Mapping Object from file in java

Question

I want map my object from text file, the text file contents are like this :

~
attribute1value
attribute2value
attribute3value
attribute4value
attribute5value
attribute6value
~
attribute1value
attribute2value
attribute3value
attribute4value
attribute5value
attribute6value
...continued same

So for each 5 attributes I want to create new object and map those 6 properties to it(that is not issue), the issue is how can I distinguish lines while reading, how can I get the first group, second group etc . thank you

Forget java, when you see the file how do you differentiate between one set and another set? Is there is a key somewhere? Any delimiters? Are the attribute values always one after another, in a particular order? Please rephrase the question, and provide more details. — Nivas, Jul 19 '10 at 12:25

score 4 · Answer 1 · answered Jul 19 '10 at 12:17

4

I suggest using a 3rd-party utility such as Flatworm to handle this for you.

answered Jul 19 '10 at 12:17

skaffman

398,947
96
818
769

thank you for yoru response, can you give me an example please – ant Jul 19 '10 at 12:23
3

@c0mrade - did you even visit the link from skaffman? there is an example there... – willcodejavaforfood Jul 19 '10 at 12:42
@willcodejavaforfood I went trough it I couldn't find it thats why I ask can he point where is that example – ant Jul 19 '10 at 12:50

score 2 · Answer 2 · edited May 23 '17 at 12:27

Adapted from here, and assuming there are always 6 properties per object:

You can use java.io.BufferedReader to read a file line by line.

BufferedReader reader = new BufferedReader(new FileReader("/path/to/file.txt"));
String line = null;
int count = 0;
MyObject obj = null;
while ((line = reader.readLine()) != null) {
    if(obj == null) obj = new MyObject();
    if(count <= 6) {
      switch(count) {
        case 0: // ignore: handles '~'
          break;
        case 1: // assign value of line to first property, like:
          obj.prop1 = line;
          break;
        // etc up to case 6
      }
      count++;
    } else {
      // here, store object somewhere, then...
      obj = null;
      count = 0;
    }
}

+1 - simple solution for a simple file format. Proves, that we still can code without using some xxx4j libraries :) — Andreas Dolk, Jul 19 '10 at 12:50

score 1 · Accepted Answer · answered Jul 19 '10 at 13:17

Here is a more flexible approach. We can specify a custom (single-line) delimiter, no delimiter is actually needed at the beginning or at the end of the file (but can be given), the number of lines of a record is flexible. The data is parsed into a simple model which can be used to validate data and create the final objects.

private String recordDelimiter = "~";

public static List<List<String>> parse(Reader reader) {

   List<List<String>> result = new ArrayList<List<String>>();
   List<String> record = new ArrayList<String>();
   boolean isFirstLine = true;

   while ((line = reader.readLine()) != null) {

      line = line.trim();

      if (line.length() == 0) {
        continue;  // we skip empty lines
      }

      if (delimiter.equals(line.trim()) {
        if (!isFirstLine) {
          result.add(record);
          record = new ArrayList<String>();
        } else {
          isFirstLine = false;   // we ignore a delimiter in the first line.
        }
        continue;
      } 

      record.add(line);
      isFirstLine = false;
   }

   if (!result.contains(record))
     result.add(record);   // in case the last line is not a separator

   return result;

}

score 0 · Answer 4 · answered Jul 19 '10 at 12:54

Primitive code, no exception handling, requires 100% perfect file structure and file which ends in the record delimiter character '~'.

Gives you a start though.

public class Record {

    private String field1 = null;
    private String field2 = null;
    private String field3 = null;
    private String field4 = null;
    private String field5 = null;
    private String field6 = null;

    private void read(DataInputStream din) throws IOException, ClassNotFoundException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(din));

        field1 = reader.readLine();
        field2 = reader.readLine();
        field3 = reader.readLine();
        field4 = reader.readLine();
        field5 = reader.readLine();
        field6 = reader.readLine();

        reader.readLine(); // Skip separator line "~".
    }


    private static void main(String[] args) throws IOException, ClassNotFoundException {
       FileInputStream fin = new FileInputStream("C:\\file.dat");
       DataInputStream din = new DataInputStream(fin);
       Collection<Record> records = new LinkedList<Record>();

       while(0 < din.available()) {
           Record record = new Record();
           record.read(din);

           records.add(record);
       }

    }
}

Mapping Object from file in java

4 Answers4