快速读取文件行数

package filesplit;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.LineNumberReader;

public class LineCount {
    public static void main(String[] args) throws IOException {
        LineCount app = new LineCount();
        app.compareBufferAndLineNumber();
    }

    public void compareBufferAndLineNumber() throws IOException {
        String fileName = "F:\\mywork\\filesplit\\AllLog";
        long time = System.currentTimeMillis();

        System.out.println("LineNumberReader" + this.getTotalLines(fileName));
        System.out.println(System.currentTimeMillis() - time);

        time = System.currentTimeMillis();

        System.out.println("BufferedReader" + this.getTotalLines2(fileName));
        System.out.println(System.currentTimeMillis() - time);

        time = System.currentTimeMillis();

        System.out.println("BufferedInputStream" + this.count(fileName));
        System.out.println(System.currentTimeMillis() - time);

        // 从输出结果来看，反而是BufferedInputStream是最快的。
        // LineNumberReader8663721
        // 6203
        // BufferedReader8663721
        // 6016
        // BufferedInputStream8663720
        // 1609

    }

    /**
     * 采用 LineNumberReader方式读取总行数
     *
     * @param fileName
     * @return
     * @throws IOException
     */
    private int getTotalLines(String fileName) throws IOException {
        FileReader in = new FileReader(fileName);
        LineNumberReader reader = new LineNumberReader(in);
        String strLine = reader.readLine();
        int totalLines = 0;
        while (strLine != null) {
            totalLines++;
            strLine = reader.readLine();
        }
        reader.close();
        in.close();
        return totalLines;
    }

    /**
     * 采用BufferedReader方式读取总行数
     *
     * @param fileName
     * @return
     * @throws IOException
     */
    private int getTotalLines2(String fileName) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(fileName));
        String strLine = br.readLine();
        int totalLines = 0;
        while (strLine != null) {
            totalLines++;
            strLine = br.readLine();
        }
        br.close();
        return totalLines;
    }

    /**
     * 采用BufferedInputStream方式读取文件行数
     *
     * @param filename
     * @return
     * @throws IOException
     */
    public int count(String filename) throws IOException {
        InputStream is = new BufferedInputStream(new FileInputStream(filename));
        byte[] c = new byte[1024];
        int count = 0;
        int readChars = 0;
        while ((readChars = is.read(c)) != -1) {
            for (int i = 0; i < readChars; ++i) {
                if (c[i] == '\n')
                    ++count;
            }
        }
        is.close();
        return count;
    }

}

 

从执行结果来看，采用BufferedInputStream方式是最快的。