Java读取文件新增内容

文章目录
  1. 通过Java的RandomAccessFile类实现读取文件新增内容
    1. Java文件生成新增内容类(LogWriter)
    2. Java读取文件新增内容类(LogReader)

通过Java的RandomAccessFile类实现读取文件新增内容

Java文件生成新增内容类(LogWriter)

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package com.child.fileread;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class LogWriter {
    private SimpleDateFormat dateFormat =
            new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    /**
     * 将信息记录到日志文件
     *
     * @param logFile 日志文件
     * @param mesInfo 信息
     * @throws IOException
     */
    public void logMsg(File logFile, String mesInfo) throws IOException {
        if (logFile == null) {
            throw new IllegalStateException("logFile can not be null!");
        }
        Writer txtWriter = new FileWriter(logFile, true);
        txtWriter.write(dateFormat.format(new Date()) + "\t" + mesInfo + "\n");
        txtWriter.flush();
    }
    public static void main(String[] args) throws Exception {
        final LogWriter logSvr = new LogWriter();
        final File tmpLogFile = new File("d:/upload/text.txt");
        if (!tmpLogFile.exists()) {
            tmpLogFile.createNewFile();
        }
        Random random = new Random();
        //启动一个线程每1秒钟向日志文件写一次数据
        ScheduledExecutorService exec =
                Executors.newScheduledThreadPool(1);
        exec.scheduleWithFixedDelay(new Runnable() {
            public void run() {
                try {
                    logSvr.logMsg(tmpLogFile, String.valueOf(random.nextInt()) + "你好");
                } catch (IOException e) {
                    System.out.println("logFile can not be null");
                    throw new RuntimeException(e);
                }
            }
        }, 0, 1, TimeUnit.SECONDS);
    }
}

Java读取文件新增内容类(LogReader)

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package com.child.fileread;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class LogReader {
	private static long lastTimeFileSize = 0;  //上次文件大小
    
	/**
     * 实时输出日志信息
     * @param logFile 日志文件
     * @throws IOException
     */
    public static void read(File logFile) throws IOException {
        // 指定文件可读可写
        final RandomAccessFile randomFile = new RandomAccessFile(logFile,"rw");
        // 启动一个线程每1秒钟读取新增的日志信息
        ScheduledExecutorService exec =
                Executors.newScheduledThreadPool(1);
        exec.scheduleWithFixedDelay(new Runnable(){
            public void run() {
                try {
                    //获得变化部分的
                    randomFile.seek(lastTimeFileSize);
                    String tmp = "";
                    while( (tmp = randomFile.readLine())!= null) {
                        System.out.println(new String(tmp.getBytes("ISO8859-1")));
                    }
                    lastTimeFileSize = randomFile.length();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }, 0, 1, TimeUnit.SECONDS);
    }
    public static void main(String[] args) throws Exception {
        final File tmpLogFile = new File("d:/test.txt");
        LogReader.read(tmpLogFile);
    }
}