selvia/html-component

A very small library to define unmodifiable HTML/XML components

html-component

A very small library to define unmodifiable HTML/XML components in Java

Html components are

• safe: the template is not string based and checked by an XML parser
• composable: a component can reference another component statically or dynamically
• lightweight: the whole jar is less than 20kb
• defined in Java: no need to learn another template language, and it works with all Java IDEs.

A html component is a record that implements the interface Component thus provides a render method.

record HelloWorld(String name) implements Component {
  public Renderer render() {
    return $."""
      <div>Hello \{name} !</div>
      """;
  } 
}

It uses the mechanism of StringTemplate Processor in preview in Java 21/22 (JEP 459) to generate XML events from a template. This makes it impossible to generate invalid fragment of an XML document.

Because it's a plain record, it can be instantiated like any Java classes using new

var hello = new HelloWorld("html component");
System.out.println(hello.render());

A html component can reference statically another html component if they are both declared in the same class The name of the component has to start with a letter in uppercase to differentiate it from a regular XML element.

record TwoHello(String name1, String name2) implements Component {
  public Renderer render() {
    return $."""
      <div>
        <HelloWord name="\{name1}"/>
        <HelloWord name="\{name2}"/>
      </div>
      """;
  }
}

A html component can reference dynamically any other components, using the method Renderer.from(stream)

record HelloList(List<HelloWorld> hellos) implements Component {
  public Renderer render() {
    return $."""
      <div>
        \{ Renderer.from(hellos.stream()) }
      </div>
      """;
  }
}

Here are 3 more demos (Demo.java, Demo2.java and DemoList.java). And that's all for the spec part.

Using html components with htmx

Html components are a good fit for htmx because it's an easy way to create XML fragments that can be downloaded and patched by the JavaScript library htmx.

HTMXDemo shows how html components can be used in the context of htmx. The demo using a Java port of the Express.js library (JExpress.java) but this is not a requirement, it makes just the demo code simpler than using Spring Boot.

To run the demo with Java 22, after calling mvn package :

  cd src/test/java
  java --enable-preview --source 22 --class-path ../../../target/*.jar HTMXDemo.java

and in the browser http://localhost:8080/university