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Brayan Monteiro
Brayan Monteiro

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Como criar e consumir uma API REST simples em Java puro

#api #apirest #java

Vou criar uma API REST simples em Java puro** (usando com.sun.net.httpserver) e consumir essa API usando java.net.HttpURLConnection.

Parte 1: Criando a API (Servidor HTTP)

Passo 1: Estrutura do Projeto 

src └── main └── java ├── api │ ├── Task.java // Modelo de dados │ ├── TaskHandler.java // Manipulador de requisições │ └── Server.java // Servidor principal └── client └── ApiClient.java // Cliente para consumir a API
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Passo 2: Código do Servidor

Classe Task (Modelo) 
package api; public class Task { private int id; private String title; private boolean completed; // Construtor, getters e setters public Task(int id, String title, boolean completed) { this.id = id; this.title = title; this.completed = completed; } public int getId() { return id; } public String getTitle() { return title; } public boolean isCompleted() { return completed; } }
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Classe TaskHandler (Manipulador de Requisições) 
package api; import com.sun.net.httpserver.HttpExchange; import com.sun.net.httpserver.HttpHandler; import java.io.IOException; import java.io.OutputStream; import java.util.ArrayList; import java.util.List; public class TaskHandler implements HttpHandler { private List<Task> tasks = new ArrayList<>(); private int nextId = 1; @Override public void handle(HttpExchange exchange) throws IOException { String method = exchange.getRequestMethod(); String path = exchange.getRequestURI().getPath(); switch (method) { case "GET": handleGet(exchange); break; case "POST": handlePost(exchange); break; default: sendResponse(exchange, 405, "{\"error\": \"Método não permitido\"}"); } } private void handleGet(HttpExchange exchange) throws IOException { String json = "["; for (Task task : tasks) { json += String.format( "{\"id\": %d, \"title\": \"%s\", \"completed\": %b},", task.getId(), task.getTitle(), task.isCompleted() ); } json = json.isEmpty() ? "[]" : json.substring(0, json.length() - 1) + "]"; sendResponse(exchange, 200, json); } private void handlePost(HttpExchange exchange) throws IOException { String body = new String(exchange.getRequestBody().readAllBytes()); // Simples parsing (em produção, use uma biblioteca JSON) String title = body.split("\"")[3]; // Extrai o título do JSON Task task = new Task(nextId++, title, false); tasks.add(task); sendResponse(exchange, 201, "{\"id\": " + task.getId() + "}"); } private void sendResponse(HttpExchange exchange, int statusCode, String response) throws IOException { exchange.getResponseHeaders().set("Content-Type", "application/json"); exchange.sendResponseHeaders(statusCode, response.getBytes().length); try (OutputStream os = exchange.getResponseBody()) { os.write(response.getBytes()); } } }
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Classe Server (Iniciar Servidor) 
package api; import com.sun.net.httpserver.HttpServer; import java.io.IOException; import java.net.InetSocketAddress; public class Server { public static void main(String[] args) throws IOException { HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0); server.createContext("/tasks", new TaskHandler()); server.start(); System.out.println("Servidor iniciado na porta 8080"); } }
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Parte 2: Consumindo a API (Cliente HTTP)

Classe ApiClient 

package client; import java.io.IOException; import java.net.HttpURLConnection; import java.net.URL; import java.io.OutputStream; import java.io.InputStream; import java.util.Scanner; public class ApiClient { public static String get(String url) throws IOException { HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection(); conn.setRequestMethod("GET"); try (InputStream is = conn.getInputStream(); Scanner scanner = new Scanner(is)) { return scanner.useDelimiter("\\A").next(); } } public static String post(String url, String jsonBody) throws IOException { HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection(); conn.setRequestMethod("POST"); conn.setRequestProperty("Content-Type", "application/json"); conn.setDoOutput(true); try (OutputStream os = conn.getOutputStream()) { os.write(jsonBody.getBytes()); } try (InputStream is = conn.getInputStream(); Scanner scanner = new Scanner(is)) { return scanner.useDelimiter("\\A").next(); } } public static void main(String[] args) { try { // POST: Criar uma tarefa String responsePost = post("http://localhost:8080/tasks", "{\"title\": \"Aprender Java\", \"completed\": false}"); System.out.println("POST Response: " + responsePost); // GET: Listar tarefas String responseGet = get("http://localhost:8080/tasks"); System.out.println("GET Response: " + responseGet); } catch (IOException e) { e.printStackTrace(); } } }
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Passo 3: Execução

  1. Inicie o Servidor: 
 java api.Server
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  1. Execute o Cliente: 
 java client.ApiClient
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Testando com cURL (Opcional) 

# Criar tarefa curl -X POST -H "Content-Type: application/json" -d "{\"title\":\"Estudar API\",\"completed\":false}" http://localhost:8080/tasks # Listar tarefas curl http://localhost:8080/tasks
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Considerações

  1. Simplicidade vs. Robustez:

    • O servidor usa com.sun.net.httpserver, ideal para protótipos. Em produção, prefira frameworks como Spring Boot ou Javalin.
    • O parsing de JSON é simplificado. Use bibliotecas como Jackson ou Gson para manipulação real de JSON.

  2. Cliente HTTP:

    • Para projetos reais, use HttpClient (Java 11+) ou bibliotecas como OkHttp.

  3. Melhorias Possíveis:

    • Adicionar tratamento de erros.
    • Implementar métodos PUT e DELETE.
    • Validar entradas.

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