Validate Email & Password with Regular Expression

 

In this video we will learn, how to validate an email address and password client side, by using regular expressions (regex).

This way we can check, if the inserted email address is formed like an email address, and if the password contains certain characters, like upper and lower case letters, digits and special characters.
For this we will use the Pattern class, with which we can compile a regex from a string and then use the matcher method to compare it with the input.

In build.gradle file add this dependency:-

implementation 'com.google.android.material:material:1.0.0'

In MainActivity.java class file add these lines of codes:-

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Patterns;
import android.view.View;
import android.widget.Toast;

import com.google.android.material.textfield.TextInputLayout;

import java.util.regex.Pattern;

public class MainActivity extends AppCompatActivity {
    private static final Pattern PASSWORD_PATTERN =
            Pattern.compile("^" +
                    //"(?=.*[0-9])" +         //at least 1 digit
                    //"(?=.*[a-z])" +         //at least 1 lower case letter
                    //"(?=.*[A-Z])" +         //at least 1 upper case letter
                    "(?=.*[a-zA-Z])" +      //any letter
                    "(?=.*[@#$%^&+=])" +    //at least 1 special character
                    "(?=\\S+$)" +           //no white spaces
                    ".{4,}" +               //at least 4 characters
                    "$");
    private TextInputLayout textInputEmail;
    private TextInputLayout textInputUsername;
    private TextInputLayout textInputPassword;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textInputEmail = findViewById(R.id.text_input_email);
        textInputUsername = findViewById(R.id.text_input_username);
        textInputPassword = findViewById(R.id.text_input_password);
    }
    private boolean validateEmail() {
        String emailInput = textInputEmail.getEditText().getText().toString().trim();
        if (emailInput.isEmpty()) {
            textInputEmail.setError("Field can't be empty");
            return false;
        } else if (!Patterns.EMAIL_ADDRESS.matcher(emailInput).matches()) {
            textInputEmail.setError("Please enter a valid email address");
            return false;
        } else {
            textInputEmail.setError(null);
            return true;
        }
    }
    private boolean validateUsername() {
        String usernameInput = textInputUsername.getEditText().getText().toString().trim();
        if (usernameInput.isEmpty()) {
            textInputUsername.setError("Field can't be empty");
            return false;
        } else if (usernameInput.length() > 15) {
            textInputUsername.setError("Username too long");
            return false;
        } else {
            textInputUsername.setError(null);
            return true;
        }
    }
    private boolean validatePassword() {
        String passwordInput = textInputPassword.getEditText().getText().toString().trim();
        if (passwordInput.isEmpty()) {
            textInputPassword.setError("Field can't be empty");
            return false;
        } else if (!PASSWORD_PATTERN.matcher(passwordInput).matches()) {
            textInputPassword.setError("Password too weak");
            return false;
        } else {
            textInputPassword.setError(null);
            return true;
        }
    }
    public void confirmInput(View v) {
        if (!validateEmail() | !validateUsername() | !validatePassword()) {
            return;
        }
        String input = "Email: " + textInputEmail.getEditText().getText().toString();
        input += "\n";
        input += "Username: " + textInputUsername.getEditText().getText().toString();
        input += "\n";
        input += "Password: " + textInputPassword.getEditText().getText().toString();
        Toast.makeText(this, input, Toast.LENGTH_SHORT).show();
    }
}

In activity_main.xml file add these lines of codes:-

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    android:padding="16dp"
    tools:context=".MainActivity">
    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/text_input_email"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:errorEnabled="true">
        <com.google.android.material.textfield.TextInputEditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Email"
            android:inputType="textEmailAddress" />
    </com.google.android.material.textfield.TextInputLayout>
    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/text_input_username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:counterEnabled="true"
        app:counterMaxLength="15"
        app:errorEnabled="true">
        <com.google.android.material.textfield.TextInputEditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Username"
            android:inputType="text" />
    </com.google.android.material.textfield.TextInputLayout>
    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/text_input_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:errorEnabled="true"
        app:passwordToggleEnabled="true">
        <com.google.android.material.textfield.TextInputEditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Password"
            android:inputType="textPassword" />
    </com.google.android.material.textfield.TextInputLayout>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="confirmInput"
        android:text="Confirm"
        tools:ignore="OnClick" />
</LinearLayout>

After adding these lines of codes run this application and see the required output.