大文件分页查询

　　当你在导入和解析Log文件的过程中，由于文件太大，文件大小一般的几百M甚至几个G的时间，一次性读取非常占用内存，

那么读取文件的时间就需要一定的技巧。

代码如下：

public class FileSegmentation
    {
        public FileStream EzoneStream { get; private set; }
        public long PageCount { get; private set; }
        public long PageSize = 1024;
        public long FileSize { get; private set; }
        public FileSegmentation(string filename)
        {
            FileInfo EzoneFile = new FileInfo(filename);
            EzoneStream = EzoneFile.OpenRead();
            PageCount = (EzoneStream.Length / PageSize);
            FileSize = EzoneFile.Length;
        }
        public byte[] GetPage(Int64 pageNumber)
        {
            if (EzoneStream == null || !EzoneStream.CanSeek || !EzoneStream.CanRead)
                return null;
            if (pageNumber < 0 || pageNumber >= PageCount)
                return null;
            Int64 offsetStart = (Int64)pageNumber * (Int64)PageSize;
            Int64 offsetEnd = 0;
            if (pageNumber < PageCount - 1)
                offsetEnd = offsetStart + PageSize - 1;
            else
                offsetEnd = FileSize - 1;

            byte[] tmp = new byte[offsetEnd - offsetStart + 1];

            EzoneStream.Seek(offsetStart, SeekOrigin.Begin);
            int rd = EzoneStream.Read(tmp, 0, (Int32)(offsetEnd - offsetStart + 1));
            return tmp;
        }
    }

public class SymphonyReadLog : AsynchronousWorkBaseEx
    {
        private FileSegmentation Segmentation;
        public event ProgressBarEventHandler ProgressBarEvent;
        public long Count { get; private set; }

        public string Filter { get; set; }
        public SymphonyReadLog(string pathFile)
        {
            this.Segmentation = new FileSegmentation(pathFile);
            this.Count = this.Segmentation.PageCount;
        }
        public List<string> SecurityReadLog(ref string buffers, Int64 pageNum)
        {
            List<string> dataList = new List<string>();
            string data = string.Empty;
            byte[] b = Segmentation.GetPage(pageNum);
            //解析文本
            if (b != null)
            {
                data = buffers + ServiceConstEx.ServiceEncoding.GetString(b);
                string[] array = data.Split('
');
                foreach (var item in array)
                {
                    if (item.IndexOf("
") >= 0)
                    {
                        dataList.Add(item);
                    }
                    else
                    {
                        buffers = item;
                    }
                }
            }
            return dataList;
        }
        /// 读取日志
        public string ReadLog(string pathFile)
        {
            string message = string.Empty;
            long sumLength = 0;
            using (FileStream stream = new FileStream(pathFile, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
            {
                BinaryReader r = new BinaryReader(stream);
                sumLength = stream.Length;
                byte[] postArray = r.ReadBytes((int)sumLength);
                if (stream.CanRead)
                {
                    int k = 1024;
                    for (int i = 0; i < postArray.Length; i += k)
                    {
                        if (i + k > postArray.Length)
                        {
                            k = postArray.Length - i;
                        }
                        r.Read(postArray, i, k);
                    }
                }
                message = ServiceConstEx.ServiceEncoding.GetString(postArray);
                r.Close();
                r.Dispose();
            }
            return message;
        }

        public List<string> SecuritySerchReadLog()
        {
            string buffers = string.Empty;
            List<string> dataList = new List<string>();
            string data = string.Empty;
            for (int i = 1; i < Segmentation.PageCount; i++)
            {
                List<string> serList = SecurityReadLog(ref buffers, i);
                foreach (string serchString in serList)
                {
                    if (serchString.IndexOf(Filter) >= 0)
                    {
                        dataList.Add(serchString);
                    }
                }
            }
            return dataList;
        }

        protected override void Run()
        {
            string buffers = string.Empty;
            string data = string.Empty;
            for (int i = 0; i < this.Segmentation.PageCount - 1; i++)
            {
                var dataList = new List<string>();
                var serList = this.SecurityReadLog(ref buffers, i);
                foreach (string serchString in serList)
                {
                    if (serchString.IndexOf(Filter) >= 0)
                    {
                        dataList.Add(serchString);
                    }
                }
                worker.ReportProgress(i + 1, dataList);
            }
        }
        protected override void worker_ProgressChanged(object sender, System.ComponentModel.ProgressChangedEventArgs e)
        {
            ProgressBarEventArgs arg = new ProgressBarEventArgs(e.ProgressPercentage, e.UserState);
            OnProgressBarEvent(arg);
        }
        protected void OnProgressBarEvent(ProgressBarEventArgs e)
        {
            if (this.ProgressBarEvent != null)
            {
                this.ProgressBarEvent(this, e);
            }
        }
    }