h3x.no » Java

GWT: “For security purposes, this type will not be serialized.”

Tor Henning Ueland — Thu, 01 Sep 2011 17:50:07 +0000

The full error message you can get is: “Foo was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.”

This is normally caused by using a non-serializable class, which can happen if your class does not implement serializable or if you have forgotten to add a empty constructor.

Java: Converting long to double

Tor Henning Ueland — Tue, 30 Aug 2011 16:15:17 +0000

While Integers has to be parsed from a String, doubles can simply be casted:

String bar = "9.99";
Double foo = (double)bar;

EXT GWT: Adding onClick to Labels

Tor Henning Ueland — Mon, 29 Aug 2011 17:25:51 +0000

I had a issue where i needed to add a click handler for labels in EXT GWT, the solution i came up with was as follows

theLabel.addListener(Events.OnClick, new Listener() {
@Override
public void handleEvent(BaseEvent be) {
    // TODO Auto-generated method stub
}});

Guice: java.lang.IllegalStateException: No SessionHandler or SessionManager

Tor Henning Ueland — Sun, 28 Aug 2011 17:21:56 +0000

One reason for this error would be that you should inject the session object directly, not via constructor:

So instead of:

@Singleton
public class Foo {
 
@Inject public Foo(HttpServletSession s) {
this.session = s  }
}

do this:

@Singleton
public class Foo{
 
@Inject Provider<HttpServletSession> session;
 
}

And it should work much better

class Foo is public, should be declared in a file named Foo.java

Tor Henning Ueland — Mon, 04 Jul 2011 20:18:00 +0000

When working with Java you might encounter this error. The reason for this is that you have tried to declare a public class in a file with a different name. Each java file can only contain one public java class, which is named the same as the java file itself. If you need another class inside your other class you should looking into private inner classes.

jpackages error: Missing Dependency: /usr/bin/rebuild-security-providers

Tor Henning Ueland — Fri, 25 Feb 2011 10:02:27 +0000

Jpackages on Red Hat has a nifty bug that causes dependency errors.

Luckily, somebody has created a fix as a rpm package

wget http://plone.lucidsolutions.co.nz/linux/centos/images/jpackage-utils-compat-el5-0.0.1-1.noarch.rpm
rpm -ivh jpackage-utils-compat-el5-0.0.1-1.noarch.rpm

And then jpackages works.

Tips for implementing a custom JAAS login module for Jetty

Tor Henning Ueland — Wed, 23 Feb 2011 08:14:52 +0000

1) jetty-web.xml

You can gather all specific settings for Jetty in the file WEB-INF/jetty-web.xml, remember to also specify paths for the role principals if you use your own classes for that.

Example jetty-web.xml file:


>
 

 name="setProperty">
	>java.security.>auth>.login.config>
	>WEB-INF/login.config>
>
 

 name="serverClasses">
	 type="java.lang.String">
		>-org.mortbay.jetty.plus.jaas.>
		>org.mortbay.jetty>
		>org.slf4j.>
	>
>
 

 name="securityHandler">
	 name="userRealm">
		>
			 name="name">*NAME OF YOUR REALM*>
			 name="LoginModuleName">*NAME OF YOUR LOGIN CLASS*>
			 name="roleClassNames">
				 type="java.lang.String">
					>*PATH TO YOUR ROLE PRINCIPAL CLASS*>
				>
			>
		>
	>
>
>

2) Adding roles to a user in commit

When you want to give a user roles(like admin, moderator etc), you can add those to the user when he or she is authenticated and commit is called upon:

	public boolean commit() throws LoginException {
		MyUserPrincipal user = new MyUserPrincipal("username");
 
		//Add logged in user as first principal
		subject.getPrincipals().add(user);
 
		//Add roles for the logged in user
		subject.getPrincipals().add( new MyGroupPrincipal("admin") );
		subject.getPrincipals().add( new MyGroupPrincipal("moderator") );
	}

Debugging GWT: Did you forget to inherit a required module?

Tor Henning Ueland — Tue, 22 Feb 2011 13:03:20 +0000

You will receive this error if you are using classes in your GWT project that GWT does not have access to. Make sure that you have added something like this in your gwt.xml file, within your module element: <source path="path.to.classes" … Continue reading →

Eclipse Workspace In Use Or Cannot Be Created

Tor Henning Ueland — Mon, 20 Dec 2010 09:20:08 +0000

You may recieve the error message “Eclipse Workspace In Use Or Cannot Be Created” From Eclipse when trying to start up Eclipse, this typically means that Eclipse is already running. If you have not started Eclipse, try to locate Eclipse in your operating systems task manager and kill it. You can also consider killing any java processes running if you cant find any Eclipse processes.

HttpClient: Target host must not be null, or set in parameters

Tor Henning Ueland — Mon, 22 Nov 2010 08:10:13 +0000

If you have the following code failing:

HttpGet httpget = new HttpGet(“www.host.com”);

Then the error is pretty easy to solve:
The problem is that you have not added a protocol to the URL, so change it to:

HttpGet httpget = new HttpGet(“http://www.host.com”);

And then it will work as wanted.