hello-world.md

synopsis	notebook	status	impl-variants
Looking for the obligatory greeting? → here you go.	true	released	true

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.

Create a Project

cds init hello-world --add tiny-sample
cd hello-world
npm install

cds init hello-world --add java,samples
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:

::: code-group

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

:::

Implement it

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

::: code-group

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

:::

... or Node.js ES6 classes style.

::: code-group

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. { .impl .node}

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

::: code-group

package customer.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":

::: code-group

cds watch

cd srv
mvn cds:watch

:::

Consume it

... for example, from your browser:

http://localhost:4004/odata/v4/say/hello(to='world') { .impl .node}

http://localhost:8080/odata/v4/say/hello(to='world') { .impl .java}

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