Java –逐行读取文本文件

柔光的暖阳◎ 2023-02-15 05:17 11阅读 0赞

本文介绍了三种逐行读取文本文件的方法：

1.  Java NIO库–读取文件的`FileChannel` 。 这是读取文件的非阻塞模式
2.  `BufferedReader` –这是一项阻止操作，即它将阻止对文件的任何其他读/写请求，直到完成任务为止。
3.  Apache Commons IO – `FileUtils` ，一种逐行读取文件的更简单方法。 这也是一个阻塞操作。

每个示例的输入文件与以下所示的文件相同：

src/com/mkyong/data.txt

A
    B
    C
    D
    1
    2
    3

## 1. Java NIO库 ##

该示例提供了读取小文件的最简单方法。 由于这是一个小文件，因此我们使用`FileChannel`大小直接将所需的内存分配给`ByteBuffer` 。

NIOFileReadExample.java

package com.mkyong;
    
    import java.io.IOException;
    import java.io.RandomAccessFile;
    import java.nio.ByteBuffer;
    import java.nio.channels.FileChannel;
    
    public class NIOFileReadExample {
    
        public static void main(String[] args) throws IOException {
    
            RandomAccessFile file = new RandomAccessFile("src/com/mkyong/data.txt", "r");
    
            FileChannel channel = file.getChannel();
    
            System.out.println("File size is: " + channel.size());
    
            ByteBuffer buffer = ByteBuffer.allocate((int) channel.size());
    
            channel.read(buffer);
    
            buffer.flip();//Restore buffer to position 0 to read it
    
            System.out.println("Reading content and printing ... ");
    
            for (int i = 0; i < channel.size(); i++) {
                System.out.print((char) buffer.get());
            }
    
            channel.close();
            file.close();
    
        }
    
    }

执行代码后，您将获得以下输出：

File size is: 19
    Reading content and printing ... 
    A
    B
    C
    D
    1
    2
    3

## 2. BufferedReader ##

ReadTextFile.java

package com.mkyong;
    
    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileReader;
    import java.io.IOException;
    
    public class ReadTextFile {
    
        public static void main(String[] args) throws IOException {
    
            try {
    
                File f = new File("src/com/mkyong/data.txt");
    
                BufferedReader b = new BufferedReader(new FileReader(f));
    
                String readLine = "";
    
                System.out.println("Reading file using Buffered Reader");
    
                while ((readLine = b.readLine()) != null) {
                    System.out.println(readLine);
                }
    
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    
    }

执行此代码的输出如下所示：

Reading file using Buffered Reader
    A
    B
    C
    D
    1
    2
    3

> **注意**  
> 更多[BufferedReader示例][BufferedReader]

## 3. Apache Commons IO ##

pom.xml

<dependency>
        <groupId>commons-io</groupId>
        <artifactId>commons-io</artifactId>
        <version>2.5</version>
      </dependency>

FileIOUtilsExample

package com.mkyong;
    
    import org.apache.commons.io.FileUtils;
    import java.io.File;
    import java.io.IOException;
    import java.util.List;
    
    public class ReadTextFile {
    
        public static void main(String[] args) throws IOException {
    
            try {
    
                File f = new File("src/com/mkyong/data.txt");
    
                System.out.println("Reading files using Apache IO:");
    
                List<String> lines = FileUtils.readLines(f, "UTF-8");
    
                for (String line : lines) {
                    System.out.println(line);
                }
    
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    
    }

执行上述代码后的输出将是：

Reading files using Apache IO:
    A
    B
    C
    D
    1
    2
    3

> **Java 8**  
> 试试这个– [Java 8流逐行读取文件][Java 8]

## 参考文献 ##

1.  [有关BufferedReader的更多信息][BufferedReader 1]
2.  [有关FileReader的更多信息][FileReader]
3.  [BufferedReader示例][BufferedReader]
4.  [Java 8流逐行读取文件][Java 8]
5.  [有关FileChannel函数的更多信息][FileChannel]
6.  [ByteBuffer flip（）和rewind（）方法之间的区别][ByteBuffer flip_rewind]
7.  [ByteBuffer javadocs][]
8.  [FileChannel Javadocs][]
9.  [Apache Commons IO用户指南][Apache Commons IO]

标签： [通用io][io] [java.io][] [java.nio][] [读取文件][Link 1]

> 翻译自: [https://mkyong.com/java/java-read-a-text-file-line-by-line/][https_mkyong.com_java_java-read-a-text-file-line-by-line]

[BufferedReader]: https://www.mkyong.com/java/how-to-read-file-from-java-bufferedreader-example/
[Java 8]: https://www.mkyong.com/java8/java-8-stream-read-a-file-line-by-line/
[BufferedReader 1]: https://docs.oracle.com/javase/7/docs/api/java/io/BufferedReader.html
[FileReader]: https://docs.oracle.com/javase/7/docs/api/java/io/FileReader.html%E2%80%9D%20target=
[FileChannel]: http://tutorials.jenkov.com/java-nio/file-channel.html
[ByteBuffer flip_rewind]: https://coderanch.com/t/611255/java/ByteBuffer-methods-flip-rewind
[ByteBuffer javadocs]: https://docs.oracle.com/javase/7/docs/api/java/nio/ByteBuffer.html
[FileChannel Javadocs]: https://docs.oracle.com/javase/7/docs/api/java/nio/channels/FileChannel.html
[Apache Commons IO]: https://commons.apache.org/proper/commons-io/description.html
[io]: https://mkyong.com/tag/common-io/
[java.io]: https://mkyong.com/tag/java-io/
[java.nio]: https://mkyong.com/tag/java-nio/
[Link 1]: https://mkyong.com/tag/read-file/
[https_mkyong.com_java_java-read-a-text-file-line-by-line]: https://mkyong.com/java/java-read-a-text-file-line-by-line/