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@PostMapping(value = "/uploadFile", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public String uploadFile(@RequestParam("file") MultipartFile file, String moduleUri) throws IOException {
    InputStream inputStream = file.getInputStream();
    String fileName = file.getOriginalFilename();
    // to save file
    ...
}

public class FileUploadByCommonsFileUploadServlet extends HttpServlet {
	public void doPost(HttpServletRequest request, HttpServletResponse response) throws Exception {
        DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
        diskFileItemFactory.setSizeThreshold(MAX_MEMORY_SIZE);
        diskFileItemFactory.setRepository(new File(System.getProperty("java.io.tmpdir")));
        ServletFileUpload servletFileUpload = new ServletFileUpload(diskFileItemFactory);
        servletFileUpload.setFileSizeMax(MAX_FILE_SIZE);
        servletFileUpload.setSizeMax(MAX_FILE_SIZE);
        List<FileItem> formItems = servletFileUpload.parseRequest(request);
        for (FileItem item : formItems) {
            if (!item.isFormField()) {
                String fileName = new File(item.getName()).getName();
                String filePath = new StringBuilder()
                    .append(UPLOAD_DIR)
                    .append(File.seperator)
                    .append(fileName)
                    .toString()
                item.write(new File(filePath));
            }
        }
    }
    ...
}

@GetMapping(value = "/download" )
public void download(HttpServletResponse response, String fileUri) {
    response.setCharacterEncoding("utf-8");
    response.setContentType("application/octet-stream");
    response.setHeader("Content-Disposition", "attachment;fileName=\"" + URLEncoder.encode(filename, "UTF-8").replace("+", "%20") + "\"");
    ServletOutputStream outputStream = response.getOutputStream();
    int bufSize = 1024;
    byte[] buffer = new byte[bufSize];
    int len;
    // get filePath by fileUri
    ...
    // get input stream by filePath
    ...
    while ((len = inputStream.read(buffer)) != -1) {
        outputStream.write(buffer, 0, len);
    }
    inputStream.close();
}

@GetMapping(value = "/download" )
public ResponseEntity<Resource> download(String fileUri) {
    // get filePath by fileUri
    //...
    String uploadDir = "D:\\upload";
    Path path = Paths.get(uploadDir).toAbsolutePath().normalize();
    path = path.resolve(fileUri).normalize();
    Resource resource = new UrlResource(path.toUri());
    String resultFileName = URLEncoder.encode(resource.getFilename().replace("%20", " "), "UTF-8").replace("+", "%20");
    return ResponseEntity.ok()
        .contentType(MediaType.parseMediaType("application/octet-stream"))
        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + resultFileName + "\"")
        .body(resource);
}

@RestController
@RequestMapping("files")
public class MyFileController {
    private static final Logger logger = LogManager.getLogger();

    public static final String UPLOAD_DIR = "D:\\My Desktop\\upload";

    public static final String DOWNLOAD_PREFIX = "/files/download";

    @PostMapping(value = "/uploadFile", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    public String uploadFile(@RequestParam("file") MultipartFile file, String moduleUri) throws IOException {
        String uploadFileUri = getUploadFileUri(file, moduleUri);
        String uploadFilePath = new StringBuilder()
                .append(UPLOAD_DIR)
                .append(File.separator)
                .append(uploadFileUri)
                .toString();
        ensureDirectoryExist(uploadFilePath);
        try (
            BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(
                new FileOutputStream(uploadFilePath));
        ) {
            byte[] buf = new byte[1024];
            int len;
            InputStream inputStream = file.getInputStream();
            while ((len = inputStream.read(buf)) != -1) {
                bufferedOutputStream.write(buf, 0, len);
            }
        }
        return new StringBuilder()
                .append(DOWNLOAD_PREFIX)
                .append("/")
                .append(uploadFileUri)
                .toString();
    }

    private String getUploadFileUri(MultipartFile file, String moduleUri) {
        String uuid = UUID.randomUUID().toString().replaceAll("-", "");
        Calendar calendar = Calendar.getInstance();
        StringBuilder dateUri = new StringBuilder()
                .append(calendar.get(Calendar.YEAR))
                .append("/")
                .append(calendar.get(Calendar.MONTH) + 1)
                .append("/")
                .append(calendar.get(Calendar.DAY_OF_MONTH));
        StringBuilder resultFileUri = new StringBuilder()
                .append(moduleUri)
                .append("/")
                .append(dateUri)
                .append("/")
                .append(uuid)
                .append("/")
                .append(file.getOriginalFilename());
        return resultFileUri.toString();
    }

    private void ensureDirectoryExist(String filePath) {
        filePath = filePath.replace("/", File.separator).replace("\\", File.separator);
        String fileDir = filePath.substring(0, filePath.lastIndexOf(File.separator));
        logger.debug("fileDir: {}", fileDir);
        File dir = new File(fileDir);
        if (!dir.exists()) {
            dir.mkdirs();
        }
    }

    @GetMapping(value = "download/**")
    public void download(HttpServletRequest request, HttpServletResponse response) throws IOException {
        String servletPath = request.getServletPath();
        String fileUri = servletPath.substring(DOWNLOAD_PREFIX.length());
        String filePath = new StringBuilder()
                .append(UPLOAD_DIR)
                .append(File.separator)
                .append(fileUri)
                .toString();
        try (
                BufferedInputStream bufferedInputStream = new BufferedInputStream(new FileInputStream(filePath))
        ) {
            ServletOutputStream outputStream = response.getOutputStream();
            byte[] buf = new byte[1024];
            int len;
            while ((len = bufferedInputStream.read(buf)) != -1) {
                outputStream.write(buf, 0, len);
            }
        }
    }
}

InputStream is = new FileInputStream("D:\\My Desktop\\test.txt");

String filepath = "D:\\My Desktop\\test.txt";
Path path = Paths.get(filepath).normalize();
//path.toUri().toString(): file:///D:/My%20Desktop/test.txt
Resource resource = new UrlResource(path.toUri()); 
InputStream is = resource.getInputStream();

String filepath = "D:\\My Desktop\\test.txt";
Path path = Paths.get(filepath).normalize();
//path.toUri().toString(): file:///D:/My%20Desktop/test.txt
InputStream is = new URL(path.toUri().toString()).openStream();

// src/main/resources/application.yml
Resource resource = new ClassPathResource("application.yml");
InputStream is = resource.getInputStream();

@Autowired
ResourceLoader resourceLoader;

resourceLoader.getResource("classpath:application.yml");
InputStream is = resource.getInputStream();

byte[] data = new String("data...").getBytes(StandardCharsets.UTF_8);
ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(data);

InputStream is = new URL("http://demo.com/test.txt").openStream();

Resource resource = new UrlResource("http://demo.com/test.txt");
InputStream is = resource.getInputStream();

URLConnection urlConnection = new URL("http://demo.com/test.txt").openConnection();
urlConnection.connect();
InputStream is = urlConnection.getInputStream();

byte[] data = new String("data").getBytes(StandardCharsets.UTF_8);
String storeFilePath = "D:/My Workspace/test/test.txt";
try (
    ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(data);
    FileOutputStream fileOutputStream = new FileOutputStream(storeFilePath)
) {
    byte[] buf = new byte[1024];
    int len = 0;
    while ((len = byteArrayInputStream.read(buf)) != -1) {
        fileOutputStream.write(buf, 0, len);
    }
} catch (IOException e) {
    e.printStackTrace();
}

byte[] data = new String("data").getBytes(StandardCharsets.UTF_8);
byte[] storeDataArray;
try (
    ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(data);
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
) {
    byte[] buf = new byte[1024];
    int len = 0;
    while ((len = byteArrayInputStream.read(buf)) != -1) {
        byteArrayOutputStream.write(buf, 0, len);
    }
    storeDataArray = byteArrayOutputStream.toByteArray();
    System.out.println(new String(storeDataArray, StandardCharsets.UTF_8));
} catch (IOException e) {
    e.printStackTrace();
}

InputStream is = new FileInputStream("D:\\My Desktop\\test.txt");
new BufferedReader(new InputStreamReader(is)).lines().forEach(System.out::println);

Path path = Paths.get("D:\\My Desktop\\test.txt");
System.out.println(new String(Files.readAllBytes(path)));

try (
    FileOutputStream fileOutputStream = new FileOutputStream("D:/My Workspace/test/test.zip");
    ZipOutputStream zipOutputStream = new ZipOutputStream(fileOutputStream)
) {
    int fileNumber = 3;
    for (int i = 1; i <= fileNumber; i++) {
        String childFilename = "file" + i + ".txt";
        zipOutputStream.putNextEntry(new ZipEntry(childFilename));
        zipOutputStream.write(("data" + i).getBytes(StandardCharsets.UTF_8));
        zipOutputStream.closeEntry();
    }
    zipOutputStream.finish();
} catch (IOException e) {
    e.printStackTrace();
}

try (
    FileOutputStream fileOutputStream = new FileOutputStream("D:/My Workspace/test/test.zip");
    ZipOutputStream zipOutputStream = new ZipOutputStream(fileOutputStream)
) {
    int fileNumber = 3;
    for (int i = 1; i <= fileNumber; i++) {
        String childFilename = "file" + i + ".zip";
        zipOutputStream.putNextEntry(new ZipEntry(childFilename));
        try (
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            ZipOutputStream nestedZipOutputStream = new ZipOutputStream(byteArrayOutputStream);
        ) {
            int nestedNumber = 3;
            for (int j = 1; j <= nestedNumber; j++) {
                String nestedFileName = new StringBuilder()
                    .append("file").append(i)
                    .append("nestFile").append(j)
                    .append(".txt").toString();
                nestedZipOutputStream.putNextEntry(new ZipEntry(nestedFileName));
                nestedZipOutputStream.write(("nest file" + j).getBytes(StandardCharsets.UTF_8));
                nestedZipOutputStream.closeEntry();
            }
            nestedZipOutputStream.finish();
            zipOutputStream.write(byteArrayOutputStream.toByteArray());
        }
        zipOutputStream.closeEntry();
    }
    zipOutputStream.finish();
} catch (IOException e) {
    e.printStackTrace();
}

String inputFilePath = "C:\\Users\\Taogen\\Desktop\\input.txt";
String outputFilePath = "C:\\Users\\Taogen\\Desktop\\output.txt";
try (
    FileInputStream fileInputStream = new FileInputStream(inputFilePath);
    FileOutputStream fileOutputStream = new FileOutputStream(outputFilePath)
) {
    byte[] buf = new byte[2048];
    int len = 0;
    while ((len = fileInputStream.read(buf)) != -1) {
        fileOutputStream.write(buf, 0, len);
    }
} catch (IOException e) {
    e.printStackTrace();
}

String inputFilePath = "C:\\Users\\Taogen\\Desktop\\input.txt";
String outputFilePath = "C:\\Users\\Taogen\\Desktop\\output.txt";
try (
    FileInputStream fileInputStream = new FileInputStream(inputFilePath);
    BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);
    FileOutputStream fileOutputStream = new FileOutputStream(outputFilePath);
    BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
) {

    int b;
    while ((b=bufferedInputStream.read()) != -1) {
        bufferedOutputStream.write(b);
    }
} catch (IOException e) {
    e.printStackTrace();
}

String inputFilePath = "C:\\Users\\Taogen\\Desktop\\recovery_data.sql";
String outputFilePath = "C:\\Users\\Taogen\\Desktop\\recovery_data2.sql";
try (
    FileInputStream fileInputStream = new FileInputStream(inputFilePath);
    BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);
    FileOutputStream fileOutputStream = new FileOutputStream(outputFilePath);
    BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
) {
    byte[] buf = new byte[1024];
    int len = 0;
    while ((len = bufferedInputStream.read(buf)) != -1) {
        bufferedOutputStream.write(buf, 0, len);
    }
} catch (IOException e) {
    e.printStackTrace();
}

System.getProperty("java.io.tmpdir")

// If you don't specify the file suffix, the default file suffix is ".tmp".
File file = File.createTempFile("temp", null);
System.out.println(file.getAbsolutePath());
file.deleteOnExit();

// 1
String mimeType = Files.probeContentType(file.toPath());
// 2
String mimeType = URLConnection.guessContentTypeFromName(fileName);
// 3
FileNameMap fileNameMap = URLConnection.getFileNameMap();
String mimeType = fileNameMap.getContentTypeFor(file.getName());
// 4
MimetypesFileTypeMap fileTypeMap = new MimetypesFileTypeMap();
String mimeType = fileTypeMap.getContentType(file.getName());

public static void main(String[] args) throws IOException {
    String resource = "mybatis/mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    try (SqlSession session = sqlSessionFactory.openSession()) {
        UserMapper userMapper = session.getMapper(UserMapper.class);
        User user = userMapper.selectByPrimaryKey(1);
        logger.debug("user is {}", user);
    }
}

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private UserDao userDao;
    
    @Override
    public List<User> listAllUsers() {
        return userDao.listAllUsers();
    }
    ...
}

@Mapper
public interface UserDao {
}

@MapperScan(value = "com.taogen.example.dao")

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private UserDao userDao;
    
    @Override
    public List<User> listAllUsers() {
        return userDao.listAllUsers();
    }
    ...
}

import com.baomidou.mybatisplus.core.mapper.BaseMapper;

@Mapper
public interface UserDao extends BaseMapper<User> {
}

@MapperScan(value = "com.taogen.example.dao")

import com.baomidou.mybatisplus.core.mapper.BaseMapper;

@Mapper
public interface UserDao extends BaseMapper<User> {
}

import com.baomidou.mybatisplus.extension.service.IService;

public interface UserService extends IService<User> {
}

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;

@Service
public class UserServiceImpl extends ServiceImpl<UserDao, User> implements UserService {
}

QueryWrapper<User> queryWrapper = new QueryWrapper();
List<User> userList = userService.list(queryWrapper);