Introduction to Java I/O and the File Class with Practical Example

I/O problems are one of the main bottlenecks in modern web applications. This series introduces the basic architecture of Java I/O libraries, the mechanisms of disk I/O, network I/O, and the working mode of NIO.

Since Java 1.4, NIO has been introduced to improve I/O performance. The I/O classes reside in the java.io package and can be divided into four groups:

Byte‑oriented I/O interfaces: InputStream and OutputStream

Character‑oriented I/O interfaces: Reader and Writer

Disk‑oriented I/O interface: File

Network‑oriented I/O interface: Socket (not in java.io but discussed together)

The first two groups mainly concern data formats, while the latter two concern data transmission methods. The core I/O issue is either the data format affecting operations or the transmission method affecting operations, ultimately answering the question of what data to write where.

File Class

The following section introduces common methods of the File class and some important concepts:

A File object represents a file or directory on disk.

File provides platform‑independent methods to operate on files or directories.

The class works directly with the file system.

File does not specify how information is read from or written to a file.

package io;
import java.io.File;
import java.io.IOException;

public class FileTest {
    public static void main(String[] args) throws IOException {
        File file = new File("f:/migu");
        file.mkdir();
        // Check if the directory exists
        if (file.exists() && file.isDirectory()) {
            System.out.println("migu 目录存在");
            File file1 = new File("f:/migu/UES.txt");
            File file2 = new File("f:\\migu\\CMU.txt");
            // Create files
            file1.createNewFile();
            file2.createNewFile();
            File file3 = new File("f:/migu/插件/支付中心");
            // Create directory and any missing parent directories
            file3.mkdirs();
            File[] files = file.listFiles();
            // List files in the directory
            for (File f : files) {
                System.out.println("migu目录下的文件名：" + f.getName());
                System.out.println("migu目录文件的绝对路径：" + f.getAbsolutePath());
            }
        } else {
            System.out.println("migu 目录不存在");
        }
    }
}

Execution result:

migu 目录存在
migu目录下的文件名：CMU.txt
migu目录文件的绝对路径：f:\migu\CMU.txt
migu目录下的文件名：UES.txt
migu目录文件的绝对路径：f:\migu\UES.txt
migu目录下的文件名：插件
migu目录文件的绝对路径：f:\migu\插件

Two important points to note:

mkdirs creates the directory represented by the abstract pathname and also creates any missing parent directories.

In lines 16‑17 the code uses two different path separators. Windows uses "\\" (escaped as "\\\\" in Java) while Linux uses "/". Using "/" works on all operating systems, so it is recommended to use forward slashes for portability.

Original article: http://www.cnblogs.com/dongguacai/p/5656471.html

If you encounter problems while learning Java or want more resources, feel free to join the Java study group QQ: 495273252 .