[Java]基础备忘：Java文件操作

工作中经常需要处理SQL文件、处理Excel，也经常有很多Word与在线文档可以转成Excel处理。
现就读取SQL文件，写入SQL文件，读取Excel表格、写入Excel做代码备份。

1、常用DEMO

1.1、常用修改文件

使用 FileWriter、BufferedWriter、PrintWriter 等常用的类。

try {
    FileWriter fileWriter = new FileWriter("filepath");
    BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
    bufferedWriter.write("data to be written");
    bufferedWriter.close();
} catch (IOException e) {
    e.printStackTrace();
}

使用 PrintWriter 向文件写入数据：

try {
    PrintWriter printWriter = new PrintWriter(new File("filepath"));
    printWriter.println("data to be written");
    printWriter.close();
} catch (FileNotFoundException e) {
    e.printStackTrace();
}

在指定的行号插入一行文本：

Path path = Paths.get("filepath");
List<String> lines = Files.readAllLines(path, Charset.forName("UTF-8"));
lines.add(lineNumber, "data to be added");
Files.write(path, lines, Charset.forName("UTF-8"));

1.2、常用读取文件

使用 FileInputStream、BufferedReader、Scanner 等类。
使用 BufferedReader 逐行读取文本文件：

try {
    BufferedReader bufferedReader = new BufferedReader(new FileReader("filepath"));
    String line;
    while ((line = bufferedReader.readLine()) != null) {
        System.out.println(line);
    }
    bufferedReader.close();
} catch (IOException e) {
    e.printStackTrace();
}

使用 Scanner 逐行读取文本文件：

try {
    Scanner scanner = new Scanner(new File("filepath"));
    while (scanner.hasNextLine()) {
        System.out.println(scanner.nextLine());
    }
    scanner.close();
} catch (FileNotFoundException e) {
    e.printStackTrace();
}

读取二进制文件：

try {
    InputStream inputStream = new FileInputStream("filepath");
    byte[] buffer = new byte[1024];
    int bytesRead;
    while ((bytesRead = inputStream.read(buffer)) != -1) {
        // 处理读取的数据
    }
    inputStream.close();
} catch (IOException e) {
    e.printStackTrace();
}

2、操作实例

怎么方便怎么来，创建一个Maven工程即够。

    <dependencies>
        <!--工具类-->
        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.7.6</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>5.0.0</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.22</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>easyexcel</artifactId>
            <version>3.0.5</version>
        </dependency>
    </dependencies>

2.1、SQL文件操作

读取SQL文件，可以选择绝对路径，也可以选择resources下。
按行读取。

    public void parseSql() {
    	File file = new File("D:\\xxx.sql");
        List<MdbDTO> result = new ArrayList<>();
        try (BufferedReader bf = new BufferedReader(new FileReader(file))) {
            //按行读取
            String line = null;
            while ((line = bf.readLine()) != null) {
                //doSomething to line;
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

把String内容写入文件

    private static void makeFile(StringBuilder sqlStr, String fileName) throws IOException {
        String path = "src/main/resources/";
        File file = new File(path + fileName);
        if (!file.exists()) {
            file.createNewFile();
        } else {
            file = new File(path + new Date().getTime() + "_" + fileName);
        }
        try (FileOutputStream outputStream = new FileOutputStream(file);) {
            outputStream.write(sqlStr.toString().getBytes(StandardCharsets.UTF_8));
        }
    }

2.2、excel文件操作

可以在Hutool官网看具体用法

    public List<List<Object>> parseExcel(){
        File file = new File("D:\\xxx\\xxx.xlsx");
        ExcelReader reader = ExcelUtil.getReader(file);
        List<List<Object>> readAll = reader.read();
        return  readAll ;
    }

2.3、文件传输接口

@RestController
@RequestMapping("/file")
public class FileController {
    
    @PostMapping("/upload")
    public String upload(@RequestParam("file") MultipartFile file) {
        try {
            // 获取原始文件名
            String fileName = file.getOriginalFilename();
            // 获取文件内容
            byte[] bytes = file.getBytes();
            
            //TODO 处理文件内容
            
            return "success";
        } catch (Exception e) {
            e.printStackTrace();
            return "failed";
        }
    }
}