onResume() {
        super.onResume();
        startAutoPolling();
    }





    public void sendCharToESP32(String character) {
        String url = IP+"send?char=" + character;

        new Thread(() -> {
            try {
                URL obj = new URL(url);
                HttpURLConnection con = (HttpURLConnection) obj.openConnection();
                con.setRequestMethod("GET");
                con.getInputStream().close(); // Eksekusi
            } catch (Exception e) {
                e.printStackTrace();
            }
        }).start();
    }

    public void getCharFromESP32() {
        String url = IP+"status";

        new Thread(() -> {
            try {
                HttpURLConnection con = (HttpURLConnection) new URL(url).openConnection();
                con.setRequestMethod("GET");

                BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
                String response = in.readLine();
                in.close();

                runOnUiThread(() -> {
                    tvAnswer.setText("ESP32 Sent: " + response);
                });

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

}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    tools:context=".GeminiLLMJava">

    <TextView
        android:id="@+id/tvTitle"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Asisten Pribadi ISTN Kampus DKI Jakarta"
        android:textSize="20sp"
        android:textStyle="bold"
        android:gravity="center"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginBottom="16dp"/>

    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/tilQuestion"
        style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:hint="Masukkan pertanyaan Anda"
        app:layout_constraintTop_toBottomOf="@id/tvTitle"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginTop="16dp">

        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/etQuestion"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="top|start"
            android:inputType="textMultiLine"
            android:maxLines="6"
            android:minLines="3" />
    </com.google.android.material.textfield.TextInputLayout>

    <Button
        android:id="@+id/btnSubmit"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Tanyakan ke AI"
        app:layout_constraintTop_toBottomOf="@id/tilQuestion"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginTop="16dp" />

    <TextView
        android:id="@+id/tvAnswerLabel"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Jawaban AI:"
        android:textSize="16sp"
        android:textStyle="bold"
        app:layout_constraintTop_toBottomOf="@id/btnSubmit"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginTop="24dp" />

    <ScrollView
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintTop_toBottomOf="@id/tvAnswerLabel"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginTop="8dp">

        <TextView
            android:id="@+id/tvAnswer"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@drawable/rounded_border"
            android:padding="12dp"
            android:text="Jawaban akan muncul di sini..."
            android:textSize="16sp"
            android:textColor="@android:color/black"
            android:fontFamily="monospace"
            android:lineSpacingExtra="4dp"
            android:scrollbars="vertical" />
    </ScrollView>

</androidx.constraintlayout.widget.ConstraintLayout>