servlet learning (7) ServletContext

I. Questions

Session can solve the problem of data sharing between different requests of the same user, so what about data sharing between different users?

Second, solution

Using the ServletContext object

Three, principle

The ServletContext object is created by the server, that is to say, there is only one ServletContext object in a project, the ServletContext object obtained by different users is the same, and the ServletContext object is shared by all users.

Four. Features

The server is created, shared by users, only one per project.

Five, life cycle

Server Start->Server Shutdown

Six, scope

Within the entire project

Seven, use

1. Get the ServletContext object

 //Four ways to get the ServletContext objectServletContext sc1=this.getServletContext();ServletContext sc2=req.getSession().getServletContext();ServletContext sc3=req.getServletContext();ServletContext sc4=this.getServletConfig().getServletContext();System.out.println(sc1==sc2);//trueSystem.out.println(sc1==sc3);//trueSystem.out.println(sc1==sc4);//true

2. Use scope for data sharing and flow

 //Data storagesc1.setAttribute("num", 1);//fetch dataint num=(int) sc1.getAttribute("num");System.out.println(num);//1

3. Get the absolute path of resources under WebRoot/WebContent

 //Get the absolute path of resources under WebContentString path=sc1.getRealPath("1.jsp");System.out.println(path);//F:\Etomcat\webapps\018-ServletXuexi\1.jsp

4. Get the global configuration in web.xml

Role: Decoupling static data and code

First configure the data in web.xml as follows:

Note: Only one key-value pair can be stored between a , and multiple groups declare multiple storages.

 charsetutf-8typetext/html

//Get the global configuration in web.xmlString type=sc1.getInitParameter("type");System.out.println(type);//text/htmlString charset=sc1.getInitParameter("charset");System.out.println(charset);//utf-8

or

Enumeration enumeration=sc1.getInitParameterNames();while(enumeration.hasMoreElements()) {String name=(String) enumeration.nextElement();String value=sc1.getInitParameter(name);System.out.println(name+" "+value);}// output//charset utf-8//type text/html

5. Get the project resource stream object under webroot/webcontent

 InputStream inputStream=sc1.getResourceAsStream("1.jsp");System.out.println(inputStream);//[email protected]

Note: This method can only obtain the resource stream object in the project root directory, and the class stream object needs to be obtained by using the class loader.