A better class to update property files?

Hemal_Pandya_18573 0
Viewed 22163

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 the property file.

Is there a PropertyFile class out there -- or some such -- that preserves comments and blank lines and updates property values in place?

properties java
8 Answers

It doesn't get much better than Apache's Commons Configuration API. This provides a unified approach to configuration from Property files, XML, JNDI, JDBC datasources, etc.

It's handling of property files is very good. It allows you to generate a PropertiesConfigurationLayout object from your property which preserves as much information about your property file as possible (whitespaces, comments etc). When you save changes to the property file, these will be preserved as best as possible.

Sample code:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStreamReader;

import org.apache.commons.configuration.ConfigurationException;
import org.apache.commons.configuration.PropertiesConfiguration;
import org.apache.commons.configuration.PropertiesConfigurationLayout;

public class PropertiesReader {
    public static void main(String args[]) throws ConfigurationException, FileNotFoundException {
        File file = new File(args[0] + ".properties");

        PropertiesConfiguration config = new PropertiesConfiguration();
        PropertiesConfigurationLayout layout = new PropertiesConfigurationLayout(config);
        layout.load(new InputStreamReader(new FileInputStream(file)));

        config.setProperty("test", "testValue");
        layout.save(new FileWriter("path\\to\\properties\\file.properties", false));
    }
}

See also:

Il-Bhima_578270
user_264570

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());
}
user_56267140

The best answer contains a small mistake: The line: 

PropertiesConfigurationLayout layout = new PropertiesConfigurationLayout(config);

Must be replaced by:

PropertiesConfigurationLayout layout = config.getLayout();
user_107917800

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.

user_136619980

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.

Aaron_Digulla_340880
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