Java Jinjava

last modified January 27, 2024

Java Jinjava tutorial shows how to create templates in Java with Jinjava.

A template engine is a library designed to combine templates with a data to produce documents. Template engines are used to generate large amounts of emails, in source code preprocessing, or to produce dynamic HTML pages.

A template consists of static data and dynamic regions. The dynamic regions are later replaced with data. The rendering function later combines the templates with data. A template engine is used to combine templates with a data model to produce documents.

The Jinjava library is a Java template engine inspired by Python's jinja template engine.

Jinjava uses various delimiters in template string:

• {% %} - statements
• {{ }} - expressions to print to the template output
• {# #} - comments which are not included in the template output
• # ## - line statements

The documents are rendered with the render method. The method accepts the template string and the context, which contains the data.

<dependency>
    <groupId>com.hubspot.jinjava</groupId>
    <artifactId>jinjava</artifactId>
    <version>2.6.0</version>
</dependency>

We use the jinjava dependency.

Jinjava simple example

The following is a Jinjava simple example.

package com.zetcode;

import com.google.common.collect.Maps;
import com.hubspot.jinjava.Jinjava;

import java.util.Map;

public class Simple {

    public static void main(String[] args)  {

        var jnj = new Jinjava();

        Map<String, Object> context = Maps.newHashMap();
        context.put("name", "John Doe");

        String res = jnj.render("Hello {{ name }}!", context);
        System.out.println(res);
    }
}

We print a simple message.

var jnj = new Jinjava();

A Jinjava object is created.

Map<String, Object> context = Maps.newHashMap();
context.put("name", "John Doe");

We create a context; it contains the data passed to the template engine.

String res = jnj.render("Hello {{ name }}!", context);

We render the final ouput with render method. It accepts a template string and the context object.

Jinjava template from file

In the next example, we read the template from the file.

{{ name }} is a {{ occupation }}.

This is the template file.

package com.zetcode;

import com.google.common.collect.Maps;
import com.hubspot.jinjava.Jinjava;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Map;

public class FromFile {

    public static void main(String[] args) throws IOException {

        var jnj = new Jinjava();

        Map<String, Object> context = Maps.newHashMap();
        context.put("name", "John Doe");
        context.put("occupation", "gardener");

        String fileName = "src/main/resources/message.jinja";
        String template = Files.readString(Paths.get(fileName));

        String res = jnj.render(template, context);
        System.out.println(res);
    }
}

We read the template file with Files.readString.

Map<String, Object> context = Maps.newHashMap();
context.put("name", "John Doe");
context.put("occupation", "gardener");

We pass two variables in the context object.

Jinjava for directive

The for directive is used to iterate over a data collection in a template.

{% for word in words -%}
    {{ word }}
{% endfor %}

In the template, we use the for directive to go through the elements of the words data structure. The - character strips whitespace characters.

package com.zetcode;

import com.google.common.collect.Maps;
import com.hubspot.jinjava.Jinjava;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.Map;

public class Words {

    public static void main(String[] args) throws IOException {

        var jnj = new Jinjava();

        var words = List.of("sky", "rock", "small", "bed", "food", "warm");

        Map<String, Object> context = Maps.newHashMap();
        context.put("words", words);

        String fileName = "src/main/resources/words.jinja";
        String template = Files.readString(Paths.get(fileName));

        String res = jnj.render(template, context);
        System.out.println(res);
    }
}

In the program, we pass an list of words to the template engine. We get a list of words as the output.

Jinjava filter

A filter can be applied to data to modify them. Filters are applied after the | character.

{% for word in words -%}
    {{ word }} has {{ word | length }} characters
{% endfor %}

The length filter returns the size of the string.

package com.zetcode;

import com.google.common.collect.Maps;
import com.hubspot.jinjava.Jinjava;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.Map;

public class WordsLen {

    public static void main(String[] args) throws IOException {

        var jnj = new Jinjava();

        var words = List.of("sky", "rock", "small", "bed", "food", "warm");

        Map<String, Object> context = Maps.newHashMap();
        context.put("words", words);

        String fileName = "src/main/resources/words.jinja";
        String template = Files.readString(Paths.get(fileName));

        String res = jnj.render(template, context);
        System.out.println(res);
    }
}

In the program, we pass a list of words to the template. We print each word and its size.

Jinjava if condition

Conditions can be created with if/endif directives.

{%- for task in tasks -%}
    {% if task.done %}
        {{ task.title }}
    {% endif %}
{%- endfor %}

In the template file, we use the if directive to output only tasks that are finished.

package com.zetcode;

public class Task {

    private String title;
    private boolean done;

    public Task(String title, boolean done) {
        this.title = title;
        this.done = done;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public boolean isDone() {
        return done;
    }

    public void setDone(boolean done) {
        this.done = done;
    }
}

This is the Task class.

package com.zetcode;

import com.google.common.collect.Maps;
import com.hubspot.jinjava.Jinjava;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.Map;

public class Tasks {

    public static void main(String[] args) throws IOException {

        var jnj = new Jinjava();

        var tasks = List.of(new Task("Task 1", true),
                new Task("Task 2", true), new Task("Task 3", false),
                new Task("Task 4", true), new Task("Task 5", false));

        Map<String, Object> context = Maps.newHashMap();
        context.put("tasks", tasks);

        String fileName = "src/main/resources/tasks.jinja";
        String template = Files.readString(Paths.get(fileName));

        String res = jnj.render(template, context);
        System.out.println(res);
    }
}

We generate on output from a list of tasks. In the output we include only finished tasks.

Source

Jinjava Github page

In this article we have covered the Jinjava template engine.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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