Question

I am trying to tackle a program take the given input file is in.properties and I want to write it out again to a new file out.properties discarding the prefix prefix from the file contents

i.e. the contents of the input file would be

prefix.sum.code.root=/compile/pkg

the contents of the output file would be

sum.code.root=/compile/pkg

Here is my Code :

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

public class Dummy {

public static void main(String args[])
{
    Properties prop =new Properties();

    try{
        //load a property file
        prop.load(new FileInputStream    ("C:\\Users\\user\\Desktop\\ant\\Filtering\\input.properties"));
        for (String key : prop.stringPropertyNames()){ 
            prop.remove(key);
        }
        prop.store(new FileOutputStream("C:\\Users\\user\\Desktop\\ant\\Filtering\\output.properties"), null);          
    }catch (IOException e)
    {
    e.printStackTrace();
    }
    }}

The returning null value for the ‘KEY’ and i am not able to update new value into this feild

Answer 1

You should be able to do this fairly easy using Properties.stringPropertyNames and Hashtable.remove, as Properties is a subclass of Hashtable.

final Properties properties = ...;
for (final String name : properties.stringPropertyNames()) {
  if (name.startsWith("prefix.")) {
    properties.setProperty(name.substring(6, name.length()), properties.remove(name));
  }
}