How to read the property file when duplicate key-value pair exist in the file?

Question

I am loading my property file using the load() of properties class.I am able to read the key-value pair of the property class using set,hashmap,treeset,enumeration, but it does not retrieve the duplicate pairs. The duplicate pairs are retrieved only once.

Solution 1

PropertiesConfiguration from Apache Commons Configuration supports loading a properties file with multiple entries with the same key.

Use the getStringArray(key) method or getList(key) method to access all values for the specified key.

Solution 2

Properties file sets key value pairs. All keys are unique so it will not catch duplicate pairs. Instead it will fetch the latest mapped pair. For example :

Sample file:

a=1
b=2
c=3
d=4
a=10
c=7

The properties class will return latest pairs i.e

a=10
b=2
c=7
d=4

Still if your requirement is to find all the pairs whether duplicate or not , Use the following code that uses Scanner class and two arraylist objects.

        ArrayList k = new ArrayList();
        ArrayList v = new ArrayList();
        Scanner scan = new Scanner(new File("E:\\abc.properties"));
        while(scan.hasNextLine()) {
            //System.out.println(scan.nextLine());
            String split[] = scan.nextLine().trim().split("=");
            if(split.length == 2) {
            k.add(split[0]);
            v.add(split[1]);
            System.out.println("pair " + split[0] + ":" + split[1]);
            }
            //System.out.println("a");*/
        }

Solution 3

you can use buffer reader to read lines of your file and split the result:

public static void main(String[] args) throws IOException {
    Reader file = new FileReader("C:/file.cfg");
    BufferedReader br = new BufferedReader(file);

    String line = br.readLine();
    while (line != null) {
        String obj[] = line.split("=");

        for (int i=0 ;  i<obj.length; i=+2  ){
            System.out.println(obj[i]+"="+obj[i+1]);

        line = br.readLine();
        }
    }
}

Comments

[user207421]

Your property file is invalid. Keys must be unique. Redesign it.

[user3089783]

@EJP: i know its invalid if duplicate values exists in the property file and that is what i want to show by comparing each key with every other key.i want to create a method that If duplicate keys are present then it must show some alert or message,is there any way to do it?

[user207421]

Nothing stopping you writing such a method yourself, but that's not what you asked.

[user3089783]

@EJP:pardon for the mistake,but for that method first i need to read all the keys from the property file even if its duplicate and i am not able to read the duplicate keys,please let me know the way to do that.... as in my property file i have a=1,a=1,a=2......i want to read all the three a but i am able to read it only once i.e. a=2....

[user207421]

You have to write it yourself. You can't use Properties.load().

[user3089783]

Actually my property file has values: a=1,a=2,a=4.......... and i want to get all the three keys as i want to compare each key with every other in the file to show that duplicate keys exists in the file,is it possible anyhow?

[Nishant Lakhara]

Then it will give a=1 as key value pair. Properties file should not contain duplicates ideally. Do you sill want to do it?

[user3089783]

No, i want to print the keys that exists more than once in the property file

[user3089783]

the code you provided above is quite helpful,its reading all the values even if its duplicate through the scan.nextLine() but throws no line found exception when storing in the Split[].

[Nishant Lakhara]

There must be some problem with your file. Terminate the last line correctly. Dont press an enter after the last line or send me the file, I check with it.

[user323094]

Updated link: commons.apache.org/proper/commons-configuration/apidocs/org/‌​…

[Emrys Myrooin]

He is not asking for a piece of code without any explanation.

[Starwarswii]

Note that this basic way of reading a property file will not properly deal with #comments and spaces before and after the equal sign, which are normally ignored.