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WebAssembly with Java

note
  • WebAssembly support for Java is good thanks to a friendly fork of TeaVM, modified to support WASI and the WebAssembly Component Model proposal.

Install Java​

Install OpenJDK (the command might vary depending on the distribution):

sudo apt install openjdk-11-jdk

Install TeaVM WASI​

Clone the TeaVM WASI repository:

git clone https://github.com/fermyon/teavm-wasi.git

Navigate to the TeaVM WASI directory and do a clean install using Maven:

cd teavm-wasi
mvn clean install

Navigate to the tests/wasi directory and execute the Maven command again:

cd tests/wasi
mvn clean install

A classes.wasm file will be generated at target/generated/wasm/teavm-wasm/.

tip

If you encounter the following error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-war-plugin:2.2:war (default-war) on project foo: Error assembling WAR: webxml attribute is required (or pre-existing WEB-INF/web.xml if executing in update mode)

Please add the following plugin to the pom.xml file located at tests/wasi:

<plugin>
  <artifactId>maven-war-plugin</artifactId>
  <version>2.2</version>
  <extensions>false</extensions>
  <configuration>
    <failOnMissingWebXml>false</failOnMissingWebXml>
  </configuration>
</plugin>

Several test examples are provided and you can run them using Enarx by passing the test name and argument with the help of an Enarx.toml file.

For example, create the following Enarx.toml file:

args = [ "catch", "Hello Enarx!" ]

[[files]]
kind = "stdin"

[[files]]
kind = "stdout"

[[files]]
kind = "stderr"

Now run this test on Enarx:

enarx run --wasmcfgfile Enarx.toml classes.wasm

Java code​

Let's try the Fibonacci example now.

Rename the Test.java file at tests/wasi/src/main/java/wasi to Fibonacci.java and replace the code with the following:

package wasi;

public class Fibonacci {
    public static void main(String[] args) {
        int n = Integer.parseInt(args[0]);
        System.out.println(fib(n));
    }

    private static int fib(int n)
    {
        if (n <= 1)
            return n;
        return fib(n - 1) + fib(n - 2);
    }
}
tip

Access the Java codex repository for code samples, including the fibonacci example.

Now edit the main class name at the pom.xml file located at tests/wasi:

<mainClass>wasi.Fibonacci</mainClass>

Compile Java code to Wasm​

Execute the Maven command to generate a new classes.wasm file:

mvn clean install

Run with Enarx​

Now create the following Enarx.toml file with the fibonacci argument of your choice:

args = [ "9" ]

[[files]]
kind = "stdin"

[[files]]
kind = "stdout"

[[files]]
kind = "stderr"

At last, run the Fibonacci example using Enarx:

enarx run --wasmcfgfile Enarx.toml classes.wasm