Servlet-客户端HTTP请求

📌 相关文章

📜 Servlet-客户端HTTP请求

📅 最后修改于: 2020-11-12 05:37:55 🧑 作者: Mango

当浏览器请求一个网页时，它会将大量信息发送到Web服务器，该信息无法直接读取，因为该信息作为HTTP请求标头的一部分传播。您可以检查HTTP协议以获取更多信息。

以下是来自浏览器端的重要标头信息，您将在网络编程中经常使用-

Sr.No.	Header & Description
1	Accept This header specifies the MIME types that the browser or other clients can handle. Values of image/png or image/jpeg are the two most common possibilities.
2	Accept-Charset This header specifies the character sets the browser can use to display the information. For example ISO-8859-1.
3	Accept-Encoding This header specifies the types of encodings that the browser knows how to handle. Values of gzip or compress are the two most common possibilities.
4	Accept-Language This header specifies the client’s preferred languages in case the servlet can produce results in more than one language. For example en, en-us, ru, etc
5	Authorization This header is used by clients to identify themselves when accessing password-protected Web pages.
6	Connection This header indicates whether the client can handle persistent HTTP connections. Persistent connections permit the client or other browser to retrieve multiple files with a single request. A value of Keep-Alive means that persistent connections should be used.
7	Content-Length This header is applicable only to POST requests and gives the size of the POST data in bytes.
8	Cookie This header returns cookies to servers that previously sent them to the browser.
9	Host This header specifies the host and port as given in the original URL.
10	If-Modified-Since This header indicates that the client wants the page only if it has been changed after the specified date. The server sends a code, 304 which means Not Modified header if no newer result is available.
11	If-Unmodified-Since This header is the reverse of If-Modified-Since; it specifies that the operation should succeed only if the document is older than the specified date.
12	Referer This header indicates the URL of the referring Web page. For example, if you are at Web page 1 and click on a link to Web page 2, the URL of Web page 1 is included in the Referrer header when the browser requests Web page 2.
13	User-Agent This header identifies the browser or other client making the request and can be used to return different content to different types of browsers.

读取HTTP标头的方法

有以下方法可用于读取servlet程序中的HTTP标头。这些方法可用于HttpServletRequest对象

Sr.No.	Method & Description
1	Cookie[] getCookies() Returns an array containing all of the Cookie objects the client sent with this request.
2	Enumeration getAttributeNames() Returns an Enumeration containing the names of the attributes available to this request.
3	Enumeration getHeaderNames() Returns an enumeration of all the header names this request contains.
4	Enumeration getParameterNames() Returns an Enumeration of String objects containing the names of the parameters contained in this request
5	HttpSession getSession() Returns the current session associated with this request, or if the request does not have a session, creates one.
6	HttpSession getSession(boolean create) Returns the current HttpSession associated with this request or, if if there is no current session and value of create is true, returns a new session.
7	Locale getLocale() Returns the preferred Locale that the client will accept content in, based on the Accept-Language header.
8	Object getAttribute(String name) Returns the value of the named attribute as an Object, or null if no attribute of the given name exists.
9	ServletInputStream getInputStream() Retrieves the body of the request as binary data using a ServletInputStream.
10	String getAuthType() Returns the name of the authentication scheme used to protect the servlet, for example, “BASIC” or “SSL,” or null if the JSP was not protected.
11	String getCharacterEncoding() Returns the name of the character encoding used in the body of this request.
12	String getContentType() Returns the MIME type of the body of the request, or null if the type is not known.
13	String getContextPath() Returns the portion of the request URI that indicates the context of the request.
14	String getHeader(String name) Returns the value of the specified request header as a String.
15	String getMethod() Returns the name of the HTTP method with which this request was made, for example, GET, POST, or PUT.
16	String getParameter(String name) Returns the value of a request parameter as a String, or null if the parameter does not exist.
17	String getPathInfo() Returns any extra path information associated with the URL the client sent when it made this request
18	String getProtocol() Returns the name and version of the protocol the request.
19	String getQueryString() Returns the query string that is contained in the request URL after the path.
20	String getRemoteAddr() Returns the Internet Protocol (IP) address of the client that sent the request.
21	String getRemoteHost() Returns the fully qualified name of the client that sent the request.
22	String getRemoteUser() Returns the login of the user making this request, if the user has been authenticated, or null if the user has not been authenticated.
23	String getRequestURI() Returns the part of this request’s URL from the protocol name up to the query string in the first line of the HTTP request.
24	String getRequestedSessionId() Returns the session ID specified by the client.
25	String getServletPath() Returns the part of this request’s URL that calls the JSP.
26	String[] getParameterValues(String name) Returns an array of String objects containing all of the values the given request parameter has, or null if the parameter does not exist.
27	boolean isSecure() Returns a Boolean indicating whether this request was made using a secure channel, such as HTTPS.
28	int getContentLength() Returns the length, in bytes, of the request body and made available by the input stream, or -1 if the length is not known.
29	int getIntHeader(String name) Returns the value of the specified request header as an int.
30	int getServerPort() Returns the port number on which this request was received.

HTTP标头请求示例

以下是使用HttpServletRequest的getHeaderNames()方法读取HTTP标头信息的示例。此方法返回一个Enumeration，其中包含与当前HTTP请求关联的标头信息。

一旦有了枚举，就可以使用hasMoreElements()方法确定何时停止并使用nextElement()方法获取每个参数名称，以标准方式循环枚举。

// Import required java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
 
// Extend HttpServlet class
public class DisplayHeader extends HttpServlet {
 
   // Method to handle GET method request.
   public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      
      // Set response content type
      response.setContentType("text/html");
 
      PrintWriter out = response.getWriter();
      String title = "HTTP Header Request Example";
      String docType =
         ""-//w3c//dtd html 4.0 " + "transitional//en\">\n";

      out.println(docType +
         "\n" +
         "" + title + "\n"+
         "\n" +
         "" + title + "\n" +
         "

Header Name
Header Value(s)


accept
*/*


accept-language
en-us


user-agent
Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; InfoPath.2; MS-RTC LM 8)


accept-encoding
gzip, deflate


host
localhost:8080


connection
Keep-Alive


cache-control
no-cache

Header Name	Header Value(s)
accept	/
accept-language	en-us
user-agent	Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; InfoPath.2; MS-RTC LM 8)
accept-encoding	gzip, deflate
host	localhost:8080
connection	Keep-Alive
cache-control	no-cache

现在调用上面的servlet将产生以下结果-

HTTP Header Request Example

标头名称	标头值
接受	* / *
接受语言	我们
用户代理	Mozilla / 4.0(兼容； MSIE 7.0； Windows NT 5.1； Trident / 4.0； InfoPath.2； MS-RTC LM 8)
接受编码	gzip，放气
主办	本地主机：8080
连接	活着
缓存控制	无缓存