Java文件与IO流详细攻略

import java.io.File;
public class FileBasicsDemo {
    public static void main(String[] args) {
        // 1) 路径与构造
        File file = new File("D:/IO/hello.txt"); // 建议使用 / 或者使用 Paths 构建
        File dir  = new File("D:/IO/sub");
        // 2) 基本信息
        System.out.println(file.getAbsolutePath());
        System.out.println(file.getName());
        System.out.println(file.exists());
        System.out.println(file.isFile());
        System.out.println(file.isDirectory());
        // 3) 创建目录/文件
        if (!dir.exists()) {
            boolean ok = dir.mkdirs(); // 递归创建目录
            System.out.println("mkdirs: " + ok);
        }
        // 创建新文件（若父目录不存在会失败）
        try {
            if (!file.exists()) {
                boolean created = file.createNewFile();
                System.out.println("createNewFile: " + created);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        // 4) 遍历目录
        File root = new File("D:/IO");
        File[] children = root.listFiles();
        if (children != null) {
            for (File f : children) {
                System.out.println((f.isDirectory() ? "[DIR] " : "[FILE]") + f.getName());
            }
        }
    }
}

import java.io.*;
import java.nio.charset.StandardCharsets;
public class ReaderDemo {
    public static void main(String[] args) {
        String path = "D:/IdeaProjects/JavaTest/src/com/qcby/a.txt";
        // 1) FileReader：简单，但依赖平台默认编码（不推荐在生产使用）
        try (FileReader reader = new FileReader(path)) {
            int ch;
            while ((ch = reader.read()) != -1) {
                System.out.print((char) ch);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 2) InputStreamReader：可指定编码（推荐）
        try (InputStreamReader reader = new InputStreamReader(
                new FileInputStream(path), StandardCharsets.UTF_8)) {
            int ch;
            while ((ch = reader.read()) != -1) {
                System.out.print((char) ch);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 3) BufferedReader：高效且支持按行读取
        try (BufferedReader br = new BufferedReader(new FileReader(path))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.io.*;
import java.nio.charset.StandardCharsets;
public class WriterDemo {
    public static void main(String[] args) {
        String outPath = "D:/IO/output.txt";
        // 1) FileWriter：简单写文本
        try (FileWriter writer = new FileWriter(outPath)) { // 默认编码
            writer.write("Hello, World!\n");
            writer.write("This is a new line.\n");
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 2) OutputStreamWriter：指定编码（推荐）
        try (OutputStreamWriter writer = new OutputStreamWriter(
                new FileOutputStream(outPath, true), StandardCharsets.UTF_8)) { // 追加写
            writer.write("追加一行，使用UTF-8编码。\n");
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 3) BufferedWriter：高效按行写
        try (BufferedWriter bw = new BufferedWriter(new FileWriter(outPath, true))) {
            bw.write("Hello, World!");
            bw.newLine();
            bw.write("This is a new line.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
public class WriterExample {
    public static void main(String[] args) {
        String out = "D:/IO/writer-demo.txt";
        try (Writer writer = new FileWriter(out)) {
            // 1. 写入单个字符
            writer.write('H');
            // 2. 写入字符数组
            char[] array = {'e', 'l', 'l', 'o'};
            writer.write(array);
            // 3. 写入字符数组的一部分（写入 "ll"）
            writer.write(array, 2, 2);
            // 4. 写入字符串
            writer.write(", World!");
            // 5. 写入字符串的一部分（写入 "This is Java"）
            String str = "\nThis is Java IO.";
            writer.write(str, 1, 12);
            System.out.println("数据已写入文件！");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.io.*;
import java.nio.charset.StandardCharsets;
public class FileInputStreamTest {
    public static void main(String[] args) {
        File file = new File("D:/IO/hello.txt");
        // 建议：优先使用 try-with-resources，避免手动 finally 关闭
        try (FileInputStream fis = new FileInputStream(file)) {
            byte[] buffer = new byte[1024];
            int len;
            while ((len = fis.read(buffer)) != -1) {
                // 如果是文本，可按编码构造字符串；若是二进制，直接处理字节
                String chunk = new String(buffer, 0, len, StandardCharsets.UTF_8);
                System.out.print(chunk);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
public class FileOutputStreamTest {
    public static void main(String[] args) {
        File file = new File("D:/IO/hello.txt");
        // true 表示追加写
        try (FileOutputStream fos = new FileOutputStream(file, true)) {
            fos.write(97); // 写入单字节 'a'
            fos.write("\r\n".getBytes(StandardCharsets.UTF_8));
            fos.write("中国人!\r\n".getBytes(StandardCharsets.UTF_8));
            fos.write("ABCDEFGH".getBytes(StandardCharsets.UTF_8), 2, 4); // 输出 CDEF
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.io.*;
public class FileCopy {
    public static void copyFile(String src, String dest) throws IOException {
        try (BufferedInputStream in = new BufferedInputStream(new FileInputStream(src));
             BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(dest))) {
            byte[] buf = new byte[8192];
            int len;
            while ((len = in.read(buf)) != -1) {
                out.write(buf, 0, len);
            }
        }
    }
    public static void main(String[] args) throws IOException {
        copyFile("D:/IO/source.bin", "D:/IO/target.bin");
    }
}

import java.io.*;
import java.nio.charset.StandardCharsets;
public class TextTransformDemo {
    public static void main(String[] args) {
        String src = "D:/IO/input-utf8.txt";
        String dest = "D:/IO/output-utf8.txt";
        try (BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(src), StandardCharsets.UTF_8));
             BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(dest), StandardCharsets.UTF_8))) {
            String line;
            int lineNo = 1;
            while ((line = br.readLine()) != null) {
                // 简单转换：在每行前加上行号
                bw.write(String.format("%04d: %s", lineNo++, line));
                bw.newLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}