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Java读取文件的几种方式详细总结

作者：C3Stones

这篇文章主要给大家介绍了关于Java读取文件的几种方式,文中通过代码示例将几种方式介绍的非常详细,对大家学习或者使用Java具有一定的参考学习价值,需要的朋友可以参考下

1. 使用流读取文件

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<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<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<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) {
            // 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：

<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依赖提供的IOtils工具类读取文件

添加依赖：

<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依赖提供的FileUtil工具类读取文件

添加依赖：

<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依赖提供的IoUtil工具类读取文件

添加依赖：

<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. 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)：

测试序号streamnioOfJDK7streamOfJDK7nioOfJDK4fileOfCommonsIOioOfCommonsIOfileOfHutoolioOfHutool
1110113852141096417860
298126772361357016959
3106122902241306816562

  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。

总结

到此这篇关于Java读取文件的几种方式的文章就介绍到这了,更多相关Java读取文件方式内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！

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