Groovy Guide — Templates: Generating Text and HTML

DodaTech Updated 2026-06-28 4 min read

In this tutorial, you will learn about Groovy Guide. We cover key concepts, practical examples, and best practices to help you master this topic.

Groovy templates generate dynamic text content using template files with embedded expressions, supporting loops, conditionals, layouts, and reusable components for web pages and reports.

What You'll Learn

SimpleTemplateEngine
Template variables
Loops and conditionals
Layouts and includes
Custom template engines

Why It Matters

Templates separate presentation from logic, making content generation maintainable. Durga Antivirus Pro uses templates for report generation.

Real-World Use

HTML email generation, web page rendering, Code Generation, and report formatting.

flowchart LR
    A["Templates"] --> B["SimpleTemplate"]
    B --> C["Variables"]
    C --> D["Loops"]
    D --> E["Layouts"]
    A:::current --> B
    style A fill:#2563eb,stroke:#2563eb,color:#fff
    style B fill:#dbeafe,stroke:#2563eb,color:#1e40af
    style C fill:#dbeafe,stroke:#2563eb,color:#1e40af
    style D fill:#dbeafe,stroke:#2563eb,color:#1e40af
    style E fill:#f1f5f9,stroke:#94a3b8,color:#64748b

SimpleTemplateEngine

import groovy.text.SimpleTemplateEngine

def engine = new SimpleTemplateEngine()
def template = engine.createTemplate('Hello, ${name}!')

def binding = [name: "Alice"]
def output = template.make(binding)

println output  // "Hello, Alice!"

Template Files

// template.groovy
// Hello, ${name}!
// You are ${age} years old.

def engine = new SimpleTemplateEngine()
def template = engine.createTemplate(new File("template.groovy"))

def output = template.make(name: "Alice", age: 30)
println output

Loops in Templates

// template.groovy
// <ul>
// <% items.each { item -> %>
//   <li>${item}</li>
// <% } %>
// </ul>

def template = engine.createTemplate(new File("template.groovy"))
def output = template.make(items: ["Apple", "Banana", "Cherry"])

// Output:
// <ul>
//   <li>Apple</li>
//   <li>Banana</li>
//   <li>Cherry</li>
// </ul>

Conditionals

// template.groovy
// <% if (user.admin) { %>
//   <span class="admin">Admin</span>
// <% } else { %>
//   <span class="user">User</span>
// <% } %>

def template = engine.createTemplate(new File("template.groovy"))
println template.make(user: [name: "Alice", admin: true])

StreamingTemplateEngine

import groovy.text.StreamingTemplateEngine

// More efficient for large templates
def engine = new StreamingTemplateEngine()
def template = engine.createTemplate("Hello, \${name}!")
def output = template.make([:], name: "Alice")

Layout Template

// layout.groovy
// <html>
// <head><title>${title}</title></head>
// <body>
//   <h1>${title}</h1>
//   ${content}
// </body>
// </html>

// page.groovy
// <% content = capture { %>
//   <% items.each { item -> %>
//     <p>${item}</p>
//   <% } %>
// <% } %>
// <% include 'layout.groovy' %>

Common Mistakes

1. Escaping dollar signs

In template strings, escape $ as $. In template files, $ is the expression marker.

2. Variable scope

Templates have their own scope. Variables from outside must be passed as bindings.

3. Performance with SimpleTemplateEngine

For repeated rendering, cache the template object. Creation has overhead.

4. XSS in web templates

Escape user content: ${content.encodeAsHTML()} or use a web framework's auto-escaping.

5. Nested template syntax

Template expressions inside template expressions are tricky. Break into multiple steps.

Practice Questions

1. What does SimpleTemplateEngine do? Processes template text with embedded Groovy expressions (${}) and scriptlets (<% %>).

2. How do you pass data to a template? Use template.make(binding) where binding is a map of variable names to values.

3. How do you iterate in a template? Use Groovy's <% items.each { item -> %> ... <% } %> inside template files.

Challenge: Create a template that generates an HTML table from a list of maps.

FAQ

{{< faq question="Is Groovy's template engine production-ready?" >} SimpleTemplateEngine is used in Grails and other frameworks. For high-traffic sites, consider Caching. {{< /faq >}}

{{< faq question="What is the difference between Simple and Streaming template engines?" >} SimpleTemplateEngine builds a full output string. StreamingTemplateEngine writes to a writer for better memory use. {{< /faq >}}

{{< faq question="Can templates call methods?" >} Yes. Any method available in the binding scope is callable from the template. {{< /faq >}}

{{< faq question="How do I include one template in another?" >} Use the include function inside a template: <% include 'header.groovy' %>. {{< /faq >}}

{{< faq question="Can templates be internationalized?" >} Yes. Pass locale-specific strings through the binding map. {{< /faq >}}

Mini Project

Build a report template system:

import groovy.text.SimpleTemplateEngine

def engine = new SimpleTemplateEngine()

def reportTemplate = '''
<html>
<head><title>${title}</title></head>
<body>
    <h1>${title}</h1>
    <p>Generated: ${new Date()}</p>
    <table border="1">
        <tr><th>Name</th><th>Value</th><th>Status</th></tr>
        <% rows.each { row -> %>
        <tr>
            <td>${row.name}</td>
            <td>${row.value}</td>
            <td style="color: ${row.status == 'OK' ? 'green' : 'red'}">
                ${row.status}
            </td>
        </tr>
        <% } %>
    </table>
</body>
</html>
'''

def template = engine.createTemplate(reportTemplate)
def output = template.make(
    title: "System Report",
    rows: [
        [name: "CPU", value: "45%", status: "OK"],
        [name: "Memory", value: "80%", status: "Warning"],
    ]
)

new File("report.html").text = output

What's Next

Now that you understand templates, explore testing in Groovy.

Topic	Description	Link
Groovy Testing	Unit Testing	{{< ref "15-testing" >}}
Groovy Spock	Spock framework	{{< ref "16-spock" >}}

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