从这节课开始看，

本节概括了一些框架特性

Spring IOC整合Service

public class ResortByDel {
    private static String BIG_FILE_NAME = "D:\\test1.txt";
    private static Integer BATCH_SIZE = 100;
    private static String LINE_SEPARATOR = ",";
    private static String SORT_FILE_NAME = "D:\\test2.txt";

    private static List<String> separateFile() {
        List<String> fileNameList = new ArrayList<>();
        try (BufferedReader reader = new BufferedReader(new FileReader(BIG_FILE_NAME))) {
            int index = 0;
            List<String> batchLineList = new ArrayList<>(BATCH_SIZE);
            String line;
            while ((line = reader.readLine()) != null || batchLineList.size() > 0) {
                if (line != null) batchLineList.add(line);

                if (batchLineList.size() == BATCH_SIZE || (line == null && batchLineList.size() > 0)) {
                    // 内容排序
                    batchLineList.sort((a, b) -> a.compareTo(b));
                    // 写小文件
                    String fileName = BIG_FILE_NAME + ".tmp." + index++;
                    try (FileWriter tmpWriter = new FileWriter(fileName)) {
                        for (String val : batchLineList) {
                            tmpWriter.write(val + "\r\n");
                        }
                    }
                    fileNameList.add(fileName);
                    batchLineList.clear();
                }
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        return fileNameList;
    }

    private static void mergeFile(List<String> fileNameList) {
        Map<BufferedReader, String> map = new HashMap<>();
        String preStr = null;
        try (FileWriter writer = new FileWriter(SORT_FILE_NAME)) {
            for (String fileName : fileNameList) {
                BufferedReader tmpReader = new BufferedReader(new FileReader(fileName));
                map.put(tmpReader, tmpReader.readLine());
            }
            while (true) {
                boolean canRead = false;
                Map.Entry<BufferedReader, String> minEntry = null;
                for (Map.Entry<BufferedReader, String> entry : map.entrySet()) {
                    String value = entry.getValue();
                    if (value == null) {
                        continue;
                    }
                    // 获取当前 reader 内容最小 entry
                    if ((minEntry == null) || (Integer.valueOf(value) < Integer.valueOf(minEntry.getValue()))) {
                        minEntry = entry;
                    }
                    canRead = true;
                }
                // 当且仅当所有 reader 内容为空时，跳出循环
                if (!canRead) {
                    break;
                }
                //去重
                if (preStr != null && preStr.equals(minEntry.getValue())) {
                    minEntry.setValue(minEntry.getKey().readLine());
                    continue;
                }
                preStr = minEntry.getValue();
                writer.write(minEntry.getValue() + "\r\n");
                minEntry.setValue(minEntry.getKey().readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 注意关闭分片文件输入流
            for (BufferedReader reader : map.keySet()) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) throws IOException {
        List<String> separateFiles = separateFile();
        mergeFile(separateFiles);
    }
}

数据库连接池配置

mybatis 连表查询