NullPointerException on loading data to java.util.Properties object

Question

Note: Please forgive me, if I have wrong in english.

I'm learning java! and now I try to load properties from file to java.util.Properties object... but I got an exception. I get filename by getClass().getResource("path/to/resource").toFile() and make a File object from it; then read content. but when I send the InputStream of file to 'load' method, get a NullPointerException.

This is my code:

final class Main
{
    protected Properties config; 

    protected Properties getConfig()
    {
        if( this.config == null )
        {
            String filename = this.getClass().getResource("/tiny.properties").getFile();
            System.out.print(  filename+ "\n" );
            File f = new File( filename );

            try(InputStream propsFile = new FileInputStream( f ) )
            {
                int ch = 0;
                while( (ch = propsFile.read() ) != -1 )
                {
                   System.out.print((char) ch); // I can get ALL content of File Here
                }
                this.config.load( propsFile ); // But here I got NullPointerException!
            }
            catch(IOException exc)
            {
               assert true : "Can't read properties file!";
            }
        }
        return this.config;
     }
}

and My exception:

Exception in thread "main" java.lang.NullPointerException
    at ir.teanlab.japp1.mavenproject1.Main.getConfig(Main.java:43) // this.config.load( ... )
    at ir.teanlab.japp1.mavenproject1.Main.getSqlConnection(Main.java:57)
    at ir.teanlab.japp1.mavenproject1.Main.<init>(Main.java:67)
    at ir.teanlab.japp1.mavenproject1.App.main(App.java:15)

viralpatel.net/blogs/loading-java-properties-files Could be an issue with your file path — RaceBase
– RaceBase, Commented Jan 31, 2014 at 6:32

Durandal · Accepted Answer · 2014-01-31 06:34:22Z

3

You're getting a NullPointerException because config is still null when you call the load method. You need to initialize your config object like this:

config = new Properties();

Probably best to put it right below your null check for it:

if( this.config == null ) 
{
    config = new Properties();
    ....

answered Jan 31, 2014 at 6:34

Durandal

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Comments

SpringLearner · Accepted Answer · 2014-01-31 06:34:12Z

1

You have just created a reference in this line Properties config; but have not created the object

Create an object like Properties config=new Properties()

answered Jan 31, 2014 at 6:34

SpringLearner

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Comments

user2314868 · Accepted Answer · 2014-01-31 06:35:45Z

Try with remove if condition ( if( this.config == null )). Final code is:

final class Main
{
    protected Properties config; 

    protected Properties getConfig()
    {

        this.config=new new Properties();
            String filename =this.getClass().getResource("/tiny.properties").getFile();
            System.out.print(  filename+ "\n" );
            File f = new File( filename );

            try(InputStream propsFile = new FileInputStream( f ) )
            {
                int ch = 0;
                while( (ch = propsFile.read() ) != -1 )
                {
                   System.out.print((char) ch); // I can get ALL content of File Here
                }
                this.config.load( propsFile ); // But here I got NullPointerException!
            }
            catch(IOException exc)
            {
               assert true : "Can't read properties file!";
            }

        return this.config;
     }
}

tom · Accepted Answer · 2014-01-31 08:21:51Z

The problem is that your config variable has not been initialized and hence is still null. So in your try/catch block you should add config = new Properties();

On a side note, there is an easier way to get the InputStream. We use the following technique (Java 6):

    InputStream inputStream = null;
    Properties config = null;
    try
    {
        config = new Properties();
        inputStream = this.getClass().getClassLoader().getResourceAsStream("path + resource name");
        if (inputStream != null)
        {
            config.load(inputStream);
        }
        else
        {
            throw new FileNotFoundException("property file '" + "path + resource name" + "' not found in the classpath");
        }
    }
    catch (IOException e)
    {
        throw new RuntimeException(e);
    }
    finally
    {
        if (inputStream != null)
        {
            try
            {
                inputStream.close();
            }
            catch (IOException e)
            {
                throw new RuntimeException(e);
            }
        }
    }

Obviously with java 7 you could you the try with resources.

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