HttpServlet 是从GenericServlet 继承而来，因此它具有GenericServlet 类似的方法和对象，是我们使用Servlet编程经常用到的包，它支持HTTP 的post 和 get 等方法。

编程思路：下面的例子，运行结果是输出简单地返回客户发送给服务器的请求行和头部信息，以及一些可访问的HTTP 信息等。


SnoopServlet.java 的源代码如下：

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.*;
import javax.servlet.http.*;


public class SnoopServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
PrintWriter out = response.getWriter();
response.setContentType("text/plain");

out.println("Snoop Servlet");
out.println();
out.println("Servlet init parameters:");
Enumeration e = getInitParameterNames();
while (e.hasMoreElements()) {
String key = (String)e.nextElement();
String value = getInitParameter(key);
out.println(" " + key + " = " + value);
}
out.println();

out.println("Context init parameters:");
ServletContext context = getServletContext();
Enumeration enum = context.getInitParameterNames();
while (enum.hasMoreElements()) {
String key = (String)enum.nextElement();
Object value = context.getInitParameter(key);
out.println(" " + key + " = " + value);
}
out.println();

out.println("Context attributes:");
enum = context.getAttributeNames();
while (enum.hasMoreElements()) {
String key = (String)enum.nextElement();
Object value = context.getAttribute(key);
out.println(" " + key + " = " + value);
}
out.println();

out.println("Request attributes:");
e = request.getAttributeNames();
while (e.hasMoreElements()) {
String key = (String)e.nextElement();
Object value = request.getAttribute(key);
out.println(" " + key + " = " + value);
}
out.println();
out.println("Servlet Name: " + getServletName());
out.println("Protocol: " + request.getProtocol());
out.println("Scheme: " + request.getScheme());
out.println("Server Name: " + request.getServerName());
out.println("Server Port: " + request.getServerPort());
out.println("Server Info: " + context.getServerInfo());
out.println("Remote Addr: " + request.getRemoteAddr());
out.println("Remote Host: " + request.getRemoteHost());
out.println("Character Encoding: " + request.getCharacterEncoding());
out.println("Content Length: " + request.getContentLength());
out.println("Content Type: "+ request.getContentType());
out.println("Locale: "+ request.getLocale());
out.println("Default Response Buffer: "+ response.getBufferSize());
out.println();
out.println("Parameter names in this request:");
e = request.getParameterNames();
while (e.hasMoreElements()) {
String key = (String)e.nextElement();
String[] values = request.getParameterValues(key);
out.print(" " + key + " = ");
for(int i = 0; i < values.length; i++) {
out.print(values[i] + " ");
}
out.println();
}
out.println();
out.println("Headers in this request:");
e = request.getHeaderNames();
while (e.hasMoreElements()) {
String key = (String)e.nextElement();
String value = request.getHeader(key);
out.println(" " + key + ": " + value);
}
out.println();
out.println("Cookies in this request:");
Cookie[] cookies = request.getCookies();
if (cookies != null) {
for (int i = 0; i < cookies.length; i++) {
Cookie cookie = cookies[i];
out.println(" " + cookie.getName() + " = "+ cookie.getValue());
}
}
out.println();

out.println("Request Is Secure: " + request.isSecure());
out.println("Auth Type: " + request.getAuthType());
out.println("HTTP Method: " + request.getMethod());
out.println("Remote User: " + request.getRemoteUser());
out.println("Request URI: " + request.getRequestURI());
out.println("Context Path: " + request.getContextPath());
out.println("Servlet Path: " + request.getServletPath());
out.println("Path Info: " + request.getPathInfo());
out.println("Path Trans: " + request.getPathTranslated());
out.println("Query String: " + request.getQueryString());

out.println();
HttpSession session = request.getSession();
out.println("Requested Session Id: " +
request.getRequestedSessionId());
out.println("Current Session Id: " + session.getId());
out.println("Session Created Time: " + session.getCreationTime());
out.println("Session Last Accessed Time: " +session.getLastAccessedTime());
out.println("Session Max Inactive Interval Seconds: " + session.getMaxInactiveInterval());
out.println();
out.println("Session values: ");
Enumeration names = session.getAttributeNames();
while (names.hasMoreElements()) {
String name = (String) names.nextElement();
out.println(" " + name + " = " + session.getAttribute(name));
}
}
}
编程技巧说明：

程序输出Init Parameters(初始化参数)、Attribute names in this request、Parameter names in this request、Headers in this request、Cookies in this request 和 Session Information等信息。
方法getRequestURI返回的对象URI 是作为URL 的一部分，是去掉URL 中用于指定机器的那部分；方法getPathInfo 返回的字符串是客户向Servlet 传送的各种选项，这些选项是跟在Servlet 的URL 之后的，方法getPathTranslated 返回的字符串是Servlet 的自己的绝对路径名，SnoopServlet.class 文件位置是C:jswdk-1.0.1examplesWEB-INFservletsSnoopServlet.class，则方法getPathTranslated 返回的字符串值就是它。

在浏览器中输入如下的地址：

http://localhost:8080/examples/servlet/SnoopServlet
则会输出结果。