A better class to update property files?

Question

Though java.util.properties allows reading and writing properties file, the writing does not preserve the formatting. Not surprising, because it is not tied to

Answer 1

The configuration2 class have different syntax. Here is an example using them:

import org.apache.commons.configuration2.PropertiesConfiguration;
import org.apache.commons.configuration2.PropertiesConfigurationLayout;

public void test() {
    PropertiesConfiguration config = new PropertiesConfiguration();
    PropertiesConfigurationLayout layout = new PropertiesConfigurationLayout();
    config.setLayout(layout);
    layout.load(config, new FileReader("config.properties"));

    config.setProperty("KEY", "VALUE");
    StringWriter stringWriter = new StringWriter();
    layout.save(config, stringWriter);
    LOG.debug("Properties:\n{}", stringWriter.toString());
}

Answer 2

I once saw a class to do this with INI files but can't find the link anymore. If you can't find anything else, you can try DecentXML. I wrote this XML parser with the specific design goal to preserve the original formatting 100% (i.e. with comments, weird spaces in elements or around the root element, everything).

During parsing the resulting XML document, you just have to remember the elements which contain the value for your options and replace the text node in them. When you save, nothing untouched will change in any way.

Answer 3

The sample code for using the Apache Commons Configuration library contributed by Patrick Boos is unnecessarily complicated. You don't need to use PropertiesConfigurationLayout explicitly unless you require some advanced control over the output. PropertiesConfiguration by itself is sufficient to preserve comments and formatting:

PropertiesConfiguration config = new PropertiesConfiguration("myprops.properties");
config.setProperty("Foo", "Bar");
config.save();

(Note: This code works for the existing 1.10 stable version. I have not checked if it works on the 2.0 alpha builds currently available.)

Answer 4

You can have a look to the Apache Commons Configuration, that contains PropertiesConfiguration class. However, as I have never used it, I don't know if it preserves the comments and formatting...

However, it worthes a try...

Answer 5

    File file = new File("src/test/resources/1automation.properties");
    PropertiesConfiguration config = new PropertiesConfiguration();
    PropertiesConfigurationLayout layout = new PropertiesConfigurationLayout(config);
    layout.load(new InputStreamReader(new FileInputStream(file)));
    FileWriter fw = new FileWriter("src/test/resources/1automation.properties",false);
    config.setProperty("myssi.admin.name", "testValue");
    layout.save(fw);

Answer 6

Just in response to Jince Martin who was having trouble with trailing spaces in the written properties files e.g. key = value instead of key=value.

You can call layout.setGlobalSeparator("=") to get around this.