FreeMarker: Hello World Application

In this post, I am going to create 'user.ftl' file which has user template data and merge the template with fields from user object using Freemarker.

 

Step 1: Create user.ftl file under src/main/resources/templates folder.

 

user.ftl

name: ${user.name}
age: ${user.age}
city: ${user.city}

Step 2: Define a model class that holds user information.

 

User.java

package com.sample.app.templates.model;

public class User {

	private String name;
	private int age;
	private String city;

	public User(String name, int age, String city) {
		super();
		this.name = name;
		this.age = age;
		this.city = city;
	}

	public String getName() {
		return name;
	}

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

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String city) {
		this.city = city;
	}

}

Step 3: Create 'FreeMarkerUtil' class that takes a model object and freemarker template file as input and merge them.

 

FreeMarkerUtil.java

package com.sample.app.util;

import java.io.StringWriter;
import java.util.Locale;

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateExceptionHandler;

public class FreeMarkerUtil {

	private static final Configuration FREE_MARKER_CONFIGURATION = new Configuration(Configuration.VERSION_2_3_30);

	static {
		FREE_MARKER_CONFIGURATION.setClassForTemplateLoading(FreeMarkerUtil.class, "/templates/");
		FREE_MARKER_CONFIGURATION.setDefaultEncoding("UTF-8");
		FREE_MARKER_CONFIGURATION.setLocale(Locale.US);
		FREE_MARKER_CONFIGURATION.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);
	}

	public static StringWriter mergeModelAndTemplate(Object modelObject, String ftlFile) throws Exception {
		StringWriter stringWriter = new StringWriter();

		Template template = FREE_MARKER_CONFIGURATION.getTemplate(ftlFile);

		template.process(modelObject, stringWriter);

		return stringWriter;
	}

}

Step 4: Define UserPopulator class like below.

 

UserPopulator.java

package com.sample.app;

import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;

import com.sample.app.templates.model.User;
import com.sample.app.util.FreeMarkerUtil;

public class UserPopulator {
	public static void main(String args[]) throws Exception {
		Map<String, Object> modelObject = new HashMap<String, Object>();

		modelObject.put("user", new User("Krishna", 31, "Bangalore"));

		StringWriter stringWriter = FreeMarkerUtil.mergeModelAndTemplate(modelObject, "user.ftl");

		System.out.println(stringWriter);
	}

}

Run UserPopulator, you will see below messages in the console.

name: Krishna
age: 31
city: Bangalore

As you see the output, placeholders ${user.name}, ${user.age}, and ${user.city} are populated with actual values from the model object.

 

You can visualize this data model as a tree kind of structure.

(root)
  |
  +- user 
      |
      +- name
      +- age
      +- city

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