Using init parameters to configure the JEE 8 Web Hello World App Module

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1. Using Context Init Parameters

Useful for setting up DB Connections, Cloud Configs etc.

You declare context init parameters in the web.xml deployment descriptor file

<context-param>
    <param-name>databaseOne</param-name>
    <param-value>sql-server</param-value>
</context-param>
<context-param>
    <param-name>cloudOne</param-name>
    <param-value>google-cloud-platform</param-value>
</context-param>

You can read in these parameters from within your servlet

@WebServlet(
name = "contextParameterServlet",
urlPatterns = {"/contextParameters"}
)
public class ContextParameterServlet extends HttpServlet
{
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
        ServletContext c = this.getServletContext();
        PrintWriter writer = response.getWriter();

        writer.append("databaseOne: ").append(c.getInitParameter("databaseOne"))
              .append(", cloudOne: ").append(c.getInitParameter("cloudOne"));
    }
}

Run the Web App - navigate to the Servlet URL to see the parameters output to the screen

http://localhost:8080/jee8webarchetype/contextParameters

These parameters are globally accessible in your web app from the point of startup

2. Using Servlet Init Parameters

Because only one servlet requires the setup

You declare servlet init parameters in the web.xml deployment descriptor file:

<servlet>
    <servlet-name>servletParameterServlet</servlet-name>
    <servlet-class>com.nicordesigns.ServletParameterServlet</servlet-class>
    <init-param>
        <param-name>database</param-name>
        <param-value>CharityAssociates</param-value>
    </init-param>
    <init-param>
        <param-name>server</param-name>
        <param-value>10.0.12.5</param-value>
    </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>servletParameterServlet</servlet-name>
    <url-pattern>/servletParameters</url-pattern>
</servlet-mapping>

Here you obtain the parameters from the ServletConfig object.

public class ServletParameterServlet extends HttpServlet
{
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
        ServletConfig c = this.getServletConfig();
        PrintWriter writer = response.getWriter();

        writer.append("database: ").append(c.getInitParameter("database"))
              .append(", server: ").append(c.getInitParameter("server"));
    }
}	

3. Using Servlet Annotation Config Init Parameters

This allows config values the be set up in running code:

@WebServlet(name = "UserServlet", urlPatterns = {"/userServlet"}, initParams={
@WebInitParam(name="name", value="Not provided"), 
@WebInitParam(name="email", value="Not provided")}))

Check in the end git branch of this slide show

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