User Management System using Spring Boot and Thymeleaf

 To create a Spring Boot CRUD application using JPA, PostgreSQL, and Thymeleaf, follow the steps below. This example will demonstrate a simple User Management System where you can create, read, update, and delete users.

1. Set up Spring Boot Application with PostgreSQL

Step 1: Add Dependencies

In your pom.xml (for Maven), add the required dependencies for Spring Boot, JPA, PostgreSQL, and Thymeleaf:

<dependencies>
    <!-- Spring Boot Starter Web (includes REST, Spring MVC, etc.) -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    
    <!-- Spring Boot Starter Data JPA (for working with databases) -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    
    <!-- PostgreSQL Database Driver -->
    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
    </dependency>
    
    <!-- Thymeleaf Template Engine -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-thymeleaf</artifactId>
    </dependency>
    
    <!-- Spring Boot Starter for Testing -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

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Step 2: Configure PostgreSQL Database Connection

In the application.properties (or application.yml) file, configure the PostgreSQL connection settings:

# PostgreSQL database configuration
spring.datasource.url=jdbc:postgresql://localhost:5432/your_database_name
spring.datasource.username=your_database_user
spring.datasource.password=your_database_password
spring.datasource.driver-class-name=org.postgresql.Driver

# JPA Configuration
spring.jpa.hibernate.ddl-auto=update  # Automatically update DB schema
spring.jpa.database-platform=org.hibernate.dialect.PostgreSQLDialect

# Enable SQL logging
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true

Replace your_database_name, your_database_user, and your_database_password with your PostgreSQL credentials.

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2. Create the User Entity (Model)

User.java

package com.example.demo.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;
    private String email;

    // Getters and Setters
    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

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

• This entity represents a user with an id, name, and email.
• The @Entity annotation tells JPA that this is a JPA entity, and @Id marks the primary key field.
• The @GeneratedValue(strategy = GenerationType.IDENTITY) ensures that the id is automatically generated by the database.

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3. Create the Repository Interface

UserRepository.java

package com.example.demo.repository;

import com.example.demo.model.User;
import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User, Long> {
}

• This interface extends JpaRepository and provides CRUD operations for the User entity.

---

4. Create the Service Layer

UserService.java

package com.example.demo.service;

import com.example.demo.model.User;
import com.example.demo.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

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

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public List<User> getAllUsers() {
        return userRepository.findAll();
    }

    public Optional<User> getUserById(Long id) {
        return userRepository.findById(id);
    }

    public User createUser(User user) {
        return userRepository.save(user);
    }

    public User updateUser(User user) {
        return userRepository.save(user);
    }

    public void deleteUser(Long id) {
        userRepository.deleteById(id);
    }
}

• The UserService class acts as a service layer to handle the logic for CRUD operations.
• It uses the UserRepository to interact with the database.

---

5. Create the Controller

UserController.java

package com.example.demo.controller;

import com.example.demo.model.User;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.*;

@Controller
public class UserController {

    @Autowired
    private UserService userService;

    // Display the list of users
    @GetMapping("/users")
    public String getAllUsers(Model model) {
        model.addAttribute("users", userService.getAllUsers());
        return "user-list";
    }

    // Show form to create a new user
    @GetMapping("/user/new")
    public String showCreateUserForm(Model model) {
        model.addAttribute("user", new User());
        return "user-form";
    }

    // Create a new user
    @PostMapping("/user/save")
    public String saveUser(@ModelAttribute User user) {
        userService.createUser(user);
        return "redirect:/users";
    }

    // Show form to edit an existing user
    @GetMapping("/user/edit/{id}")
    public String showEditUserForm(@PathVariable("id") Long id, Model model) {
        User user = userService.getUserById(id).orElseThrow(() -> new IllegalArgumentException("Invalid user ID: " + id));
        model.addAttribute("user", user);
        return "user-form";
    }

    // Update an existing user
    @PostMapping("/user/update")
    public String updateUser(@ModelAttribute User user) {
        userService.updateUser(user);
        return "redirect:/users";
    }

    // Delete a user
    @GetMapping("/user/delete/{id}")
    public String deleteUser(@PathVariable("id") Long id) {
        userService.deleteUser(id);
        return "redirect:/users";
    }
}

• @GetMapping("/users"): Fetches all users from the database and displays them.
• @GetMapping("/user/new"): Displays a form to create a new user.
• @PostMapping("/user/save"): Saves the newly created user to the database.
• @GetMapping("/user/edit/{id}"): Displays the form to edit an existing user based on the id.
• @PostMapping("/user/update"): Updates the user in the database.
• @GetMapping("/user/delete/{id}"): Deletes the user by id.

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6. Create Thymeleaf Templates

user-list.html (To display the list of users)

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>User List</title>
</head>
<body>
    <h1>User List</h1>
    <a href="/user/new">Create New User</a>
    <table>
        <thead>
            <tr>
                <th>ID</th>
                <th>Name</th>
                <th>Email</th>
                <th>Actions</th>
            </tr>
        </thead>
        <tbody>
            <tr th:each="user : ${users}">
                <td th:text="${user.id}"></td>
                <td th:text="${user.name}"></td>
                <td th:text="${user.email}"></td>
                <td>
                    <a th:href="@{/user/edit/{id}(id=${user.id})}">Edit</a>
                    <a th:href="@{/user/delete/{id}(id=${user.id})}">Delete</a>
                </td>
            </tr>
        </tbody>
    </table>
</body>
</html>

user-form.html (Form for creating or editing a user)

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>User Form</title>
</head>
<body>
    <h1 th:text="${user.id == null ? 'Create' : 'Edit'} + ' User'"></h1>

    <form th:action="@{${user.id == null ? '/user/save' : '/user/update'}}" th:object="${user}" method="post">
        <label for="name">Name:</label>
        <input type="text" th:field="*{name}" id="name"/>
        <br/>
        <label for="email">Email:</label>
        <input type="text" th:field="*{email}" id="email"/>
        <br/>
        <button type="submit">Submit</button>
    </form>
</body>
</html>

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7. Run the Application

1. Start the Spring Boot application.
2. Access the application: Go to http://localhost:8080/users to view the list of users.
3. Use the "Create New User" link to add new users or edit existing ones.