Traverse all files under a certain path and its sub-paths
- Traversing the file tree directly and sequentially and judging whether the File object in it is a file type can be regarded as the leaf node of traversing the file tree . But due to the use of recursion , the efficiency is low .
- If you change another method, using tree-level traversal (non-recursive, using queues ), the efficiency will be improved to a certain extent .
Method 1: Recursive method:
AllFiles class:
package com.cao.demo.allFiles;
import java.io.File;
/**
* 作者：曹浩东
* 使用递归遍历某一路径下的所有文件
*/
public class AllFiles {
private int fileCount = 0;//文件计数器
//递归遍历所有文件的方法
public void show(String path) {
File file = new File(path);//根据形参path实例化一个File对象
File[] files = file.listFiles();//返回path路径下 所有文件的File对象
//判断该目录是否为空
if (files.length > 0) {
//遍历该目录下的File对象
for (int i = 0; i < files.length; i++) {
//判断该对象是否为文件夹，如果是则递归访问
if (files[i].isDirectory()) {
show(files[i].getPath());
} else if (files[i].isFile()) {
//如果是该对象是文件，则打印。或者进行其他文件操作。
System.out.println(files[i].getPath());
//计数器加一
++fileCount;
}
}
} else {
//如果该目录为空，则打印该目录为空
System.out.println(path + "目录为空...");
}
}
//打印文件数量的方法
public void count() {
if (fileCount != 0) {
System.out.println("共扫描了" + fileCount + "个文件...");
} else {
System.out.println("还未进行遍历...");
}
}
}
Test class:
package com.cao.demo.allFiles;
public class Test {
public static void main(String[] args) {
//用于计时
long start;
long end;
//开始时间
start = System.currentTimeMillis();
//实例化AllFiles对象
AllFiles allFiles = new AllFiles();
//传入path参数
allFiles.show("C:\iweb\root");
//打印文件数量
allFiles.count();
//结束时间
end = System.currentTimeMillis();
//输出程序耗时
System.out.println("耗时" + ((end - start) / 1000.000D) + "秒...");
}
}
Result:
Method 2: Queue (level traversal)
allFiles class:
package com.cao.demo.allFiles2;
import java.io.File;
/**
* 作者：曹浩东
* 使用队列遍历某一路径下的所有文件
*/
public class AllFiles {
private int fileCount = 0;//计数器
public void show(String path) {
//根据形参path实例化一个File对象
File file = new File(path);
//创建File类型的队列
File[] Queue = new File[100000];
//队头和队尾
int front = -1, rear = -1;
//入队
Queue[++front] = file;
//当队列不为空时循环
while (front != rear) {
//出队
File fileInQueue = Queue[++rear];
//判断出队的对象是否是文件
if (fileInQueue.isFile()) {
//是文件则打印。或者执行其他文件操作
System.out.println(fileInQueue.getPath());
//计数器加一
++fileCount;
} else {
//如果出队的对象是文件夹类型，则返回其下所有文件的File对象
File[] fileIn = new File(fileInQueue.getPath()).listFiles();
//依次入队
for (int i = 0; i < fileIn.length; i++) {
Queue[++front] = fileIn[i];
}
}
}
}
//打印文件数量的方法
public void count() {
if (fileCount != 0) {
System.out.println("共扫描了" + fileCount + "个文件...");
} else {
System.out.println("还未进行遍历...");
}
}
}
Result: The
following table shows the time taken by the two methods to traverse the same folder containing 8296 files.
| Recursion (post-order traversal) | Queue (level traversal) |
|---|---|
| 3.041 seconds | 2.168 seconds |
Although the degree of efficiency improvement is not as great as I imagined, method 2 is still about 30% more efficient than method 1.
Copy files or folders
- For a folder: copy the folder to the target path in the order of traversal first
- For files, copy directly to the target path
package com.cao.demo;
import java.io.*;
public class CopyAllFiles {
public void copy(String src,String dst) throws IOException {
//创建源文件的文件类型
File srcFile=new File(src);
//如果是文件夹
if(srcFile.isDirectory()){
//创建目标路径+待复制文件夹名对象
File file=new File(dst+"\\"+srcFile.getName());
//创建该文件夹
file.mkdir();
//生成源目录下的所有文件或文件夹的文件对象
File[] allFiles=srcFile.listFiles();
//在文件夹不为空的情况下
if(allFiles.length>0){
//遍历源文件夹下的文件或文件夹对象
for (int i = 0; i < allFiles.length; i++) {
//递归调用
copy(allFiles[i].getPath(),file.getPath());
}
}
}else if(srcFile.isFile()){
FileInputStream fileInputStream=new FileInputStream(src);
FileOutputStream fileOutputStream=new FileOutputStream(dst+"\\"+srcFile.getName());
byte[] buff=new byte[1024];
int len;
while((len=fileInputStream.read(buff))!=-1){
fileOutputStream.write(buff,0,len);
fileOutputStream.flush();
}
fileInputStream.close();
fileOutputStream.close();
}
}
public static void main(String[] args) throws IOException {
CopyAllFiles copyAllFiles=new CopyAllFiles();
copyAllFiles.copy("C:\\iweb\\1","C:\\iweb\\copy");
}
}