java类库详细讲解

				
				
				
				Getting a Request Header in a Servlet
				(Java Developers Almanac Example)
				
				
				
				
				
				
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				The Java Developers Almanac 1.4
				
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				    javax.servlet
				         [11 examples]
				        
				        >
				        Requests
				             [6 examples]
				            
				
				  
				    e1042.  
				    Getting a Request Header in a Servlet
				
				This example demonstrates how to get the value of a request header
				in either a GET or POST request.
				
				
				
				    // See also e1034 The Quintessential Servlet
				    
				    // This method is called by the servlet container to process a GET request.
				    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
				        doGetOrPost(req, resp);
				    }
				    
				    // This method is called by the servlet container to process a POST request.
				    public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
				        doGetOrPost(req, resp);
				    }
				    
				    // This method handles both GET and POST requests.
				    private void doGetOrPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
				        PrintWriter out = resp.getWriter();
				        resp.setContentType("text/plain");
				    
				        // Get the value of a request header; the name is case-insensitive
				        String name = "user-agent";
				        String value = req.getHeader(name);
				        if (value == null) {
				            // The request header was not present
				        }
				    
				        // Get all request headers
				        Enumeration enum = req.getHeaderNames();
				        for (; enum.hasMoreElements(); ) {
				            // Get the name of the request header
				            name = (String)enum.nextElement();
				            out.println(name);
				    
				            // Get a value of the request header
				            value = req.getHeader(name);
				    
				            // If the request header can appear more than once, get all values
				            Enumeration valuesEnum = req.getHeaders(name);
				            for (; valuesEnum.hasMoreElements(); ) {
				                // Get a value of the request header
				                value = (String)valuesEnum.nextElement();
				    
				                out.println("    "+value);
				            }
				        }
				        out.close();
				    }
				
				
				
				
				             Related Examples
				        
				
				
				
				
				e1039. 
				    Getting a Request Parameter in a Servlet
				
				
				
				e1040. 
				    Preventing Concurrent Requests to a Servlet
				
				
				
				e1041. 
				    Getting the Requesting URL in a Servlet
				
				
				
				e1043. 
				    Processing a HEAD Request in a Servlet
				
				
				
				e1044. 
				    Getting the Client's Address in a Servlet
				
				
				
				
				
				
				
				
				© 2002 Addison-Wesley.