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‎pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>3.4.0</version>
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<relativePath/> <!-- lookup parent from repository -->
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</parent>
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<groupId>com.javatechie</groupId>
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<artifactId>locking-demo</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<name>locking-demo</name>
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<description>Demo project for Spring Boot</description>
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<properties>
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<java.version>21</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-data-jpa</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springdoc</groupId>
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<artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
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<version>2.0.4</version>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-web</artifactId>
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</dependency>
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<dependency>
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<groupId>com.mysql</groupId>
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<artifactId>mysql-connector-j</artifactId>
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<scope>runtime</scope>
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</dependency>
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<dependency>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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<optional>true</optional>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-test</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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<configuration>
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<excludes>
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<exclude>
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<groupId>org.projectlombok</groupId>
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<artifactId>lombok</artifactId>
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</exclude>
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</excludes>
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</configuration>
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</plugin>
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</plugins>
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</build>
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</project>

‎src/main/java/com/javatechie/LockingDemoApplication.java

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package com.javatechie;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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@SpringBootApplication
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public class LockingDemoApplication {
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public static void main(String[] args) {
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SpringApplication.run(LockingDemoApplication.class, args);
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}
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}

‎src/main/java/com/javatechie/controller/BookingTestController.java

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package com.javatechie.controller;
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import com.javatechie.service.OptimisticSeatBookingTestService;
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import com.javatechie.service.PessimisticSeatBookingTestService;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.web.bind.annotation.*;
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@RestController
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@RequestMapping("/booking")
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public class BookingTestController {
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@Autowired
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private OptimisticSeatBookingTestService optimisticSeatBookingTestService;
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@Autowired
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private PessimisticSeatBookingTestService pessimisticSeatBookingTestService;
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@GetMapping("/optimistic/{seatId}")
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public String testOptimistic(@PathVariable Long seatId) throws InterruptedException {
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optimisticSeatBookingTestService.testOptimisticLocking(seatId);
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return "Optimistic locking test started! Check logs for results.";
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}
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@GetMapping("/pessimistic/{seatId}")
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public String testPessimistic(@PathVariable Long seatId) throws InterruptedException {
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pessimisticSeatBookingTestService.testPessimisticLocking(seatId);
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return "Pessimistic locking test started! Check logs for results.";
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}
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}

‎src/main/java/com/javatechie/entity/Seat.java

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package com.javatechie.entity;
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import jakarta.persistence.*;
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import lombok.Data;
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@Entity
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@Data
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public class Seat {
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@Id
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@GeneratedValue(strategy = GenerationType.IDENTITY)
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private Long id;
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private String movieName;
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private boolean booked;
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@Version
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private int version;
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}

‎src/main/java/com/javatechie/repository/SeatRepository.java

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package com.javatechie.repository;
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import com.javatechie.entity.Seat;
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import jakarta.persistence.LockModeType;
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import org.springframework.data.jpa.repository.JpaRepository;
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import org.springframework.data.jpa.repository.Lock;
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import org.springframework.data.jpa.repository.Query;
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public interface SeatRepository extends JpaRepository<Seat, Long> {
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@Lock(LockModeType.PESSIMISTIC_WRITE)
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@Query("SELECT s FROM Seat s WHERE s.id= :seatId")
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Seat findByIdAndLock(Long seatId);
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}

‎src/main/java/com/javatechie/service/MovieTicketBookingService.java

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package com.javatechie.service;
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import com.javatechie.entity.Seat;
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import com.javatechie.repository.SeatRepository;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.stereotype.Service;
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import org.springframework.transaction.annotation.Transactional;
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@Service
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public class MovieTicketBookingService {
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@Autowired
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private SeatRepository seatRepository;
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@Transactional
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public Seat bookSeat(Long seatId) {
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//fetch the existing seat by id
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Seat seat = seatRepository.findById(seatId)
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.orElseThrow(() -> new RuntimeException("Seat not found with id " + seatId));
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System.out.println(Thread.currentThread().getName() + " fetched seat with version " + seat.getVersion());
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if (seat.isBooked()) {
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throw new RuntimeException("Seat already booked !");
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}
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//booking seat
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seat.setBooked(true);
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//version check will occurs here
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return seatRepository.save(seat);
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}
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@Transactional
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public void bookSeatWithPessimistic(Long seatId) {
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System.out.println(Thread.currentThread().getName() + " is attempting to fetch the seat");
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//fetch the seat with Pessimistic lock
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Seat seat = seatRepository.findByIdAndLock(seatId);
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System.out.println(Thread.currentThread().getName() + " acquired the lock for seat id " + seatId);
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if (seat.isBooked()) {
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System.out.println(Thread.currentThread().getName() + " failed Seat Id " + seatId + " is already booked ");
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throw new RuntimeException("Seat already booked !");
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}
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//booking seat
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System.out.println(Thread.currentThread().getName() + " booking the seat " + seatId);
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seat.setBooked(true);
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//version check will occurs here
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seatRepository.save(seat);
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System.out.println(Thread.currentThread().getName() + " successfully book the seat with ID " + seatId);
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}
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}

‎src/main/java/com/javatechie/service/OptimisticSeatBookingTestService.java

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package com.javatechie.service;
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import com.javatechie.entity.Seat;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.stereotype.Service;
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@Service
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public class OptimisticSeatBookingTestService {
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@Autowired
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private MovieTicketBookingService movieTicketBookingService;
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public void testOptimisticLocking(Long seatId) throws InterruptedException {
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// 2 thread
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Thread th1 = new Thread(() -> {
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try {
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System.out.println(Thread.currentThread().getName() + " is attempting to book the seat");
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Seat seat = movieTicketBookingService.bookSeat(seatId);
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System.out.println(Thread.currentThread().getName() + " successfully booked the seat with version " + seat.getVersion());
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} catch (Exception ex) {
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System.out.println(Thread.currentThread().getName() + " failed : " + ex.getMessage());
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}
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});
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Thread th2 = new Thread(() -> {
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try {
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System.out.println(Thread.currentThread().getName() + " is attempting to book the seat");
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Seat seat = movieTicketBookingService.bookSeat(seatId);
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System.out.println(Thread.currentThread().getName() + " successfully booked the seat with version " + seat.getVersion());
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} catch (Exception ex) {
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System.out.println(Thread.currentThread().getName() + " failed : " + ex.getMessage());
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}
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});
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th1.start();
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th2.start();
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th1.join();
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th2.join();
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}
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}

‎src/main/java/com/javatechie/service/PessimisticSeatBookingTestService.java

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package com.javatechie.service;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.stereotype.Service;
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@Service
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public class PessimisticSeatBookingTestService {
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@Autowired
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private MovieTicketBookingService movieTicketBookingService;
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public void testPessimisticLocking(Long seatId) throws InterruptedException {
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Thread thread1 = new Thread(() -> {
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try {
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movieTicketBookingService.bookSeatWithPessimistic(seatId);
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} catch (RuntimeException e) {
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System.out.println(Thread.currentThread().getName() + " failed: " + e.getMessage());
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}
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});
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Thread thread2 = new Thread(() -> {
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try {
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movieTicketBookingService.bookSeatWithPessimistic(seatId);
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} catch (RuntimeException e) {
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System.out.println(Thread.currentThread().getName() + " failed: " + e.getMessage());
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}
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});
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thread1.start();
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thread2.start();
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thread1.join();
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thread2.join();
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}
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}

‎src/main/resources/application.properties

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spring.application.name=locking-demo
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server.port=9191
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#DataBase PROPERTIES
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spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
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spring.datasource.url = jdbc:mysql://localhost:3306/javatechie
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spring.datasource.username = root
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spring.datasource.password = Password
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#spring.jpa.show-sql = true
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spring.jpa.hibernate.ddl-auto = update
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spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQLDialect
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spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
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‎src/test/java/com/javatechie/LockingDemoApplicationTests.java

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package com.javatechie;
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import org.junit.jupiter.api.Test;
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import org.springframework.boot.test.context.SpringBootTest;
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@SpringBootTest
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class LockingDemoApplicationTests {
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@Test
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void contextLoads() {
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}
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}

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