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

问题

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...)

回答1:

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");

回答2:

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

回答3:

One way is to read xml file and parse it.

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

回答4:

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>

回答5:

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

来源：https://stackoverflow.com/questions/4195688/how-can-i-read-context-parameter-web-xml-values-in-a-non-servlet-java-file

标签

java

servlets

web.xml