Practical parameter file reading in java

I recommend using XML files and using JAXB to load them.

Why? Because of the following pros:

• Because it is awefully simple.
• No external libraries are needed.
• The config file is well readable (simple XML), it can be edited with any text editors or advanced XML editors.
• It is flexible enough to add other data later on to the parameters.
• Also very easy to modify/save parameters from code at runtime (see at the end).
• Thanks to XML you don't have to worry about character encoding (like in case of properties files).

Modelling:

First you need to create classes to "model" your parameters:

class Parameters {
    @XmlElement(name = "item")
    public List<Item> items;
}

class Item {
    public String fileName;
    public String contentType;
}

Example input XML file:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<parameters>
    <item>
        <fileName>item1.txt</fileName>
        <contentType>individual</contentType>
    </item>
    <item>
        <fileName>item2.txt</fileName>
        <contentType>group</contentType>
    </item>
</parameters>

Loading the parameters

And this is how you can load it, it's only 1 method call:

Parameters p = JAXB.unmarshal(new File("params.xml"), Parameters.class);

for (Item item : p.items)
    System.out.println(item.fileName + ": " + item.contentType);

Output:

item1.txt: individual
item2.txt: group

Alternative (simplified) XML input

To make the input XML file shorter, more easily readable, we can make the following change:

class Item {
    @XmlAttribute
    public String fileName;
    @XmlAttribute
    public String contentType;
}

Here we basically specified to store/read the data of an Item as XML attributes and not as child elements. With this modification the input XML:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<parameters>
    <item fileName="item1.txt" contentType="individual" />
    <item fileName="item2.txt" contentType="group" />
</parameters>

Modifying and Saving parameters at runtime

If we want to modify the parameters and save them at runtime, it is just as easy as loading them: one line only. Below I modify the first item, and I also create and add a new third item:

// Modify item #1
p.items.get(0).fileName = "item11.txt";
p.items.get(0).contentType = "short";

// Create and add a new item
Item item3 = new Item();
item3.fileName = "item3.txt";
item3.contentType = "newtype";
p.items.add(item3);

// Save the modified parameters: 1 line:
JAXB.marshal(p, new File("params-out.xml"));

Output of the modified parameters:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<parameters>
    <item fileName="item11.txt" contentType="short"/>
    <item fileName="item2.txt" contentType="group"/>
    <item fileName="item3.txt" contentType="newtype"/>
</parameters>