HTML(HyperText Markup Language)：超文本标记语言
HTTP(HyperText Transfer Protocol)：超文本传输协议
URL(Uniform Resource Locator)：统一资源定位符，以文字的方式来说明因特网上的资源如何取得。
URN(Uniform Resource Name)：代表某个资源独一无二的名称，如图书的ISBN。
URI(Uniform Resource Identifier)：URL和URN是URI的子集。
一个简单的html范例程序：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>HTML范例</title>
</head>
<body>
<form method="get" action="hello.do" name="sample">
姓名：
<input type="text" name="name">
<br />
<button>发送</button>
</form>
</body>
</html>HTML学习资源：http://www.w3school.com.cn/html/index.aspHTTP：指架构在TCP/IP之上应用层的一种协议。它的两个特点：
1、无状态（stateless）通信协议。（无记忆性）
2、基于请求（request）/响应（response）模型。
客户端对服务器发出一个取得资源的请求，服务器将要求的资源响应给客户端，每次的联机只作一次请求/响应，是一种很简单的通信协议，没有请求就没有响应。
在HTTP 协议下，服务器是个健忘的家伙，服务器响应客户端之后，就不会记得客户端的信息，更不会去维护与客户端有关的状态，因此HTTP又称为无状态的通信协议。
浏览器在使用http发送请求，最重要的就是GET和POST。
GET：就是向服务器取得指定的资源。
POST请求：就是请求时发布(POST)信息给服务器。
对于两者如何进行选择？
1、get方式请求参数长度是有限的，过长的或者如文件上传应该使用post请求。
2、get请求参数会出现在地址栏。
3、get请求纯粹是为了取得资源，而不改变服务器上的资源的状态。而post相反。
对于java，JVM(java virtual machine)是java程序唯一认得的操作系统，其可执行文件为.class文件。
对于JSP/Servlet，Web容器是JSP/Servlet唯一认得的http服务器。
URL编解码：
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;
/**
* Created by N3verL4nd on 2017/1/2.
*/
public class HelloWorld
{
public static void main(String[] args) throws UnsupportedEncodingException {
System.out.println(URLEncoder.encode("http://www.baidu.com", "UTF-8"));
System.out.println(URLDecoder.decode("%3A", "UTF-8"));
}
}URL编码针对的字符是UTF-8编码的8个位数值。
对于ascii字符使用1个字节，非ascii如中文使用3个字节。
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;
/**
* Created by N3verL4nd on 2017/1/2.
*/
public class HelloWorld
{
public static void main(String[] args) throws UnsupportedEncodingException {
System.out.println(URLEncoder.encode("我", "UTF-8"));
System.out.println(URLDecoder.decode("%E6%88%91", "UTF-8"));
}
}HTTP规范下的URL编码，并不限使用UTF-8，例如在一个BIG5网页中，若窗体使用get发送中文，则是使用BIG5编码的参数。System.out.println(URLEncoder.encode("我", "BIG5"));
第一个Servlet程序(打印http header)：
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
/**
* Created by N3verL4nd on 2017/1/4.
*/
@WebServlet(name = "testServlet",urlPatterns = {"/test.do"})
public class testServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>TEST</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Hello World</h1>");
out.println("</body>");
out.println("</html>");
out.close();
}
}
/test.do /Servlet /Servlet/test.do host:localhost:8080 connection:keep-alive upgrade-insecure-requests:1 user-agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36 accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8 accept-encoding:gzip, deflate, sdch, br accept-language:zh-CN,zh;q=0.8 cookie:JSESSIONID=CDD8329D5BB881383911AC4CFAB4A159; Idea-e643fc73=b918ddfe-f8fa-43a0-b608-e1670a29b80a
@WebServlet(name = "testServlet",urlPatterns = {"/test.do"})这表示该Servlet名称为testServlet，当请求的URL是/test.do，如http://localhost:8080/Servlet/test.do就会由testServlet处理。
HttpServletRequest
代表请求对象，封装了HTTP请求信息。
HttpServletResponse代表对客户端的响应。
Servlet的编译(需servlet-api.jar。位于D:Tomcatapache-tomcat-9.0.0.M15lib)：
一个简易的Servlet程序对应的文件目录结构如下：
| E:MyDocumentDesktopjspRunwebWEB-INF>tree /f 文件夹 PATH 列表 卷序列号为 025427CF 32D1:7CF3 E:. │ web.xml │ ├─classes │ testServlet.class │ └─lib E:MyDocumentDesktopjspRunwebWEB-INF> |
将web.war拷贝到webapps目录下（D:Tomcatapache-tomcat-9.0.0.M15webapps ）
运行bin目录下的startup.bat
servlet、genericservlet、httpservlet之间的关系：
package javax.servlet;
import java.io.IOException;
public interface Servlet {
public void init(ServletConfig config) throws ServletException;
public ServletConfig getServletConfig();
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException;
public String getServletInfo();
public void destroy();
}
package javax.servlet;
import java.io.IOException;
import java.util.Enumeration;
public abstract class GenericServlet implements Servlet, ServletConfig,
java.io.Serializable {
private static final long serialVersionUID = 1L;
private transient ServletConfig config;
public GenericServlet() {
// NOOP
}
@Override
public void destroy() {
// NOOP by default
}
@Override
public String getInitParameter(String name) {
return getServletConfig().getInitParameter(name);
}
@Override
public Enumeration<String> getInitParameterNames() {
return getServletConfig().getInitParameterNames();
}
@Override
public ServletConfig getServletConfig() {
return config;
}
@Override
public ServletContext getServletContext() {
return getServletConfig().getServletContext();
}
@Override
public String getServletInfo() {
return "";
}
@Override
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
public void init() throws ServletException {
// NOOP by default
}
public void log(String msg) {
getServletContext().log(getServletName() + ": " + msg);
}
public void log(String message, Throwable t) {
getServletContext().log(getServletName() + ": " + message, t);
}
@Override
public abstract void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException;
@Override
public String getServletName() {
return config.getServletName();
}
}package javax.servlet.http;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.DispatcherType;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public abstract class HttpServlet extends GenericServlet {
private static final long serialVersionUID = 1L;
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 final ResourceBundle lStrings =
ResourceBundle.getBundle(LSTRING_FILE);
public HttpServlet() {
// NOOP
}
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(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
} else {
resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
}
}
protected long getLastModified(HttpServletRequest req) {
return -1;
}
protected void doHead(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
if (DispatcherType.INCLUDE.equals(req.getDispatcherType())) {
doGet(req, resp);
} else {
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(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
} else {
resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
}
}
...
}Servlet接口：定义了Servlet应当有的基本行为，所有的Servlet程序都必须实现Servlet接口（GenericServlet或者HttpServlet）。
GenericServlet：实现了Servlet接口，没有规范任何与HTTP相关的方法，而是由继承它的HttpServlet来定义。
HttpServlet的service方法流程：
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String method = req.getMethod(); if (method.equals(METHOD_GET)) { long lastModified = getLastModified(req); if (lastModified == -1) { // servlet doesn't support if-modified-since, no reason // to go through further expensive logic doGet(req, resp); } else { long ifModifiedSince; try { ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE); } catch (IllegalArgumentException iae) { // Invalid date header - proceed as if none was set ifModifiedSince = -1; } if (ifModifiedSince < (lastModified / 1000 * 1000)) { // If the servlet mod time is later, call doGet() // Round down to the nearest second for a proper compare // A ifModifiedSince of -1 will always be less maybeSetLastModified(resp, lastModified); doGet(req, resp); } else { resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED); } } } else if (method.equals(METHOD_HEAD)) { long lastModified = getLastModified(req); maybeSetLastModified(resp, lastModified); doHead(req, resp); } else if (method.equals(METHOD_POST)) { doPost(req, resp); } else if (method.equals(METHOD_PUT)) { doPut(req, resp); } else if (method.equals(METHOD_DELETE)) { doDelete(req, resp); } else if (method.equals(METHOD_OPTIONS)) { doOptions(req,resp); } else if (method.equals(METHOD_TRACE)) { doTrace(req,resp); } else { // // Note that this means NO servlet supports whatever // method was requested, anywhere on this server. // String errMsg = lStrings.getString("http.method_not_implemented"); Object[] errArgs = new Object[1]; errArgs[0] = method; errMsg = MessageFormat.format(errMsg, errArgs); resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg); } }当请求到来时，容器会调用Servlet的service()方法。