SERVLET CONFIG

• A servlet specific configuration object created by a servlet container(W.C) to pass information to a servlet during initialization.

Defined in

  //interface
  javax.servlet.ServletConfig 

• Servlet Config's empty instance is created by the Web container(WC) after instantiation of servlet instance and before call to init() using dependency injection.

• To pass servlet specific initialization parameters, we need this servlet config instance, as we cannot pass servlet specific initialization parameter through default constructor() there is no parametrized servlet constructor. (i.e the init-param is accessible to one servlet only or you can say that the init-param data is private for a particular servlet.)

• Where to add these servlet specific initialization parameters?

  • Can be added either in web.xml or @WebServlet annotation.

  • But preferable is web.xml so as to keep these configuration external to java code, so that changes to java source code and hassles of recompilation can be avoided.

    • XML Tags

      <servlet>
          <servlet-name>init</servlet-name>
          <servlet-class>ex.TestInitParam</servlet-class>
          <!- 
          the below tags are used to pass servlet specific init parameters
          one tag per initialization parameter
          ->
          <init-param>
            <param-name>name</param-name>
            <param-value>value</param-value>
          </init-param>
      </servlet>
      <servlet-mapping>
        <servlet-name>init</servlet-name>
        <url-pattern>/test_init</url-pattern>
      </servlet-mapping>

    • Annotations

      @WebServlet(
        value="/url-pattern", 
        initParams= {@WebInitParam(name="some_name", value="some_value")})

• To access servlet specific initialization parameters from a servlet, override the init() method.

• To get Servlet Config object of the servlet class use,

    //Method of javax.servlet.GenericServlet
    public ServletConfig getServletConfig()

• To get the init parameters from ServletConfig

  //Method of ServletConfig i/f
  String getInitparameter(String name) 
  //rets the parameter value.