CODEWITHSUNDEEP
javagwt
john
john

Reputation: 777

GWT ServleContext and retrieving a file

I am working on a GWT application, and I'm trying to retrieve the file from "war/config/config.properties". In GWT server side I made a class called Config.java which creates a new Properties object and populates it from config.properties, I've extended Config with RemoteServiceServlet to be able to use getServletContext(). I am using the following line to load the properties 

prop.load(ServletContext.class.getResourceAsStream("config/config.properties"));

and my config.properties file looks like this

database=db
host=192.168.1.1
password=pass
user=user

and my config class looks like this

public class Config extends RemoteServiceServlet {

Properties prop = new Properties();

public Config(){
    //load a properties file
    try {           
        ServletContext sc = getServletContext();            
        prop.load(sc.getResource("/config/config.properties").openStream());

        //System.out.println("Get Real Path" + getServletContext().getRealPath("config") + "/config.properties");
        //FileInputStream input = (FileInputStream) getServletContext().getResourceAsStream("/config/config.properties");
        //prop.load(new FileInputStream(getServletContext().getRealPath("/config/config.properties")));
        //prop.load(input);
        System.out.println("properties file loaded successfully");

    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        System.out.println("Could not find properties file");
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (NullPointerException e) {
        System.out.println("null pointer exception in loading properties file");
        e.printStackTrace();
    }
}

public String getProperty(String name){
    return prop.getProperty(name);
}

}

and yet for the life of me I can't figure out why I'm getting a null pointer exception when I am loading properties, simply refuses to work. Stack trace is here, any idea's what I'm doing wrong? 

java.lang.NullPointerException
    at java.util.Properties$LineReader.readLine(Unknown Source)
    at java.util.Properties.load0(Unknown Source)
    at java.util.Properties.load(Unknown Source)
    at com.cbs.ioma.server.Config.<init>(Config.java:19)
    at com.cbs.ioma.server.DatabaseServiceImpl.<init>(DatabaseServiceImpl.java:61)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at org.mortbay.jetty.servlet.Holder.newInstance(Holder.java:153)
    at org.mortbay.jetty.servlet.ServletHolder.getServlet(ServletHolder.java:339)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:463)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:324)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)``

edit: I changed my code to reflect a comment below, new error is posted here 

> java.lang.NullPointerException    at
> javax.servlet.GenericServlet.getServletContext(GenericServlet.java:160)
>   at com.cbs.ioma.server.Config.<init>(Config.java:19)

edit: I changed my class, could you take a look and tell me how I'm supposed to call the servlet? I don't get how I'm supposed to override the method, if its called by another method in Servlet. how do I implement it?

public class Config extends RemoteServiceServlet {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    Properties prop = new Properties();

    public Config(){

    }

    public String getProperty(String name){
        return prop.getProperty(name);

    }

    @Override
    public void init(ServletConfig config) throws ServletException
    {
        super.init(config);
        try {           
            prop.load(config.getServletContext().getResource("/config/config.properties").openStream());
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

Upvotes: 1

Views: 1373

Answers (2)

manubot
manubot

Reputation: 290

I propose you use a higher level library to take care of that for you.

For example use ResourceBundle

ResourceBundle bundle = ResourceBundle.getBundle(fully.qualified.path.using.dots.to.properties);
bundle.getString("your_property_key");

Upvotes: 0

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 280092

I misread your question. If the file is in war/config/config.properties, you should use

ServletContext sc = ...// get servlet context; 
sc.getResource("/config/config.properties");

as described in the javadoc:

Returns a URL to the resource that is mapped to a specified path. The path must begin with a "/" and is interpreted as relative to the current context root.

Edit

When a Servlet container starts up, it instantiates your Servlet (Config for you) class using the no-args constructor. It then calls its Servlet#init(ServletConfig) method where you can finally have access to the ServletContext. This is where you should initialize your Properties object. So override the method and move your current constructor code to it.

For your information

Don't do this

ServletContext.class.getResourceAsStream("config/config.properties")

If config/config.properties is at the root of the classpath, use

ServletContext.class.getResourceAsStream("/config/config.properties")

The top case will take the name of the package that ServletContext is in and try to resolve your specified path with it. For example, ServletContext is in javax.servlet, so

/javax/servlet/config/config.properties

Your resource is clearly not in there. The rules for what path you should specify are described in the javadoc of Class#getResource(String).

Upvotes: 1

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