Including and Reading Resources with Maven/Java/Scala

  In last few days, I tended to make a Maven dependency to read resources from its own jar. And I suddenly found that I have no experience of that before. After some googling and experiments, I managed to read the resources, and here is the notes.

  Let's say, you want to publish a jar library which associated a few default configuration files, of course, you never want to write the configuration into your code.(don't do that if you had ever thought about it before.) Then how do you keep the file in the jar? Experienced Java developer should know that jar is a compress file, or more literally, a zip file, so being able to keep a file inside it is reasonable, isn't it? If you are using Maven as your publishing tool, thing should be easy.

  Setting up your pom.xml, assign the resource setup like a boss, uh, I mean, like the following.

<project>
  ...
  <name>My Resources Plugin Practice Project</name>
  ...
  <build>
    ...
    <resources>
      <resource>
        <directory>src/resources</directory>
        <includes>
          <include>**/*</include>
        </includes>
      </resource>
      ...
    </resources>
    ...
  </build>
  ...
</project>

Of course you can assign wherever you want, but in practical, I would recommend to put the resources directory under src/, or src/main if you want to separate resources between the main and the test program.

  Another tip, for some files that are included for a specific package or class, you may want to put the files into the directory same as the package name. For example, I got a picture chick.jpg for net.sunshire.farm.Chick, I would put the picture at the path src/main/resources/net/sunshire/farm/chick.jpg. By doing so, Maven packages the chick.jpg in the package net/sunshire/farm, which allows you keep the independency of each jar.(You won't mass resources between different jars when you are importing many different dependencies.)

  Now you are done with including resources, if you package the jar with Maven, you can see the resource that you just included inside your jar file.(To inspect a jar file, simply change the extension to .zip and decompress it.)

  And how do we read the resource that we included with Scala? It is actually pretty simple, there is a method getResourceAsStream of Class. Here is the usage in Scala:

package net.sunshire.farm;

class Chick {
  val picPath: String = "/net/sunshire/farm/chick.jpg";
  // relative one: "chick.jpg", do NOT recommend
  val chickPic: InputStream = getClass.getResourceAsStream(picPath);
  // do whatever you want with the stream.
}

The above demonstration is pretty straightforward, I guess most most problem is that we do not know the method. The worth mentioning part is that getResourceAsStream takes either relative path or absolute path, same as UNIX/POSIX system ,/ represents root path. To clarify, the absolute path did not mean from the root of the file system, it is from the root of the jar. And the relative path is start from the package declared on the top(/net/sunshire/farm/ in the example).
  Another thing, if you specify the relative path, it is going to read the relative path of the run time package.(net.sunshire.house.Chicken extends Chick, and Chick specified the path with the relative one, then the path is going to be /net/sunshire/house/chick.jpg)

  If you do not understand Scala and need a Java example, the pom.xml part is the same, for the code part please refer to the 2nd reference. This is all about how to including and reading resources, hope it is helpful. :D

References:
[1] Resources Packaging - Maven Official
[2] Read a Resource in Java - Stack Overflow