Java，NetBean：从Web Service方法访问web.xml上下文参数？

Question

I am new to java so excuse my lame questions:)

I am trying to build a web service in Java NetBeans 6.1 , but I have some troubles with configuration parameters ( like .settings in .net).

What is the right way to save and access such settings in a java web service.

Is there a way to read context parameters from web.xml in a web method?

If no what are the alternatives for storing your configuration variables like pathnames ?

Thank you

Answer 1

Is there a way to read context parameters from web.xml in a web method?

No, this is not easily done using the out-of-the-box. The Web Service system (JAX-WS) has minimal awareness of the Servlet engine (Tomcat). They are designed to be isolated.

If you wanted to use the context parameters, your web service class would need to implement ServletContextListener and retrieve the desired parameters in the initialization parameter (or save the context for later use). Since the Servlet engine and JAX-WS would each have different instances of the object, you'd need to save the values to a static member.

As Lars mentioned, the Properties API or JNDI are your best bets as they're included with Java and are fairly well-known ways to retrieve options. Use Classloader.getResource() to retrieve the Properties in a web context.

Answer 2

If you are using servlets, you can configure parameters in web.xml:

<servlet>
  <servlet-name>jsp</servlet-name>
  <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
    <init-param>
      <param-name>fork</param-name>
      <param-value>false</param-value>
     </init-param>
</servlet>

These properties will be passed in a ServletConfig object to your servlet's "init" method.

Another way is to read your system's environment variables with

System.getProperty(String name);

But this is not recommended for other than small programs and tests.

There is also the Properties API if you want to use ".properties" files. http://java.sun.com/javase/6/docs/api/java/util/Properties.html

Finally, I believe looking up configurations with JNDI is pretty common when developing modern web service applications, Netbeans and app containers have pretty good support for that. Google it.

Answer 3

MessageContext ctx = MessageContext.getCurrentThreadsContext();       
Servlet wsServlet = (Servlet) ctx.getProperty(HTTPConstants.MC_HTTP_SERVLET);         
ServletConfig wsServletConfig = wsServlet.getServletConfig();                 
ServletContext wsContext = wsServletConfig.getServletContext();   

Answer 4

I think the correct answer is ... as always ... "It depends". If you are just running a small implementation with a single server then it depend much on the WS technology you want to use. Some make the servlet context and the context-params easy to access, others don't, in which case accessing properties from a properties file may be easier. Are you going to have an array of servers in a load balanced environment with high traffic where updating the setting for all servers must be instant and centralized in-case of fail-over? If that's the case then do you really want to update the config files for all servers in the farm? How do you synchronize those changes to all those servers? Does it matter to you? If you're storing path-names in a config file then you probably intend to be able to update the path-names to another host in case certain host goes down ("\\file_server_host\\doc_store" --> "\\backup_file_server_host\\doc_store") in which case is may actually be better to fail-over using DNS instead. There are too many variables. It really depends on the design; needs; scale of the app.

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For simplicity sake, if you just want a simple equivalent of a .settings file then you want a .properties file. Here is an example where I have recently used this in a project: https://github.com/sylnsr/docx4j-ws/blob/master/src/docx4j/TextSubstitution.java