準備技術:

1. Java
2. Web Server
3. IO
4. Net Socket
5. Class Loader
6. HTTPServlet Request/Response

從Java Web Server，可以觀察Java技巧，Web Server的原理，網路程式設計，最重要的是要了解HTTP的原理，這是Web Server的基本。

1. 主程式，簡單的Java 應用程式，呼叫JavaHTTPServer 啟動Server，然後進入await方法維持上線狀態。

   public class JavaHttpServer {

   private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";
   private boolean shutdown = false;

   public static void main(String[] args) {

    JavaHttpServer server = new JavaHttpServer();
    server.await();
   

   }
   }

2. await方法如下，首先設定一個ServerSocket，設定主機IP(hostIP)和Port，ServerSocket綁定主機IP，接下來While迴圈的!shutdown參數，是讓Server維持上線狀態，迴圈內容是設定一個Socket透過InputStream/OutStream的JavaIO方法，啟動SeverSocket，這樣Web Server有接收輸出資料的能力。然後我們要處理Request/Response ，如果需求是Servlet，需要ServletProcessor，如果是靜態html，需要StaticResourceProcessor。

   public void await() {

    ServerSocket serverSocket = null;
   
    String hostIP="127.0.0.1";
    int port = 10000;
   
    try {
      serverSocket =  new ServerSocket(port, 1, InetAddress.getByName(hostIP));
      System.out.println("Java Web Server  start Host  at "+hostIP+" and  port="+port);
    }
    catch (IOException e) {
      e.printStackTrace();
      System.exit(1);
    }
   
   
    while (!shutdown) {
      Socket socket = null;
      InputStream input = null;
      OutputStream output = null;
      try {
        socket = serverSocket.accept();
        input = socket.getInputStream();
        output = socket.getOutputStream();
   
   
        Request request = new Request(input);
        request.parse();
   
   
        Response response = new Response(output);
        response.setRequest(request);
   
        //假如是Servlet
        if (request.getUri().startsWith("/servlet/")) {
          ServletProcessor processor = new ServletProcessor();
          processor.process(request, response);
        }
        else {
        //假如是html靜態程式
          StaticResourceProcessor processor = new StaticResourceProcessor();
          processor.process(request, response);
        }
   
   
        socket.close();
   
        shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
      }
      catch (Exception e) {
        e.printStackTrace();
        System.exit(1);
      }
    }
   

   }

3. 看ServletProcessor處理Request/Response，呼叫process方式來處理。我們先將request的URL拆開，設定一個字串repository後使用URLClassLoader 載入一個class，我們希望將這個class轉型成Servlet，這樣可以使用Servlet的HTTPServletRequest/Response來當Resquest/Response的資料處理。

   public class ServletProcessor1 {

   public void process(Request request, Response response) {

    String uri = request.getUri();
    String servletName = uri.substring(uri.lastIndexOf("/") + 1);
    URLClassLoader loader = null;
   
    try {
   
      URL[] urls = new URL[1];
      URLStreamHandler streamHandler = null;
      File classPath = new File(Constants.WEB_ROOT);
   
      String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;
   
      urls[0] = new URL(null, repository, streamHandler);
      loader = new URLClassLoader(urls);
    }
    catch (IOException e) {
      System.out.println(e.toString() );
    }
    Class myClass = null;
    try {
      myClass = loader.loadClass(servletName);
    }
    catch (ClassNotFoundException e) {
      System.out.println(e.toString());
    }
   
    Servlet servlet = null;
   
    try {
      servlet = (Servlet) myClass.newInstance();
      servlet.service((ServletRequest) request, (ServletResponse) response);
    }
    catch (Exception e) {
      System.out.println(e.toString());
    }
    catch (Throwable e) {
      System.out.println(e.toString());
    }
   

   }
   }

4. 看StaticResourceProcessor，單純處理Request/Response。

   public class StaticResourceProcessor {

   public void process(Request request, Response response) {
   try {
   response.sendStaticResource();
   }
   catch (IOException e) {
   e.printStackTrace();
   }
   }
   }

5. 啟動Web Server。

Day1 結束