README.md

Example Java Function: String Reverse

This example provides an HTTP trigger endpoint for reversing strings.

$ curl -d "Hello World" http://localhost:8080/t/string-reverse-app/string-reverse
dlroW olleH

Demonstrated FDK features

This example uses none of the Fn FDK for Java features, in fact it doesn't have any dependency on the FDK for Java. It is just plain old Java code.

Step by step

Ensure you have the Fn server running to host your function and provide the HTTP endpoint that invokes it:

(1) Start the server

$ fn start

(2) Create an app for the function

$ fn create app string-reverse-app

(3) Deploy the function to your app from the string-reverse directory.

fn deploy --app string-reverse-app --local

(4) Invoke the function and reverse the string.

echo "Hello World" | fn invoke string-reverse-app string-reverse
dlroW olleH

(5) Invoke the function using curl and a trigger to reverse a string.

$ curl -d "Hello World" http://localhost:8080/t/string-reverse-app/string-reverse
dlroW olleH

Code walkthrough

The entrypoint to the function is specified in func.yaml in the cmd key. It is set to com.example.fn.StringReverse::reverse. The whole class StringReverse is shown below:

package com.example.fn;

public class StringReverse {
    public String reverse(String str) {
        return new StringBuilder(str).reverse().toString();
    }
}

As you can see, this is plain Java with no references to the Fn API. The Fn FDK for Java handles the marshalling of the HTTP body into the str parameter as well as the marshalling of the returned reversed string into the HTTP response body (see Data Binding for more information on how marshalling is performed).