14 Servlet——ServletContext

The concept ServletContext object

ServletContext object implement some common data among different memory users

Features:

• The server creates
• Users share

 

Scope : The entire project within

Life Cycle : The server starts to shut down the server

Get ServletContext object

The first way

• ServletContext sc=this.getServletContext();

The second way

• ServletContext sc2=this.getServletConfig().getServletContext();

The third way

• ServletContext sc3=req.getSession().getServletContext();

Use ServletContext object for data sharing

data storage

• sc.setAttribute(String name, Object value);

data collection

• sc.getAttribute ( "str") returns the type Object

note:

• Different users can access the data to ServletContext object.
• Acquired data does not exist return null.

Get in touch with the configuration global configuration data

Some web project needs to keep some users to share static data, then we put these data configuration in web.xml.

Obtain

• sc.getInitParameter (String name); Return Value web.xml configured in accordance with Global Data key name, return type String.
• sc.getInitParameterNames (); returns the key enumeration
• If the data does not exist return null.

Configuration

Add the following code in web.xml

Note: a group <context-param> tag can store a set of key-value pairs of data, a plurality of sets can declare multiple <context-param> are stored.

<context-param>

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

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

</context-param>

　　

Role : static data and code decoupling.

Absolute path to get the project under webroot resources.

• Route entry in the root directory path for the project // get root directory, path parameters; String path = sc.getRealPath (String path)

Get a stream object resources under the webroot

• InputStream is = sc.getResourceAsStream(String path);

note:

• In this way can only get a stream object resources under the project root directory, the file stream object class is required to obtain class loader
• path parameter is a path to the root directory items such as: /doc/1.txt