SpringBoot jpa project with basic authentication swagger

 

entity class

package com.javatechnology.springboot.employees.entity;


import jakarta.persistence.*;


@Entity
@Table(name = "employee")

public class Employee {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column
    private long id;

   @Column(name = "first_name")
    private String firstName;
    @Column(name = "last_name")
    private String lastName;

    @Column(name = "email")
    private String email;

    public Employee(){
    }
    public Employee(long id, String firstName, String lastName, String email) {
        this.id = id;
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                '}';
    }
}

====================================================================================

request

package com.javatechnology.springboot.employees.request;

import jakarta.validation.constraints.Email;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.Size;

public class EmployeeRequest {


    @NotBlank(message = "First name is mandatory")
    @Size(min = 2,max = 50,message = "First Name mst be between 2 and 50 character")
    private String firstName;

    @NotBlank(message = "Last name is mandatory")
    @Size(min = 2,max = 50,message = "Last Name mst be between 2 and 50 character")
    private String lastName;

    @NotBlank(message = "Email is mandatory")
    @Email(message = "Please provide a valid email")
    private  String email;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public EmployeeRequest(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }


}
=================================================================
dao

package com.javatechnology.springboot.employees.dao;

import com.javatechnology.springboot.employees.entity.Employee;
import org.springframework.data.jpa.repository.JpaRepository;

public interface EmployeeRepository extends JpaRepository<Employee,Long> {

}

============================================================
service
package com.javatechnology.springboot.employees.service;

import com.javatechnology.springboot.employees.entity.Employee;
import com.javatechnology.springboot.employees.request.EmployeeRequest;

import java.util.List;

public interface EmployeeService {


    List<Employee> findAll();

    public Employee findById(long theId);

    public  Employee save(EmployeeRequest theEmployeeRequest);

    public Employee convertToEmployee(long id,EmployeeRequest employeeRequest);

    public Employee update(long id,EmployeeRequest employeeRequest);

    void deleteById(long theId);
}

=====================================================================

package com.javatechnology.springboot.employees.service;

import com.javatechnology.springboot.employees.dao.EmployeeRepository;
import com.javatechnology.springboot.employees.entity.Employee;
import com.javatechnology.springboot.employees.request.EmployeeRequest;
import jakarta.transaction.Transactional;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Optional;

@Service
public class EmployeeServiceImpl implements EmployeeService {

    private EmployeeRepository employeeRepository;

    @Autowired
    public EmployeeServiceImpl(EmployeeRepository employeeRepository) {
        this.employeeRepository = employeeRepository;
    }


    @Override
    public List<Employee> findAll() {
        return employeeRepository.findAll();
    }

    @Override
    public Employee findById(long theId) {
        Optional<Employee> result = employeeRepository.findById(theId);

        Employee theEmployee = null;
        if (result.isPresent()) {
            theEmployee = result.get();
        } else {
            throw new RuntimeException("Did not find employee id" + theId);
        }
        return theEmployee;
    }

    @Transactional
    @Override
    public Employee save(EmployeeRequest theEmployeeRequest) {
        Employee theEmployee = convertToEmployee(0, theEmployeeRequest);
        return employeeRepository.save(theEmployee);

    }

    @Override
    public Employee convertToEmployee(long id, EmployeeRequest employeeRequest) {


        return new Employee(id, employeeRequest.getFirstName(), employeeRequest.getLastName(), employeeRequest.getEmail());
    }

    @Transactional
    @Override
    public Employee update(long id, EmployeeRequest theEmployeeRequest) {
        Employee theEmployee = convertToEmployee(id, theEmployeeRequest);
        return employeeRepository.save(theEmployee);
    }

    @Transactional
    @Override
    public void deleteById(long theId) {
        employeeRepository.deleteById(theId);
    }


}

=====================================================================================
security

package com.javatechnology.springboot.employees.security;


import org.springframework.boot.autoconfigure.security.SecurityProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.security.config.Customizer;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.core.userdetails.User;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.provisioning.InMemoryUserDetailsManager;
import org.springframework.security.provisioning.JdbcUserDetailsManager;
import org.springframework.security.provisioning.UserDetailsManager;
import org.springframework.security.web.AuthenticationEntryPoint;
import org.springframework.security.web.SecurityFilterChain;

import javax.sql.DataSource;
import java.net.http.HttpRequest;

@Configuration
public class SecurityConfig {

//   hardcoded users
  /*  @Bean
    public InMemoryUserDetailsManager userDetailsManager() {
        UserDetails Govind = User.builder().username("Govind").password("{noop}Pass@123456").roles("EMPLOYEE").build();
        UserDetails Rishabh = User.builder().username("Rishabh").password("{noop}Pass@123456").roles("EMPLOYEE", "MANAGER").build();
        UserDetails Vicky = User.builder().username("Vicky").password("{noop}Pass@123456").roles("EMPLOYEE", "MANAGER", "ADMIN").build();
        return new InMemoryUserDetailsManager(Govind, Rishabh, Vicky);

    }*/


    //add support  for jdbc no more hardcoded users
   /* @Bean
    public UserDetailsManager userDetailsManager(DataSource datasource)
    {
        return new JdbcUserDetailsManager(datasource);
    }*/


    @Bean
    public UserDetailsManager userDetailsManager(DataSource datasource)
    {
        JdbcUserDetailsManager jdbcUserDetailsManager=new JdbcUserDetailsManager(datasource);
        //define query to retrieve a user by username
        jdbcUserDetailsManager.setUsersByUsernameQuery("select user_id,password,active from system_users where user_id=?");
        //define query to retrieve a roles/authorities by username

        jdbcUserDetailsManager.setAuthoritiesByUsernameQuery("select user_id,role from roles where user_id=?");

        return jdbcUserDetailsManager;
    }


    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http.authorizeHttpRequests(configurer -> configurer.
                requestMatchers(HttpMethod.GET, "/h2-console/**").permitAll().
                requestMatchers(HttpMethod.POST, "/h2-console/**").permitAll().
                requestMatchers("/docs/**", "/swagger-ui/**", "/v3/api-docs/**", "/swagger-ui.html").permitAll().
                requestMatchers(HttpMethod.GET, "/api/employees").hasRole("EMPLOYEE").
                requestMatchers(HttpMethod.GET, "/api/employees/**").hasRole("EMPLOYEE").
                requestMatchers(HttpMethod.POST, "/api/employees").hasRole("MANAGER").
                requestMatchers(HttpMethod.PUT, "/api/employees/**").hasRole("MANAGER").
                requestMatchers(HttpMethod.DELETE, "/api/employees/**").hasRole("ADMIN")

        );
        http.httpBasic(httpBasicCustomizer -> httpBasicCustomizer.disable());
        //use http basic authentication
        http.httpBasic(Customizer.withDefaults());
        http.csrf(csrf -> csrf.disable());
        http.exceptionHandling(exceptionHandling -> exceptionHandling.authenticationEntryPoint(authenticationEntryPoint()));
        http.headers(header -> header.frameOptions(frameOptions -> frameOptions.disable()));

        return http.build();
    }


    @Bean
    public AuthenticationEntryPoint authenticationEntryPoint() {
        return ((request, response, authException) -> {
            //send 401 unauthorized status without triggering a basic auth
            response.setStatus(HttpStatus.UNAUTHORIZED.value());
            response.setContentType("application/json");
            //removes the WWW-Authenticate header to prevent browser popup
            response.setHeader("WWW-Authenticate", "");
            response.getWriter().write("{\"error\":\"Unauthorized access\"}");
        });

    }
}

===================================================================================

package com.javatechnology.springboot.employees.security;

import io.swagger.v3.oas.annotations.OpenAPIDefinition;
import io.swagger.v3.oas.annotations.enums.SecuritySchemeType;
import io.swagger.v3.oas.annotations.info.Info;
import io.swagger.v3.oas.annotations.security.SecurityRequirement;
import io.swagger.v3.oas.annotations.security.SecurityScheme;
import org.springframework.context.annotation.Configuration;

@Configuration
@OpenAPIDefinition(info=@Info(title = "My API",version = "v1"),security = @SecurityRequirement(name = "basicAuth"))
@SecurityScheme(name = "basicAuth",type = SecuritySchemeType.HTTP ,scheme = "basic")
public class SwaggerConfig {
}

======================================================================================

package com.javatechnology.springboot.employees;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class EmployeesApplication {

    public static void main(String[] args) {
       SpringApplication.run(EmployeesApplication.class, args);
    }

}

============================================================================
application.properties
spring.application.name=employees
springdoc.swagger-ui.path=/docs

#H2 Database configurations

spring.datasource.url=jdbc:h2:file:./data/employeedb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.userName=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

#H2 console configurations

spring.h2.console.enabled=true
spring.h2.console.path=/h2-console
spring.jpa.hibernate.ddl-auto=update


spring.security.user.name=scott
spring.security.user.password=Pass@123456

==============================================================================


DROP TABLE IF EXISTS authorities;
DROP TABLE IF EXISTS users;

--
-- Table structure for table `users`
--

CREATE TABLE users (
  username VARCHAR(50) NOT NULL,
  password VARCHAR(50) NOT NULL,
  enabled BOOLEAN NOT NULL,
  PRIMARY KEY (username)
);

--
-- Inserting data for table `users`
--

INSERT INTO users (username, password, enabled)
VALUES
('john', '{noop}test123', TRUE),
('mary', '{noop}test123', TRUE),
('susan', '{noop}test123', TRUE);

--
-- Table structure for table `authorities`
--

CREATE TABLE authorities (
  username VARCHAR(50) NOT NULL,
  authority VARCHAR(50) NOT NULL,
  UNIQUE (username, authority),
  FOREIGN KEY (username) REFERENCES users (username)
);

--
-- Inserting data for table `authorities`
--

INSERT INTO authorities (username, authority)
VALUES
('john', 'ROLE_EMPLOYEE'),
('mary', 'ROLE_EMPLOYEE'),
('mary', 'ROLE_MANAGER'),
('susan', 'ROLE_EMPLOYEE'),
('susan', 'ROLE_MANAGER'),
('susan', 'ROLE_ADMIN');


=========================================================


-- Drop tables if they exist
DROP TABLE IF EXISTS authorities;
DROP TABLE IF EXISTS users;

--
-- Table structure for table `users`
--

CREATE TABLE users (
  username VARCHAR(50) NOT NULL,
  password CHAR(68) NOT NULL,
  enabled BOOLEAN NOT NULL,
  PRIMARY KEY (username)
);

--
-- Inserting data for table `users`
--
-- The passwords are encrypted using BCrypt
-- A generation tool is available at: https://www.luv2code.com/generate-bcrypt-password
-- Default passwords here are: fun123
--

INSERT INTO users (username, password, enabled)
VALUES
('john', '{bcrypt}$2a$10$qeS0HEh7urweMojsnwNAR.vcXJeXR1UcMRZ2WcGQl9YeuspUdgF.q', TRUE),
('mary', '{bcrypt}$2a$10$qeS0HEh7urweMojsnwNAR.vcXJeXR1UcMRZ2WcGQl9YeuspUdgF.q', TRUE),
('susan', '{bcrypt}$2a$10$qeS0HEh7urweMojsnwNAR.vcXJeXR1UcMRZ2WcGQl9YeuspUdgF.q', TRUE);

--
-- Table structure for table `authorities`
--

CREATE TABLE authorities (
  username VARCHAR(50) NOT NULL,
  authority VARCHAR(50) NOT NULL,
  UNIQUE (username, authority),
  FOREIGN KEY (username) REFERENCES users (username)
);

--
-- Inserting data for table `authorities`
--

INSERT INTO authorities (username, authority)
VALUES
('john', 'ROLE_EMPLOYEE'),
('mary', 'ROLE_EMPLOYEE'),
('mary', 'ROLE_MANAGER'),
('susan', 'ROLE_EMPLOYEE'),
('susan', 'ROLE_MANAGER'),
('susan', 'ROLE_ADMIN');


=========================================================================================




-- Drop tables if they exist
DROP TABLE IF EXISTS authorities;
DROP TABLE IF EXISTS users;
 
CREATE TABLE system_users (
  user_id VARCHAR(50) NOT NULL,
  password CHAR(68) NOT NULL,
  active BOOLEAN NOT NULL,
  PRIMARY KEY (user_id)
);
  
INSERT INTO system_users (user_id, password, active)
VALUES
('john', '{bcrypt}$2a$10$qeS0HEh7urweMojsnwNAR.vcXJeXR1UcMRZ2WcGQl9YeuspUdgF.q', TRUE),
('mary', '{bcrypt}$2a$10$qeS0HEh7urweMojsnwNAR.vcXJeXR1UcMRZ2WcGQl9YeuspUdgF.q', TRUE),
('susan', '{bcrypt}$2a$10$qeS0HEh7urweMojsnwNAR.vcXJeXR1UcMRZ2WcGQl9YeuspUdgF.q', TRUE);
  
CREATE TABLE roles (
  user_id VARCHAR(50) NOT NULL,
  role VARCHAR(50) NOT NULL,
  UNIQUE (user_id, role),
  FOREIGN KEY (user_id) REFERENCES system_users (user_id)
);
  
INSERT INTO roles (user_id, role)
VALUES
('john', 'ROLE_EMPLOYEE'),
('mary', 'ROLE_EMPLOYEE'),
('mary', 'ROLE_MANAGER'),
('susan', 'ROLE_EMPLOYEE'),
('susan', 'ROLE_MANAGER'),
('susan', 'ROLE_ADMIN');

===================================================================================


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-parent</artifactId>
       <version>3.5.5</version>
       <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.javatechnology.springboot</groupId>
    <artifactId>employees</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>employees</name>
    <description>employees project for Spring Boot</description>
    <url/>
    <licenses>
       <license/>
    </licenses>
    <developers>
       <developer/>
    </developers>
    <scm>
       <connection/>
       <developerConnection/>
       <tag/>
       <url/>
    </scm>
    <properties>
       <java.version>17</java.version>
    </properties>
    <dependencies>
       <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-security</artifactId>
       </dependency>

       <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-data-jpa</artifactId>
       </dependency>
       <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-web</artifactId>
       </dependency>

       <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-devtools</artifactId>
          <scope>runtime</scope>
          <optional>true</optional>
       </dependency>
       <dependency>
          <groupId>com.h2database</groupId>
          <artifactId>h2</artifactId>
          <scope>runtime</scope>
       </dependency>

       <dependency>
          <groupId>org.springdoc</groupId>
          <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
          <version>2.8.3</version>
       </dependency>

       <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-validation</artifactId>

       </dependency>
       <dependency>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-starter-test</artifactId>
          <scope>test</scope>
       </dependency>
    </dependencies>

    <build>
       <plugins>
          <plugin>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-maven-plugin</artifactId>
          </plugin>
       </plugins>
    </build>

</project>

 

State Design Pattern

The State Design Pattern is a behavioral design pattern that lets an object change its behavior when its internal state changes. It appears as if the object changed its class.

---

🧠 Key Concepts

Concept	Description
Context	The object whose behavior changes depending on its state
State	An interface that defines common behavior for all states
ConcreteState	Classes that implement the State interface with specific behavior

---

🧾 Problem It Solves

Without the State pattern, you might have code like this:

if (state.equals("RED")) {

    stop();

} else if (state.equals("GREEN")) {

    go();

}

This becomes harder to maintain as you add more states and behaviors.

---

🚦 Example: Traffic Light System

A traffic light can be in 3 states:

• 🔴 Red – Cars must stop.
• 🟢 Green – Cars can go.
• 🟡 Yellow – Cars should slow down.

The light should change from:

➡️ Red → Green → Yellow → Red → ...

 

 

 

ADVANTAGES OF STATE PATTERN

Benefit	Description
Removes complex if-else logic	Each state has its own class
Easy to add new states	Just create a new class implementing State
Promotes Open/Closed Principle	Classes are open for extension, closed for modification

---

⚠️ DISADVANTAGES

Drawback	Description
More classes to manage	One class per state can be a lot in large systems
Overhead for simple state logic	Sometimes an enum + switch is simpler

---

🏁 When to Use the State Pattern

• When an object must change behavior based on its state
• When there are many conditionals based on the state
• When the state transitions are complex or likely to grow

 

 

Exmple:1

 

package statedesignpattern;

 

public interface State {

               void handleRequest();

}

 

 

 

 

 

package statedesignpattern;

 

public class DraftState implements State {

 

               @Override

               public void handleRequest() {

                              System.out.println("Document is in Draft state.");

 

               }

 

}

 

 

package statedesignpattern;

 

public class ModerationState implements State{

 

               @Override

               public void handleRequest() {

                               System.out.println("Document is under Moderation.");

                             

               }

 

}

 

 

package statedesignpattern;

 

public class PublishState implements State {

 

               @Override

               public void handleRequest() {

                              System.out.println("Document is Published.");

 

               }

 

}

 

package statedesignpattern;

 

public class DocumentContext {

 

               private State currentState;

 

               public DocumentContext() {

                              // default state

                              this.currentState = new DraftState();

               }

 

               public void setState(State state) {

                              this.currentState = state;

               }

 

               public void applyState() {

                              currentState.handleRequest();

               }

              

              

              

 

}

 

 

 

package statedesignpattern;

 

public class Main {

               public static void main(String[] args) {

                              DocumentContext context = new DocumentContext();

 

                              context.applyState(); // Draft

 

                              context.setState(new ModerationState());

                              context.applyState(); // Moderation

 

                              context.setState(new PublishState());

                              context.applyState(); // Published

               }

}

 

o/p:

Document is in Draft state.

Document is under Moderation.

Document is Published.

 

Example :2

package statedesignpattern.trafficlightexample;

 

public interface State {

 

               void handle(TrafficLightContext context);

              

}

 

package statedesignpattern.trafficlightexample;

 

public class RedLightState implements State {

 

               @Override

               public void handle(TrafficLightContext context) {

                               System.out.println("🔴 Red Light - STOP");

                       context.setState(new GreenLightState());

                             

               }

 

}

 

package statedesignpattern.trafficlightexample;

 

public class GreenLightState implements State{

 

               @Override

               public void handle(TrafficLightContext context) {

                              System.out.println("🟢 Green Light - GO");

        context.setState(new YellowLightState());

                             

               }

 

}

 

package statedesignpattern.trafficlightexample;

 

public class YellowLightState implements State {

 

               @Override

               public void handle(TrafficLightContext context) {

                               System.out.println("🟡 Yellow Light - SLOW DOWN");

                       context.setState(new RedLightState());

                             

               }

 

}

 

package statedesignpattern.trafficlightexample;

 

public class TrafficLightContext {

 

               private State currentState;

 

               public TrafficLightContext() {

                              this.currentState = new RedLightState();// Initial state

               }

 

               public void setState(State state) {

                              this.currentState = state;

               }

 

               public void change() {

                              currentState.handle(this);

               }

}

 

 

package statedesignpattern.trafficlightexample;

 

public class Main {

 

               public static void main(String[] args) {

 

                              TrafficLightContext trafficLightContext = new TrafficLightContext();

                              for (int i = 0; i < 6; i++) {

                                             trafficLightContext.change();

 

                                             try {

                                                            Thread.sleep(1000); // simulate delay

                                             } catch (InterruptedException e) {

                                                            e.printStackTrace();

                                             }

                              }

 

               }

}

 

o/p:

 

🔴 Red Light - STOP

🟢 Green Light - GO

🟡 Yellow Light - SLOW DOWN

🔴 Red Light - STOP

🟢 Green Light - GO

🟡 Yellow Light - SLOW DOWN

 

 

 

 

 

 

Iterator Design Pattern

 

                                                                  Iterator Design Pattern

The Iterator Design Pattern is one of the behavioral design patterns. It provides a standard way to traverse or iterate through a collection of objects (like lists, trees, or other data structures) without exposing the underlying representation of the collection.

Intent

• To access elements of a collection sequentially without exposing its underlying representation.

Key Components

1. Iterator (Interface)
• Defines the interface for accessing and traversing elements.
• Example methods: hasNext(), next()
2. Concrete Iterator
• Implements the Iterator interface.
• Keeps track of the current position in the traversal.
3. Aggregate / Collection (Interface)
• Defines the interface for creating an iterator object.
4. Concrete Aggregate
• Implements the Aggregate interface.
• Returns an instance of the concrete iterator.

---

📘 Advantages

• Hides the internal structure of collections.
• Provides a uniform interface for traversing different collection types.
• Supports multiple simultaneous iterations on the same collection.

⚠️ Disadvantages

• Adds complexity in custom collections.
• Might lead to overhead if used in simple structures.

---

✅ Java Built-in Support

Java provides built-in support for this pattern through the Iterator interface found in the java.util package.

Iterator<String> iterator = list.iterator();

while (iterator.hasNext()) {

    String element = iterator.next();

    System.out.println(element);

}

 

 

Example :

Step 1: Create the Iterator interface

package iteratordesignpattern;

 

public interface Iterator {

               boolean hasNext(); 

    Object next();

}

 

Step 2: Create the Container interface

 

package iteratordesignpattern;

 

public interface Container {

 

               Iterator getItertaor();

}

 

 

 

Step 3: Create NameRepository class

package iteratordesignpattern;

public class NameRepository implements Container {

               public String[] names = { "Govind", "Ballabh", "Khan", "Java", "Technology" };

 

               @Override

               public Iterator getItertaor() {

                              // TODO Auto-generated method stub

                               return new NameIterator();

               }

               private class NameIterator implements Iterator {

                              int index;

 

                              @Override

                              public boolean hasNext() {

                                             // TODO Auto-generated method stub

                                             return index < names.length;

                              }

 

                              @Override

                              public Object next() {

                                             if (this.hasNext()) {

                                                            return names[index++];

                                             }

                                             return null;

                              }

 

               }

 

}

 

Step 4: Test the Iterator

package iteratordesignpattern;

 

public class IteratorPatternDemo {

               public static void main(String[] args) {

                              NameRepository nameRepository = new NameRepository();

 

                              for (Iterator iterator = nameRepository.getItertaor(); iterator.hasNext();) {

          String name = (String)iterator.next();

          System.out.println(name);

                              }

               }

}

 

 

o/p:

Govind

Ballabh

Khan

Java

Technology

 

Example :2

 

package iteratordesignpattern;

 

public class Book {

 

               private String title;

               private String author;

 

               public Book(String title, String author) {

                              super();

                              this.title = title;

                              this.author = author;

               }

 

               public String getTitle() {

                              return title;

               }

 

               public void setTitle(String title) {

                              this.title = title;

               }

 

               public String getAuthor() {

                              return author;

               }

 

               public void setAuthor(String author) {

                              this.author = author;

               }

 

}

 

 

 

 

 

package iteratordesignpattern;

 

public interface Iterator {

               boolean hasNext(); 

    Object next();

}

 

 

 

package iteratordesignpattern;

 

public interface Container {

 

               Iterator getItertaor();

}

 

 

 

 

package iteratordesignpattern;

 

public class BookRepository implements Container {

 

               private int count = 0;

               private Book[] books;

 

               public BookRepository(int size) {

                              books = new Book[size];

               }

 

               public void addBook(Book book) {

                              if (count < books.length) {

                                             books[count] = book;

                                             count++;

                              }

               }

 

               @Override

               public Iterator getItertaor() {

                              return new BookIterator();

 

               }

 

               public class BookIterator implements Iterator {

                              private int index = 0;

 

                              @Override

                              public boolean hasNext() {

                                             // TODO Auto-generated method stub

                                             return index < count && books[index] != null;

                              }

 

                              @Override

                              public Object next() {

                                             if (this.hasNext()) {

                                                            return books[index++];

                                             }

                                             return null;

                              }

 

               }

 

}

 

 

package iteratordesignpattern;

 

public class BookIteratorDemo {

 

               public static void main(String[] args) {

                              BookRepository bookRepository = new BookRepository(5);

                              bookRepository.addBook(new Book("OS", "Galvin"));

                              bookRepository.addBook(new Book("Java", "Durga Sir"));

                              bookRepository.addBook(new Book("C++", "Yashwantkanetkar"));

 

                              Iterator iterator = bookRepository.getItertaor();

 

                              while (iterator.hasNext()) {

                                             Book book = (Book) iterator.next();

                                             System.out.println("Book: " + book.getTitle() + ", Author: " + book.getAuthor());

                              }

               }

}

 

 

 

o/p:

 

Book: OS, Author: Galvin

Book: Java, Author: Durga Sir

Book: C++, Author: Yashwantkanetkar