How can I read context parameter/web.xml values in a non-servlet java file?

Question

I've got a regular java file that I use to update and query a mysql database but I need to take configurable options in that file (like host name, password, etc) and put it in the web.xml file (or perhaps another file if that's an option, but ideally in web.xml).

But I don't know how to get access to web.xml values from a regular non-servlet java file.

Or would I need to read the xml (like any other xml file... or is there a shortcut route to this...)

You had really to mention that this "regular non-servlet Java file" is instantiated and executed in `ServletContextListener#contextInitialized()` (as per your previous question). That would make a lot difference in the correct answer... — BalusC, Nov 16 '10 at 17:34
What server are you using? Tomcat, JBoss, ???. Depending on the server params can be set at the server instance level in several ways. — stjohnroe, Nov 17 '10 at 16:10

stjohnroe · Answer 1 · 2015-09-16T14:15:00.210

32

You need to put the required parameters in env-entry entries of your web.xml file:

<env-entry> 
    <env-entry-name>dbhost</env-entry-name>
    <env-entry-type>java.lang.String</env-entry-type>
    <env-entry-value>localhost</env-entry-value> 
</env-entry>

and then access them via the jndi context

import javax.naming.Context;
import javax.naming.InitialContext;
...
// Get the base naming context
Context env = (Context)new InitialContext().lookup("java:comp/env");

// Get a single value
String dbhost = (String)env.lookup("dbhost");

edited Sep 16 '15 at 14:15

answered Nov 16 '10 at 15:32

stjohnroe

3,168
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Be sure to specify env-entry-type before the env-entry-value, or you might get XML validation errors. – luke Jun 06 '14 at 12:33
Maybe you can add the imports. :) – alexander May 06 '15 at 14:14
@alexander there you go – stjohnroe Sep 16 '15 at 14:16
can your solution be achieved using annotations? – qualebs May 19 '17 at 05:43

score 11 · Answer 2 · answered Nov 16 '10 at 15:33

You could use context-parameters in your web.xml and a javax.servlet.ServletContextListener to populate some static fields.

In you normal java class you read this this static fields.

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
...
<context-param>
    <description>Prameter</description>
    <param-name>myParam</param-name>
    <param-value>123456790</param-value>
</context-param>
...
</web-app>

You can access this context parameter with ServletContext.getInitParameter

score 3 · Answer 3 · answered Nov 16 '10 at 15:26

3

One way is to read xml file and parse it.

You can put it on some static map in after parsing in ServletContextListener

answered Nov 16 '10 at 15:26

jmj

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score 1 · Answer 4 · answered Jun 08 '16 at 08:38

Implement a ServletContextListener:

package util;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyConfigListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        ServletContext ctx = sce.getServletContext();

        String hostname = ctx.getInitParameter("my.config.hostname");

        // now go and do something with that
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {}

}

And don't forget to register it in web.xml:

<context-param>
  <param-value>somewhere.example.org</param-value>
  <param-name>my.config.hostname</param-name>
</context-param>
<listener>
  <listener-class>util.MyConfigListener</listener-class>
</listener>

score 0 · Answer 5 · answered Nov 16 '10 at 15:36

0

Create a static class that would be initialized from one of the servlets init.

answered Nov 16 '10 at 15:36

Eugene Kuleshov

31,461
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1

The difficulty here is in *which* servlet's init. You don't want your application to depend on when Servlet is initialized first. – Eric Wilson Jan 25 '12 at 13:29

How can I read context parameter/web.xml values in a non-servlet java file?

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