Text Templates in Logo

Java provides built-in support for creating dynamic content or showing customized output to the user with the java.util.StringTemplate class (introduced in Java 21) or the java.text.MessageFormat class for earlier versions. For HTML generation, consider using a dedicated templating engine like Thymeleaf or FreeMarker.

import java.util.StringTemplate;
import java.util.List;
import java.util.Map;

public class TextTemplates {
    public static void main(String[] args) {
        // We can create a new template and parse its body from a string.
        // Templates are a mix of static text and placeholders enclosed in
        // #{...} that are used to dynamically insert content.
        StringTemplate t1 = StringTemplate.of("Value is #{value}\n");

        // By "processing" the template we generate its text with
        // specific values for its placeholders.
        System.out.print(t1.render(Map.of("value", "some text")));
        System.out.print(t1.render(Map.of("value", 5)));
        System.out.print(t1.render(Map.of("value", List.of("Java", "Kotlin", "Scala", "Groovy"))));

        // If the data is a record we can use the #{fieldName} placeholder to access
        // its fields.
        record Person(String name) {}
        StringTemplate t2 = StringTemplate.of("Name: #{name}\n");

        System.out.print(t2.render(new Person("Jane Doe")));

        // The same applies to maps.
        System.out.print(t2.render(Map.of("name", "Mickey Mouse")));

        // Conditional execution can be achieved using the ternary operator
        // inside the placeholder.
        StringTemplate t3 = StringTemplate.of("#{value ? 'yes' : 'no'}\n");
        System.out.print(t3.render(Map.of("value", "not empty")));
        System.out.print(t3.render(Map.of("value", "")));

        // For looping through collections, we can use String.join() method
        // along with the template.
        List<String> languages = List.of("Java", "Kotlin", "Scala", "Groovy");
        StringTemplate t4 = StringTemplate.of("Range: #{String.join(' ', languages)}\n");
        System.out.print(t4.render(Map.of("languages", languages)));
    }
}

To run the program, compile and execute it:

$ javac TextTemplates.java
$ java TextTemplates
Value is some text
Value is 5
Value is [Java, Kotlin, Scala, Groovy]
Name: Jane Doe
Name: Mickey Mouse
yes
no
Range: Java Kotlin Scala Groovy

This example demonstrates how to use Java’s StringTemplate class to create and process text templates. It covers basic substitution, working with different data types, conditional rendering, and iterating over collections. Note that StringTemplate is a preview feature in Java 21, so you might need to enable preview features when compiling and running the code.

For more complex templating needs or when working with earlier Java versions, consider using libraries like FreeMarker or Thymeleaf, which offer more advanced templating capabilities.

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