Java文件IO

按字符读写Reader、Writer

FileWrite、FileReader

FileWriter writer = new FileWriter(file, true)为追加写

public static void main(String[] args) throws Exception {
    String dir = "E:\\aaa.txt";
    File file = new File(dir);
    //如果文件不存在，创建文件
    if (!file.exists())
        file.createNewFile();
    //创建FileWriter对象
    FileWriter writer = new FileWriter(file);
    //向文件中写入内容
    writer.write("aaa");
    writer.flush();
    writer.close();

    //创建FileReader对象，读取文件中的内容
    FileReader reader = new FileReader(file);
    char[] ch = new char[100];
    reader.read(ch);
    for (char c : ch) {
        System.out.print(c);
    }
    System.out.println();
    reader.close();
}

通过套一层BufferedWrite、BufferedReader，可以一行行来读

public static void main(String[] args) throws Exception {
    String dir = "E:\\aaa.txt";
    File file = new File(dir);
    //如果文件不存在，创建文件
    if (!file.exists())
        file.createNewFile();
    //创建BufferedWriter对象
    BufferedWriter bw = new BufferedWriter(new FileWriter(file));
    //向文件中写入内容
    bw.write("aaa");
    bw.flush();
    bw.close();

    //创建BufferedReader对象，读取文件中的内容
    BufferedReader br = new BufferedReader(new FileReader(file));
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
    System.out.println();
    br.close();
}

按字节读写InputStream、OutputStream

FileOutputStream、FileInputStream

FileOutputStream fos = new FileOutputStream(file, true)为追加写

public static void main(String[] args) throws Exception {
    String dir = "E:\\aaa.txt";
    File file = new File(dir);
    //如果文件不存在，创建文件
    if (!file.exists())
        file.createNewFile();
    //创建FileOutputStream对象，写入内容
    FileOutputStream fos = new FileOutputStream(file);
    //向文件中写入内容
    fos.write("aaa".getBytes());
    fos.close();

    //创建FileInputStream对象，读取文件内容
    FileInputStream fis = new FileInputStream(file);
    byte[] bys = new byte[100];
    while (fis.read(bys, 0, bys.length) != -1) {
        //将字节数组转换为字符串
        System.out.println(new String(bys));
    }
    fis.close();
}