@[TOC]
2 Request Object
2.1 Overview of request Objects
2.1.1 About Requests
A request, by definition, is that the user wants to get some resources from the server and make inquiries to the server. In the B/S architecture, the client browser issues a query to the server. In our JavaEE project, the client browser issues queries that comply with the HTTP protocol.
The request object is the object used to send the request in JavaEE project. Our common objects are ServletRequest and HttpServletRequest, and the difference is whether or not they are related to the HTTP protocol.
2.1.2 Common Request Objects
2.2 Common methods
Website:Javaee. Making. IO/javaee – spec… 
2.3 Example of using request Objects
2.3.1 Common methods for requesting objects 1- Obtaining various paths
/** * Request the object to obtain various information */
public class RequestDemo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Local address: server address
String localAddr = request.getLocalAddr();
// Local name: server name
String localName = request.getLocalName();
// Local port: server port
int localPort = request.getLocalPort();
// Client IP address
String remoteAddr = request.getRemoteAddr();
// Call the host
String remoteHost = request.getRemoteHost();
// Visitor port
int remotePort = request.getRemotePort();
// Uniform Resource Identifier
String URI = request.getRequestURI();
// Uniform resource locator
String URL = request.getRequestURL().toString();
// Get the query string
String queryString = request.getQueryString();
// Get the Servlet mapping path
String servletPath = request.getServletPath();
// Output the content
System.out.println("getLocalAddr() is :"+localAddr);
System.out.println("getLocalName() is :"+localName);
System.out.println("getLocalPort() is :"+localPort);
System.out.println("getRemoteAddr() is :"+remoteAddr);
System.out.println("getRemoteHost() is :"+remoteHost);
System.out.println("getRemotePort() is :"+remotePort);
System.out.println("getRequestURI() is :"+URI);
System.out.println("getRequestURL() is :"+URL);
System.out.println("getQueryString() is :"+queryString);
System.out.println("getServletPath() is :"+servletPath);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response); }}Copy the codeRunning results:
2.3.2 Request Object Common Method 2- Obtain request header information
/** * get the request header *@authorDark horse programmer *@Company http://www.itheima.com
*/
public class RequestDemo2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1. Get the header value by name
String value = request.getHeader("Accept-Encoding");
System.out.println("getHeader():"+value);
//2. Get the value of the header by name
Enumeration<String> values = request.getHeaders("Accept");
while(values.hasMoreElements()){
System.out.println("getHeaders():"+values.nextElement());
}
//3. Get an enumeration of the names of the request headers
Enumeration<String> names = request.getHeaderNames();
while(names.hasMoreElements()){
String name = names.nextElement();
String value1 = request.getHeader(name);
System.out.println(name+":"+value1); }}public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response); }}Copy the codeThe result is shown below
2.3.3 Common Methods for Request Objects 3- Get request parameters (very important)
The content is more, please remove drive another blog: yangyongli.blog.csdn.net/article/det…
2.3.4 Read request information in stream form
In addition to obtaining the request parameters as described in section 2.3.3, we can also obtain them in the following code:
/** * Read the request body as a stream */
public class RequestDemo4 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1. Get the byte input stream of the request body
ServletInputStream sis = request.getInputStream();
//2. Read the data in the stream
int len = 0;
byte[] by = new byte[1024];
while((len = sis.read(by)) ! = -1){
System.out.println(new String(by,0,len)); }}public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response); }}Copy the code2.3.5 Chinese Encoding Problem in the Request Body
Too much content, please remove drive another blog: yangyongli.blog.csdn.net/article/det…
2.3.6 Request Forwarding (Difference with Redirection)
In real development, redirection and request forwarding are both responses we use, so what’s the difference between them? Let’s look at the following example:
/ redirection features: * * * * two requests, the browser behavior, change the address bar, request scope of data will be lost * forward requests: * a request, the server, the address bar, the request data is not lost in the domain of * * request domain scope: * the current request (request), and the current request forward *@authorDark horse programmer *@Company http://www.itheima.com
*/
public class RequestDemo6 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1. Get the request scheduling object
RequestDispatcher rd = request.getRequestDispatcher("/RequestDemo7");// If it is for the browser to read, / can write without writing. If you are showing the server, in general, / is required.
// Put the data into the request field
request.setAttribute("CityCode"."bj-010");
//2. Implement the actual forwarding operation
rd.forward(request, response);// Implement the actual forward operation
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response); }}Copy the code/** * the forwarding destination *@authorDark horse programmer *@Company http://www.itheima.com
*/
public class RequestDemo7 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Get the data in the request field
String value = (String)request.getAttribute("CityCode");
response.getWriter().write("welcome to request demo 7 "+value);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response); }}Copy the code2.3.7 Request Contains
In actual development, we may need to combine the contents of two servlets together to respond to the browser, and you all know that HTTP protocol is characterized by one request, one response.
== So it is absolutely impossible to have two servlets responding at the same time. = =
Then we need to use the request contain to combine the output of the responses from both servlets. Let’s look at a specific use example:
/** * the request contains ** which combines the output of the responses from both servlets. * Note: * This inclusion is a dynamic inclusion. * * Dynamic inclusion features: * compile separately, only merge the output at the end. * /
public class RequestDemo8 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.getWriter().write("I am request demo8 ");
//1. Get the request scheduling object
RequestDispatcher rd = request.getRequestDispatcher("/RequestDemo9");
//2. Implement the included operation
rd.include(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response); }}Copy the code/** ** included */
public class RequestDemo9 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.getWriter().write("include request demo 9 ");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { doGet(request, response); }}Copy the code2.3.8 More details
Note the following when requesting forwarding: == The Servlet responsible for forwarding, the response body before and after forwarding is lost, and the forwarding destination responds to the browser. = =
Note for request inclusion: == The included’s response header is missing. Because it’s included. = =