Spring and Constants class from property file

Question

I want to create Constants class with public static final fields, which I get from Properties file. The issue is that ClassLoader always null, and i can't get properties file InputStream.

I'm using Spring Java Configuration and I know about @PropertySource and @Value spring annotations, but I think old-style Constants class more readable in code.

@Autowired
Constants constants;//in every class that needs constant
//...
constants.getArticleLimit()

vs simple

Constants.ARTICLES_LIMIT //static var version

Here's my code:

package org.simpletest.utils

import org.apache.log4j.Logger;

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

public class Constants {

    private static final Logger LOG = Logger.getLogger(Constants.class);

    public static final int ARTICLES_LIMIT;

    public static final String PROPERTIES_LOCATION = "constants.properties";

    static {
        Properties p = new Properties();

        //default values
        int articlesLimit = 10;

        Class<?> clazz = Constants.class.getClass(); 

        ClassLoader cl = clazz.getClassLoader();

        //try to load from properties file
        try(final InputStream is = cl.getResourceAsStream(PROPERTIES_LOCATION)){

            p.load(is);

            articlesLimit= Integer.parseInt(p.getProperty("articleslimit"));

        } catch (IOException e) {
            LOG.debug(String.format("Unable to load {0} properties file. Getting constants by default values.",PROPERTIES_LOCATION),e);
        }

        ARTICLES_LIMIT = articlesLimit;
    }
}

Why don't you use @Environment to read from properties file? — Pratik Ambani, Mar 13 '17 at 16:33
If you use PropertyPlaceholder in your context, you can just use the property values directly in your Spring beans. See http://stackoverflow.com/questions/9259819/how-to-read-values-from-properties-file — Michael Peacock, Mar 13 '17 at 16:35
@MichaelPeacock, if i correctly understand this will force me to add all constants in every class which uses them. — memor1s, Mar 13 '17 at 16:42
Seems like the classloader isn't set until after the static block? I can't reproduce this though. What version of JVM? — Christopher Schneider, Mar 13 '17 at 16:55

Christopher Schneider · Accepted Answer · 2017-03-13T17:38:51.957

1

After a bit of testing, this is the issue:

System.out.println(Constants.class.getClass());

This prints java.lang.Class which may not have been loaded by the classloader. This is because the class of a SomeClass.class is java.lang.class.

Remove the getClass() and the Classloader won't be null. No need for the clazz variable. This should be all you need to do:

ClassLoader cl = Constants.class.getClassLoader();

edited Mar 13 '17 at 17:38

answered Mar 13 '17 at 16:59

Christopher Schneider

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Thanks, this helped. – memor1s Mar 13 '17 at 17:06

Spring and Constants class from property file

1 Answers1