// StringManager的source code.
// 该类用于处理 properties文件， 这些文件记录其所在包的类的错误信息；
public class StringManager {private static Hashtable managers = new Hashtable();private String packageName;private StringManager(String packageName) {this.packageName = packageName;}public synchronized static StringManager getManager(String packageName) {StringManager manager = (StringManager) managers.get(packageName);if(manager == null) {manager = new StringManager(packageName);managers.put(packageName, manager);}return manager;}
}

StringManager  manager = StringManger.getManager("com.baidu");

httpConnector.alreadyInitialized=HTTP connector has already been initialized

调用 StringManager 的 getString() 方法，传入httpConnector.alreadyInitialized 就可以返回 value=HTTP connector has already been initialized

t1）连接器及其支持类（HttpConnector and HttpProcessor）；

t2）表示HTTP 请求的类（HttpRequest）及其支持类；

t3）表示HTTP响应的类（HttpResponse）及其支持类；

t4）外观类（HttpRequestFacade and HttpResponseFacade）；

t5）常量类；

d1）启动应用程序；

d2）连接器；

d3）创建 HttpRequest 对象；

d4）创建 HttpResponse 对象；

d5）静态资源处理器和 servlet处理器；

d6）运行应用程序；

// 启动应用程序
public final class Bootstrap {public static void main(String[] args) {HttpConnector connector = new HttpConnector(); // 连接器connector.start(); //启动一个线程}
}

创建服务器套接字并接受 client发出的HTTP请求，之后调用连接器的支持类 HttpProcessor(HTTP处理器)的process方法.
）

o1）等待HTTP请求；

o2）为每个请求创建一个 HttpProcessor实例；

o3）调用 HttpProcessor 对象的 process（） 方法；（干货——我们赶紧转向 HttpProcessor）：

// 等待HTTP 请求 的工作(连接器)
public class HttpConnector implements Runnable { // 创建服务器套接字并接受 client发出的HTTP请求，之后调用连接器的支持类 HttpProcessor(HTTP处理器)的process方法.boolean stopped;private String scheme = "http";public String getScheme() {return scheme;}public void run() {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);}while (!stopped) {// Accept the next incoming connection from the server socketSocket socket = null;// 负责创建一个服务器套接字。try {socket = serverSocket.accept(); // 等待HTTP请求}catch (Exception e) {continue;}// Hand this socket off to an HttpProcessorHttpProcessor processor = new HttpProcessor(this);processor.process(socket);}}public void start() {Thread thread = new Thread(this);thread.start();}
}

o1）创建一个 HttpRequest对象；

o2）创建一个 HttpResponse对象；

o3）解析HTTP 请求的第一行内容和请求头信息，填充 HttpRequest对象；

o4）将 HttpRequest 对象和 HttpResponse对象传递给 servletProcessor 或 StaticResourceProcessor 的process（） 方法；

public void process(Socket socket) {@SuppressWarnings("deprecation")SocketInputStream input = null;OutputStream output = null;try {input = new SocketInputStream(socket.getInputStream(), 2048);output = socket.getOutputStream();// create HttpRequest object and parserequest = new HttpRequest(input);// create HttpResponse objectresponse = new HttpResponse(output);response.setRequest(request);response.setHeader("Server", "Pyrmont Servlet Container"); // 向客户发送响应头信息parseRequest(input, output); // 解析请求，填充HttpReqeust对象（请求的是静态资源还是servlet，具体是什么静态资源或servlet）parseHeaders(input); // 解析请求头，//check if this is a request for a servlet or a static resource//a request for a servlet begins with "/servlet/"if (request.getRequestURI().startsWith("/servlet/")) {ServletProcessor processor = new ServletProcessor();processor.process(request, response);}else {StaticResourceProcessor processor = new StaticResourceProcessor();processor.process(request, response);}// Close the socketsocket.close();// no shutdown for this application}catch (Exception e) {e.printStackTrace();}}

step1）读取套接字的输入流；

step2）解析请求行；

step3）解析请求头；

step4）解析Cookie；

step5）获取参数；

3.2.1）parseRequest方法首先会调用 SocketInputStream类的readRequestLine方法；

3.2.2）parseRequest方法从请求行中获取请求方法，URI 和 请求协议的版本信息：（对parseRequest()方法进行分解阐述）

  private void parseRequest(@SuppressWarnings("deprecation") SocketInputStream input, OutputStream output)throws IOException, ServletException {input.readRequestLine(requestLine); <span style="font-family: 宋体;">// Parse the incoming request line</span>String method =new String(requestLine.method, 0, requestLine.methodEnd);String uri = null;String protocol = new String(requestLine.protocol, 0, requestLine.protocolEnd);

3.2.3）在URI后面可能还有查询字符串，调用setQueryString方法来解决；（干货——查询字符串如name=tang&pwd=123456）

 // Parse any query parameters out of the request URIint question = requestLine.indexOf("?"); // 询问是否有查询字符串if (question >= 0) {request.setQueryString(new String(requestLine.uri, question + 1,requestLine.uriEnd - question - 1));uri = new String(requestLine.uri, 0, question);}else {request.setQueryString(null);uri = new String(requestLine.uri, 0, requestLine.uriEnd);}

3.2.4）parseRequest会进行相对路径和绝对路径的检查；

 // Checking for an absolute URI (with the HTTP protocol)if (!uri.startsWith("/")) {int pos = uri.indexOf("://");// Parsing out protocol and host nameif (pos != -1) {pos = uri.indexOf('/', pos + 3);if (pos == -1) {uri = "";}else {uri = uri.substring(pos);}}}

3.2.5）检查查询字符串中是否包含会话标识符（jsessionid），解析后并将其填充到 HttpRequest；（干货——会话标识符：浏览器的会话使用存储在 SessionID 属性中的唯一标识符进行标识。）

 // 检查是否有会话标识符，如果有的话，做进一步解析// Parse any requested session ID out of the request URIString match = ";jsessionid=";int semicolon = uri.indexOf(match);if (semicolon >= 0) {String rest = uri.substring(semicolon + match.length());int semicolon2 = rest.indexOf(';');if (semicolon2 >= 0) {request.setRequestedSessionId(rest.substring(0, semicolon2));rest = rest.substring(semicolon2);}else {request.setRequestedSessionId(rest);rest = "";}request.setRequestedSessionURL(true);uri = uri.substring(0, semicolon) + rest;}else {request.setRequestedSessionId(null);request.setRequestedSessionURL(false);}// Normalize URI (using String operations at the moment)String normalizedUri = normalize(uri);    

3.2.6）parseRequest方法将URI 传入到 normaliza方法，对非正常的URL 进行修正；（如，出现'\'将其修正为 '/'）

3.2.7）最后，parseRequest方法会设置HttpRequest对象的一些属性

// Set the corresponding request properties((HttpRequest) request).setMethod(method);request.setProtocol(protocol);if (normalizedUri != null) {((HttpRequest) request).setRequestURI(normalizedUri);}else {((HttpRequest) request).setRequestURI(uri);}if (normalizedUri == null) {throw new ServletException("Invalid URI: " + uri + "'");}}

t1）可以通过无参构造器创建HttpHeader 实例；

t2）可以将其实例传给 SocketInputStream类的readHeader（） 方法；

t3）获取请求头的名字和值，使用如下方法：

t4）parseHeaders() 方法有一个while循环，后者不断从SocketInputStream 中读取请求头信息，直到全部读完；

t5）然后，可以通过检查HttpHeader实例的nameEnd 和valueEnd 字段来判断是否已经从输入流中读取了所有的请求头信息；

3.3.1）当读取完请求头的名称和值之后，调用 HttpReqeust 的 addHeader() 方法，将其添加到HttpRequest 对象的HashMap请求头中：request.addHeader(name, value);

 // protected HashMap headers = new HashMap(); headers 就是一个hashmap（键值对）public void addHeader(String name, String value) {name = name.toLowerCase();synchronized (headers) {ArrayList values = (ArrayList) headers.get(name);if (values == null) {values = new ArrayList();headers.put(name, values);}values.add(value);}}

3.3.2）某些请求头包含一些属性设置信息

 private void parseHeaders(@SuppressWarnings("deprecation") SocketInputStream input)throws IOException, ServletException {while (true) {@SuppressWarnings("deprecation")HttpHeader header = new HttpHeader();;// Read the next headerinput.readHeader(header);if (header.nameEnd == 0) {if (header.valueEnd == 0) {return;}else {throw new ServletException(sm.getString("httpProcessor.parseHeaders.colon"));}}String name = new String(header.name, 0, header.nameEnd);String value = new String(header.value, 0, header.valueEnd);request.addHeader(name, value); // this line.// do something for some headers, ignore others.if (name.equals("cookie")) {Cookie cookies[] = RequestUtil.parseCookieHeader(value); // this line , parse Cookie infofor (int i = 0; i < cookies.length; i++) {if (cookies[i].getName().equals("jsessionid")) {// Override anything requested in the URLif (!request.isRequestedSessionIdFromCookie()) {// Accept only the first session id cookierequest.setRequestedSessionId(cookies[i].getValue());request.setRequestedSessionCookie(true);request.setRequestedSessionURL(false);}}request.addCookie(cookies[i]);}}else if (name.equals("content-length")) {int n = -1;try {n = Integer.parseInt(value);}catch (Exception e) {throw new ServletException(sm.getString("httpProcessor.parseHeaders.contentLength"));}request.setContentLength(n);}else if (name.equals("content-type")) {request.setContentType(value);}} //end while}

3.4.1）intro to Cookie：Cookie是由浏览器作为HTTP请求头的一部分发送的。这样的请求头名称是 cookie，其对应值是一些名值对。（干货——intro to Cookie）

Cookie是由服务器端生成，发送给User-Agent（一般是浏览器），浏览器会将Cookie的key/value保存到某个目录下的文本文件内，下次请求同一网站时就发送该Cookie给服务器（前提是浏览器设置为启用cookie）。Cookie名称和值可以由服务器端开发自己定义，对于JSP而言也可以直接写入jsessionid，这样服务器可以知道该用户是否是合法用户以及是否需要重新登录等，服务器可以设置或读取Cookies中包含信息，借此维护用户跟服务器会话中的状态。（干货——Cookie的作用）

3.4.2）看个荔枝：下面是一个Cookie请求头的荔枝，包含两个Cookie：userName 和 password；

Cookie：userName=tang； password=xiao；

3.4.3）对Cookie的解析 通过 RequestUtil.parseCookieHeader() 方法来完成：解析完Cookie后，交由 HttpProcessor 类 的 parseHeader() 方法处理；

 if (parsed)return;

ParameterMap results = parameters;
if (results == null)results = new ParameterMap();

results.setLocked(false);

String encoding = getCharacterEncoding();if (encoding == null)encoding = "ISO-8859-1";

// Parse any parameters specified in the query stringString queryString = getQueryString();try {RequestUtil.parseParameters(results, queryString, encoding);}catch (UnsupportedEncodingException e) {;}

protected void parseParameters() {if (parsed)return;ParameterMap results = parameters;if (results == null)results = new ParameterMap();results.setLocked(false);String encoding = getCharacterEncoding();if (encoding == null)encoding = "ISO-8859-1";// Parse any parameters specified in the query stringString queryString = getQueryString();try {RequestUtil.parseParameters(results, queryString, encoding);}catch (UnsupportedEncodingException e) {;}// Parse any parameters specified in the input streamString contentType = getContentType();if (contentType == null)contentType = "";int semicolon = contentType.indexOf(';');if (semicolon >= 0) {contentType = contentType.substring(0, semicolon).trim();}else {contentType = contentType.trim();}if ("POST".equals(getMethod()) && (getContentLength() > 0)&& "application/x-www-form-urlencoded".equals(contentType)) {try {int max = getContentLength();int len = 0;byte buf[] = new byte[getContentLength()];ServletInputStream is = getInputStream();while (len < max) {int next = is.read(buf, len, max - len);if (next < 0 ) {break;}len += next;}is.close();if (len < max) {throw new RuntimeException("Content length mismatch");}RequestUtil.parseParameters(results, buf, encoding);}catch (UnsupportedEncodingException ue) {;}catch (IOException e) {throw new RuntimeException("Content read fail");}}// Store the final resultsresults.setLocked(true);parsed = true;parameters = results;}

 // Store the final resultsresults.setLocked(true);parsed = true;parameters = results;

public PrintWriter getWriter() throws IOException {ResponseStream newStream = new ResponseStream(this);newStream.setCommit(false);OutputStreamWriter osr =new OutputStreamWriter(newStream, getCharacterEncoding());writer = new ResponseWriter(osr);return writer;}

public void process(HttpRequest request, HttpResponse response) {

((HttpResponse) response).finishResponse();

public class ServletProcessor {public void process(HttpRequest request, HttpResponse response) {String uri = request.getRequestURI();String servletName = uri.substring(uri.lastIndexOf("/") + 1);URLClassLoader loader = null;try {// create a URLClassLoaderURL[] 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("servlet." + servletName);}catch (ClassNotFoundException e) {System.out.println(e.toString());}Servlet servlet = null;try {servlet = (Servlet) myClass.newInstance();HttpRequestFacade requestFacade = new HttpRequestFacade(request);HttpResponseFacade responseFacade = new HttpResponseFacade(response);servlet.service(requestFacade, responseFacade);((HttpResponse) response).finishResponse();}...}
}

E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot com.tomcat.chapter3.startup.Bootstrap