【JavaSE】文件 IO 的常用核心类 && File 类 && try-with-resources && 字节流 && 字符流

// 字节流包裹
BufferedInputStream in = new BufferedInputStream(new FileInputStream("file.txt")); 

// 字符流包裹    
BufferedReader br = new BufferedReader(new FileReader("test.txt"))                 

File file = new File("../test.txt");
System.out.println("getPath(): " + file.getPath());
System.out.println("getAbsolutePath(): " + file.getAbsolutePath());
System.out.println("getCanonicalPath(): " + file.getCanonicalPath());

// 结果：
getPath(): ../test.txt
getAbsolutePath(): /home/user/../test.txt
getCanonicalPath(): /home/test.txt

try {
    BufferedReader reader = new BufferedReader(new FileReader("file.txt"));
    String line = reader.readLine();
    System.out.println(line);
} catch (IOException e) {
    e.printStackTrace();
} finally {
    if (reader != null) {
        try {
            reader.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) {
    String line = reader.readLine();
    System.out.println(line);
} catch (IOException e) {
    e.printStackTrace();
}

public static void main(String[] args) {
    // try-with-resources风格：
    try(InputStream in = new FileInputStream("./main.txt")) {
        byte[] buf = new byte[1024];
        while(true) {
            int n = in.read(buf); // 磁盘数据读取到buf中
            if(n == -1) {
                System.out.println("读取完毕");
                break;
            }
            
            // 处理数据，比如输出数据
            for(int i = 0; i < n; ++i) {
                System.out.printf("0x%x\n", buf[i]); // 十六进制输出
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public static void main(String[] args) {
    try(OutputStream out = new FileOutputStream("./main1.txt")) {
        byte[] buf = {
            97, 98, 99, 100
        };
        out.write(buf); // 将buf数据写入到文件中去
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public static void main(String[] args) {
    try(InputStream in = new FileInputStream("./main.txt");
        Scanner sc = new Scanner(in, "UTF-8")) {
        
        // 循环读入每一行，然后输出
        while(sc.hasNext()) {
            String line = sc.nextLine();
            System.out.println(line);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public static void main(String[] args) {
    try(OutputStream out = new FileOutputStream("./main2.txt", "UTF-8");
        PrintWriter pw = new PrintWriter(out)) {

        // 将文本输出到文件中，可以直接传String类型
        pw.write("啊啊~利刃啊liren\n利刃阿斯顿");
    } catch (IOException e) {
        e.printStackTrace();
    }
}