3.1 StringManager

为啥要先讲StringManager呢?
话说tomcat算是一个大型项目了（最新的tomcat7大概有35W行代码），因此处理报错信息就要狠小心，因为报错信息为开发者和系统管理员提供有用的线索。
tomcat把错误信息保存在properties文件中，项目又太大，不能只用一个文件，tomcat为每个需要错误信息的package都提供了一个properties文件。
每一个properties文件都是有一个StringManager的实例负责处理。于是tomcat启动后会存在很多StringManager实例。
每个package中的类共享一个StringManager实例。

public class StringManager {//private构造器,单例private StringManager(String packageName) {...}//包名---StringManager实例映射private static Hashtable<String, StringManager> managers =new Hashtable<String, StringManager>();//考虑了多线程安全,根据包名返回一个StringManager实例     public static final synchronized StringManager getManager(String packageName) {StringManager mgr = managers.get(packageName);if (mgr == null) {mgr = new StringManager(packageName);managers.put(packageName, mgr);}return mgr;}//根据errorCode拿到errorMessage//e.g.  httpConnector.alreadyInitialized=HTTP connector has already been initializedpublic String getString(String key) {...}
}

3.2  模块化

分为三个模块：connector , startup , core .
startup 模块只有一个类Bootstrap, 负责启动应用
connector 模块包含HttpConnector,HttpProcessor,HttpRequest和HttpResponse
core 模块包含ServletProcessor和StaticResourceProcessor

我们把《How Tomcat Works》读书笔记（二）中的HttpServer拆分成两个类：HttpConnector和HttpProcessor,把Request改成HttpRequest,Response改成HttpResponse。

• HttpConnector：等待http请求、构建HttpProcessor，并把请求的socket转交给HttpProcessor
• HttpProcessor：生成request、response对象，传递给ServletProcessor或StaticResourceProcessor
• HttpRequest  ：implements javax.servlet.http.HttpServletRequest
• HttpResponse：implements javax.servlet.http.HttpServletResponse

Bootstrap

public final class Bootstrap {public static void main(String[] args) {HttpConnector connector = new HttpConnector();//启动连接器connector.start();}
}

HttpConnector

import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
/**
*http连接器
**/
public class HttpConnector implements Runnable {//停止flagboolean 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) {// 等待下一个到达ServerSocket的连接Socket socket = null;try {socket = serverSocket.accept();}catch (Exception e){continue;}// 把socket转交给HttpProcessorHttpProcessor processor = new HttpProcessor(this);processor.process(socket);}}public void start(){Thread thread = new Thread(this);thread.start ();}
}

我们再来看一下HTTP请求的第一行：
GET /myApp/ModernServlet? userName=tarzan&password=pw d HTTP/1.1 
绿色部分叫做query string

我们再来看一个HTTP请求对应的类：
这一行对应的类就是RequestLine
它下面的请求头对应的类就是HttpHeader

HttpProcessor

public class HttpProcessor{HttpRequest request;HttpResponse response;private HttpRequestLine requestLine = new HttpRequestLine();public void process(Socket socket) {SocketInputStream input = null;OutputStream output = null;try {input = new SocketInputStream(socket.getInputStream(), 2048);output = socket.getOutputStream();request = new HttpRequest(input);response = new HttpResponse(output);response.setRequest(request);response.setHeader("Server", "Pyrmont Servlet Container");parseRequest(input, output);parseHeaders(input);if (request.getRequestURI().startsWith("/servlet/")) {ServletProcessor processor = new ServletProcessor();processor.process(request, response);}else {StaticResourceProcessor processor = new StaticResourceProcessor();processor.process(request, response);}socket.close();} catch (Exception e) {e.printStackTrace ();}}//解析RequestLineprivate void parseRequest(SocketInputStream input, OutputStream output){...}//解析Headersprivate void parseHeaders(SocketInputStream input,OutputStream output){...}
}

3.2.1 Parsing RequestLine

//从SocketInputStream中读入requestLine
input.readRequestLine(requestLine);

//获取http方法
String method = new String(requestLine.method, 0, requestLine.methodEnd);
//获取协议
String protocol = new String(requestLine.protocol, 0, requestLine.protocolEnd);

//获取queryString并从URI中排除
int question = requestLine.indexOf("?");
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); }

//检查URI是不是绝对路径(with the HTTP protocol),如果是把URI转化成相对路径
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);}}
}

//检查jsessionid是否存在，如果存在，设置request相关属性并从URI中排除
String 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);
}

// 纠正URI的错误（如把￥替换成/)
String normalizedUri = normalize(uri);
// 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 + "'");
}

3.2.2 Parsing Headers

//构造一个HttpHeader
HttpHeader header = new HttpHeader();

//从SocketInputStream中读出下一个Header
input.readHeader(header);

//判断下一个header是否存在
if (header.nameEnd == 0) {if (header.valueEnd == 0) {return;}else {throw new ServletException(sm.getString("httpProcessor.parseHeaders.colon"));    }
}

//获取下一个header的name、value
String name = new String(header.name, 0, header.nameEnd);
String value = new String(header.value, 0, header.valueEnd);

//加入到HttpRequest的HashMap<String,String> headers中
request.addHeader(name, value);

除了普通的header还存在一些需要特殊处理的header,如：
content-length header
cookie header

if (name.equals("cookie")) {... // process cookies here
} 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);
}

3.2.3 Parsing Cookies
下面看一个cookie header的示例 Cookie: userName=budi; password=pwd;
解析cookie用的是org.apache.catalina.util.RequestUtil这个类：

public static Cookie[] parseCookieHeader(String header){if ((header == null) || (header.length 0 < 1) )return (new Cookie[0]); ArrayList cookies = new ArrayList();while (header.length() > 0) {int semicolon = header.indexOf(';');if (semicolon < 0)semicolon = header.length();if (semicolon == 0)break;String token = header.substring(0, semicolon);if (semicolon < header.length())header = header.substring(semicolon + 1);elseheader = "";try {int equals = token.indexOf('=');if (equals > 0) {String name = token.substring(0, equals).trim();String value = token.substring(equals+1).trim();cookies.add(new Cookie(name, value)); }}catch (Throwable e) {; }}return ((Cookie[]) cookies.toArray (new Cookie [cookies.size ()]));
}

在HttpProcessor中我们这样就使用它来解析cookie：

else if (header.equals(DefaultHeaders.COOKIE_NAME)) {Cookie cookies[] = RequestUtil.ParseCookieHeader (value);for (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]);}
}

3.2.4 Obtaining Parameters
请求参数可能存在queryString和Http request body中。我们都要进行检查。

//解析queryString中的参数
String queryString = getQueryString();
try {RequestUtil.parseParameters(results, queryString, encoding);
} catch (UnsupportedEncodingException e) {;
}

//解析request body中的参数
String 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");}
}