读取文件排序写文件

import java.io.*;
import java.util.*;

public class Main {

    private static final String logName = "j.log";
    private static final String parentPath = "E:\\taskId";

    /**
     * 读取文件的内容，追加到j.log
     *
     * @param filePath filePath
     * @param out out
     */
    public static void readTxtFile(String filePath,
                                   BufferedWriter out) throws IOException {
        InputStreamReader read = null;
        BufferedReader bufferedReader = null;
        try {
            String encoding = "UTF8";
            File file = new File(filePath);
            //判断文件是否存在
            if (file.isFile() && file.exists()) {
                // 考虑到编码格式
                read = new InputStreamReader(
                        new FileInputStream(file), encoding);
                bufferedReader = new BufferedReader(read);
                String lineTxt;
                while ((lineTxt = bufferedReader.readLine()) != null) {
                    out.append(lineTxt).append(System.getProperty("line.separator"));
                }
            } else {
                System.out.println("找不到指定的文件");
            }
        } catch (Exception e) {
            System.out.println("读取文件内容出错");
            e.printStackTrace();
        } finally {
            bufferedReader.close();
            read.close();
        }
    }

    /**
     * 写入文件
     *
     * @param m
     */
    public static void writeTxtFile(String m) {
        try {
            BufferedWriter out = new BufferedWriter(new FileWriter("runoob.txt"));
            out.append(m);
            out.close();
            System.out.println("文件创建成功！");
        } catch (IOException e) {
        }
    }

    /**
     * 获取某个目录下所有直接下级文件，不包括目录下的子目录的下的文件，所以不用递归获取
     *
     * @param path
     * @return
     */
    public static List<String> getFiles(String path) {
        List<String> files = new ArrayList<>();
        File file = new File(path);
        File[] tempList = file.listFiles();

        for (File value : tempList) {
            if (value.isFile()) {
                files.add(value.getName().toString());
            }
        }
        return files;
    }

    public static void main(String[] argv) throws IOException {
        long t1 = System.currentTimeMillis();
        List<String> fileNames = getFiles(parentPath);
        fileNames.remove(logName);
        fileNames.sort((s1, s2) -> {
            int i1 = Integer.parseInt(s1.split("-")[0]);
            int i2 = Integer.parseInt(s2.split("-")[0]);
            return i1 - i2;
        });
        BufferedWriter out = new BufferedWriter(new FileWriter(parentPath + File.separator + logName, true));
        fileNames
                .forEach(fileName -> {
                    try {
                        readTxtFile(parentPath + File.separator + fileName, out);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                });
        out.close();
        System.out.println((System.currentTimeMillis() - t1) / 1000);
    }
}