XML property files
None of this should be new to you. This is how the Properties
class has always worked. What is new, however, is the option of loading
a set of properties from an XML file. The DTD for that is shown in
Listing 4.
Listing 4. Properties DTD
<?xml version="1.0" encoding="UTF-8"?>
<!-- DTD for properties -->
<!ELEMENT properties ( comment?, entry* ) >
<!ATTLIST properties version CDATA #FIXED "1.0">
<!ELEMENT comment (#PCDATA) >
<!ELEMENT entry (#PCDATA) >
<!ATTLIST entry key CDATA #REQUIRED>
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If you're not into reading XML DTDs, this essentially says that wrapped within an outer <properties> tag is a <comment> tag, followed by any number of <entry> tags. For each <entry>
tag, there is a key attribute, with the contents of the entry being its
value. Listing 5 shows what the XML version of the properties file in Listing 1 would look like.
Listing 5. XML version of the Properties file
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
<comment>Hi</comment>
<entry key="foo">bar</entry>
<entry key="fu">baz</entry>
</properties>
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As Listing 6 shows, reading the XML version of the Properties file isn't much different than reading the older style format.
Listing 6. Reading the XML Properties file
import java.util.*;
import java.io.*;
public class LoadSampleXML {
public static void main(String args[]) throws Exception {
Properties prop = new Properties();
FileInputStream fis =
new FileInputStream("sampleprops.xml");
prop.loadFromXML(fis);
prop.list(System.out);
System.out.println("\nThe foo property: " +
prop.getProperty("foo"));
}
}
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A note about resource bundles
While the java.util.Properties
class now supports properties files as XML files in addition to
key-value pairs, unfortunately, there is no built-in option available
to treat a ResourceBundle as an XML file. Yes, a PropertyResourceBundle does use a Properties object to load the bundle; however, the use of the load method is hard-coded into the class, and the newer loadFromXML() method is not used. |
Running the program in Listing 6 produces the same output as the original program, which is shown in Listing 2.
