User defined custom Runtime/Unchecked exception example

What is user defined or custom exception in java?

User defined exceptions is concrete class extending exceptions like Exception, RuntimeException etc.
Create an unchecked exception by extending RuntimeException class in java
In our application, sometimes we would like to pass custom information to exception.
User defined exceptions are used to handle application specific inputs.
- e.g. If we unable to find any user from database, we would like to pass input user id, while throwing exception. (refer UserNotFoundException in trailing code)..
We will take an example to create unchecked or custom exception.

Program – create user defined or custom runtime exception.

1.) UserNotFoundException Class (Custom exception class)

Create a custom runtime exception class extending RuntimeExcception class.
UserNotFoundException is unchecked exception.
We have overloaded different constructors to demonstrate custom exception class.

package org.learn.exception;
 
public class UserNotFoundException extends RuntimeException {
    private static final long serialVersionUID = 13216733298798717L;
    private final String userId;
 
    public UserNotFoundException(String message, String userId) {
        super(message);
        this.userId = userId;
    }
 
    public UserNotFoundException(String message, Throwable error, String userId) {
        super(message, error);
        this.userId = userId;
    }
 
    public UserNotFoundException(Throwable e, String userId) {
        super(e);
        this.userId = userId;
    }
 
    public String getUserId() {
        return userId;
    }
}

2.) UserDao Class (throwing UserNotFoundException if user does not exists):

UserDao class simulating database operations.
We have created the hashmap simulate database, to store user objects.
We will perform some CRUD operations with UserDao class.
If we unable to find user in database, we will throw UserNotFoundException.

package org.learn.dao;
 
import org.learn.exception.UserNotFoundException;
import org.learn.model.User;
 
import java.util.HashMap;
import java.util.Map;
 
public class UserDao {
 
    @SuppressWarnings("serial")
    private Map<String, User> databaseUser = new HashMap<String, User>() {
        {
            put("1", new User("1", "Angelina", 35, "Cambodia", "Female"));
            put("2", new User("2", "Brad", 46, "Shawnee", "Male"));
            put("3", new User("3", " Jennifer", 41, "LA", "Female"));
            put("4", new User("4", "Justin", 38, " Washington", "Male"));
            put("5", new User("5", "Marcel ", 42, "Cambodia", "Male"));
        }
    };
 
    public User getUserById(String id) {
        if (!isUserExists(id)) {
            throw new UserNotFoundException("User does not exists in database", id);
        }
        return databaseUser.get(id);
    }
 
    public User update(String id, User user) {
        if (!isUserExists(id)) {
            throw new UserNotFoundException("Update failed, User does not exist", id);
        }
        return databaseUser.put(id, user);
    }
 
    public User delete(String id) {
        if (!isUserExists(id)) {
            throw new UserNotFoundException("User does not exists in database", id);
        }
        return databaseUser.remove(id);
    }
 
    private boolean isUserExists(String id) {
        return databaseUser.containsKey(id);
    }
}

3.) User Class:

User class representing the POJO of user.

package org.learn.model;
 
public class User {
     
    private String id;
    private String name;
    private int age;
    private String city;
    private String gender;
 
    public User() {
         
    }
    public User(String id, String name, int age, String city, String gender) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.city = city;
        this.gender = gender;
    }
 
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", city='" + city + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }
     
    public String getId() {
        return id;
    }   
}

4.) UserService Class (catching exceptions thrown by Dao):

UserService class act as client of UserDao class, we are performing db operations in UserService class.
We are catching the UserNotFoundException in-case user does not exist in database.

package org.learn.client;
 
import org.learn.dao.UserDao;
import org.learn.exception.UserNotFoundException;
import org.learn.model.User;
 
public class UserService {
    public static void main(String[] args) {
        UserDao userDao = new UserDao();
        String id = "1";
        // Get user by id 1
        User user = userDao.getUserById(id);
        System.out.printf("1. Got user with id %s is :%s\n", id, user);
 
        System.out.printf("2. Delete user with id %s\n", id);
        user = userDao.delete(id);
 
        // Get user by id 1, which does not exist
        try {
            user = userDao.getUserById(id);
            System.out.printf("3. Got user with id %s is :%s", id, user);
        } catch (UserNotFoundException e) {
            System.out.printf("3. Unable to get user, userId=%s, message:%s\n", e.getUserId(), e.getMessage());
        }
 
        // delete user by id 10, which does not exist
        id = "20";
        try {
            user = userDao.delete(id);
            System.out.printf("4. deleted user with id %s is :%s", id, user);
        } catch (UserNotFoundException e) {
            System.out.printf("4. Unable to delete user, userId=%s, message:%s\n", e.getUserId(), e.getMessage());
        }
 
        // delete user by id 10, which does not exist
        id = "1";
        try {
            user = userDao.update(id, null);
            System.out.printf("5. update user with id %s is :%s", id, user);
        } catch (UserNotFoundException e) {
            System.out.printf("5. Unable to update user, userId=%s, message:%s\n", e.getUserId(), e.getMessage());
        }
    }
}

Output: custom or user defined runtime exception

Got user with id 1 is :User{name='Angelina', age=35, city='Cambodia', gender='Female'}
Delete user with id 1
Unable to get user, userId=1, message:User does not exists in database
Unable to delete user, userId=20, message:User does not exists in database
Unable to update user, userId=1, message:Update failed, User does not exist

What is user defined or custom exception in java?

Program – create user defined or custom runtime exception.

1.) UserNotFoundException Class (Custom exception class)

2.) UserDao Class (throwing UserNotFoundException if user does not exists):

3.) User Class:

4.) UserService Class (catching exceptions thrown by Dao):

Output: custom or user defined runtime exception

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