DataManager.java

package heyingzhe;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.util.*;

public class DataManager {
    private List<Map<String, String>> records;
    private Set<String> fieldNames;

    public DataManager(List<Map<String, String>> records) {
        this.records = records;
        this.fieldNames = new HashSet<>();
        // 获取所有字段名
        for (Map<String, String> record : records) {
            fieldNames.addAll(record.keySet());
            fieldNames.add("id");
        }
        // 添加索引
        for (int index=0; index<records.size(); index++) {
            Map<String, String> record = records.get(index);
            record.put("id", String.valueOf(index));
        }
    }

    // 获取所有字段名
    public Set<String> getFieldNames() {
        return fieldNames;
    }

    // 查询某一字段的所有数据
    public List<String> getColumnData(String fieldName) {
        List<String> columnData = new ArrayList<>();
        for (Map<String, String> record : records) {
            columnData.add(record.getOrDefault(fieldName, ""));
        }
        return columnData;
    }

    // 添加一个新字段，并为每条记录填充值
    public void addColumn(String fieldName, String defaultValue) {
        fieldNames.add(fieldName);
        for (Map<String, String> record : records) {
            record.put(fieldName, defaultValue);
        }
    }

    // 删除一个字段
    public void removeColumn(String fieldName) {
        fieldNames.remove(fieldName);
        for (Map<String, String> record : records) {
            record.remove(fieldName);
        }
    }

    // 修改某一条记录的字段值
    public void updateFieldValue(int rowIndex, String fieldName, String newValue) {
        if (rowIndex >= 0 && rowIndex < records.size()) {
            records.get(rowIndex).put(fieldName, newValue);
        }
    }

    // 打印所有记录
    public void printRecords() {
        for (Map<String, String> record : records) {
            System.out.println(record);
        }
    }

    // 保存数据到文件
    public void saveToFile(String filePath, String delimiter) throws IOException {
        BufferedWriter writer = new BufferedWriter(new FileWriter(filePath));
        // 写入标题行
        writer.write(String.join(delimiter, fieldNames));
        writer.newLine();

        // 写入数据行
        for (Map<String, String> record : records) {
            List<String> values = new ArrayList<>();
            for (String fieldName : fieldNames) {
                values.add(record.getOrDefault(fieldName, ""));
            }
            writer.write(String.join(delimiter, values));
            writer.newLine();
        }
        writer.close();
    }

    public List<Map<String, String>> getData () {
        return records;
    }

    // 根据 Map 中某个键值查找对应位置，从而方便定位到
    public Map<String, String> findMap(List<Map<String, String>> list, String targetField, String targetValue) {
        // 遍历 List
        for (Map<String, String> map : list) {
            if (map.containsKey(targetField) && map.get(targetField).equals(targetValue)) {
                return map;
            }
        }
        System.out.println("No map found with the target that you input.");
        return list.getFirst();
    }

    // 根据 Map 中两个键值查找对应位置，从而方便定位到
    public Map<String, String> findMap(List<Map<String, String>> list, String targetField1, String targetValue1,
                                       String targetField2, String targetValue2) {
        // 遍历 List
        for (Map<String, String> map : list) {
            if (map.containsKey(targetField1) && map.get(targetField1).equals(targetValue1) && map.containsKey(targetField2) && map.get(targetField2).equals(targetValue2)) {
                return map;
            }
        }
        System.out.println("No map found with the target that you input.");
        return list.getFirst();
    }
}