TeaVM: convertir código Java a WebAssembly

TeaVM es un compilador ahead-of-time que transforma bytecode de Java en JavaScript o WebAssembly, permitiendo ejecutar aplicaciones Java directamente en el navegador sin necesidad de reescribirlas en JavaScript.

Es útil para quienes quieren aprovechar su código Java (o incluso Kotlin y Scala) en entornos web modernos.

Es similar a lo que se hacía con GWT (Google Web Toolkit). Convertir tu código Java a código Javascript.

En este blog ya hemos hablado de WebAssembly:

• WebAssembly con Rust.
• WebAssembly con Python.
• WebAssembly con C/C++

Creando un proyecto Java (y TeaVM)

1. Creamos nuestro proyecto Java con Maven:

$ mvn -DarchetypeCatalog=local -DarchetypeGroupId=org.teavm -DarchetypeArtifactId=teavm-maven-webapp -DarchetypeVersion=0.13.1 archetype:generate
$ cd demo-teavm

2. Una vez ubicados en el directorio creado modificaremos el programa principal ``MainClass.java``.

package com.inforhomex.web;

import org.teavm.jso.dom.html.HTMLDocument;

public class MainClass {
    public static void main(String[] args) {
        var document = HTMLDocument.current();
        var div = document.createElement("div");
        div.appendChild(document.createTextNode("TeaVM va a generar un elemento HTML."));
        document.getBody().appendChild(div);
    }
}

3. Modificaremos el archivo ``pom.xml``:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.inforhomex.web</groupId>
  <artifactId>demo-teavm</artifactId>
  <version>1</version>
  <packaging>war</packaging>

  <properties>
    <java.version>11</java.version>
    <teavm.version>0.13.1</teavm.version>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <!-- Emulator of Java class library for TeaVM -->
    <dependency>
      <groupId>org.teavm</groupId>
      <artifactId>teavm-classlib</artifactId>
      <version>${teavm.version}</version>
      <scope>provided</scope>
    </dependency>

    <!-- JavaScriptObjects (JSO) - a JavaScript binding for TeaVM -->
    <dependency>
      <groupId>org.teavm</groupId>
      <artifactId>teavm-jso-apis</artifactId>
      <version>${teavm.version}</version>
      <scope>provided</scope>
    </dependency>

    <!-- Servlet specification -->
    <dependency>
      <groupId>jakarta.servlet</groupId>
      <artifactId>jakarta.servlet-api</artifactId>
      <version>6.0.0</version>
      <scope>provided</scope>
    </dependency>
  </dependencies>

  <build>
    <plugins>
	
	
      <!-- Configure Java compiler to use Java 8 syntax  -->
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.13.0</version>
        <configuration>
          <source>${java.version}</source>
          <target>${java.version}</target>
        </configuration>
      </plugin>

      <!-- Configure WAR plugin to include JavaScript files generated by TeaVM -->
      <plugin>
        <artifactId>maven-war-plugin</artifactId>
        <version>3.4.0</version>
        <configuration>
          <webResources>
            <resource>
              <directory>${project.build.directory}/generated/js</directory>
            </resource>
          </webResources>
        </configuration>
      </plugin>

      <!-- Configure TeaVM -->
      <plugin>
        <groupId>org.teavm</groupId>
        <artifactId>teavm-maven-plugin</artifactId>
        <version>${teavm.version}</version>
        <executions>
          <execution>
            <id>web-client</id>
            <goals>
              <goal>compile</goal>
            </goals>
            <configuration>
              <!-- Directory where TeaVM should put generated files. This configuration conforms to the settings
                   of the WAR plugin -->
              <targetDirectory>${project.build.directory}/generated/js/teavm</targetDirectory>

              <!-- Main class, containing static void main(String[]) -->
              <mainClass>com.inforhomex.web.MainClass</mainClass>

              <!-- Whether TeaVM should produce minified JavaScript. Can reduce JavaScript file size more than
                   two times -->
              <minifying>true</minifying>

              <!-- Whether TeaVM should produce debug information for its built-in debugger -->
              <debugInformationGenerated>true</debugInformationGenerated>

              <!-- Whether TeaVM should produce source maps file -->
              <sourceMapsGenerated>true</sourceMapsGenerated>

              <!-- Whether TeaVM should also put source files into output directory,
                   for compatibility with source maps -->
              <sourceFilesCopied>true</sourceFilesCopied>

              <!-- Optimization level. Valid values are: SIMPLE, ADVANCED, FULL -->
              <optimizationLevel>ADVANCED</optimizationLevel>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

4. Construimos el proyecto:

$ mvn clean package

5. Abrimos la página HTML generada en ``index.html``

<!DOCTYPE html>
<html>
  <head>
    <title>Main page</title>
    <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
    <script type="text/javascript" charset="utf-8" src="teavm/classes.js"></script>
	<script>
    
    </script>
  </head>
  <body onload="main()">
    
  </body>
</html>

Abrimos el archivo en un navegador. La salida será la siguiente:

TeaVM va a generar un elemento HTML.

¡Hemos generado código JS a través de TeaVM!

En próximas entregas continuaremos con este tema.

Enlaces:

https://teavm.org/
https://webassembly.org/
https://onlyhaskellforyou.blogspot.com/2026/04/webassembly-con-haskell.html
https://codemonkeyjunior.blogspot.com/2026/04/webassembly-con-dlang.html
https://codemonkeyjunior.blogspot.com/2026/04/grain-un-lenguaje-para-webassembly.html