maven2

when software engineering is still complicated

by frankdu • January 23, 2010 • 0 Comments

While writing code, programmers run into issue after issue. As examples, I will talk about the issues I encountered, and wish it may help others who run into similar issues. I wrote the program to monitor certain web pages. Therefore it should download web pages in correct encoding, in multi-threading environment. It should save the page to back-end database. The issues I encountered:

1. Threading issue

HttpClient from Apache is used as a web client. From their explanation page, we see no issue in the Multithreading section. There is no problem to run their multithreading example. However, you will run into problem if you create the HttpClient instance not in current Thread or it’s parent thread. This issue is not documented there, but very confusing to new users.

2. Implicit Dependency

I use Hibernate to persistent data, and maven 2 for dependency management. Maven 2 is awesome. However, what if some dependencies are missed out? Antlr v2.7.5H3 is for HQL parsing. However, Hibernate maven guide doesn’t statement it clearly. When you start to run HQL, the error will pop-up. Additionally, the antlr dependency is not available in official maven 2 repository. You will need to use the JBoss repository.

3. Session cache

After saving the data to database, another thread will take out the data for further processing. However, if you call getCurrentSession() on SessionFactory instance, you will get nothing. If you stopped the program, and run it again, you will get data from last run, but not data from new run. The issue is caused by the Session cache, which was designed for performance improvement. The solution is to call openSession() on the SessionFactory instance (or call openStatelessSession() if you hate cache).

I encountered other issues as well, such as encoding issue. However, the preceding issues are typical confusing issues.Why is software engineering so complicated?

It’s because people try to ask software to address the whole world, which is much more complicated.

Tire production can use assemble line, because the requirement is simple: I need a production for my Toyota car.

The car production can use assemble line, because the requirement is simple as well: I need a transportation tool from city A to city B, in land.

What if clients ask for a transportation vehicle to travel from any two point in a 3-dimension space? What if clients add the dimension of time?

People wish software to be capable of handling situations more intelligently, therefore people can be more lazy. There is nothing wrong here. But it can be an issue of feasibility, if the requirements have no boundary.

Set the source level to Java 6 for maven 2 compiler

by frankdu • January 10, 2010 • 0 Comments

By default, the source level is 1.3 in maven 2. We need to config maven compiler to use Java 1.6. Add the following snippet to your pom:

<build>
	<plugins>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-compiler-plugin</artifactId>
			<configuration>
				<source>1.6</source>
				<target>1.6</target>
			</configuration>
		</plugin>
	</plugins>
</build>

<build>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-compiler-plugin</artifactId>

</configuration>

</plugin>

</plugins>

</build>

Use maven dependency plugin to copy all dependencies to a folder

by frankdu • July 5, 2009 • 0 Comments

In some cases, we’d like to get all the dependency jar files for a project. There is a maven plugin to do it simply, via a simple way. Just add the build sections to your pom file, as shown below:

<project>
<!-- ....... -->
<build>
	<plugins>
		<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-dependency-plugin</artifactId>
				<executions>
					<execution>
						<id>copy-dependencies</id>
						<phase>process-sources</phase>
						<goals>
							<goal>copy-dependencies</goal>
						</goals>
						<configuration>
							<outputDirectory>c:output</outputDirectory>
							<overWriteReleases>false</overWriteReleases>
							<overWriteSnapshots>false</overWriteSnapshots>
							<overWriteIfNewer>true</overWriteIfNewer>
						</configuration>
					</execution>
				</executions>
			</plugin>
			</plugins>
	</build>

<!-- ....... -->

</project>

<build>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-dependency-plugin</artifactId>

<id>copy-dependencies</id>

<phase>process-sources</phase>

<goals>

<goal>copy-dependencies</goal>

</goals>

<outputDirectory>c:output</outputDirectory>

<overWriteReleases>false</overWriteReleases>

<overWriteSnapshots>false</overWriteSnapshots>

</configuration>

</execution>

</executions>

</plugin>

</plugins>

</build>

</project>

Write Xml editor by Extending WTP Xml Editor

by frankdu • April 6, 2009 • 0 Comments

Several months ago, I posted a blog about writing a Xml editor based on JFace Text Framework. What has changed in the past months?

On my side, I went to frequently the eclipse newsgroups. I went to EclipseCon’09 and listened to Xml editor tutorial by WTP committers. While more gained experience, I would recommend that you extend WTP xml editor to build your own. Reasons are simple:

1. You don’t need to invent wheels from scratch
2. You can improve yourselves by reading WTP source codes
3. There are active communities you can turn to for help.

I’d like to recommend some additional resources for building your own xml editors:

1. The slides and code “Extending the XML and JSP editors from the WTP Project“, by IBM WTP committers
2. The lecture at EclipseCon2009 “Building the XML Editor you’ve always wanted“, and slides/sample.

Hope it helps.