servlet解析演进（1）
写程序的人，尤其是写web程序的人都不会对servlet感到陌生。在我们实现自己servlet的时候只要在web页面配置下servlet信息，并且实现servlet的service方法就完事儿大吉了。
简单的实现servlet解析至少需要实现连接器、处理器。连接器负责打开连接门户socket。处理器负责创建数据处理对象，解析http请求。
1、连接器职责：
ServerSocket serverSocket = null;
int port = 8080;
try {//生成服务器socket
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 socket
Socket socket = null;
try {//打开socket
socket = serverSocket.accept();
}
catch (Exception e) {
continue;
}
//调用处理器处理请求
HttpProcessor processor = new HttpProcessor(this);
processor.process(socket);
}
2、处理器的职责
2.1、创建HttpRequest、HttpResponse
//通过socket的输入流生成输入流缓冲区
input = new SocketInputStream(socket.getInputStream(), 2048);
//创建socket输出流缓冲区
output = socket.getOutputStream();
// 创建HttpRequest实例
request = new HttpRequest(input);
// 创建HttpResponse实例对象
response = new HttpResponse(output);
response.setRequest(request);
response.setHeader("Server", "Pyrmont Servlet Container");
2.2、解析请求行 parseRequest(input, output);
// 解析请求行
input.readRequestLine(requestLine);
//获得方法名称 post/get
String method =
new String(requestLine.method, 0, requestLine.methodEnd);
String uri = null;
//获得协议名称http/1.1
String protocol = new String(requestLine.protocol, 0, requestLine.protocolEnd);
// Validate the incoming request line
if (method.length() < 1) {
throw new ServletException("Missing HTTP request method");
}
else if (requestLine.uriEnd < 1) {
throw new ServletException("Missing HTTP request URI");
}
// Parse any query parameters out of the request URI
//解析uri以外的参数
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);
}
//获取uri的绝对路径，将http://等信息跳过去
if (!uri.startsWith("/")) {
int pos = uri.indexOf("://");
// Parsing out protocol and host name
if (pos != -1) {
pos = uri.indexOf('/', pos + 3);
if (pos == -1) {
uri = "";
}
else {
uri = uri.substring(pos);
}
}
}
// uri之外的jessionid信息，如果有设置到request的sessionId之中
String match = ";jsessionid=";
int semicolon = uri.indexOf(match);
if (semicolon >= 0) {
String rest = uri.substring(semicolon + match.length());
//该行除了jessionid之外还有别的字符串
int semicolon2 = rest.indexOf(';');
if (semicolon2 >= 0) {
request.setRequestedSessionId(rest.substring(0, semicolon2));
rest = rest.substring(semicolon2);
}
else {
//只有jessionid信息，直接设置其到requestedSessionId字段中
request.setRequestedSessionId(rest);
rest = "";
}
request.setRequestedSessionURL(true);
uri = uri.substring(0, semicolon) + rest;
}
else {
//如果没有jsessionid，则对应字段置空
request.setRequestedSessionId(null);
request.setRequestedSessionURL(false);
}
// Normalize URI (using String operations at the moment)
String normalizedUri = normalize(uri);
// 设置方法和协议
((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 + "'");
}
}
2.3、解析请求头 parseHeaders(input)
while (true) {
HttpHeader header = new HttpHeader();;
// 按行解析请求行
input.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);
// 设置httprequest 头字段
request.addHeader(name, value);
//设置cookie字段
if (name.equals("cookie")) {
Cookie cookies[] = RequestUtil.parseCookieHeader(value);
for (int i = 0; i < cookies.length; i++) {
if (cookies[i].getName().equals("jsessionid")) {
// Override anything requested in the URL
if (!request.isRequestedSessionIdFromCookie()) {
// Accept only the first session id cookie
request.setRequestedSessionId(cookies[i].getValue());
request.setRequestedSessionCookie(true);
request.setRequestedSessionURL(false);
}
}
request.addCookie(cookies[i]);
}
}
//设置contentLength字段
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);
}
//设置contentType字段
else if (name.equals("content-type")) {
request.setContentType(value);
}
} //end while
2.4、servlet创建，并执行service方法。
public void process(HttpRequest request, HttpResponse response) {
String uri = request.getRequestURI();
String servletName = uri.substring(uri.lastIndexOf("/") + 1);
URLClassLoader loader = null;
try {
// 创建类加载器 URLClassLoader
URL[] urls = new URL[1];
URLStreamHandler streamHandler = null;
//获取类路径
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 {
//类路径中加载类
myClass = loader.loadClass(servletName);
}
catch (ClassNotFoundException e) {
System.out.println(e.toString());
}
Servlet servlet = null;
try {
//实例化类
servlet = (Servlet) myClass.newInstance();
//创建request门面模式
HttpRequestFacade requestFacade = new HttpRequestFacade(request);
//创建response门面模式
HttpResponseFacade responseFacade = new HttpResponseFacade(response);
//调用实例的service方法
servlet.service(requestFacade, responseFacade);
//servlet执行完毕，调用fresh方法将数据写入输出流中
((HttpResponse) response).finishResponse();
}
catch (Exception e) {
System.out.println(e.toString());
}
catch (Throwable e) {
System.out.println(e.toString());
}
}
题外话：
Facate设计模式：
有的时候不想暴露一些方法，可以通过门面模式去实现。
类A有方法B不想暴漏。类A实现了接口C。 那么生成类D，让其实现接口C。并将接口C放置到类D中去。这样，在调用类A的时候，我们可以将其包装成门面模式去暴露给外部接口使用。这样即能够暴露需要暴露的方法，又能够不暴露不需要暴露的方法。
在tomcat实现httpRequest的时候，使用了门面模式。也就是说暴露给我们自定义servlet的不是httpRequest实例，而是httpRequest的门面类实例。原因就是上面说的。