# HTTP server

* Java ServerSocket
* Blocking vs Non-Blocking
* Readable
* InputStreamReader
* CharBuffer
* Writer
* OutputStreamWriter

```
package http_server;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.CharBuffer;
  
public class App { 
	int port = 8080;
	public static void main(String[] args) throws IOException {
		App app = new App();
		app.run();
	}
	
	/* 
	 * java에서넌 Server용으로 ServerSocket이라는 클래스를 별도로 사용한다.
	 * Socket을 상속한 것이 아니라는 점에 유의
	 */
	private void run() throws IOException {
		// 1. Listen
		ServerSocket listener= new ServerSocket(8080, 0); // port, backlog count
		System.out.println("Listen!"); 
		
		// 2. Accept
		/*
		 * I/O에서 기다리는 것을 Blocking이라고 한다. 파일 읽기, 쓰기 등도 모두 Blocking이지만, 
		 * TCP통신에서 네트워크 상태 요인에 따라 지연될 수 있고, 상대방의 요청이 없다면 끝없이 기다릴 수 있다.
		 * 때문에 멀티스레드나, 비동기, 이벤트 기반 처리 등이 필요하다.
		 */
		
		while(true) { 
			Socket socket = listener.accept();
			System.out.println("Accept!");
			
			// 3. Request 
			Readable reader = new java.io.InputStreamReader(socket.getInputStream());
			CharBuffer charBuffer = CharBuffer.allocate(1_000_000);
			reader.read(charBuffer);
			
			charBuffer.flip();
			System.out.println(charBuffer.toString()); 
			
			// 4. Response
			String body = "Hello world!";
			byte[] bytes = body.getBytes();
			String message = ""
					+ "HTTP/1.1 200 OK\n"
					+ "Content-type: text/html; charset=UTF-8\n"
					+ "Content-Length: " + bytes.length + "\n\n" + body;
			 
			Writer writer = new OutputStreamWriter(socket.getOutputStream());
			writer.write(message);
			writer.flush();
			
			// 5. close
			socket.close();
		} 
	}
}

```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://isaacs-dev-note.gitbook.io/dev_wiki/http/http-server.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.