java - 从java中的文本文件中读取对象数据

Question

我正在做关于 java I/O 数据的作业，问题是我不允许使用对象序列化从二进制文件加载数据。

作业要求如下:

Persistence, writing objects to file and reading objects from file (Text format)

• All objects should be written to a single file in a text format
• All objects should be read form the same file
• You should use JFileChooser

我有 3 个类:Unit、Assessment 和 Task。

Assessment 类是抽象的，而 IndividualAssessment 和 GroupAssessment 是具体的子类。

Unit 有一个 Assessment 的集合，Assessment 有一个 Task 的集合。

我可以使用 FileWriter 将所有数据保存到一个文本文件，但我不知道如何将文本文件的每一行读入正确的 Assessment 类。

我的意思是您如何识别哪一行是IndividualAssessment 或GroupAssessment 类。

这是我试过但不起作用的代码:

BufferedReader bf = new BufferedReader(file);
While (bf.readLine != null){
    Unit u = new Unit(bf);
    diary.add(u);
    try{
        Assessment a = new IndividualAssessment(bf);
    } catch (IOException ex){
        Assessment a = new GroupAssessment(bf);
            }
    u.add(a);
    Task t = new Task(bf);
    a.add(t);

Answer 1

您可能应该先将读取到的行的内容存储在一个字符串对象中。所以它看起来像这样:

String line = bf.readLine();
while(line != null) {
    // Add code to look at your line to figure out what kind of object it 
    // represents.   For example you could add a one character prefix to each 
    // line when you write it to specify which object it is ('U', 'A' or 'T').
    // Based on that, you can call a constructor of the appropriate object that
    // takes a String as input. Then let the constructor deal with parsing the
    // line for the object it represents. This way you don't end up with some
    // massive parsing routine.

    char code = line.charAt(0);
    if(code == 'T') {
        Task task = new Task();
        task.initFromString(line.sustring(1));
        ... Do something with your task
    }
    else if(code == ...) {
    }

    line = bf.readLine();    // Read the next line
}

定义一些你所有的对象都应该实现的接口(interface):

public interface TextExportable {
    public char getClassIdentifier();
    public void initFromString(String s);
}

我不确定你的对象是什么样子的，但让我们举个例子:

public class Task implements TextExportable {
    private String name;

    public Task() {} // For the pseudo-serialization

    public Task(String name) { // For creating the object by hand
        this.name = name;
    }

    public char getClassIdentifier() {
        return 'T';
    }

    public String toString() {
        return getClassIdentifier()+name;
    }

    public void initFromString(String line) {
        this.name = line;
        // Here, you would need extra parsing if you have more than one attribute
        // and dissect the line
    }
}