ZetCode

Java Jinjava

last modified July 15, 2022

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:

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.

com/zetcode/Simple.java
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.

src/main/resources/message.jinja
{{ name }} is a {{ occupation }}.

This is the template file.

com/zetcode/FromFile.java
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.

src/main/resources/words.jinja
{% 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.

com/zetcode/Words.java
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 tempate 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.

src/main/resources/words.jinja
{% for word in words -%}
    {{ word }} has {{ word | length }} characters
{% endfor %}

The length filter returns the size of the string.

com/zetcode/WordsLen.java
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.

src/main/resources/tasks.jinja
{%- 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.

com/zetcode/Task.java
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.

com/zetcode/Tasks.java
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.

In this article, we have covered the Jinjava template engine.

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