Java.Servlets.What is ServletContext?

If ServletConfig is like a servlet’s private config, then ServletContext is like a global shared workspace for the entire web application.

🌍 What Is ServletContext?

ServletContext is an object provided by the servlet container that:

✅ Represents the web application’s runtime environment and
✅ Provides a way for all servlets to share information and resources

📦 Key Use Cases of ServletContext:

Use Case	Example
Sharing data between servlets	Store an object globally with setAttribute()
Reading global config	Get app-level parameters from web.xml
Accessing resources	Load files with getResource() or getRealPath()
Logging	Write to server logs via log()
Getting environment details	Server info, context path, MIME types, etc.

🧪 Example: Sharing Data Between Servlets

Servlet A — set attribute:

@Override
public void init() {
    getServletContext().setAttribute("appStartTime", System.currentTimeMillis());
}

Servlet B — get attribute:

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
    Long startTime = (Long) getServletContext().getAttribute("appStartTime");
    res.getWriter().write("App started at: " + startTime);
}

✅ Works across all servlets in the same app.

📄 web.xml – Global Init Parameters

<context-param>
    <param-name>globalSetting</param-name>
    <param-value>enabled</param-value>
</context-param>

Servlet:

String value = getServletContext().getInitParameter("globalSetting");

🔧 Useful Methods in ServletContext

Method	Purpose
getInitParameter(String)	Get app-wide init param from web.xml
getAttribute(String)	Get a shared app-wide attribute
setAttribute(String, Object)	Set a shared app-wide attribute
removeAttribute(String)	Remove an attribute
getRealPath(String)	Get physical path on the server
getResource(String)	Get resource as URL
getMimeType(String)	Get MIME type based on file extension
getContextPath()	Get the web app’s context root (like /myapp)
log(String)	Write to server log

🧠 ServletContext vs ServletConfig

Feature	ServletConfig	ServletContext
Scope	Per servlet	Entire web app
Data Sharing	Not shared	Shared between all servlets
Defined in	<servlet>	<context-param>
Purpose	Servlet-specific config	App-level config & resource sharing
Access	getServletConfig()	getServletContext()

🧩 Real Use Case Example

@Override
public void contextInitialized(ServletContextEvent sce) {
    ServletContext ctx = sce.getServletContext();
    ctx.setAttribute("appStartTime", Instant.now());
}

This is from a ServletContextListener — perfect for setting shared values at startup.

✅ Summary

Concept	Description
What is it?	A global config and data-sharing object for the entire app
Provided by	Servlet container
Shared?	Yes — among all servlets, filters, listeners
Typical Uses	Config, file access, logging, data sharing
Access via	getServletContext() in servlet or ServletContextListener