Java REST API metódusokra bontva

• Szerző: Sallai András
• Copyright © 2022, Sallai András
• Szerkesztve: 2022, 2023, 2024
• Licenc: CC BY-SA 4.0
• Web: https://szit.hu

Ebben a leírásban egy példát látunk a JSON.simple használatával REST API elérésre.

App.java

import java.util.ArrayList;
 
import models.EmployeeModel;
import models.RestClient;
 
public class App {
    public static void main(String[] args) throws Exception {
        System.out.println("REST API lekérés");
 
        RestClient restClient = new RestClient();
        ArrayList<EmployeeModel> employees = restClient.getEmployees();
        for(EmployeeModel emp : employees) {
            System.out.printf(
                "%20s %14s %14.2f\n",
                emp.name,
                emp.city,
                emp.salary
                );
        }
    }
}

EmployeeModel.java

package models;
 
public class EmployeeModel {    
    public String name;
    public String city;
    public double salary;
    public EmployeeModel(String name, String city, double salary) {
        this.name = name;
        this.city = city;
        this.salary = salary;
    }
}

RestClient.java

package models;
 
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Scanner;
 
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
 
public class RestClient {
    private String host = "http://localhost:8000/api/";
 
    public InputStream getDataAsStream() {
        InputStream inputStream = null;
        try {
            inputStream = tryGetDataAsStream();
        } catch (MalformedURLException e) {
            System.err.println("Hiba! Az url nem jó");
        }catch (IOException e) {
            System.err.println("Hiba! A lekérés sikertelen");
        }
        return inputStream;
    }
 
    public InputStream tryGetDataAsStream() throws MalformedURLException, IOException{
        String endpoint = "employees";
        String urlStr = host + endpoint;
        URL url = new URL(urlStr);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.connect();
        int response = conn.getResponseCode();
        if(response != HttpURLConnection.HTTP_OK) {
            throw new RuntimeException("HttpResponseCode:" + response);
        }else {
            return url.openStream();
        }
    }
 
    public String getDataAsString(InputStream inputStream) {
        Scanner sc = new Scanner(inputStream, "UTF-8");
        String content = "";
        while(sc.hasNext()) {
            content += sc.nextLine();
        }
        sc.close();
        return content;
    }
 
    public ArrayList<EmployeeModel> getEmployeeAsArray(String content) {
        ArrayList<EmployeeModel> list = null;
        try {
            list = tryGetEmployeeAsArray(content);
        }catch(ParseException e) {
            System.err.println("Hiba! Az értelmezés sikertelen!");
        }
        return list;
    }
 
    public ArrayList<EmployeeModel> tryGetEmployeeAsArray(String content) throws ParseException {
        JSONParser parser = new JSONParser();
        Object obj = parser.parse(content);
        JSONArray ja = (JSONArray) obj;
        ArrayList<EmployeeModel> list = new ArrayList<>();
 
        for(int i=0; i<ja.size(); i++) {
            JSONObject jobj = (JSONObject) ja.get(i);
            String name = (String) jobj.get("name");
            String city = (String) jobj.get("city");
            double salary = Double.parseDouble((String)jobj.get("salary"));
 
            EmployeeModel employeeModel = new EmployeeModel(name, city, salary);
            list.add(employeeModel);
        }
 
        return list;
    }
 
    public ArrayList<EmployeeModel> getEmployees() {
        InputStream inputStream = this.getDataAsStream();
        String content = this.getDataAsString(inputStream);        
        return getEmployeeAsArray(content);
    }
 
}