Java按行分割大文件

簡介

工作的時候，需要將一個大的文本文件按行分割成幾個小文件。本來懶得寫，想網上copy一下得了，但是 google 了一遍，找了幾個代碼寫的有點亂，嘗試了之後發現效率太慢了，一個 1000000 行 200M 的文件，按每個文件 2000 行分割，要6分多鐘才能跑完。沒辦法自己寫了個，試了幾次，基本都是 4 秒內跑完，貼出來記錄下，下次用就直接 copy 出來用。

代碼

public static List<File> splitDataToSaveFile(int rows, File sourceFile, String targetDirectoryPath) {
        long startTime = System.currentTimeMillis();
        List<File> fileList = new ArrayList<>();
        log.info("開始分割文件");
        File targetFile = new File(targetDirectoryPath);
        if (!sourceFile.exists() || rows <= 0 || sourceFile.isDirectory()) {
            return null;
        }
        if (targetFile.exists()) {
            if (!targetFile.isDirectory()) {
                return null;
            }
        } else {
            targetFile.mkdirs();
        }

        try (FileInputStream fileInputStream = new FileInputStream(sourceFile);
             InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream, StandardCharsets.UTF_8);
             BufferedReader bufferedReader = new BufferedReader(inputStreamReader)) {
            StringBuilder stringBuilder = new StringBuilder();
            String lineStr;
            int lineNo = 1, fileNum = 1;
            while ((lineStr = bufferedReader.readLine()) != null) {
                stringBuilder.append(lineStr).append("\r\n");
                if (lineNo % rows == 0) {
                    File file = new File(targetDirectoryPath + File.separator + fileNum + sourceFile.getName());
                    writeFile(stringBuilder.toString(), file);
                    //清空文本
                    stringBuilder.delete(0, stringBuilder.length());
                    fileNum++;
                    fileList.add(file);
                }
                lineNo++;
            }
            if ((lineNo - 1) % rows != 0) {
                File file = new File(targetDirectoryPath + File.separator + fileNum + sourceFile.getName());
                writeFile(stringBuilder.toString(), file);
                fileList.add(file);
            }
            long endTime = System.currentTimeMillis();
            log.info("分割文件結束，耗時：{}秒", (endTime - startTime) / 1000);
        } catch (Exception e) {
            log.error("分割文件異常", e);
        }
        return fileList;
    }

    private static void writeFile(String text, File file) {
        try (
                FileOutputStream fileOutputStream = new FileOutputStream(file);
                OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream, StandardCharsets.UTF_8);
                BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter, 1024)
        ) {
            bufferedWriter.write(text);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }