java LineNumberReader的使用

前段時間須要讀報表打印，需求是能夠從第N行讀到第N行，發現百度出來的LineNumberReader方法都不怎麼理想

而後就找到一篇和衆百度裏脫穎而出的好文章，因此分享之：

 

從類 的命名來看，貌似LineNumberReader能夠支持從任意行讀取的功能，而且提供了setLineNumber()的方法，可是這個按照並不能改變文件指針的位置，只是你調用getLineNumber()這個函數時，結果會變。API上面說它並不能改變文件物理的指針位置。看來之後得當心使用。

 

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.LineNumberReader;

 

public class Ex7 {

     public void dataReader(String nameFile, int start, int finish) {

          if (start > finish) {

               System.out.println("Error start or finish!");

               return;

          }

          InputStream inputStream = null;

          LineNumberReader reader = null;

          try {

               inputStream = new FileInputStream(new File(nameFile));

               reader = new LineNumberReader(

                         new InputStreamReader(inputStream));

               int lines = getTotalLines(new File(nameFile));

               if (start < 0 || finish < 0 || finish > lines || start > lines) {

                    System.out.println("Line not found!");

                    return;

               }

              

               String line = reader.readLine();

             lines = 0;

             while (line != null) {

                 lines++;

                 if(lines >= start && lines <= finish){

                      System.out.println(line);

                 }

                 line = reader.readLine();

             }

             inputStream.close();

               reader.close();

          } catch (FileNotFoundException e) {

               e.printStackTrace();

          } catch (IOException e) {

               System.err.println("IO Error");

               System.exit(0);

          }

 

     }

    

     private int getTotalLines(File file) throws IOException{

          FileReader in = new FileReader(file);

        LineNumberReader reader = new LineNumberReader(in);

        String line = reader.readLine();

        int lines = 0;

        while (line != null) {

            lines++;

            line = reader.readLine();

        }

        reader.close();

        in.close();

        return lines;

     }

 

     public static void main(String[] args) {

          new Ex7().dataReader("data.txt", 2, 4);

          new Ex7().dataReader("data.txt",3,8);

     }

}