Spring Boot and Thymeleaf Tutorial

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1- What is Thymeleaf?

Thymeleaf is a Java XML/XHTML/HTML5 Template Engine that can work both in web (Servlet-based) and non-web environments. It is better suited for serving XHTML/HTML5 at the view layer of MVC-based web applications, but it can process any XML file even in offline environments. It provides full Spring Framework integration.
The template file of Thymeleaf in essence are only a ordinary document file with the format of  XML/XHTML/HTML5. Thymeleaf Engine will read a template file and combine with Java objects to generate another document.
Thymeleaf can be used to replace JSP on the  View Layer of Web MVC application. Thymeleaf  is open source code software, licensed under the   Apache 2.0.
Below is the image of the application that we will perform in this lesson: 

2- Create application

On  Eclipse, select:
  • File/New/Other...
Enter:
  • Name: SpringBootThymeleaf
  • Group: org.o7planning
  • Artifact: SpringBootThymeleaf
  • Description: Spring Boot and Thymeleaf
  • Package: org.o7planning.thymeleaf
Select 2   Web and  Thymeleaf technologies.
Your Project has been created:

3- Thymeleaf Template

Thymeleaf Template is a template file. Its contents are in the XML/XHTML/HTML5 format. We will create 3 files and place it in the  src/main/resources/templates ​​​​​​​folder:
index.html
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8" />
      <title>Welcome</title>
      <link rel="stylesheet" type="text/css" th:href="@{/css/style.css}"/>
   </head>
   <body>
      <h1>Welcome</h1>
      <h2 th:utext="${message}">..!..</h2>
      
      <!--  
      
         In Thymeleaf the equivalent of
         JSP's ${pageContext.request.contextPath}/edit.html
         would be @{/edit.html}
         
         -->
         
      <a th:href="@{/personList}">Person List</a>  
      
   </body>
   
</html>
 
personList.html
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8" />
      <title>Person List</title>
      <link rel="stylesheet" type="text/css" th:href="@{/css/style.css}"/>
   </head>
   <body>
      <h1>Person List</h1>
      <a href="addPerson">Add Person</a>
      <br/><br/>
      <div>
         <table border="1">
            <tr>
               <th>First Name</th>
               <th>Last Name</th>
            </tr>
            <tr th:each ="person : ${persons}">
               <td th:utext="${person.firstName}">...</td>
               <td th:utext="${person.lastName}">...</td>
            </tr>
         </table>
      </div>
   </body>
</html>
 
addPerson.html
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8" />
      <title>Add Person</title>
      <link rel="stylesheet" type="text/css" th:href="@{/css/style.css}"/>
   </head>
   <body>
      <h1>Create a Person:</h1>
      
      <!--  
         In Thymeleaf the equivalent of
         JSP's ${pageContext.request.contextPath}/edit.html
         would be @{/edit.html}         
         -->
         
      <form th:action="@{/addPerson}"
         th:object="${personForm}" method="POST">
         First Name:
         <input type="text" th:field="*{firstName}" />    
         <br/>
         Last Name:
         <input type="text" th:field="*{lastName}" />     
         <br/>
         <input type="submit" value="Create" />
      </form>
      
      <br/>
      
      <!-- Check if errorMessage is not null and not empty -->
      
      <div th:if="${errorMessage}" th:utext="${errorMessage}"
         style="color:red;font-style:italic;">
         ...
      </div>
      
   </body>
</html>
I have created 3 HTML files above. The above HTML files need to be appropriate to the standards of XML. All tags must have open and close, for example: 
<div>A div tag</div>

<br />

<meta charset="UTF-8" />
All  HTML files need declaring use of Thymeleaf Namespace:
<!-- Thymeleaf Namespace -->

<html xmlns:th="http://www.thymeleaf.org">
In template files, there are  Thymeleaf Markers (markers of Thymeleaf) which are  instructions helping Thymeleaf Engine process data.
Thymeleaf Engine analyses template files and combines them with Java data to generate a new document.
Below are examples to use the  Context-Path in the  Thymeleaf:
<!-- Example 1:  -->

<a th:href="@{/mypath/abc.html}">A Link</a>

Output: ==>

<a href="/my-context-path/mypath/abc.html">A Link</a>


<!-- Example 2:  -->

<form th:action="@{/mypath/abc.html}"
          th:object="${personForm}" method="POST">

Output: ==>

<form action="/my-context-path/mypath/abc.html"  method="POST">
 

4- Static Resource & Properties File

For Static Resources, for example, css, javascript, image files,.. you need to put them into src/main/resources/static folder or its subfolders.
style.css
h1 {
    color:#0000FF;
}

h2 {
    color:#FF0000;
}

table {
    border-collapse: collapse;
}

table th, table td {
    padding: 5px;
}
application.properties

welcome.message=Hello Thymeleaf
error.message=First Name & Last Name is required!

5- Model, Form, Controller classes

Person.java
package org.o7planning.thymeleaf.model;

public class Person {

    private String firstName;
    private String lastName;

    public Person() {

    }

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

    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;
    }

}
PersonForm class  represents for the data of   FORM when you create a new  Person on  addPerson page..
PersonForm.java
package org.o7planning.thymeleaf.form;
 

public class PersonForm {

    private String firstName;
    private String lastName;

    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;
    }
    
}
MainController is a controller class. It processes a user's requests and controls the flow of the application.
MainController.java
package org.o7planning.thymeleaf.controller;

import java.util.ArrayList;
import java.util.List;

import org.o7planning.thymeleaf.form.PersonForm;
import org.o7planning.thymeleaf.model.Person;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class MainController {

	private static List<Person> persons = new ArrayList<Person>();

	static {
		persons.add(new Person("Bill", "Gates"));
		persons.add(new Person("Steve", "Jobs"));
	}

	// Inject via application.properties
	@Value("${welcome.message}")
	private String message;

	@Value("${error.message}")
	private String errorMessage;

	@RequestMapping(value = { "/", "/index" }, method = RequestMethod.GET)
	public String index(Model model) {

		model.addAttribute("message", message);

		return "index";
	}

	@RequestMapping(value = { "/personList" }, method = RequestMethod.GET)
	public String personList(Model model) {

		model.addAttribute("persons", persons);

		return "personList";
	}

	@RequestMapping(value = { "/addPerson" }, method = RequestMethod.GET)
	public String showAddPersonPage(Model model) {

		PersonForm personForm = new PersonForm();
		model.addAttribute("personForm", personForm);

		return "addPerson";
	}

	@RequestMapping(value = { "/addPerson" }, method = RequestMethod.POST)
	public String savePerson(Model model, //
			@ModelAttribute("personForm") PersonForm personForm) {

		String firstName = personForm.getFirstName();
		String lastName = personForm.getLastName();

		if (firstName != null && firstName.length() > 0 //
				&& lastName != null && lastName.length() > 0) {
			Person newPerson = new Person(firstName, lastName);
			persons.add(newPerson);

			return "redirect:/personList";
		}

		model.addAttribute("errorMessage", errorMessage);
		return "addPerson";
	}

}

6- Run the application

To run the application, right click on Project and select:
  • Run As/Spring Boot App.
The application has been deployed on an Embedded Web Server.
Run the following  URL on the browser:

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