Question

I’m a begginner java programmer; now I’m using J2SE and NetBeans 6.9.1 to code an application.

The issue I’m facing now is to load properties from a well known location in my local filesystem using a singleton class. What annoys me is that I get an error which is claiming for a throws clause or catch the exception where the INSTANCE variable is being initialized. May anyone help me undestand this.

Thanks in advance.

The code is as follows :

package cat.oai.atapplications.phot;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Properties;

/**
 *
 * @author fdalmau
 */
public class PhotPropertiesManager {

    private static Properties photProperties;

    private PhotPropertiesManager() throws FileNotFoundException, IOException {
        photProperties = LoadProperties();
    }

    public static PhotPropertiesManager getInstance() {
        return PhotPropertiesManagerHolder.INSTANCE;
    }

    public static Properties getPhotProperties() {
        return PhotPropertiesManager.photProperties;
    }

    private static Properties LoadProperties() throws FileNotFoundException,
                                                      IOException {

        Properties defaultPhotProperties = new Properties();

        FileInputStream in = new FileInputStream("defaultphot");
        defaultPhotProperties.load(in);
        in.close();

        Properties applicationPhotProperties = 
                                     new Properties(defaultPhotProperties);

        in = new FileInputStream("lastexecutionphot");
        applicationPhotProperties.load(in);
        in.close();

        return applicationPhotProperties;
    }

    private static class PhotPropertiesManagerHolder {

        /******
          The problem is is this line of code:
         ******/
        static final PhotPropertiesManager INSTANCE = new PhotPropertiesManager();

    }
}

Answer 1

The problem is that a static field cannot throw a check exception. I would simplify the code like this.

public enum PhotPropertiesManager {;
    private static final Properties PHOT_PROPERTIES = new Properties();

    static {
        try {
            load("defaultphot");
            load("lastexecutionphot");
        } catch (IOException e) {
            throw new IllegalStateException(e);
        }
    }

    private static void load(String filename) throws IOException {
        FileInputStream in = new FileInputStream(filename);
        PHOT_PROPERTIES.load(in);
        in.close();
    }

    public static Properties getPhotProperties() {
        return PHOT_PROPERTIES;
    }
}