1、调整项目结构；

2、servlet源码赏析

README.md

@@ -125,11 +125,11 @@
 - [基于Netty的客户端开发](docs/Netty/基于Netty开发服务端及客户端/基于Netty的客户端开发.md)
 
 ### Netty 主要组件的源码分析
-- [ByteBuf组件]()
+- [ByteBuf组件](docs/Netty/Netty主要组件源码分析/ByteBuf组件.md)
-- [Channel组件 和 Unsafe组件]()
+- [Channel组件 和 Unsafe组件](docs/Netty/Netty主要组件源码分析/Channel和Unsafe组件.md)
-- [ChannelPipeline 和 ChannelHandler组件]()
+- [ChannelPipeline 和 ChannelHandler组件](docs/Netty/Netty主要组件源码分析/ChannelPipeline和ChannelHandler组件.md)
-- [EventLoop 和 EventLoopGroup组件]()
+- [EventLoop 和 EventLoopGroup组件](docs/Netty/Netty主要组件源码分析/EventLoop和EventLoopGroup组件.md)
-- [Future 和 Promise组件]()
+- [Future 和 Promise组件](docs/Netty/Netty主要组件源码分析/Future和Promise组件.md)
 
 ### Netty 高级特性
 - [Netty 架构设计](docs/Netty/AdvancedFeaturesOfNetty/Netty架构设计.md)
@@ -137,7 +137,9 @@
 - [Netty 高可靠性设计](docs/Netty/AdvancedFeaturesOfNetty/Netty高可靠性设计.md)
 
 ## Tomcat
-- 努力编写中...
+- [一个简单的Web服务器]()
+- [一个简单的servlet容器]()
+- [servlet容器详解]()
 
 ## Redis
 - 努力编写中...

docs/Netty/Netty主要组件源码分析/ByteBuf组件.md

@@ -0,0 +1 @@
+努力编写中...

docs/Netty/Netty主要组件源码分析/ChannelPipeline和ChannelHandler组件.md

@@ -0,0 +1 @@
+努力编写中...

docs/Netty/Netty主要组件源码分析/Channel和Unsafe组件.md

@@ -0,0 +1 @@
+努力编写中...

docs/Netty/Netty主要组件源码分析/EventLoop和EventLoopGroup组件.md

@@ -0,0 +1 @@
+努力编写中...

docs/Netty/Netty主要组件源码分析/Future和Promise组件.md

@@ -0,0 +1 @@
+努力编写中...

docs/Tomcat/servlet容器详解.md

@@ -0,0 +1 @@
+努力编写中...

docs/Tomcat/servlet源码赏析.md

@@ -0,0 +1,566 @@
+## Servlet 基础
+### Servlet 简介
+Servlet（Server Applet），是用 Java 编写的服务器端程序。其主要功能在于交互式地（Request 和 Response）浏览和修改数据，生成动态 Web内容。Servlet 运行于支持 Java的应用服务器中，如 Tomcat。从实现上讲，Servlet 可以响应任何类型的请求，但绝大多数情况下 Servlet 只用来扩展基于 HTTP协议 的 Web服务器。servlet 的工作模式如下：
+- 客户端发送请求至服务器；
+- 服务器启动并调用相应的 servlet，servlet 根据客户端请求生成响应内容并将其传给服务器；
+- 服务器将响应返回客户端；
+
+另外，由于各种MVC框架的兴起，现在几乎没人会直接使用 servlet 来处理请求咯，往往都是把 SpringMVC 在 Tomcat 中一配，各种请求都交由 DispatcherServlet 来分发。
+
+### Servlet生命周期
+- 加载 : 客户端第一次访问该 Servlet 时，Tomcat 会创建该 Servlet 的实例，一般只创建1次，所以 servlet对象 在 Tomcat 是单例的；
+- 初始化 : Tomcat 调用 该 Servlet 的 init()方法 进行初始化；
+- 服务 : 每当客户端访问 该Servlet 时，Tomcat 就会调用一次该 Servlet 的 service()方法 处理请求；
+- 销毁 : Tomcat关闭 或 检测到 该Servlet 要从 Tomcat 删除时，会自动调用 该servlet 的 destroy()方法，让该实例释放掉所占的资源。一个Servlet如果长时间不被使用的话，也会被Tomcat自动销毁；
+
+简单总结一下就是，只要访问 Servlet，service()方法 就会被调用。init()方法 只有第一次访问 Servlet 的时候才会被调用。destroy()方法 会在 Tomcat 关闭的时候被调用。
+
+### <load-on-startup>
+在 web.xml 中配置 Servlet 时有个属性 <load-on-startup>1</load-on-startup>。翻译过来就是 “在启动时加载”，其作用如下：  
+1. load-on-startup 元素标记容器是否应该在 web应用程序 启动的时候就加载这个 Servlet，实例化并调用其 init()方法；
+2. 它的值必须是一个整数，表示 Servlet 被加载的先后顺序；
+3. 如果值为正整数或者0时，表示容器在应用启动时就加载并初始化这个 Servlet，值越小，Servlet 的优先级越高，就越先被加载。值相同时，容器就会自己选择顺序来加载；
+4. 如果该元素的值为负数或者没有设置，则容器会在 Servlet 被请求时才加载。
+
+### Servlet的多线程并发问题
+servlet对象 在 Tomcat服务器 是 单实例多线程的，比如 DispatcherServlet对象 只会被创建一次，但多个请求同时过来时，Tomcat线程池 的多个工作线程就会并发地访问该 DispatcherServlet对象。所以，若一个servlet对象中存在被并发修改的共享数据（成员变量 等），又没有加锁控制并发安全，就很可能会出现线程安全问题。
+
+解决方案：  
+1. 把使用到共享数据的代码块进行同步（使用synchronized 或 Lock对象）；
+2. 建议在 Servlet类 中尽量不要使用成员变量。若使用成员变量，则必须同步，并尽量缩小同步代码块的范围，以避免因为同步而导致并发效率降低。
+
+### Servlet 实现请求和响应
+对于每次客户端请求，Web容器 都会创建一个新的 HttpServletRequest请求对象 和 一个新的HttpServletResponse响应对象，然后将这两个对象作为参数传递给相应的 Servlet对象 的 service()方法，service()方法 再根据请求方式分别调用 doXXX()方法。经过一系列业务层处理，最后将结果封装到 response对象中，交由 Socket对象传输响应给客户端。
+
+## Servlet 源码解析
+javax.servlet 包主要对 Servlet 的一些主要行为和接口进行了定义和简单实现，它是 Servlet规范 的体现，具体的实现交由下游厂商或开发者，就像体现了JDBC规范的 java.sql包 一样，主要负责定义标准和规范。其源码和注释如下。
+```java
+public interface Servlet {
+    /**
+     * 初始化servlet
+     */
+    public abstract void init(ServletConfig servletconfig) throws ServletException;
+    
+    /**
+     * 提供服务
+     */
+    public abstract void service(ServletRequest servletrequest, ServletResponse servletresponse)
+            throws ServletException, IOException;
+    
+    /**
+     * 销毁本servlet
+     */		
+    public abstract void destroy();
+                
+    public abstract ServletConfig getServletConfig();
+    
+    public abstract String getServletInfo();
+}
+
+/**
+ * ServletConfig 主要用于保存一些 servlet的配置信息，与 servlet对象 成对出现
+ */
+public interface ServletConfig {
+
+    public abstract String getServletName();
+    
+    public abstract ServletContext getServletContext();
+    
+    public abstract String getInitParameter(String s);
+    
+    public abstract Enumeration getInitParameterNames();
+}
+
+/**
+ * 一个web应用对应一个ServletContext，ServletContext实例包含了所有servlet共享的资源信息
+ */
+public interface ServletContext {
+
+    public abstract ServletContext getContext(String s);
+    
+    public abstract Servlet getServlet(String s) throws ServletException;
+    
+    public abstract Enumeration getServlets();
+    
+    public abstract Enumeration getServletNames();
+    
+    public abstract int getMajorVersion();
+    
+    public abstract Set getResourcePaths(String s);
+    
+    public abstract URL getResource(String s) throws MalformedURLException;
+    
+    public abstract InputStream getResourceAsStream(String s);
+    
+    public abstract RequestDispatcher getRequestDispatcher(String s);
+    
+    public abstract RequestDispatcher getNamedDispatcher(String s);
+    
+    public abstract String getRealPath(String s);
+    
+    public abstract String getServerInfo();
+    
+    public abstract String getInitParameter(String s);
+    
+    public abstract Enumeration getInitParameterNames();
+    
+    public abstract Object getAttribute(String s);
+    
+    public abstract Enumeration getAttributeNames();
+    
+    public abstract void setAttribute(String s, Object obj);
+    
+    public abstract void removeAttribute(String s);
+    
+    public abstract String getServletContextName();
+}
+
+/**
+ *定义了 Servlet 要处理的 Request请求信息，调用 Servlet 的 service()方法 时，会作为参数传入
+ */
+public interface ServletRequest {
+
+    public abstract Object getAttribute(String s);
+    
+    public abstract Enumeration getAttributeNames();
+    
+    public abstract String getCharacterEncoding();
+    
+    public abstract void setCharacterEncoding(String s) throws UnsupportedEncodingException;
+    
+    public abstract int getContentLength();
+    
+    public abstract String getContentType();
+    
+    public abstract ServletInputStream getInputStream() throws IOException;
+    
+    public abstract String getParameter(String s);
+    
+    public abstract Enumeration getParameterNames();
+    
+    public abstract String[] getParameterValues(String s);
+    
+    public abstract Map getParameterMap();
+    
+    public abstract String getProtocol();
+    
+    public abstract String getScheme();
+    
+    public abstract String getServerName();
+    
+    public abstract int getServerPort();
+    
+    public abstract BufferedReader getReader() throws IOException;
+    
+    public abstract String getRemoteAddr();
+    
+    public abstract String getRemoteHost();
+    
+    public abstract void setAttribute(String s, Object obj);
+    
+    public abstract void removeAttribute(String s);
+    
+    public abstract Locale getLocale();
+    
+    public abstract Enumeration getLocales();
+    
+    public abstract boolean isSecure();
+    
+    public abstract RequestDispatcher getRequestDispatcher(String s);
+}
+
+/**
+ * 定义了 Servlet 要返回的 Response响应信息，调用Servlet 的 service()方法 时，会作为参数传入
+ */
+public interface ServletResponse {
+
+    public abstract String getCharacterEncoding();
+    
+    public abstract ServletOutputStream getOutputStream() throws IOException;
+    
+    public abstract PrintWriter getWriter() throws IOException;
+    
+    public abstract void setContentLength(int i);
+    
+    public abstract void setContentType(String s);
+    
+    public abstract void setBufferSize(int i);
+    
+    public abstract int getBufferSize();
+    
+    public abstract void flushBuffer() throws IOException;
+    
+    public abstract void resetBuffer();
+    
+    public abstract boolean isCommitted();
+    
+    public abstract void reset();
+    
+    public abstract void setLocale(Locale locale);
+    
+    public abstract Locale getLocale();
+}
+```
+其主要部分的类图 如下。
+
+![avatar](images/Tomcat/Servlet主要类图.png)
+
+下面看一下 javax.servlet.http 包下的内容，它提供了很多 我经常用到的类和接口，比如：HttpServlet、HttpServletRequest、HttpServletResponse。其源码如下。
+```java
+public abstract class HttpServlet extends GenericServlet implements Serializable {
+
+    private static final String METHOD_DELETE = "DELETE";
+    private static final String METHOD_HEAD = "HEAD";
+    private static final String METHOD_GET = "GET";
+    private static final String METHOD_OPTIONS = "OPTIONS";
+    private static final String METHOD_POST = "POST";
+    private static final String METHOD_PUT = "PUT";
+    private static final String METHOD_TRACE = "TRACE";
+    private static final String HEADER_IFMODSINCE = "If-Modified-Since";
+    private static final String HEADER_LASTMOD = "Last-Modified";
+    private static final String LSTRING_FILE = "javax.servlet.http.LocalStrings";
+    private static ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.http.LocalStrings");
+    
+    /**
+     * 将 请求及响应 转换成 HttpServletRequest 及 HttpServletResponse，
+     * 再调用 service() 的重载方法
+     */
+    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
+        HttpServletRequest request;
+        HttpServletResponse response;
+        try {
+            request = (HttpServletRequest) req;
+            response = (HttpServletResponse) res;
+        } catch (ClassCastException e) {
+            throw new ServletException("non-HTTP request or response");
+        }
+        service(request, response);
+    }
+    
+    /**
+     * 对HTTP协议 各种类型的请求分别进行处理
+     */
+    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        String method = req.getMethod();
+        if (method.equals("GET")) {
+            long lastModified = getLastModified(req);
+            if (lastModified == -1L) {
+                doGet(req, resp);
+            } else {
+                long ifModifiedSince = req.getDateHeader("If-Modified-Since");
+                if (ifModifiedSince < (lastModified / 1000L) * 1000L) {
+                    maybeSetLastModified(resp, lastModified);
+                    doGet(req, resp);
+                } else {
+                    resp.setStatus(304);
+                }
+            }
+        } else if (method.equals("HEAD")) {
+            long lastModified = getLastModified(req);
+            maybeSetLastModified(resp, lastModified);
+            doHead(req, resp);
+        } else if (method.equals("POST"))
+            doPost(req, resp);
+        else if (method.equals("PUT"))
+            doPut(req, resp);
+        else if (method.equals("DELETE"))
+            doDelete(req, resp);
+        else if (method.equals("OPTIONS"))
+            doOptions(req, resp);
+        else if (method.equals("TRACE")) {
+            doTrace(req, resp);
+        } else {
+            String errMsg = lStrings.getString("http.method_not_implemented");
+            Object errArgs[] = new Object[1];
+            errArgs[0] = method;
+            errMsg = MessageFormat.format(errMsg, errArgs);
+            resp.sendError(501, errMsg);
+        }
+    }
+    
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        String protocol = req.getProtocol();
+        String msg = lStrings.getString("http.method_get_not_supported");
+        if (protocol.endsWith("1.1"))
+            resp.sendError(405, msg);
+        else
+            resp.sendError(400, msg);
+    }
+    
+    protected long getLastModified(HttpServletRequest req) {
+        return -1L;
+    }
+    
+    protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        NoBodyResponse response = new NoBodyResponse(resp);
+        doGet(req, response);
+        response.setContentLength();
+    }
+    
+    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        String protocol = req.getProtocol();
+        String msg = lStrings.getString("http.method_post_not_supported");
+        if (protocol.endsWith("1.1"))
+            resp.sendError(405, msg);
+        else
+            resp.sendError(400, msg);
+    }
+    
+    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        String protocol = req.getProtocol();
+        String msg = lStrings.getString("http.method_put_not_supported");
+        if (protocol.endsWith("1.1"))
+            resp.sendError(405, msg);
+        else
+            resp.sendError(400, msg);
+    }
+    
+    protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        String protocol = req.getProtocol();
+        String msg = lStrings.getString("http.method_delete_not_supported");
+        if (protocol.endsWith("1.1"))
+            resp.sendError(405, msg);
+        else
+            resp.sendError(400, msg);
+    }
+    
+    private Method[] getAllDeclaredMethods(Class c) {
+        if (c.getName().equals("javax.servlet.http.HttpServlet"))
+            return null;
+        int j = 0;
+        Method parentMethods[] = getAllDeclaredMethods(c.getSuperclass());
+        Method thisMethods[] = c.getDeclaredMethods();
+        if (parentMethods != null) {
+            Method allMethods[] = new Method[parentMethods.length + thisMethods.length];
+            for (int i = 0; i < parentMethods.length; i++) {
+                allMethods[i] = parentMethods[i];
+                j = i;
+            }
+    
+            for (int i = ++j; i < thisMethods.length + j; i++)
+                allMethods[i] = thisMethods[i - j];
+    
+            return allMethods;
+        } else {
+            return thisMethods;
+        }
+    }
+    
+    protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        Method methods[] = getAllDeclaredMethods(getClass());
+        boolean ALLOW_GET = false;
+        boolean ALLOW_HEAD = false;
+        boolean ALLOW_POST = false;
+        boolean ALLOW_PUT = false;
+        boolean ALLOW_DELETE = false;
+        boolean ALLOW_TRACE = true;
+        boolean ALLOW_OPTIONS = true;
+        for (int i = 0; i < methods.length; i++) {
+            Method m = methods[i];
+            if (m.getName().equals("doGet")) {
+                ALLOW_GET = true;
+                ALLOW_HEAD = true;
+            }
+            if (m.getName().equals("doPost"))
+                ALLOW_POST = true;
+            if (m.getName().equals("doPut"))
+                ALLOW_PUT = true;
+            if (m.getName().equals("doDelete"))
+                ALLOW_DELETE = true;
+        }
+    
+        String allow = null;
+        if (ALLOW_GET && allow == null)
+            allow = "GET";
+        if (ALLOW_HEAD)
+            if (allow == null)
+                allow = "HEAD";
+            else
+                allow = allow + ", HEAD";
+        if (ALLOW_POST)
+            if (allow == null)
+                allow = "POST";
+            else
+                allow = allow + ", POST";
+        if (ALLOW_PUT)
+            if (allow == null)
+                allow = "PUT";
+            else
+                allow = allow + ", PUT";
+        if (ALLOW_DELETE)
+            if (allow == null)
+                allow = "DELETE";
+            else
+                allow = allow + ", DELETE";
+        if (ALLOW_TRACE)
+            if (allow == null)
+                allow = "TRACE";
+            else
+                allow = allow + ", TRACE";
+        if (ALLOW_OPTIONS)
+            if (allow == null)
+                allow = "OPTIONS";
+            else
+                allow = allow + ", OPTIONS";
+        resp.setHeader("Allow", allow);
+    }
+    
+    protected void doTrace(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        String CRLF = "\r\n";
+        String responseString = "TRACE " + req.getRequestURI() + " " + req.getProtocol();
+        for (Enumeration reqHeaderEnum = req.getHeaderNames(); reqHeaderEnum.hasMoreElements();) {
+            String headerName = (String) reqHeaderEnum.nextElement();
+            responseString = responseString + CRLF + headerName + ": " + req.getHeader(headerName);
+        }
+    
+        responseString = responseString + CRLF;
+        int responseLength = responseString.length();
+        resp.setContentType("message/http");
+        resp.setContentLength(responseLength);
+        ServletOutputStream out = resp.getOutputStream();
+        out.print(responseString);
+        out.close();
+    }
+    
+    private void maybeSetLastModified(HttpServletResponse resp, long lastModified) {
+        if (resp.containsHeader("Last-Modified"))
+            return;
+        if (lastModified >= 0L)
+            resp.setDateHeader("Last-Modified", lastModified);
+    }
+}
+
+/**
+ * 对 HTTP 请求信息进行定义
+ */
+public interface HttpServletRequest extends ServletRequest {
+
+    public static final String BASIC_AUTH = "BASIC";
+    public static final String FORM_AUTH = "FORM";
+    public static final String CLIENT_CERT_AUTH = "CLIENT_CERT";
+    public static final String DIGEST_AUTH = "DIGEST";
+    
+    public abstract String getAuthType();
+    
+    public abstract Cookie[] getCookies();
+    
+    public abstract long getDateHeader(String s);
+    
+    public abstract String getHeader(String s);
+    
+    public abstract Enumeration getHeaders(String s);
+    
+    public abstract Enumeration getHeaderNames();
+    
+    public abstract int getIntHeader(String s);
+    
+    public abstract String getMethod();
+    
+    public abstract String getPathInfo();
+    
+    public abstract String getPathTranslated();
+    
+    public abstract String getContextPath();
+    
+    public abstract String getQueryString();
+    
+    public abstract String getRemoteUser();
+    
+    public abstract boolean isUserInRole(String s);
+    
+    public abstract Principal getUserPrincipal();
+    
+    public abstract String getRequestedSessionId();
+    
+    public abstract String getRequestURI();
+    
+    public abstract StringBuffer getRequestURL();
+    
+    public abstract String getServletPath();
+    
+    public abstract HttpSession getSession(boolean flag);
+    
+    public abstract HttpSession getSession();
+    
+    public abstract boolean isRequestedSessionIdValid();
+    
+    public abstract boolean isRequestedSessionIdFromCookie();
+    
+    public abstract boolean isRequestedSessionIdFromURL();
+}
+
+/**
+ * 对 HTTP 响应信息进行定义
+ */
+public interface HttpServletResponse extends ServletResponse {
+
+    public static final int SC_CONTINUE = 100;
+    public static final int SC_SWITCHING_PROTOCOLS = 101;
+    public static final int SC_OK = 200;
+    public static final int SC_CREATED = 201;
+    public static final int SC_ACCEPTED = 202;
+    public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;
+    public static final int SC_NO_CONTENT = 204;
+    public static final int SC_RESET_CONTENT = 205;
+    public static final int SC_PARTIAL_CONTENT = 206;
+    public static final int SC_MULTIPLE_CHOICES = 300;
+    public static final int SC_MOVED_PERMANENTLY = 301;
+    public static final int SC_MOVED_TEMPORARILY = 302;
+    public static final int SC_SEE_OTHER = 303;
+    public static final int SC_NOT_MODIFIED = 304;
+    public static final int SC_USE_PROXY = 305;
+    public static final int SC_TEMPORARY_REDIRECT = 307;
+    public static final int SC_BAD_REQUEST = 400;
+    public static final int SC_UNAUTHORIZED = 401;
+    public static final int SC_PAYMENT_REQUIRED = 402;
+    public static final int SC_FORBIDDEN = 403;
+    public static final int SC_NOT_FOUND = 404;
+    public static final int SC_METHOD_NOT_ALLOWED = 405;
+    public static final int SC_NOT_ACCEPTABLE = 406;
+    public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
+    public static final int SC_REQUEST_TIMEOUT = 408;
+    public static final int SC_CONFLICT = 409;
+    public static final int SC_GONE = 410;
+    public static final int SC_LENGTH_REQUIRED = 411;
+    public static final int SC_PRECONDITION_FAILED = 412;
+    public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;
+    public static final int SC_REQUEST_URI_TOO_LONG = 414;
+    public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;
+    public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
+    public static final int SC_EXPECTATION_FAILED = 417;
+    public static final int SC_INTERNAL_SERVER_ERROR = 500;
+    public static final int SC_NOT_IMPLEMENTED = 501;
+    public static final int SC_BAD_GATEWAY = 502;
+    public static final int SC_SERVICE_UNAVAILABLE = 503;
+    public static final int SC_GATEWAY_TIMEOUT = 504;
+    public static final int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
+    
+    public abstract void addCookie(Cookie cookie);
+    
+    public abstract boolean containsHeader(String s);
+    
+    public abstract String encodeURL(String s);
+    
+    public abstract String encodeRedirectURL(String s);
+    
+    public abstract void sendError(int i, String s) throws IOException;
+    
+    public abstract void sendError(int i) throws IOException;
+    
+    public abstract void sendRedirect(String s) throws IOException;
+    
+    public abstract void setDateHeader(String s, long l);
+    
+    public abstract void addDateHeader(String s, long l);
+    
+    public abstract void setHeader(String s, String s1);
+    
+    public abstract void addHeader(String s, String s1);
+    
+    public abstract void setIntHeader(String s, int i);
+    
+    public abstract void addIntHeader(String s, int i);
+    
+    public abstract void setStatus(int i);
+}
+```

docs/Tomcat/一个简单的Web服务器代码设计.md

@@ -0,0 +1 @@
+努力编写中...

docs/Tomcat/一个简单的servlet容器代码设计.md

@@ -0,0 +1 @@
+努力编写中...