File类

File file = new File( String pathname );

常用方法

代码示例

	public static void main(String[] args) {
        //1.创建文件对象
        //File studentFile = new File("files");
        File studentFile = new File("files/studentInfo.txt");
        System.out.println("文件是否存在？" + studentFile.exists());
        System.out.println("是否是一个文件？" + studentFile.isFile());
        System.out.println("是否是一个目录？" + studentFile.isDirectory());
        String path = studentFile.getPath();
        System.out.println("相对路径是：" + path);
        String absolutePath = studentFile.getAbsolutePath();
        System.out.println("绝对路径是：" + absolutePath);
        System.out.println("文件的名称是：" + studentFile.getName());
        System.out.println("删除文件：" + studentFile.delete());
        System.out.println("删除之后该文件是否存在？" + studentFile.exists());
        try {
            System.out.println("重新创建studentInfo.txt文件：" + studentFile.createNewFile());
        } catch (IOException e) {
            e.printStackTrace();
        }

        File kd50File = new File("files/kd50.txt");
        System.out.println("kd50.txt的文件大小是：" + kd50File.length());

        File newFile = new File("files/kgc/kd50/wang");
        if(!newFile.exists()){
            //newFile.mkdir();//创建文件夹的
            newFile.mkdirs();//级联创建文件夹
        }
        System.out.println(newFile.exists());
        System.out.println("----------------------------------");
        /*File directory = new File("files");
        String[] files = directory.list();
        for (String s : files) {
            System.out.println(s);
        }*/
        System.out.println("----------------------------------");
        /*File directory = new File("files");
        File[] files = directory.listFiles();
        for (File file : files) {
            System.out.println(file.getName() + " -------- " + file.isFile());
        }*/
        System.out.println("----------------------------------");
        /*File directory = new File("files");
        File[] files = directory.listFiles(File::isFile);
        for (File file : files) {
            System.out.println(file.getName() + " -------- " + file.isFile());
        }*/
        System.out.println("----------------------------------");
        File directory = new File("files");
        File[] files = directory.listFiles(File::isDirectory);
        for (File file : files) {
            System.out.println(file.getName() + " -------- " + file.isDirectory());
        }
    }

流

通过流来读写文件：流是一组有序的数据序列，以先进先出方式发送信息的通道

分类

当然除了这些之外还有二进制流、对象流…

字节流输入流

public class MyFileInput {
    public static void main(String[] args) throws IOException {
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("D:\\KD50\\project\\API\\files\\stuedntInfo.txt");
            //读取内容
            int read;
            while ((read = fis.read()) != -1) {
                System.out.print((char) read);
            }
            System.out.println();
            System.out.println("文件读取完毕");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

字节流输出流

public class MyFileOutput {
    public static void main(String[] args) {
        String words = "HelloWorld!!!";
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream("files/code.txt");
            byte[] bytes = words.getBytes();
            fos.write(bytes,0,bytes.length);
            fos.flush();
            System.out.println("内容输出完毕！！！");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fos!=null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

字节流复制粘贴效果

public class CopyFile {
    public static void main(String[] args) {
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream("files/code.txt");
            fos = new FileOutputStream("files/copy.txt",true);
            int read ;
            while ((read = fis.read())!=-1){
                fos.write(read);
            }
            fos.flush();
        }catch (FileNotFoundException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(fos!=null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fis!=null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

字符流输入流

public static void main(String[] args) {
        FileReader fr = null;
        try {
            fr = new FileReader("files/studentInfo.txt");
            int read;
            while ((read=fr.read())!=-1){
                System.out.print((char)read);
            }
            System.out.println("读取完毕");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (fr!=null) {
                try {
                    fr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

字符流输出流

public static void main(String[] args) {
        FileWriter fw = null;
        try {
            fw = new FileWriter("files/kgc/info.txt");
            String words = "Hello World!!!\n" +
                    "大吉大利，今晚吃鸡！！！";
            fw.write(words);
            fw.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (fw!=null) {
                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

Buff版输入输出流

	public static void main(String[] args) {
        BufferedReader br = null;
        FileReader fr = null;
        try {
            fr = new FileReader("files/studentInfo.txt");
            br = new BufferedReader(fr);
            String line;
            while ((line = br.readLine())!=null){
                System.out.println(line);
            }
            System.out.println("内容读取完毕！");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(fr!=null){
                try {
                    fr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(br!=null){
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

public static void main(String[] args) {
        FileReader fr = null;
        BufferedReader br = null;
        FileWriter fw = null;
        BufferedWriter bw = null;
        try {
            fr = new FileReader("files/studentInfo.txt");
            br = new BufferedReader(fr);
            fw = new FileWriter("files/kgc/studentInfo.txt");
            bw = new BufferedWriter(fw);
            String line;
            while ((line=br.readLine())!=null){
                bw.write(line + "\n");
            }
            System.out.println("复制完毕");
            bw.flush();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if (fr != null) {
                try {
                    fr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fw != null) {
                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bw != null) {
                try {
                    bw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }
    }

二进制流

public static void main(String[] args) {
        FileInputStream fis = null;
        FileOutputStream fos = null;
        DataInputStream dis = null;
        DataOutputStream dos = null;
        List<String> typeList = new ArrayList<>();
        Collections.addAll(typeList,".jpg",".png");
        File file = new File("files");
        File[] files = file.listFiles(File::isFile);
        try {
            for (File f : files) {
                if(typeList.contains(f.getName().substring(f.getName().lastIndexOf(".")))){
                    fis = new FileInputStream(file.getPath()+File.separator+f.getName());
                    dis = new DataInputStream(fis);
                    fos = new FileOutputStream(file.getPath()+File.separator+"images"+File.separator+f.getName());
                    dos = new DataOutputStream(fos);
                    int read;
                    while ((read=dis.read())!=-1){
                        dos.write(read);
                    }
                    dos.flush();
                }
            }
            System.out.println("文件全部复制完毕");
        }catch (FileNotFoundException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(fis!=null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(dis!=null){
                try {
                    dis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fos!=null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(dos!=null){
                try {
                    dos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

序列化和反序列化

• 注册：先读取文件中的对象(反序列化)，如果为空就创建一个新的Map，不为空就将读取的流转为Map对象，每当用户注册后，将信息写到Map里，然后再把Map序列化到文件中，以实现用户注册后信息能够持久化起来。
• 登录时从Map中进行校验

public class Menu {
    Scanner sc = new Scanner(in);
    static Map<String,User> userMap;
 
    static{
        InputStream is = null;
        ObjectInputStream ois = null;
        try {
            is = new FileInputStream("files/user/userMap.txt");
            ois = new ObjectInputStream(is);
            userMap =  (Map<String,User>)ois.readObject();
        }catch (FileNotFoundException e){
            userMap = new HashMap<>();
            //e.printStackTrace();
        }catch (IOException e){
            userMap = new HashMap<>();
            //e.printStackTrace();
        } catch (ClassNotFoundException e) {
            userMap = new HashMap<>();
            //e.printStackTrace();
        } finally {
            if(is != null){
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(ois != null){
                try {
                    ois.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
 
    public void register(){
        System.out.print("请输入用户名：");
        String userCode = sc.next();
        System.out.print("请输入密码：");
        String userPassword = sc.next();
        User user = new User(userCode,userPassword);
        userMap.put(userCode,user);
        //将注册的信息序列化
        oosObject();
    }
 
    public User login(){
        System.out.println("***************用户登录***************");
        System.out.print("请输入用户名：");
        String userCode = sc.next();
        System.out.print("请输入密码：");
        String userPassword = sc.next();
        if(!userMap.containsKey(userCode) || !userPassword.equals(userMap.get(userCode).getUserPassword())){
            return null;
        }
        return userMap.get(userCode);
    }
    private void oosObject(){
        //将注册的信息保存到外部文件中
        ObjectOutputStream oos = null;
        OutputStream os = null;
        try {
            os = new FileOutputStream("files/user/userMap.txt");
            oos = new ObjectOutputStream(os);
            oos.writeObject(userMap);
            oos.flush();
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(os != null){
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(oos != null){
                try {
                    oos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

用户实体类

public class User implements Serializable {
    private String userCode;
    private String userPassword;
 
    public User(String userCode, String userPassword) {
        this.userCode = userCode;
        this.userPassword = userPassword;
    }
    
    public User() {
    }
 
    @Override
    public String toString() {
        return "User{" +
                "userCode='" + userCode + '\'' +
                ", userPassword='" + userPassword + '\'' +
                '}';
    }
 
    public String getUserCode() {
        return userCode;
    }
 
    public void setUserCode(String userCode) {
        this.userCode = userCode;
    }
 
    public String getUserPassword() {
        return userPassword;
    }
 
    public void setUserPassword(String userPassword) {
        this.userPassword = userPassword;
    }
}

测试

	public static void main(String[] args) {
        Menu menu = new Menu();
        //menu.register();
        User user = menu.login();
        if(user!=null){
            System.out.println("登录成功，登录信息为：" + user);
        }else {
            System.out.println("登录失败！");
        }
    }