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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-1.0.1\examples\WEB-INF\servlets\SnoopServlet.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。
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