java server serving 404 without dependencies

NativeHttpServer.java

package main;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Map;

public class NativeHttpServer {

  public static void main(String[] args) throws IOException {
    Map<String, String> env = System.getenv();
    String hostname = InetAddress.getLocalHost().getHostName();
    ServerSocket serverSocket = new ServerSocket(Integer.parseInt(env.get("PORT")));
    while (true) {
      Socket clientSocket = serverSocket.accept();
      PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
      BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
      String s = in.readLine();
      System.out.println(s);
      if (s == "GET /_ah/health HTTP/1.1") {
        out.println("HTTP/1.1 200 OK");
      } else {
        out.println("HTTP/1.1 404 Not Found");
      }
      out.println("Connection: close");
      out.println();    
      out.flush();
      clientSocket.close();
    }
  }
}