java - java通用对象反序列化和序列化

Question

您好，我正在学习泛型，但我在将对象从文件反序列化回泛型列表然后打印时遇到问题。

结果是一个空屏幕，即使我知道创建了一个 dat 文件

我尝试过很多种方法。

我使用带有 ActionListener 的框架..

这是 ActionListener

 private class AddButtonActionListener implements ActionListener {

    @Override
    public void actionPerformed(ActionEvent e) {
        // variables    
        String inputfName;
        String inputlName;
        String idInput;
        //String studentID;

        // capture input
        inputfName = sFirstName.getText();
        inputlName = sLastName.getText();
        idInput = sID.getText();

        //hold Student data


        //convert to Int
        //studentID = Integer.parseInt(idInput);

        //Create file
        StudentAddProcess sFile = new StudentAddProcess();
        sFile.writesFile(inputfName, inputlName, idInput );

    }

这些处理输入

公共(public)类 StudentAddProcess 实现可序列化{

    String inputFirstName ;
    String inputLastName;
     String  inputID;


private Component Frame;

// Create File 
public void  writesFile ( String fName, String  lName, String Id ){

    // create T fields for student

     inputFirstName = fName;
     inputLastName = lName;
     inputID = Id;


try {


    ObjectOutputStream objectInputFile = new ObjectOutputStream(outStream);

    //Linkeked List of Student Objects
    GenericLinkedList<Student> studentList = new GenericLinkedList<>();

    // add Student Object to student 
    studentList.add(new Student(inputID, inputFirstName, inputLastName));

    //Where am i
    JOptionPane.showMessageDialog(Frame, "writing ...");

    //  for loop cycle and write student to fill

        for (int i =0 ;  i < studentList.size();i++) {
            objectInputFile.writeObject(studentList.get(i));
        }

       JOptionPane.showMessageDialog(Frame, "Complete :");
       //close file 
       objectInputFile.close();

现在我们查看添加的对象

    public class StudentViewFile implements Serializable {

    //variables 
    private String studentID; // holds passed user request to view
    private Component Frame;

    public void readFile(String  sID) throws IOException {

    studentID = sID;  // take passed variable
    //int studentID2 =Integer.getInteger(sID);

    try {
        //open read file 


        FileInputStream inStream = new         FileInputStream("StudentObjects.dat");// Stream of Objects

        ObjectInputStream objectInputFile = new ObjectInputStream(inStream);

       GenericLinkedList <Student> readRecord = new  GenericLinkedList<>();

         readRecord.add(new Student(studentID));

        for (int i = 0; i < readRecord.size(); i++) {
            readRecord = (GenericLinkedList) objectInputFile.readObject();

            // Diplay  records 
            System.out.println("File Objects" + readRecord.get(i) + " \n   next positions");

             // was going to try to print my test here  

            System.out.println(readRecord.toString());
        }

        // Read the serialized objects from the file.
        while (true) {

           readRecord = (GenericLinkedList) objectInputFile.readObject();



            // Display  records 
            System.out.println( "File Objects" + readRecord+ " \n next positions");

            //close file 
           objectInputFile.close();
          }

       } catch (EOFException e) {
        System.out.print("\n Exception caught ");

任何想法都会很棒。预先感谢您的时间和知识

Answer 1

将编写对象的方式与尝试读取对象的方式进行比较。

    for (int i =0 ;  i < studentList.size();i++) {
        objectInputFile.writeObject(studentList.get(i));
    }

这会写入一系列 Student 对象。

    readRecord = (GenericLinkedList) objectInputFile.readObject();

这会尝试读取某些内容并将其转换为GenericLinkedList。但它不会是其中之一。它实际上是一个Student，所以你会得到一个异常。

另一个问题是:

    GenericLinkedList <Student> readRecord = new  GenericLinkedList<>();
    readRecord.add(new Student(studentID));
    for (int i = 0; i < readRecord.size(); i++) {
        readRecord = (GenericLinkedList) objectInputFile.readObject();

你到底想绕圈多少次？这个数字实际上是从哪里来的？

有多种方法可以解决这个问题；例如:

1. 将整个列表作为单个对象写入(然后读取)
2. 通过将列表大小 (studentList.size()) 写入 int 来启动流。读取时，首先读取列表大小，然后读取 Student 对象的数量。
3. 使用 while (true) 循环读取并捕获/处理 EOFException。

(我注意到您已尝试按照损坏的代码执行替代方案 3 ...。当然，这不会超越您损坏的代码，因此这是行不通的。是什么你在想吗？)