门面设计模式

下面就是GoFo设计模式的UML设计图

PS ： 门面模式就是隐藏细节，让对方知道更少东东。原则就是迪特米原则

其实说白了，看这个图一般还是看不明白有什么毛用。

举例
1，比如说我们吃的，坑的鸡，香村鸡，我们去点一个狮子头双拼，鸡店暴露给我们的直接就是我们包装好点，菜，饭，筷子。
具体的细节，比如说菜谱，菜，饭是怎么做的。其实我们不是知道的。

2，我们天天乘坐的电梯也是，电梯暴露给我们就只是几个按钮。具体电梯是这么运转的，其实我们是不知道的。

装逼完了，大家应该明白了，下面的案例就是简单版Servlet的功能：

public class Request implements ServletRequest {

  private InputStream input;
  private String uri;

  public Request(InputStream input) {
    this.input = input;
  }

  public String getUri() {
    return uri;
  }

  private String parseUri(String requestString) {
    int index1, index2;
    index1 = requestString.indexOf(' ');
    if (index1 != -1) {
      index2 = requestString.indexOf(' ', index1 + 1);
      if (index2 > index1)
        return requestString.substring(index1 + 1, index2);
    }
    return null;
  }
  //通过输入流转换url 这个方法是属于Request对象的，但是这个方法又不想让外面的系统知道。
  public void parse() {
    // Read a set of characters from the socket
    StringBuffer request = new StringBuffer(2048);
    int i;
    byte[] buffer = new byte[2048];
    try {
      i = input.read(buffer);
    }
    catch (IOException e) {
      e.printStackTrace();
      i = -1;
    }
    for (int j=0; j<i; j++) {
      request.append((char) buffer[j]);
    }
    System.out.print(request.toString());
    uri = parseUri(request.toString());
  }

  /* implementation of the ServletRequest*/
  public Object getAttribute(String attribute) {
    return null;
  }

  public Enumeration getAttributeNames() {
    return null;
  }

  public String getRealPath(String path) {
    return null;
  }

  public RequestDispatcher getRequestDispatcher(String path) {
    return null;
  }

  public boolean isSecure() {
    return false;
  }

  public String getCharacterEncoding() {
    return null;
  }

  public int getContentLength() {
    return 0;
  }

  public String getContentType() {
    return null;
  }

  public ServletInputStream getInputStream() throws IOException {
    return null;
  }

  public Locale getLocale() {
    return null;
  }

  public Enumeration getLocales() {
    return null;
  }

  public String getParameter(String name) {
    return null;
  }

  public Map getParameterMap() {
    return null;
  }

  public Enumeration getParameterNames() {
    return null;
  }

  public String[] getParameterValues(String parameter) {
    return null;
  }

  public String getProtocol() {
    return null;
  }

  public BufferedReader getReader() throws IOException {
    return null;
  }

  public String getRemoteAddr() {
    return null;
  }

  public String getRemoteHost() {
    return null;
  }

  public String getScheme() {
   return null;
  }

  public String getServerName() {
    return null;
  }

  public int getServerPort() {
    return 0;
  }

  public void removeAttribute(String attribute) {
  }

  public void setAttribute(String key, Object value) {
  }

  public void setCharacterEncoding(String encoding)
    throws UnsupportedEncodingException {
  }

}



public class RequestFacade implements ServletRequest {

  private ServletRequest request = null;

  //这里有一个真实处理对象的依赖
  public RequestFacade(Request request) {
    this.request = request;
  }

  /* implementation of the ServletRequest*/
  public Object getAttribute(String attribute) {
    return request.getAttribute(attribute);
  }

  public Enumeration getAttributeNames() {
    return request.getAttributeNames();
  }

  public String getRealPath(String path) {
    return request.getRealPath(path);
  }

  public RequestDispatcher getRequestDispatcher(String path) {
    return request.getRequestDispatcher(path);
  }

  public boolean isSecure() {
    return request.isSecure();
  }

  public String getCharacterEncoding() {
    return request.getCharacterEncoding();
  }

  public int getContentLength() {
    return request.getContentLength();
  }

  public String getContentType() {
    return request.getContentType();
  }

  public ServletInputStream getInputStream() throws IOException {
    return request.getInputStream();
  }

  public Locale getLocale() {
    return request.getLocale();
  }

  public Enumeration getLocales() {
    return request.getLocales();
  }

  public String getParameter(String name) {
    return request.getParameter(name);
  }

  public Map getParameterMap() {
    return request.getParameterMap();
  }

  public Enumeration getParameterNames() {
    return request.getParameterNames();
  }

  public String[] getParameterValues(String parameter) {
    return request.getParameterValues(parameter);
  }

  public String getProtocol() {
    return request.getProtocol();
  }

  public BufferedReader getReader() throws IOException {
    return request.getReader();
  }

  public String getRemoteAddr() {
    return request.getRemoteAddr();
  }

  public String getRemoteHost() {
    return request.getRemoteHost();
  }

  public String getScheme() {
   return request.getScheme();
  }

  public String getServerName() {
    return request.getServerName();
  }

  public int getServerPort() {
    return request.getServerPort();
  }

  public void removeAttribute(String attribute) {
    request.removeAttribute(attribute);
  }

  public void setAttribute(String key, Object value) {
    request.setAttribute(key, value);
  }

  public void setCharacterEncoding(String encoding)
    throws UnsupportedEncodingException {
    request.setCharacterEncoding(encoding);
  }
}

public class ServletProcessor {

  public void process(Request request, Response response) {

    String uri = request.getUri();
    String servletName = uri.substring(uri.lastIndexOf("/") + 1);
    URLClassLoader loader = null;

    try {
      // create a URLClassLoader
      URL[] urls = new URL[1];
      URLStreamHandler streamHandler = null;
      File classPath = new File(Constants.WEB_ROOT);
      // the forming of repository is taken from the createClassLoader method in
      // org.apache.catalina.startup.ClassLoaderFactory
      String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;
      // the code for forming the URL is taken from the addRepository method in
      // org.apache.catalina.loader.StandardClassLoader class.
      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;
    //这里暴露给Servlet里的Service方法，就是包装处理过的
    RequestFacade requestFacade = new RequestFacade(request);
    ResponseFacade responseFacade = new ResponseFacade(response);
    try {
      servlet = (Servlet) myClass.newInstance();
      servlet.service((ServletRequest) requestFacade, (ServletResponse) responseFacade);
    }
    catch (Exception e) {
      System.out.println(e.toString());
    }
    catch (Throwable e) {
      System.out.println(e.toString());
    }
  }
}


public class HttpServer {

  // shutdown command
  private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

  // the shutdown command received
  private boolean shutdown = false;

  public static void main(String[] args) {
    HttpServer server = new HttpServer();
    server.await();
  }

  public void await() {
    ServerSocket serverSocket = null;
    int port = 8080;
    try {
      serverSocket =  new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
    }
    catch (IOException e) {
      e.printStackTrace();
      System.exit(1);
    }

    // Loop waiting for a request
    while (!shutdown) {
      Socket socket = null;
      InputStream input = null;
      OutputStream output = null;
      try {
        socket = serverSocket.accept();
        input = socket.getInputStream();
        output = socket.getOutputStream();

        // create Request object and parse
        Request request = new Request(input);
        request.parse();

        // create Response object
        Response response = new Response(output);
        response.setRequest(request);

        //check if this is a request for a servlet or a static resource
        //a request for a servlet begins with "/servlet/"
        if (request.getUri().startsWith("/servlet/")) {
          ServletProcessor processor = new ServletProcessor();
          processor.process(request, response);
        }
        else {
          StaticResourceProcessor processor = new StaticResourceProcessor();
          processor.process(request, response);
        }

        // Close the socket
        socket.close();
        //check if the previous URI is a shutdown command
        shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
      }
      catch (Exception e) {
        e.printStackTrace();
        System.exit(1);
      }
    }
  }
}

tomcat 的门面模式使用很多。init（ServletConfig）就是包装之后的，Service（Request，respone）也是包装之后的，doFilter（Request，respone） 也是包装之后的
ServletContext也是包装之后的。

网关系统就是门面模式的写真