Hello World!

Let's create a simple Hello World OData service using the SAP Cloud Application Programming Model in six lines of code and in under 2 minutes.

You can also download the sample from github.com.

Let's create a simple Hello World OData service using the SAP Cloud Application Programming Model with a few lines of code and in under 2 minutes.

This guide is available for Node.js and Java.

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This guide is available as a CAP Notebook. 

Download the notebook to run it locally in your VS Code editor.

Create a Project

cds init hello-world
cd hello-world

cds init hello-world --java --java:mvn -DgroupId=com.sap.capire --add tiny-sample
cd hello-world

With the cds init command above you also created a sample schema and service. It's not relevant and can be ignored for now, but a CAP Java service currently needs persistence in order to startup correctly.

Define a Service

... using CDS:

srv/world.cds

service say {
  function hello (to:String) returns String;
}

Implement it

... for example, using Node.js express.js handlers style.

srv/world.js

module.exports = (say)=>{
  say.on ('hello', req => `Hello ${req.data.to}!`)
}

... or Node.js ES6 classes style.

srv/world.js

module.exports = class say {
  hello(req) { return `Hello ${req.data.to}!` }
}

That has limited flexibility, for example, you can register only one handler per event.

... for example, using a CAP Java custom handler like this:

srv/src/main/java/com/sap/capire/hello_world/handlers/HelloHandler.java

package com.sap.capire.hello_world.handlers;

import org.springframework.stereotype.Component;

import com.sap.cds.services.handler.EventHandler;
import com.sap.cds.services.handler.annotations.On;
import com.sap.cds.services.handler.annotations.ServiceName;

import cds.gen.say.HelloContext;
import cds.gen.say.Say_;

@Component
@ServiceName(Say_.CDS_NAME)
public class HelloHandler implements EventHandler {

  @On
  public void onHello(HelloContext ctx) {
    ctx.setResult("Hello " + ctx.getTo());
    ctx.setCompleted();
  }

}

Run it

... for example, from your command line in the root directory of your "Hello World":

cds watch

cd srv
mvn cds:watch

Consume it

... for example, from your browser:

http://localhost:4004/odata/v4/say/hello(to='world')

http://localhost:8080/odata/v4/say/hello(to='world')

You should see the value "Hello world!" being returned.