How to load a properties file from classpath in Java

Question

I'm trying to create a config file to save the username and ip data for a client inside the classpath, as in a resources folder in the project. I'm able to retrieve the properties like this:

public String getProperty(String property){

    String result = null;

    try{

        InputStream inputStream = this.getClass().getResourceAsStream(filename);
        Properties properties = new Properties();

        if (inputStream != null){

            properties.load(inputStream);
            System.out.println(this.getClass().getResource(filename).toString());

        }else {

            System.out.println("File not found or loaded: "+filename);

        }

        result = properties.getProperty(property, null);

        inputStream.close();

    }catch (Exception e){
        e.printStackTrace();            
    }

    return result;

}

But I also want to be able to set those values which I can get from the file, so to attempt to do that, I use this method:

public void setProperty(String property, String value){

    try{

        OutputStream out = new FileOutputStream(this.getClass().getResource(filename).getFile());
        Properties properties = new Properties();

        properties.setProperty(property, value);
        properties.store(out, "Optional comment");
        out.close();

    }catch (Exception e){

        System.out.println("Unable to load:"+filename);
        e.printStackTrace();

    }

}

However, running that method gives me the following error:

java.io.FileNotFoundException: file:/home/andrew/Documents/Programming/Executable-JARs/SchoolClient.jar!/client-config.properties (No such file or directory)
at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
at java.io.FileOutputStream.<init>(FileOutputStream.java:110)
at com.andrewlalis.utils.DataSaver.setProperty(DataSaver.java:54)
at com.andrewlalis.MainClient.getNewIp(MainClient.java:173)
at com.andrewlalis.ClientWindow$4.mouseClicked(ClientWindow.java:142)

Now, I have confirmed that the file client-config.properties does exist, as I am able to read data from it, but it seems I'm unable to create an output stream for it. Why is that? Thank you in advance.

The problem I have is that I cannot open an output stream from the file in my classpath.

That question is quite ambiguous, because I feel that the answer is not simply, "No, you cannot save a file in the classpath." — Andrew Lalis, Dec 05 '15 at 12:40
Write output file into some other location without loading using ResourceAsStream. Try absolute path. — Ravindra babu, Dec 05 '15 at 12:43

score 0 · Accepted Answer · answered Dec 05 '15 at 13:24

That property is inside your .jar-file. So your question should rather be "how to modify contents of the .jar file currently executing" which is not a good idea.

The main question here would be:

Do you need those values persisted?

If the values you set should stay active only while program run that's fine - just .setProperty(key, value); and all's fine.

If on the other hand you want those values to be persisted for the next start of the application, you'd might want to consider Preferences instead.

How to load a properties file from classpath in Java

1 Answers1