Question

output data from java collection to csv file

Asked by: youneverknoweverything

I am trying to output the contents of a Java Collection ( preferably LL or Array List)
into a csv file. I want the objects in the collection to sorted based on instance variables in the objects sorted in order of priority.

Eg I want to sort the collection first on name value of each object, then acc no , etc.

Any ideas on how this can be done?

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Asked On
2009-10-06 at 20:23:16ID24791217
Tags

Java collection

,

file handling

,

csv file

,

collection sorting

Topic

Java Standard Edition

Participating Experts
2
Points
500
Comments
8

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Answers

 

by: ksivananthPosted on 2009-10-06 at 21:00:20ID: 25512125

check this example to sort the elements in list http://java.sun.com/docs/books/tutorial/collections/interfaces/order.html

 

by: ksivananthPosted on 2009-10-06 at 21:02:54ID: 25512128

use open csv for java to create the csv directly from the bean http://opencsv.sourceforge.net/#javabean-integration

 

by: javaexpertoPosted on 2009-10-06 at 21:08:23ID: 25512150

You only need to implement the Comparable interface in the Class wich its object are in the arrayList, then override the compareTo method. Example, lets say you have a class Employe and you need to sort by name:

import java.util.*;
 
class Employe implements Comparable<Employe> {
	
    private String name;
   
 
    public Employe(String name) {
    	
    	this.name =  name;
    }
 
    public int compareTo(Employe emp) {
		
		return name.compareTo(emp.getName());
 
    }
 
    public String getName() {
        return name;
    }
    
    public static void main(String args[]) {
    	
    	ArrayList<Employe> array = new ArrayList<Employe>();
    	array.add(new Employe("John"));
    	array.add(new Employe("Peter"));
    	array.add(new Employe("Mary"));
    	
    	Collections.sort(array);
    	
    	for(Employe e: array) {
    		
    		System.out.print(e.getName());
    	}
    }
}

                                              
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by: youneverknoweverythingPosted on 2009-10-06 at 21:18:11ID: 25512176

I want a way to sort like in database, that is orderby first name, then surname, then number etc. not surein this case if compare to will help and then how do export it to csv?

 

by: javaexpertoPosted on 2009-10-06 at 21:24:50ID: 25512204

To export to a file, each instance var separated by comma:

import java.io.*;
import java.util.*;
 
class Employe implements Comparable<Employe> {
	
    private String name;
    private int id;
   
 
    public Employe(String name, int id) {
    	
    	this.name =  name;
    	this.id = id;
    }
 
    public int compareTo(Employe emp) {
		
		return name.compareTo(emp.getName());
 
    }
 
    public String getName() {
        return name;
    }
    
    public int getId() {
        return id;
    }
    
    public static void main(String args[]) throws IOException{
    	
    	ArrayList<Employe> array = new ArrayList<Employe>();
    	array.add(new Employe("John", 123));
    	array.add(new Employe("Peter", 456));
    	array.add(new Employe("Mary", 789));
    	BufferedWriter bf = null;
    	try {
    	
    		bf = new BufferedWriter(new FileWriter("csv.txt"));
    		for(Employe emp : array) {
    	
    			bf.write(emp.getName() + ", " + emp.getId());
        		bf.newLine(); 
        	}
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            //Close the BufferedWriter
            try {
                if (bf != null) {
                    bf.flush();
                    bf.close();
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }	
    }
}

                                              
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by: javaexpertoPosted on 2009-10-06 at 21:28:21ID: 25512212

You can only order your objects in a collection only by one of the instance vars. Name or surname or number etc.

 

by: javaexpertoPosted on 2009-10-06 at 21:28:59ID: 25512216

I meant sort.

 

by: ksivananthPosted on 2009-10-07 at 03:26:04ID: 25513747

>>orderby first name, then surname, then number etc. not surein this case if compare to will help

try this,

public int compareTo(Employe emp) {
            
            int i = name.compareTo(emp.getName());
if( i != 0 ) return i
i = surName.compareTo(emp.getSurName());
if( i != 0 ) return i
return number - emp.getNumber() ; //if its a numeric
    }

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