Tutorials : Plug-in to Reusability in Java :

Step 2: Define the format for the parameter file

We chose to define the parameter file in XML format. It could just as well be in Java property-file format, but XML is more flexible and it's so easy to define a hierarchy. The three plug- ins are defined as three XML elements:

<?xml version="1.0"?>
<root>
  <Read class="Java package and class name" 
	...attributes...  />
  <Transform class="Java package and class name" 
	...attributes... />
  <Write class="Java package and class name" 
	...attributes... />
</root>

Each plug-in tag (Read, Transform and Write) has a class-attribute, which gives the full Java class name for the plug-in. Other attributes in the plug-in tags may be used for options used by the specific plug-in. With a parameter file like this it's possible for the driver to instantiate the given classes. It's the job of the plug-ins to continue by fetching the options in the file.

Step 3: Define Interfaces

The next thing to do is to define the Java Interfaces for the plug-ins that we will use. Our case calls for three Interfaces:

1. the temperature reader
2. the data transformer  
3. the temperature writer

You may set up the interfaces in several ways, according to what your specific situation and needs are. I've chosen the following definitions:

The temperature reader delivers data as a List of Strings from the receive method. The format for each String is city=temperature, for example:

CPH=36

The reader Interface will also need a method, initialize, used to extract the options given as XML attributes in the parameter file:

public interface IReceive {

  public List receive() 
throws Exception;

  public void initialize(Element e) throws Exception;

}

The data transformer takes the List of Strings from the reader and converts the city=temperature format to some other format, for example a sentence like "The temperature in CPH is 40":  

public interface ITransform {

  public List transform(List data);

  public void initialize(Element e) throws Exception;

}

The initialize method has the same function as the reader.

The temperature writer finally takes the List from the transformer and sends it to the target(s):

public interface ISend {

  public void send(List data) throws Exception;

  public void initialize(Element e) throws Exception;

}

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