Java SE学习记录*_读取文件

文件对象

构建File对象

import java.io.*;
public class Main {
	public static void main(String[] args){
		// 绝对路径
		File f = new File("D:\\java\\Program.exe");
		// 相对路径 当前路径为D:\java
		File f = new File(".\\Program.exe");
	}
} 

File常用方法

File对象可以返回路径

		f.getPath(); // 返回构造时传入的路径
		f.getAbsolutePath(); // 返回绝对路径
		f.getCanonicalPath(); // 返回规范路径

File对象可以给出当前系统的分隔符

		f.separator(); // Windows: '\'; Ubuntu: '/'

判断File是否是一个已存在的文件/目录

		f.isFile();
		f.isDirectory();

创建/删除文件

		f.createNewFile("FileNmae", ".txt");
		f.delete();
		
		f.createTempFile("FileNmae", ".txt"); // 创建临时文件
		f.deleteOnExit(); // 在JVM退出时自动删除临时文件；

遍历文件/目录

		File[] fs = f.listFiles();
		for (File f : fs){
			System.out.println(f);
		}

Path对象

public class Main {
    public static void main(String[] args) throws IOException {
        Path p1 = Paths.get(".", "project", "study"); // 构造一个Path对象
        System.out.println(p1);
        Path p2 = p1.toAbsolutePath(); // 转换为绝对路径
        System.out.println(p2);
        Path p3 = p2.normalize(); // 转换为规范路径
        System.out.println(p3);
        File f = p3.toFile(); // 转换为File对象
        System.out.println(f);
        for (Path p : Paths.get("..").toAbsolutePath()) { // 可以直接遍历Path，..为上一层目录
            System.out.println("  " + p);
        }
    }

文件读写

读写

import java.io.*;
public class Main {
	public static void main(String[] args) throws IOException {
		String path = "./test.txt";
		String content = "你好，再见"; 
		
//		File f1 = new File("./src/test.txt");
//		if (f1 == null) {f1.createNewFile();}
		
		writeFile(path, content);
		System.out.println(readFile(path));
	}
	
	public static String readFile(String path) throws IOException {
		try(InputStream input = new FileInputStream(path)) {
			byte[] buffer = new byte[1024];
			int n;
			StringBuilder sb = new StringBuilder();
			while ((n = input.read(buffer)) != -1) {
				sb.append(new String(buffer, "UTF-8"));
			}
			return sb.toString();
		}
	} 
	
	public static void writeFile(String path, String content) throws IOException {
		try(OutputStream output = new FileOutputStream(path)){
			output.write(content.getBytes("UTF-8"));
			output.flush();
		}
	}
}

复制文件

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class CopyFile {
	public static void main(String[] args) throws IOException {
		if (args.length != 2) {
			System.err.println("Usage:\n  java CopyFile.java <source> <target>");
			System.exit(1);
		}
		copy(args[0], args[1]);
		System.out.println("Done !");
	}

	static void copy(String source, String target) throws IOException {
		try (InputStream input = new FileInputStream(source);
			 OutputStream output = new FileOutputStream(target))
		{
			byte[] buffer = new byte[1024];
			int n;
			String s;
			StringBuilder sb = new StringBuilder();
			while ((n = input.read(buffer)) != -1) {
				sb.append(new String(buffer, "UTF-8" ));
			}
			s = sb.toString();
			output.write(s.getBytes("UTF-8"));
		} 
	}
}