Java文件操作之按行读取文件和遍历目录的方法

按行读取文件

package test; 
 
import java.io.*; 
import java.util.*; 
 
public class readtest { 
 
  public static list<string> first_list; 
  public static list<string> second_list; 
 
  public readtest() { 
    first_list = new linkedlist<>(); 
    second_list = new linkedlist<>(); 
  } 
 
  public static void readfile() { 
    final string filename = "d://aa.txt"; 
    string str = null; 
    int i = 0; 
    try { 
      linenumberreader reader = null; 
      reader = new linenumberreader(new filereader(filename)); 
      while ((str = reader.readline()) != null) { 
        if (!str.isempty()) { 
          string values[] = str.split("  "); 
          first_list.add(values[0]); 
          second_list.add(values[1]); 
        } 
      } 
    } catch (ioexception e) { 
      e.printstacktrace(); 
    } 
  } 
 
  public static void main(string args[]) { 
 
    readtest reader = new readtest(); 
    reader.readfile(); 
 
    for (int i = 0; i < first_list.size(); i++) { 
      system.out.println(first_list.get(i) + ":" + second_list.get(i)); 
    } 
  } 
} 

递归遍历目录

class listfiles{ 
  public static arraylist filelist = new arraylist(); 
   
  public static void listfiles(string dir){   
    file file = new file(dir); 
    file[] files = file.listfiles(); 
    if(null == files){ 
      return; 
    } 
    for(int i = 0; i < files.length; i++){ 
      if(files[i].isdirectory()) 
      { 
        listfiles(files[i].getabsolutepath()); 
      } 
      else{ 
        system.out.println(files[i]); 
        filelist.add(files[i]); 
      } 
    } 
  } 
} 

上面遍历目录是一种递归的方法，我们再来看一下非递归的实现：

//非递归
  public static void scandirnorecursion(string path){
   linkedlist list = new linkedlist();
    file dir = new file(path);
    file file[] = dir.listfiles();
    for (int i = 0; i < file.length; i++) {
      if (file[i].isdirectory())
        list.add(file[i]);
      else{
        system.out.println(file[i].getabsolutepath());
        num++;
      }
    }
    file tmp;
    while (!list.isempty()) {
      tmp = (file)list.removefirst();//首个目录
      if (tmp.isdirectory()) {
        file = tmp.listfiles(); 
        if (file == null)
          continue;
        for (int i = 0; i < file.length; i++) {
          if (file[i].isdirectory())
            list.add(file[i]);//目录则加入目录列表，关键
          else{
            system.out.println(file[i]);
            num++;
          }
        }
      } else {
        system.out.println(tmp);
        num++;
      }
    }
  }

我们可以写一个类来简单测试一下：

import java.io.file;
import java.util.linkedlist;
public class filesystem {
 
 public static int num;
 
  public static void main(string[] args) {
    
    long a = system.currenttimemillis();
    //string path="c:";
    num=0;
    string[] lists={"c:","d:"};
    /*
    for(int i=0;i<lists.length;i++){
     file file=new file(lists[i]);
     scandirrecursion(file);
    */
    for(int i=0;i<lists.length;i++){
      scandirnorecursion(lists[i]);
    }
    
    system.out.print("文件总数:"+num);
    system.out.print("总耗时:");
    system.out.println(system.currenttimemillis() - a);
  }

测试结果：
递归：
文件总数:189497  总耗时:39328
非递归：
文件总数:189432 总耗时:37469
这里非递归相对要好~