java - 使用对象编写器。即使我关闭文件，也会给我 EOF 异常。

Question

/*该程序对学生进行序列化。 *如果文件存在，则程序加载它。 *否则它会创建一个新的类列表。 *学生对象被添加到类(class)列表中然后保存 */它是作业的一部分，但我以前从未使用过 objectWriter。

import java.util.Scanner; 
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.FileNotFoundException;
import java.lang.ClassNotFoundException;
import java.util.List;
import java.util.ArrayList;
import java.io.EOFException;

public class ClassList{

 public static void find(int sN, String fN, String lN){
    boolean found = false;

    try{
    ObjectOutputStream objectOS = new ObjectOutputStream(new FileOutputStream("ClassList.data"));
        ObjectInputStream objectIS = new ObjectInputStream(new FileInputStream("ClassList.data"));
        int i=0;
        Assignment readAssign = (Assignment) objectIS.readObject();
    Student studentRead = readAssign.getStudents().get(i);

        /*Search the student objects & compare student number.
         *If found, boolean returns true, else the boolean is false
         */ 
        while (readAssign.getStudents() != null){
             studentRead = readAssign.getStudents().get(i);
             if (studentRead.getID() == sN){
                  found = true;
                  break;
             }
             i++;
        }

        /*If the boolean found is true error message is produced
         *If the boolean found is false then it adds a new Student object
         */
        if (found = true){
             System.out.println("A student with this id number already exists by the name:");
             System.out.print(studentRead.getFName() + " " + studentRead.getLName());
         objectOS.flush();
     objectOS.close();
        }
        else{
             Student student = new Student();
             student.setFName(fN);
             student.setLName(lN);
             student.setID(sN);
             Assignment assign = new Assignment();
     List<Student> students = new ArrayList<>();
     students.add(student);
     assign.setStudents(students);
             System.out.println("Done");
             objectOS.writeObject(assign);
         objectOS.flush();
     objectOS.close();


        }

    }
    catch(ClassNotFoundException cnf){
     cnf.printStackTrace();
}
    catch(FileNotFoundException fnf){
     fnf.printStackTrace();
}
catch(EOFException of) {
     eof.printStackTrace();
}
    catch(IOException ioe) {
     //ioe.printStackTrace();
}

 }



  public static void main(String args[]){
        Scanner stuIn = new Scanner(System.in);

        //Use student Input to create students
        System.out.println("What is your first name: ");
        String fName = stuIn.nextLine();

        System.out.println("What is your last name: ");
        String lName = stuIn.nextLine();

        System.out.println("What is your student number: ");
        int sNum = stuIn.nextInt();

        find(sNum, fName, lName);

 }


}

错误消息:

java.io.EOFException 在 java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2601) 在 java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1319) 在 java.io.ObjectInputStream.readObject(ObjectInputStream.java:371) 在 ClassList.find(ClassList.java:28) 在 ClassList.main(ClassList.java:100)

Answer 1

此声明:

ObjectOutputStream objectOS = new ObjectOutputStream(new 
    FileOutputStream("ClassList.data"));

...用空文件覆盖现有文件。然后，您尝试从该空文件中读取对象。

您应该先阅读，然后打开文件进行输出。

我实际上会将这段代码分解为单独的方法:

• 阅读作业(打开、阅读、关闭)
• 进程分配(无 IO)
• 写入作业(打开、写入、关闭)

另请注意:

if (found = true)

没有做你想做的事。它将分配给found，然后始终执行if block 的主体。你想要:

if (found == true)

或者更好

if (found)