Getting Started with Compile-Time Templates With Spring

Getting Started with Compile-Time Templates With Spring

Often, runtime template parsing adds overhead and risk to applications, potentially failing when encountering malformed templates or unexpected data. Libraries like JStachio, Rocker, JTE and ManTL compile templates to Java classes at build time, enabling compiler safety and often reflection-free execution.

Why This Matters

Traditional runtime templating introduces performance overhead and potential runtime failures due to parsing and data binding. Compile-time templating addresses these issues by shifting the processing to build time, catching errors early and improving efficiency; a runtime templating failure in a high-volume e-commerce system could cause significant revenue loss.

Key Insights

• JStachio is reflection-free: Facilitates use in environments like GraalVM native image builds.
• Rocker offers a custom template language: Provides flexibility but relies on reflection.
• JTE is reflection-free and Spring Boot compatible: Simplifies integration with Spring applications.

Working Example

// JStachio Example
@JStache(path = "templates/jstachio.mustache")
public record JStachioModel(String name) { }

// Rendering the template
JStachioModel model = new JStachioModel("Baeldung");
StringBuilder sb = new StringBuilder();
JStachioModelRenderer.of().execute(model, sb);

Practical Applications

• Stripe: Uses compile-time templates for generating dynamic email content and agreement terms.
• Pitfall: Over-reliance on complex template logic can lead to hard-to-debug issues; favor simpler templates and delegate complex logic to Java code.

References:

• https://www.baeldung.com/spring-compile-time-templates