JStachio Filters: Avoiding Repetitive Lambdas

Are you tired of repeatedly writing @JStacheLambdas in your JStachio templates? Do you wish there was a more streamlined way to apply transformations, similar to the filters found in Trimou or PebbleTemplate? This article explores the possibility of implementing a simplified filter mechanism in JStachio and offers alternative approaches to reduce boilerplate code.

The Quest for JStachio Filters

JStachio, the Big Beautiful Template Engine, offers a powerful and type-safe approach to templating in Java. However, one common pain point arises when you need to apply the same transformation logic across multiple templates. This often leads to the repetitive use of @JStacheLambdas, which can clutter your code and make it harder to maintain. In templating engines like Trimou and Pebble, filters provide a clean way to encapsulate such transformations and reuse them throughout your templates. The question is, can we achieve a similar level of convenience in JStachio?

Understanding the Need for Filters

Before diving into potential solutions, let's clarify what we mean by "filters" in the context of templating. A filter is essentially a function that takes an input value and returns a modified output value. This could involve formatting dates, escaping HTML, truncating strings, or performing any other transformation that you need to apply consistently across your templates. Without filters, you'd have to implement these transformations directly within your templates, leading to code duplication and reduced maintainability. JStachio's @JStacheLambdas provide a mechanism for defining such transformations, but their repetitive use can become cumbersome.

Exploring Alternatives to Repetitive @JStacheLambdas

While JStachio doesn't have built-in filters in the traditional sense, there are several ways to achieve a similar result and reduce the amount of boilerplate code in your templates. Here are a few approaches you can consider:

• Centralized Lambda Definitions: Instead of defining @JStacheLambdas directly within each component, you can create a central class or interface to house your lambda definitions. This promotes code reuse and makes it easier to manage your transformations. For example, you could define a TemplateHelpers class with static methods annotated with @JStacheLambda. These methods can then be referenced from your JStachio components.
• Custom Data Types with Formatting Logic: Another approach is to encapsulate the data and its formatting logic within a custom data type. This allows you to define the transformation once, within the data type, and then reuse it across multiple templates. For instance, if you have a Product class with a price field, you could add a formattedPrice() method that applies the necessary currency formatting. This method can then be directly referenced in your templates.
• JStachio Formatters: JStachio formatters offer a way to customize the output of your data. By implementing a custom formatter, you can control how specific data types are rendered in your templates. This is particularly useful for applying consistent formatting rules across your application. Create a class that implements Formatter<T>. Then register the class by annotating it with @JStacheFormatter. This formatter would need to be registered with the JStachio runtime.

Example: Centralized Lambda Definitions

Let's illustrate the centralized lambda definition approach with a simple example. Suppose you need to escape HTML in multiple templates. Instead of defining the escaping logic in each component, you can create a TemplateHelpers class like this:

import org.jstachio.jstache.JStacheLambda;

public class TemplateHelpers {

    @JStacheLambda
    public static String escapeHtml(String input) {
        // Implement HTML escaping logic here
        return input.replace("<", "&lt;").replace(">", "&gt;");
    }
}

Then, in your JStachio component, you can reference this lambda:

import org.jstachio.jstache.JStache;

@JStache(template = "Hello {{escapeHtml name }}!")
public class MyComponent {
    String name = "<b>World</b>";
}

Example: Custom Data Types with Formatting Logic

Consider formatting a date. Instead of formatting date directly within the template we can add a method to the class of the data we are rendering that formats the date.

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class Event {

	LocalDate date;

	public String getFormattedDate() {
		DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMMM d, yyyy");
		return date.format(formatter);
	}
}

Example: JStachio Formatters

Here is an example of using the JStachio formatter.

import org.jstachio.spi.Formatter;
import org.jstachio.jstache.JStacheFormatter;

@JStacheFormatter(String.class)
class MyStringFormatter implements Formatter<String> {

	@Override
	public String format(String value) {
		return value.toUpperCase();
	}
	
}

Choosing the Right Approach

The best approach depends on the specific requirements of your application. If you have a small number of simple transformations, centralized lambda definitions might be sufficient. If you need to apply complex formatting logic or want to encapsulate data and its presentation, custom data types might be a better choice. JStachio formatters provide more custom control.

Addressing the Root Cause: Template Design

While the techniques discussed above can help reduce boilerplate, it's also worth considering whether the need for filters stems from the way your templates are designed. Sometimes, a complex template structure can lead to the need for numerous transformations. By simplifying your templates and breaking them down into smaller, more manageable components, you might be able to reduce the overall need for filters.

Component-Based Templating

JStachio encourages a component-based approach to templating. By breaking your UI into reusable components, you can encapsulate logic and presentation within each component. This promotes modularity and reduces the complexity of individual templates. When designing your templates, think about how you can break them down into smaller, self-contained units. This can often lead to a more elegant and maintainable solution than relying heavily on filters.

Leveraging Inheritance and Composition

JStachio's support for inheritance and composition allows you to create more flexible and reusable templates. You can define base templates with common elements and then extend them with specific content for different scenarios. You can also compose templates by including other templates within them. These techniques can help you avoid code duplication and reduce the need for filters by reusing existing template logic.

Conclusion: Embracing JStachio's Strengths

While JStachio may not have traditional filters like Trimou or PebbleTemplate, it offers a range of powerful features that can help you achieve similar results with less boilerplate. By centralizing lambda definitions, using custom data types with formatting logic, and embracing a component-based approach to templating, you can create clean, maintainable, and efficient JStachio templates. Remember to focus on clear template design and leverage JStachio's strengths to create a Big Beautiful Template Engine experience. Consider these alternatives to achieve similar functionality and improve your JStachio development workflow.

For more information on JStachio and its features, refer to the official JStachio Documentation.