Spring Boot with FreeMarker

FreeMarker is a powerful Java-based template engine used to generate dynamic web pages. This guide covers the key concepts and steps for using FreeMarker with Spring Boot, including setting up dependencies, creating controllers, designing FreeMarker templates, and rendering views.

Key Concepts of Spring Boot with FreeMarker

Template Engine: FreeMarker is a template engine for generating dynamic web content.
Template Resolver: FreeMarker uses template resolvers to find and process templates.
Context: A data container used for passing variables to templates.
Expressions: FreeMarker provides various expressions for variable substitution, text, and URL creation.

Setting Up Dependencies

Include the Spring Boot Starter FreeMarker dependency in your pom.xml file:

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

Creating a Controller

Create a controller to handle web requests and return FreeMarker templates:

Example: HomeController.java

// HomeController.java
package com.example.demo.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class HomeController {

    @GetMapping("/")
    public String home(Model model) {
        model.addAttribute("message", "Hello, FreeMarker with Spring Boot!");
        return "index";
    }
}

Designing FreeMarker Templates

Create FreeMarker templates to render HTML views. Place your templates in the src/main/resources/templates directory:

Example: index.ftl

<!DOCTYPE html>
<html>
<head>
    <title>Spring Boot with FreeMarker</title>
</head>
<body>
    <h1>Welcome to Spring Boot with FreeMarker</h1>
    <p>Message: ${message}</p>
</body>
</html>

Rendering Views

When the controller method returns a view name, Spring Boot will resolve the view using FreeMarker and render the template:

// HomeController.java
package com.example.demo.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class HomeController {

    @GetMapping("/")
    public String home(Model model) {
        model.addAttribute("message", "Hello, FreeMarker with Spring Boot!");
        return "index";
    }
}

Using FreeMarker Expressions

FreeMarker provides various expressions for variable substitution, text, and URL creation:

Variable Expressions: ${...}
Directives: <#...>...</#...>
Built-ins: Functions for manipulating variables, such as ?upper_case
Functions: Built-in and custom functions for complex operations

Example: Using FreeMarker Expressions

<!DOCTYPE html>
<html>
<head>
    <title>FreeMarker Expressions</title>
</head>
<body>
    <h1>FreeMarker Expressions</h1>
    <p>Variable Expression: ${message}</p>
    <p>Upper Case: ${message?upper_case}</p>
    <p>Date: ${.now}</p>
</body>
</html>

Handling Form Submissions

FreeMarker provides support for handling form submissions:

Example: UserController.java

// UserController.java
package com.example.demo.controller;

import com.example.demo.model.User;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;

@Controller
public class UserController {

    @GetMapping("/user")
    public String showForm(Model model) {
        model.addAttribute("user", new User());
        return "userForm";
    }

    @PostMapping("/user")
    public String submitForm(User user, Model model) {
        model.addAttribute("user", user);
        return "userResult";
    }
}

Example: userForm.ftl

<!DOCTYPE html>
<html>
<head>
    <title>User Form</title>
</head>
<body>
    <h1>User Form</h1>
    <form action="/user" method="post">
        <label>Name: <input type="text" name="name" /></label><br/>
        <label>Email: <input type="email" name="email" /></label><br/>
        <button type="submit">Submit</button>
    </form>
</body>
</html>

Example: userResult.ftl

<!DOCTYPE html>
<html>
<head>
    <title>User Result</title>
</head>
<body>
    <h1>User Result</h1>
    <p>Name: ${user.name}</p>
    <p>Email: ${user.email}</p>
</body>
</html>

Key Points

Template Engine: FreeMarker is a template engine for generating dynamic web content.
Template Resolver: FreeMarker uses template resolvers to find and process templates.
Context: A data container used for passing variables to templates.
Expressions: FreeMarker provides various expressions for variable substitution, text, and URL creation.
Include the Spring Boot Starter FreeMarker dependency in your pom.xml file.
Create controllers to handle web requests and return FreeMarker templates.
Design FreeMarker templates to render HTML views and place them in the src/main/resources/templates directory.
Use FreeMarker expressions for variable substitution, text, and URL creation in templates.
Handle form submissions using FreeMarker and Spring Boot.

Conclusion

Spring Boot and FreeMarker provide a powerful combination for building dynamic web applications. By understanding and using the capabilities of FreeMarker with Spring Boot, developers can create flexible and maintainable web applications with ease. Happy coding!