Reversing a properties file content

Question

I've a properties file (say exmp.properties) which is something like this

1. k5=500
2. k4=400
3. k3=300
4. k2=200
5. k1=100

I need to reverse the content of this file like

1. k1=100
2. k2=200
3. k3=300
4. k4=400
5. k5=500

Is there any way I can achieve this using ANT task or Java code?

Apart from the answers why you want to reverse the contents of the properties file? As you can fetch any property you want where order do not matters? — Nakul91, Jun 26 '15 at 07:18
Why? Order is immaterial in a properties file. It's a hash map. There is no sequential access in file order. — user207421, Jun 26 '15 at 07:19

Manuel Allenspach · Answer 1 · 2015-06-26T07:29:09.193

You need to do something like this:

String input = "in.txt";
String output = "out.txt";

try (FileWriter fw = new FileWriter(output)) {
    //read all lines
    List<String> lines = Files.readAllLines(Paths.get(input), Charset.defaultCharset());

    //clear contents of the output file
    fw.write("");
    //write all lines in reverse order
    for (int i = lines.size() - 1; i >= 0; i--) {
        fw.append(lines.get(i) + System.lineSeparator());
    }
} catch (Exception e) {}

This reads all lines of the file and then writes them in reverse order.

score 0 · Answer 2 · edited May 23 '17 at 11:51

0

Thats just a text file. "Read in the file line by line" "reverse it" and "write to the file again".

edited May 23 '17 at 11:51

Community

1
1

answered Jun 26 '15 at 07:11

Stefan

12,108
5
47
66

Rebse · Accepted Answer · 2015-06-26T09:10:16.907

Here's a solution with loadresource and nested filterchain.
To make it work correctly your propertyfile needs a linefeed after last property, means :

k5=500
k4=400
k3=300
k2=200
k1=100
-- empty line --

snippet :

<project>
 <loadfile property="unsorted" srcfile="foobar.properties"/>
 <echo>unsorted: ${line.separator}${unsorted}</echo>

 <loadresource property="sorted">
  <string value="${unsorted}" />
   <filterchain>
    <sortfilter />
   </filterchain>
 </loadresource>
 <echo>sorted: ${line.separator}${sorted}</echo>
 <!-- write file -->
 <echo file="foobar_sorted.properties">${sorted}</echo>
</project>

output :

[echo] unsorted:
[echo] k5=500   
[echo] k4=400   
[echo] k3=300   
[echo] k2=200   
[echo] k1=100   
[echo] sorted:  
[echo] k1=100   
[echo] k2=200   
[echo] k3=300   
[echo] k4=400   
[echo] k5=500

Reversing a properties file content

3 Answers3