Med Java

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====== Simple REST Api backend implementation using Node.js and Express.js ======

===== Project implementation =====

First, [[java-script:node-js:setup|setup node.js for a new project]]. \\ 
Then, install [[java-script:node-js:express-js|Express.js]]:
<code>
npm install express
</code>

Create a src folder, inside it we'll place the following files.

==== Simple Hello World rest service ====

<code javascript node-rest-express-hello.js>
import express from "express";

let port = 3000;

let app = express();

//define endpoints

app.get('/hello', (request, response) => {
    response.send("Hello World!");
})

app.listen(port, () => {
    console.log(`App listening on port ${port}`);
});
</code>

To start the server:
<code>
node src/node-rest-express-hello.js
</code>

To access the /hello endpoint, open in a browser: http://localhost:3000/hello
Hello World! will be displayed.

==== Simple GET, GET by an attribute, POST ====

Data is loaded from person.js here but in a real-world application usually it is loaded from a database like mongodb.

<code javascript people.js>
export let people = [{
    name: "John",
    age: 35,
    hairColor: "brown"
}, {
    name: "Joe",
    age: 20,
    hairColor: "blonde"
}, {
    name: "Jane",
    age: 40,
    hairColor: "red"
}];
</code>

<code javascript node-rest-express-people.js>
import express from "express";
import { people } from './people.js';

let port = 3000;

let app = express();

// used for the POST endpoint
// takes the extra data that the client sends along with the request and puts it on the request argument of the POST endpoint.
app.use(express.json()); // built-in body-parsing middleware
app.use(express.urlencoded({ extended: true })); // for parsing application/x-www-form-urlencoded

//define endpoints

app.get('/people', (request, response) => {
    response.json(people);
})

app.get('/people/:name', (request, response) => {
    
    let { name } = request.params;
    let person = people.find(x => x.name === name);
    
    response.json(person);
})

app.post('/people', (request, response) => {
    
    let newPerson = request.body;
    people.push(newPerson);
    
    response.json(people);
})

app.listen(port, () => {
    console.log(`App listening on port ${port}`);
});
</code>

=== Test the /people POST endpoint ===

<note warning>
By default, web browsers use the GET method when you enter a URL in the address bar. This means you can't directly send a POST request using the address bar of a browser.
</note>

To test the POST endpoint we can use Postman, but there [[java-script:send-post-requests|are alternative ways to do it]].

After defining the body request, hit SEND button. \\ 
Here is how the postman POST request and response will look like: \\ 
{{:java-script:pasted:20230805-155718.png}}

==== Load data from a file (server side) ====

We'll use now people-data.json to load the people data.

<code javascript people-data.json>
[{
    "name": "John",
    "age": 35,
    "hairColor": "brown"
}, {
    "name": "Joe",
    "age": 20,
    "hairColor": "blonde"
}, {
    "name": "Jane",
    "age": 40,
    "hairColor": "red"
}]
</code>

We'll define a GET endpoint at /file-data. When a GET request is made to this endpoint, the server reads data from a JSON file (people-data.json), parses that data into a JavaScript object (people), and sends that object as a JSON response.

<code javascript node-rest-express-load-data.js>
import express from 'express';
import { promises as fs } from 'fs';
import { fileURLToPath } from 'url';
import { dirname } from 'path';

const __filename = fileURLToPath(import.meta.url);
const __dirname = dirname(__filename);

let port = 3000;

let app = express();

//define endpoints

app.get('/file-data', async (request, response) => {
    let data = await fs.readFile(__dirname + '/people-data.json');
    let people = JSON.parse(data);

    response.json(people);
})

app.listen(port, () => {
    console.log(`App listening on port ${port}`);
});
</code>

Result will be available at http://localhost:3000/file-data/