Java讀取文件的幾種方式詳細(xì)總結(jié)

更新時間：2023年08月18日 09:14:11 作者：C3Stones

這篇文章主要給大家介紹了關(guān)于Java讀取文件的幾種方式,文中通過代碼示例將幾種方式介紹的非常詳細(xì),對大家學(xué)習(xí)或者使用Java具有一定的參考學(xué)習(xí)價值,需要的朋友可以參考下

1. 使用流讀取文件
2. 使用JDK1.7提供的NIO讀取文件(適用于小文件)
3. 使用JDK1.7提供的NIO讀取文件(適用于大文件)
4. 使用JDK1.4提供的NIO讀取文件(適用于超大文件)
5. 使用cmmons-io依賴提供的FileUtils工具類讀取文件
6. 使用cmmons-io依賴提供的IOtils工具類讀取文件
7. 使用hutool依賴提供的FileUtil工具類讀取文件
8. 使用hutool依賴提供的IoUtil工具類讀取文件
9. 測試耗時
總結(jié)

1. 使用流讀取文件

public static void stream() {
    String fileName = "D:\\test.txt";
    final String CHARSET_NAME = "UTF-8";
    List<String> content = new ArrayList<>();
    try (BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(fileName), CHARSET_NAME))) {
        String line;
        while ((line = br.readLine()) != null) {
            content.add(line);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
//        content.forEach(System.out::println);
    System.out.println(content.size());
}

2. 使用JDK1.7提供的NIO讀取文件(適用于小文件)

public static void nioOfJDK7() {
    String fileName = "D:\\test.txt";
    final String CHARSET_NAME = "UTF-8";
    List<String> content = new ArrayList<>(0);
    try {
        content = Files.readAllLines(Paths.get(fileName), Charset.forName(CHARSET_NAME));
    } catch (Exception e) {
        e.printStackTrace();
    }
//        content.forEach(System.out::println);
    System.out.println(content.size());
}

3. 使用JDK1.7提供的NIO讀取文件(適用于大文件)

public static void streamOfJDK7() {
    String fileName = "D:\\test.txt";
    final String CHARSET_NAME = "UTF-8";
    List<String> content = new ArrayList<>();
    try (BufferedReader br = Files.newBufferedReader(Paths.get(fileName), Charset.forName(CHARSET_NAME))) {
        String line;
        while ((line = br.readLine()) != null) {
            content.add(line);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
//        content.forEach(System.out::println);
    System.out.println(content.size());
}

4. 使用JDK1.4提供的NIO讀取文件(適用于超大文件)

public static void nioOfJDK4() {
    String fileName = "D:\\test.txt";
    final String CHARSET_NAME = "UTF-8";
    final int ASCII_LF = 10; // 換行符
    final int ASCII_CR = 13; // 回車符
    List<String> content = new ArrayList<>();
    try (FileChannel fileChannel = new RandomAccessFile(fileName, "r").getChannel()) {
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024 * 100);
        byte[] lineByte;
        byte[] temp = new byte[0];
        while (fileChannel.read(byteBuffer) != -1) {
            // 獲取緩沖區(qū)位置，即讀取長度
            int readSize = byteBuffer.position();
            // 將讀取位置置0，并將讀取位置標(biāo)為廢棄
            byteBuffer.rewind();
            // 讀取內(nèi)容
            byte[] readByte = new byte[readSize];
            byteBuffer.get(readByte);
            // 清除緩存區(qū)
            byteBuffer.clear();
            // 讀取內(nèi)容是否包含一整行
            boolean hasLF = false;
            int startNum = 0;
            for (int i = 0; i < readSize; i++) {
                if (readByte[i] == ASCII_LF) {
                    hasLF = true;
                    int tempNum = temp.length;
                    int lineNum = i - startNum;
                    // 數(shù)組大小已經(jīng)去掉換行符
                    lineByte = new byte[tempNum + lineNum];
                    System.arraycopy(temp, 0, lineByte, 0, tempNum);
                    temp = new byte[0];
                    System.arraycopy(readByte, startNum, lineByte, tempNum, lineNum);
                    String line = new String(lineByte, 0, lineByte.length, CHARSET_NAME);
                    content.add(line);
                    // 過濾回車符和換行符
                    if (i + 1 < readSize && readByte[i + 1] == ASCII_CR) {
                        startNum = i + 2;
                    } else {
                        startNum = i + 1;
                    }
                }
            }
            if (hasLF) {
                temp = new byte[readByte.length - startNum];
                System.arraycopy(readByte, startNum, temp, 0, temp.length);
            } else {
                // 單次讀取的內(nèi)容不足一行的情況
                byte[] toTemp = new byte[temp.length + readByte.length];
                System.arraycopy(temp, 0, toTemp, 0, temp.length);
                System.arraycopy(readByte, 0, toTemp, temp.length, readByte.length);
                temp = toTemp;
            }
        }
        // 最后一行
        if (temp.length > 0) {
            String lastLine = new String(temp, 0, temp.length, CHARSET_NAME);
            content.add(lastLine);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
//        content.forEach(System.out::println);
    System.out.println(content.size());
}

5. 使用cmmons-io依賴提供的FileUtils工具類讀取文件

添加依賴：

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.11.0</version>
</dependency>

public static void fileOfCommonsIO() {
        String fileName = "D:\\test.txt";
        final String CHARSET_NAME = "UTF-8";
        List<String> content = new ArrayList<>(0);
        try {
            content = FileUtils.readLines(new File(fileName), CHARSET_NAME);
        } catch (Exception e) {
            e.printStackTrace();
        }
//        content.forEach(System.out::println);
        System.out.println(content.size());
    }

6. 使用cmmons-io依賴提供的IOtils工具類讀取文件

添加依賴：

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.11.0</version>
</dependency>

public static void ioOfCommonsIO() {
        String fileName = "D:\\test.txt";
        final String CHARSET_NAME = "UTF-8";
        List<String> content = new ArrayList<>(0);
        try {
            content = IOUtils.readLines(new FileInputStream(fileName), CHARSET_NAME);
        } catch (Exception e) {
            e.printStackTrace();
        }
//        content.forEach(System.out::println);
        System.out.println(content.size());
    }

7. 使用hutool依賴提供的FileUtil工具類讀取文件

添加依賴：

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-core</artifactId>
    <version>5.8.10</version>
</dependency>
或者：
<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.8.10</version>
</dependency>

public static void fileOfHutool() {
        String fileName = "D:\\test.txt";
        final String CHARSET_NAME = "UTF-8";
        List<String> content = FileUtil.readLines(fileName, CHARSET_NAME);
//        content.forEach(System.out::println);
        System.out.println(content.size());
    }

8. 使用hutool依賴提供的IoUtil工具類讀取文件

添加依賴：

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-core</artifactId>
    <version>5.8.10</version>
</dependency>
或者：
<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.8.10</version>
</dependency>

public static void ioOfHutool() {
        String fileName = "D:\\test.txt";
        final String CHARSET_NAME = "UTF-8";
        List<String> content = new ArrayList<>();
        try {
            IoUtil.readLines(new FileInputStream(fileName), CharsetUtil.charset(CHARSET_NAME), content);
        } catch (Exception e) {
            e.printStackTrace();
        }
//        content.forEach(System.out::println);
        System.out.println(content.size());
    }

9. 測試耗時

測試文件：30000行、21.8 MB

public static void main(String[] args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start("stream");
    stream();
    stopWatch.stop();
    stopWatch.start("nioOfJDK7");
    nioOfJDK7();
    stopWatch.stop();
    stopWatch.start("streamOfJDK7");
    streamOfJDK7();
    stopWatch.stop();
    stopWatch.start("nioOfJDK4");
    nioOfJDK4();
    stopWatch.stop();
    stopWatch.start("fileOfCommonsIO");
    fileOfCommonsIO();
    stopWatch.stop();
    stopWatch.start("ioOfCommonsIO");
    ioOfCommonsIO();
    stopWatch.stop();
    stopWatch.start("fileOfHutool");
    fileOfHutool();
    stopWatch.stop();
    stopWatch.start("ioOfHutool");
    ioOfHutool();
    stopWatch.stop();
    for (StopWatch.TaskInfo taskInfo : stopWatch.getTaskInfo()) {
        System.out.println(taskInfo.getTaskName() + " -> " + taskInfo.getTimeMillis() + " ms");
    }
//    System.out.println(stopWatch.prettyPrint());
}

測試3次耗時統(tǒng)計(單位：ms)：