Reading Properties File by One Jar from Another

[Dennis Putnam]

I have 2 jar files (A and B) where A is an obsolete version and B is the new version of my app. To do the "update" all I need is to obtain the properties from A. How can I programatically read A's properties from B? When I search for examples of this I can only find JarInJar situations rather than external jars. TIA.

[Kemal Sokolovic]

You can access A jar content with ZipInputStream as:

ZipInputStream inputStream = new ZipInputStream(new FileInputStream("jarfile.jar"));
ZipEntry entry;
// Iterate over entries in jar and find the one that matches your properties file
while((entry = inputStream.getNextEntry()) != null)
{
    if(entry.getName().equals("YourPropertiesFile.properties"))
    {
        // Here you can read it's content with BufferedReader
    }
}

[Dennis Putnam]

Perfect. I will give it a try. Thanks.

[Dennis Putnam]

This is not doing what I expected in that it is not traversing directories. I have exactly 2 directories at the top level of the jar: KCBSEvents and META-INF. However, the only one it finds is META-INF. The main directory is not showing up. Here is my class:

public class UpdateProperties {
	
	public static void updateProperties() {
		ZipInputStream inputStream=null;
		ZipEntry entry=null;
		JFileChooser chooser=new JFileChooser();
		File file=null;
		
		chooser.setDialogTitle("This is an update: Select old application file");
		int ret=chooser.showOpenDialog(null);
		if (ret==JFileChooser.APPROVE_OPTION) {
			try {
				file=chooser.getSelectedFile();
				inputStream=new ZipInputStream(new FileInputStream(file));
			} catch (FileNotFoundException e) {
				System.exit(-1);
			}
		}
		else {
			System.exit(-1);
		}
		try {
			while ((entry=inputStream.getNextEntry())!=null) {
				System.out.println(entry.getName());
				if (entry.getName().equals("build.properties")) {
					BufferedReader br=new BufferedReader(new FileReader(file));
					String thisLine="";
					while ((thisLine=br.readLine())!=null) {
						System.out.println(thisLine);
					}
					br.close();
				}
				else {
					System.exit(-1);
				}
			}
		} catch (IOException e) {
			System.exit(-1);
		}
	}

}

How do I drill down to the file I need. It is in 'KCBSEvents/resources'? I don't think the way I am setting up BufferedReader is right either but I haven't gotten that far yet. TIA.

[Kemal Sokolovic]

That else block (33 - 35) shouldn't be there. What you did actually is this: get the first entry from the jar, and if it's not what I'm looking for, exit application.

Edit: I hope you don't plan to handle your exceptions by exiting application. Suppose this is just a testing version.

[Dennis Putnam]

DOH! How dumb is that? Yes this is a work in progress. I'll clean up all the exception handling when I have it working.

Can you also tell me how to set up the BufferedReader for my file? I can't seem to get anything that results in an inputStreamReader.

Thanks.

[Kemal Sokolovic]

Once you are in that while loop and you find the file you want to read:

...
while((entry = inputStream.getNextEntry()) != null)
{
    if(entry.getName().equals("build.properties"))
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
        String thisLine = "";
        while((thisLine = br.readLine()) != null)
        {
            // Do whatever with the line
        }
    }
}

Don't forget to close those input streams you are using (I think you omitted inputStream.close() after while loop). Or use try-with-resources instead.

[Dennis Putnam]

Sheesh, that was too easy. No wonder I couldn't find it. Thanks.

[Kemal Sokolovic]

You're welcome.