File Stream C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Collections.Specialized;
using System.Diagnostics;
public static class FileUtils
{
    public static void ReplaceStringInFile(string fileName, string source, string target)
    {
        try
        {
            StreamReader streamReader = null;
            StreamWriter streamWriter = null;
            string contents = null;
            streamReader = File.OpenText(fileName);
            contents = streamReader.ReadToEnd();
            streamReader.Close();
            streamWriter = File.CreateText(fileName);
            streamWriter.Write(contents.Replace(source, target));
            streamWriter.Close();
        }
        catch (Exception ex)
        {
            Trace.TraceError("File I/O Error: {0}, StackTrace: {1}", ex.Message, ex.StackTrace);
        }
    }
}