Java.Servlet.What is the difference between ServletContext and ServletConfig?

Both ServletContext and ServletConfig are part of the Servlet API, but they serve different scopes and purposes. Let’s break them down side by side 👇

🧠 Core Difference

Feature	ServletConfig	ServletContext
Scope	One servlet only	Entire web application
Purpose	Passes init parameters to a specific servlet	Shares global configuration and resources
Data sharing	❌ Not shared across servlets	✅ Shared across all servlets and filters
Defined in	<servlet> tag in web.xml or @WebServlet	<context-param> tag in web.xml or via listener
Accessed via	getServletConfig()	getServletContext()
Lifecycle	Created per servlet	Created once per application
Typical use case	Read servlet-specific config like db URL	Share app-wide info like version, cache, shared objects

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📄 Example: web.xml with Both

<context-param>
  <param-name>appVersion</param-name>
  <param-value>1.0.0</param-value>
</context-param>

<servlet>
  <servlet-name>MyServlet</servlet-name>
  <servlet-class>com.myapp.MyServlet</servlet-class>
  <init-param>
    <param-name>dbUrl</param-name>
    <param-value>jdbc:mysql://localhost/mydb</param-value>
  </init-param>
</servlet>

🔧 Accessing Values in Servlet

@Override
public void init(ServletConfig config) throws ServletException {
    super.init(config);

    // From ServletConfig (specific to this servlet)
    String dbUrl = config.getInitParameter("dbUrl");

    // From ServletContext (shared by all servlets)
    String version = config.getServletContext().getInitParameter("appVersion");
}

Or in modern style (if you override init() without arguments):

String dbUrl = getServletConfig().getInitParameter("dbUrl");
String version = getServletContext().getInitParameter("appVersion");

🧪 ServletConfig vs ServletContext: Analogy

Analogy	ServletConfig	ServletContext
👤 Per-employee data	Their desk nameplate	Company-wide notice board
📦 Per-component config	Your specific component’s config	App-level shared resources and settings

✅ Summary

Key Point	ServletConfig	ServletContext
For what?	One specific servlet	Entire application
Shared?	❌ No	✅ Yes
Common usage	Read servlet init parameters	Read global parameters or share data
Who creates it?	Container (one per servlet)	Container (one per app)