Java读取文件的几种方式

1. 使用流读取文件

public static void stream() {    String fileName = "D:\\test.txt";    final String CHARSET_NAME = "UTF-8";    List 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读取文件(适用于小文件)

public static void nioOfJDK7() {    String fileName = "D:\\test.txt";    final String CHARSET_NAME = "UTF-8";    List 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读取文件(适用于大文件)

public static void streamOfJDK7() {    String fileName = "D:\\test.txt";    final String CHARSET_NAME = "UTF-8";    List 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读取文件(适用于超大文件)

public static void nioOfJDK4() {    String fileName = "D:\\test.txt";    final String CHARSET_NAME = "UTF-8";    final int ASCII_LF = 10; // 换行符    final int ASCII_CR = 13; // 回车符    List 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) {            // 获取缓冲区位置，即读取长度            int readSize = byteBuffer.position();            // 将读取位置置0，并将读取位置标为废弃            byteBuffer.rewind();            // 读取内容            byte[] readByte = new byte[readSize];            byteBuffer.get(readByte);            // 清除缓存区            byteBuffer.clear();            // 读取内容是否包含一整行            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;                    // 数组大小已经去掉换行符                    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);                    // 过滤回车符和换行符                    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 {                // 单次读取的内容不足一行的情况                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依赖提供的FileUtils工具类读取文件

添加依赖：

    commons-io    commons-io    2.11.0

public static void fileOfCommonsIO() {        String fileName = "D:\\test.txt";        final String CHARSET_NAME = "UTF-8";        List 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依赖提供的IOtils工具类读取文件

添加依赖：

    commons-io    commons-io    2.11.0

public static void ioOfCommonsIO() {        String fileName = "D:\\test.txt";        final String CHARSET_NAME = "UTF-8";        List 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依赖提供的FileUtil工具类读取文件

添加依赖：

    cn.hutool    hutool-core    5.8.10或者：    cn.hutool    hutool-all    5.8.10

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

8. 使用hutool依赖提供的IoUtil工具类读取文件

添加依赖：

    cn.hutool    hutool-core    5.8.10或者：    cn.hutool    hutool-all    5.8.10

public static void ioOfHutool() {        String fileName = "D:\\test.txt";        final String CHARSET_NAME = "UTF-8";        List 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. 测试耗时

  测试文件：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());}

  测试3次耗时统计(单位：ms)：

  从测试结果来看，Hutool提供的IoUtil、commons-io提供的IoUtil以及JDK1.7提供的NIO基于流方式耗时更优，但测试还应参考内存占用情况，具体可自行测试。

来源地址：https://blog.csdn.net/qq_48008521/article/details/129312430