ServletContext、request、response

One 、 Context object

1、 summary

ServletContext Official call servlet Context , It's an interface . Created when the server starts , Destroy when the server is shut down , At startup, an object will be created for each project , This object is ServletContext object . This object is globally unique , And everything inside the project servlet All share this object . So it's called global application sharing object .

2、 How to get

adopt servlet Medium init Methods servletConfig Object acquisition

httpservlet Medium direct acquisition ServletContext servletContext   = getServletContext();

3、 effect

1.       Is a domain object

The domain object is the storage space created by the server in memory , Used in different dynamic resources （servlet） Transfer and share data between , All domain objects have the following 3 A way

setAttribute(name,value);name yes String type ,value yes Object type ;

Add data to the domain object , Add with key-value Form add

getAttribute(name);

According to the designation key Read the data in the domain object

removeAttribute(name);

According to the designation key Delete data from the domain object

2.       You can read global configuration parameters

getServletContext().getInitParameter(name);// Get the parameter value according to the specified parameter name

getServletContext().getInitParameterNames();// Get a list of all parameter names

stay web.xml Configure global parameters in

 <!--  Global configuration parameter , Because it doesn't belong to any one servlet, But all servlet Both can pass servletContext Read this data  -->

  <context-param>

         <param-name>param1</param-name>

         <param-value>value1</param-value>

  </context-param>

   <context-param>

         <param-name>param2</param-name>

         <param-value>value2</param-value>

  </context-param>

  In dynamic resources servlet It uses servletcontext Read the global parameter code

ublic void doGet(HttpServletRequest request, HttpServletResponse response)

                    throws ServletException, IOException {

          

           // Use servletContext Read the global configuration parameter data 

           // The core approach 

           /*getServletContext().getInitParameter(name);// Get the parameter value according to the specified parameter name 

           getServletContext().getInitParameterNames();// Get a list of all parameter names */

          

           // Print all parameters 

           //1. First get the names of all global configuration parameters 

           Enumeration<String> enumeration =  getServletContext().getInitParameterNames();

           //2. Ergodic iterator 

           while(enumeration.hasMoreElements()){

                    // Get the parameter name of each element 

                    String parameName = enumeration.nextElement();

                    // Get the parameter value according to the parameter name 

                    String parameValue = getServletContext().getInitParameter(parameName);

                    // Print 

                    System.out.println(parameName+"="+parameValue);

           }

         }

3.       You can search the resource files under the current project directory

getServletContext().getRealPath(path), Get the absolute path of resources on the server according to the relative path

getServletContext().getResourceAsStream(path), Get the input byte stream of resources on the server according to the relative path

4.       You can get the current project name （ understand ）

publicvoid doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Get the project name ,getServletContext().getContextPath()
        response.getOutputStream().write((" Project name ："+getServletContext().getContextPath()).getBytes());

    }

Two 、 Request object request

1、 summary

We're creating Servlet It will cover service() Method , or doGet()/doPost(), These methods have two parameters , A request for request And representatives respond response.service（） Method is called according to different request methods doget() and dopost().

service Methods request The type is ServletRequest, and doGet/doPost Methodical request type HttpServletRequest,HttpServletRequest yes ServletRequest Sub interface of , More powerful functions and methods

request Operation process

2、 Grab http package , Grasp the request line respectively , Request header , Request body （post The request method will have ）

Request line

Get the client's request mode ---StringgetMethod()

web Name of application ---StringgetContextPath() 

obtain URL---StringBuffer getRequestURL(); Such as ：http://localhost:8080/request/info

obtain URI---String getRequestURI(); Such as ：/request/info

Get access to the client IP Address ---request.getRemoteAddr()

obtain get Request parameters ---String getQueryString();

Request header

Get all request header names

// All request header names 
        Enumeration<String> headerNames = request.getHeaderNames();
        // Traverse all request headers 
        while (headerNames.hasMoreElements()){
            // name 
            String s = headerNames.nextElement();
            // The value corresponding to the name 
            String requestHeader = request.getHeader(s);
            System.out.println(requestHeader);
        }

Get the source of this visit referer

String referer= request.getHeader("referer");

Only by requesting in the following way can we get referer

• Direct use <a href="">
• submit Submit Form
• s Submitted forms （get \post)

Request body

Forwarding and redirection

3、 ... and 、 The response object

Set the response line

response.setState(Int code)

Set the response header

add Yes add new

addHeader(String name,String value)

addIntHeader(String name,int value)

addDateHeader(String name,date)

set The setting already exists

setHeader(String name,String value)

setIntHeader(String name,int value)

setDateHeader(String name,Date value)

Set the response body

1、 adopt write() Method to write

response.getWriter().write("hello test ");

By default, Chinese characters written will be garbled , When saving the written content to the buffer for use ISO8859, and ISO8859 No Chinese support , So random code

// Set the stored code before saving 
response.setCharacterEncoding("UTF-8");
// Then tell the browser the encoding used 
response.setHeader("Content-Type","text/html;charset=UTF-8");
response.getWriter().write("hello  test ");

 Be careful 
 The above can only tell the browser the code used ,tomcat See, it's set to utf-8  It will also be used in storage utf-8
 Or directly use the encapsulated method 
response.setContentType("text/html;charset=UTF-8");
response.getWriter().write("hello  test ");

2、 adopt OutPutStream() To write

Be careful getWrite() and getOutputSteam Cannot call at the same time

response.setContentType("text/html;charset=UTF-8");
response.getOutputStream().write("hello  test ".getBytes());

Redirect

servlet1 There is no such resource , Tell you to find servlet2, Send another request to servlet2, To access the server twice , Status code is 302, The browser address bar has changed

response.setStatus(302);
response.setHeader("location","/userInfo");
 Write the status code every time , and location More trouble , It encapsulates a method 
response.sendRedirect("/userInfo");

Regular refresh redirection

response.setHeader("refresh","5;url=http://www.baidu.com")

url The value of is 5 The address to jump in seconds