Java

Using Nexus and the Nexus REST API for implementing a software update tool

Nexus is using a pretty well documented REST API which is usable externally as well.
For one of my customers I implemented a kind of automatic software update tool that can be embedded into any product. It is based on the Sonatype NEXUS repository manager.

Java5 Generics are implemented by type erasure, but …

… still it is possible to get hold of the actual type parameters of parameterized types. Even if classical reflection does not deliver type information, this type parameters can still be extremely useful. I have a few pieces of code (DAO, controllers, etc.) that are parameterized by class objects.

Rendering a FacesMessage reliably

Quite a while ago I had posted about generating a FacesMessage within a method that is called during the RENDER_RESPONSE phase. Today I had to find a way to display those at the very top of a page and none of the message should get lost.

So I came up with trying that with jQuery (in my case it is already included in Rich-Faces that I was using here). The idea is to actually render all FacesMessage objects at the very bottom of the page and once the page has finished loading move its DOM tree up where it was supposed to be displayed.

ServiceLoader or "Sometimes you just don't need a full blown dependency injection container"

I like Springframework very much and use it in my day to day business as it eases development in many places. A few days ago I started using Hibernate Envers in order to implement a simple auditing solution for a JPA based application. I was faced with the (typical) requirement that the username of the user currently logged in was written into the audit entity. With Envers you would do that using a org.hibernate.envers.RevisionListener. This is instantiated by the Envers runtime. That listener required access to the FacesContext (it’s a JSF based application) to get the user principal from the HTTP request. Not a big deal in general! Still I wanted to keep that testable and usable in various environments, so an abstraction was needed and finally something would have to inject that into my listener.
As I said I’m a fan of Spring and this would be the perfect job and eventually one would propose “yeah, let’s do Spring AOP with AspectJ weaving”. As this application was already in production I didn’t want to add that at this time and was seeking for something more simple but still elegant.

Java as of 1.6 has the concept of SPI and ServiceLoader already built-in. I had never used it before. Here it seemed to perfectly match and it did.

import java.security.Principal;
public interface UserPrincipalProvider {
	Principal getUserPrincipal();
}

import java.security.Principal;
public class TestUserPrincipalProvider implements UserPrincipalProvider {

	public Principal getUserPrincipal() {
		return new Principal() {
			public String getName() {
				return "TEST";
			}
		};
	}
}

A file named META-INF/services/at.package.auditing.UserPrincipalProvider would be responsible for registering the provider implementation, it only contains one or multiple class names:

at.package.auditing.TestUserPrincipalProvider

For getting a runtime instance of such a provider I implemented a helper like

public static <T> T lookup(Class<T> clazz) {
	Iterator<T> iterator = ServiceLoader.load(clazz).iterator();
	return iterator.hasNext() ? iterator.next() : null;
}

It is called like ...lookup(UserPrincipalProvider.class).

eclipse 3.5

Since eclipse 1.0 has been released back in November 2001 it has evolved into a pretty popular and feature rich IDE. I remember using eclipse 2.0.1 first time, it was pretty much only a Java development IDE with little support for application containers.
Soon eclipse 3.5 (galileo) arrives supporting a wide palette of programming languages, programming models and execution environments, application containers, etc. The past 3 months I had been testing galileo from early milestone releases and been happy with it – also with my favourite eclipse plugins that I use in my daily business.

Here I briefly show some of the many features that I like:

Install New Software

I believe with eclipse 3.4 the user interface for updating/installing plugins has been pretty much messed up. Seems the eclipse engineers have done a good job to fix it up again. It has never been so easy and intuitive (with drag & drop support for update-site URLs) to install and update an eclipse plugin. But even more important, now it is possible to export bookmarks of your favourite plugins (you can select them plugin by plugin) and import them into another eclipse installation (e.g. for switching to a new eclipse release).

available-software-export

Type Filter (eclipse 3.4)

With a large number of libraries in the classpath it gets pretty overloaded in the type search dialogs. Mostly you find lots of classes that you never want to deal with directly. E.g. classes from the com.sun.* packages. Still you have to skip over them while searching for some other classes.
By defining a type filter you can suppress any package you are not interested in.

type-filter

toString() Method

I usually would use the ToStringBuilder from the Apache commons-lang package to implement any toString() method.
As of eclipse 3.5 the Source->generate toString()… feature can be customized to support the commons-lang ToStringBuilder pattern.

tostring

Format edited lines only (eclipse 3.4)

In a team environment it is important that everybody is using the same formatting rules for auto-formatting the source code. Otherwise code comparison / mergeing can get pretty nasty. However sometimes this is not the case. Still eclipse can help to minimize the impact of autoformatting. You can choose the option to format only the code portion that has been actually changed.

format-edited-lines

Breadcrumbs (eclipse 3.4)

Eclipse has always had a perspective called Java Browsing (some heritage from good old Visual Age). I never really liked it, as it consumes quite a lot of space of the workbench.
With eclipse 3.4 the eclipse team introduced the so called breadcrumbs (Alt-Shift-B) which is showing almost they same information but much is more compact. It allows you to quickly jump between packages, classes, members, etc.

breadcrumbs

Block selection

Alt-Shift-A activates a special editing mode where it is possible to select any rectangular text area and copy / paste it.

block-selection

java.util.logging

Sun mostly sticks with java.util.logging (jul) in their products. jul is fairly unflexible but we need to live with it. However I usually would use log4j with slf4j as logging facade. In order to get more control over jul logging output you can use the slf4j to java.util.logging bridge. Here I show how to set it up with Spring and Maven

		
			org.slf4j
			jul-to-slf4j
			1.5.4
		
		
			org.slf4j
			slf4j-log4j12
			1.5.4
		
		
			log4j
			log4j
			1.2.15
			
				
					com.sun.jmx
					jmxri
				
				
					com.sun.jdmk
					jmxtools

java.net.SocketException: Address family not supported by protocol family: bind

Today I encountered a strange phenomen on Windows Vista. I was implementing a JAX-WS web service and trying to bind an endpoint with the JDK6 built-in JAX-WS.

Endpoint endpoint = Endpoint.publish("http://localhost:8090/queryservice", endpointImplementation);

I got this strange

java.net.SocketException: Address family not supported by protocol family: bind

execption and did a search for this. Fortunately very recently somebody else had the same issue.

The workaround is to either update your System32\drivers\etc\hosts file, replace “::1 localhost” with “127.0.0.1 localhost”
or use 127.0.0.1 as a replacement for localhost when creating the socket.

Bytecode version check

Currently I’m doing deployment tests and proof-of-concept tests for various technologies (RMI, Session Bean, JNDI, JSF, Seam, Web Services, Spring, Hibernate, .etc.) on different application servers (JBoss, IBM WebSphere, SAP Netweaver).
Some of the app servers are only certified or supported with Java5. So I frequently ran into problems resulting from having classes around compiled for Java6. I was already thinking of writing a tool that could analyze a Jar or class file and get its version information. But luckily I found a tool ready to do the job.

el-ri

Occasionally I need the EL reference implementation in my projects. JARS are hard to find. They seem to be provided by JBoss MAven2 repositories only. The repository URL is http://repository.jboss.org/maven2 .

<dependency>
	<groupId>javax.el</groupId>
	<artifactId>el-api</artifactId>
	<version>1.2</version>
	<scope>provided</scope>
</dependency>
 
<dependency>
	<groupId>javax.el</groupId>
	<artifactId>el-ri</artifactId>
	<version>1.2</version>
	<scope>provided</scope>
</dependency>

VisualVM 1.0 RC

One of the sessions of TheServerSide Java Symposium in Prague was about JMX support in Java. During the talk Jean Francoise Denise briefly demoed a new tool VisualVM based on the Netbeans Platform. Today I did some experiments and found it quite useful. It is also utilizing the NetBeans plugin mechanisms to provide extensibility (e.g in order to monitor JMX Beans you must install the MBeans plugin).
.

The tool even provides a profiler. I haven’t even looked at it closer. Though I believe it is quite useful to have it available for ad doc profiling without requiring any external tools!

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