用流API Java解析文本文件

Question

我有这个文件要处理，我正试图找出如何将第二行作为不同的对象来读取。在这一行的末尾，最后一项是公交车的数量。第二行、第四行等应包含idBus和noOfBus，并用逗号分隔。

1,Harvard University,2
1,140,2,56
2,Massachusetts Institute of Technology,2
1,240,5,56
3,University of California Berkeley,3
1,112,2,56,3,28
4,Columbia University,4
1,84,2,84,3,84,7,28

基于这些课程

 class University {
    public int idUniversity;
    public String nameOfUniversity;
    public int noOfBuses;
 }

 class Bus {
    public int idBus;
    public int noOfBus;
 }

我想要一个函数来处理CSV文件中所有公交车和大学线路的列表。它必须使用流API。我不知道这是否可能或如何进行。

当然，可以根据类进行更改，但保留变量，不添加任何额外内容。

我认为最方便的方法是浏览文件，根据两个班级（大学和公共汽车）得到两个列表，最后将它们添加到第三个列表中，然后进行处理，但我不知道如何处理。

基于这个文件，我必须使用Stream API进行处理，例如"按ID对公共汽车进行排序"或"哪些大学有更多的公共汽车？"或"哪辆公共汽车去几所大学？"。

这就是我一直在努力做的。通常这就是我浏览CSV文件的方式。

private static List<University> readListOfUniversities() throws IOException {
    try (BufferedReader bufferedReader = new BufferedReader(new FileReader(PATH_UNIVERSITIES_TEXT_FILE))) {
        return bufferedReader.lines().map(line -> {
            String[] tokens = line.split(",");
            var idUniversity = Integer.parseInt(tokens[0]);
            var nameOfUniversity = tokens[1].trim();
            var noOfBuses = Integer.parseInt(tokens[2]);
            var university = new University(idUniversity, nameOfUniversity, noOfBuses);
            return university;
        }).collect(Collectors.toList());
    }
}

就像这个：

1,Harvard University,2
2,Massachusetts Institute of Technology,2
3,University of California Berkeley,3
4,Columbia University,4

Answer 1

以下是我将如何做到这一点（我对您的类做了一些轻微的修改）

public class University {
    private int id;
    private String name;
    private List<Bus> busList;
    //let the constructor do the work
    public University(String [] data, List<Bus> busList) {
        id = Integer.parseInt(data[0]);
        name = data[1];
        this.busList = busList; 
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public List<Bus> getBusList() {
        return busList;
    }

    @Override
    public String toString() {
        return "University [id=" + id + ", name=" + name + ", busList=" + busList + "]";
    }
    
}

public class Bus {
    private int id;
    private int num;
    
    public Bus(int id, int num) {
        this.id = id;
        this.num = num;
    }
    
    public int getId() {
        return id;
    }

    public int getNum() {
        return num;
    }
    //Method to parse the data into usuable objects
    public static List<Bus> generateBusInfo(String [] data) {
        List<Bus> buses = new ArrayList<>();
        for (int i = 0; i < data.length-1; i+=2) {
            int id = Integer.parseInt(data[i]);
            int num = Integer.parseInt(data[i+1]);
            buses.add(new Bus(id, num));
        }
        return buses;
    }

    @Override
    public String toString() {
        return "Bus [id=" + id + ", num=" + num + "]";
    }
}


public static void main(String[] args) throws IOException {
    //This is just so I dont have to bother with creating a file.
    String input = "1,Harvard University,2\n" + 
            "1,140,2,56\n" + 
            "2,Massachusetts Institute of Technology,2\n" + 
            "1,240,5,56\n" + 
            "3,University of California Berkeley,3\n" + 
            "1,112,2,56,3,28\n" + 
            "4,Columbia University,4\n" + 
            "1,84,2,84,3,84,7,28\n";
    List<University> universities = new ArrayList<>();
    //replace StringReader with a FileReader to the path of your file.
    try(BufferedReader reader = new BufferedReader(new StringReader(input))) {
        //read the first line
        String line = reader.readLine();
        while (line != null) { //keep reading until you're done
            String [] uniData = line.split(","); //convert string into an array
            line = reader.readLine(); //read the next line
            if (line != null) {
                String [] busData = line.split(","); //convert
                List<Bus> busList = Bus.generateBusInfo(busData); //make busses
                universities.add(new University(uniData, busList)); //create university and add it to the list
                line = reader.readLine(); //read the next line
            }
        }
    }
    
    //output the list
    for (University uni : universities) {
        System.out.println(uni);
    }
}

您还可以将大学和公共汽车读入Maps以方便访问。