Java-读取大文本文件

待我称王封你为后i 2022-05-08 02:12 252阅读 0赞

介绍读取大文本文件的两种方式，避免堆内存溢出。

#### 1.生成测试文件 ####

package com.example.demo;
    
    import org.apache.commons.io.IOUtils;
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.io.RandomAccessFile;
    import java.util.List;
    
    /**
     * @author Walker
     * @since 1.0 2018-10-08
     */
    public class RandomAccessFileTest {
    
        public static void main(String[] args) throws IOException {
        	//写文件
            RandomAccessFile randomAccessFile = new RandomAccessFile(new File("C:\\result.txt"), "rw");
            randomAccessFile.seek(randomAccessFile.length());
            long count = 0;
            while (true) {
                randomAccessFile.write(("测试数据" + System.getProperty("line.separator")).getBytes("utf-8"));
                if (count >= Long.MAX_VALUE) {
                    break;
                }
                count++;
            }
            randomAccessFile.close();
            //读文件
            List<String> list = IOUtils.readLines(new FileInputStream("C:\\result.txt"), "utf-8");
            System.out.println(list.size());
    
        }
    
    }

生成测试文件后，调用读取文件的方法将报错。

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    	at java.util.Arrays.copyOf(Arrays.java:3210)
    	at java.util.Arrays.copyOf(Arrays.java:3181)
    	at java.util.ArrayList.grow(ArrayList.java:265)
    	at java.util.ArrayList.ensureExplicitCapacity(ArrayList.java:239)
    	at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:231)
    	at java.util.ArrayList.add(ArrayList.java:462)
    	at org.apache.commons.io.IOUtils.readLines(IOUtils.java:1461)
    	at org.apache.commons.io.IOUtils.readLines(IOUtils.java:1416)
    	at org.apache.commons.io.IOUtils.readLines(IOUtils.java:1440)
    	at com.example.demo.RandomAccessFileTest.main(RandomAccessFileTest.java:50)

#### 2.使用Apache common-io中的FileUtils类读取文件 ####

package com.example.demo;
    
    import org.apache.commons.io.FileUtils;
    import org.apache.commons.io.LineIterator;
    
    import java.io.File;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.OutputStream;
    
    /**
     * @author Walker
     * @since 1.0 2018-10-08
     */
    public class RandomAccessFileTest {
    
        public static void main(String[] args) throws IOException {
            LineIterator lineIterator = FileUtils.lineIterator(new File("C:\\result.txt"), "utf-8");
            while (lineIterator.hasNext()) {
                String result = lineIterator.next();
                System.out.println(result);
            }
        }
    
    }

#### 3.使用Scanner读取 ####

package com.example.demo;
    
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.util.Scanner;
    
    /**
     * @author Walker
     * @since 1.0 2018-10-08
     */
    public class RandomAccessFileTest {
    
        public static void main(String[] args) throws IOException {
            FileInputStream fileInputStream = new FileInputStream("C:\\result.txt");
            Scanner scanner = new Scanner(fileInputStream, "utf-8");
            while (scanner.hasNext()) {
                String result = scanner.nextLine();
                System.out.println(result);
            }
            fileInputStream.close();
            scanner.close();
        }
    
    }