I can not read object file in Java

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I can not read object file in Java

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#1 by (0 votes)
#2 by (0 votes)

0

My problem is with ObjectOutputStream , it only works when I write an object the first time. If I add another object to that file, it sends me the following Exception:

java.io.StreamCorruptedException: invalid type code: AC
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1596)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:428)
at Ejemplo.leer(Ejemplo.java:62)
at Ejemplo.main(Ejemplo.java:17)

Next I show you the code of how I am saving and recovering the objects:

public static void main(String[] args) {

      Alumno alu = new Alumno("29521268D", "Pepe García");
    Alumno alu2 = new Alumno("23456789L", "Jose Ramón");
      escribir(alu, "alumnos_prueba.dat");
    //escribir(alu2, "alumnos_prueba.dat");

    leer("alumnos_prueba.dat");


}

public static <T> void escribir(T objeto,String nombre_archivo){
    FileOutputStream fos = null;
    ObjectOutputStream oos = null;
    try {
        fos = new FileOutputStream(nombre_archivo,true);
        oos = new ObjectOutputStream(fos);
        oos.writeObject(objeto);
        oos.flush();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (oos!=null) {
            try {
                oos.close();
                fos.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }


}

@SuppressWarnings("unchecked")
public static <T> void leer(String nombre_archivo) {

    FileInputStream fis = null;
    ObjectInputStream ois = null;

    try {

        fis = new FileInputStream(nombre_archivo);
        ois = new ObjectInputStream(fis);
        T objeto;
        while(fis.available()>0) {
            objeto = (T)ois.readObject();
            System.out.println(objeto);
        }
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}}

The Student class has implemented the serializable interface and put a serialVersionUID

public class Alumno implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

private String dni;
private String nombre;

public Alumno(String dni, String nombre) {
    this.setNombre(nombre);
    this.setDni(dni);
}

public String getDni() {
    return dni;
}

public void setDni(String dni) {
    this.dni = dni;
}

public String getNombre() {
    return nombre;
}

public void setNombre(String nombre) {
    this.nombre = nombre;
}

@Override
public String toString() {
    // TODO Auto-generated method stub
    return "DNI: "+this.getDni()+" Nombre: "+this.getNombre();
}}

java

asked by Luis Alberto Murcia Solivella 18.05.2018 в 13:21

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2 answers

0

Try this to see if it works for you

public static <T> void escribir(T objeto,String nombre_archivo){
    FileOutputStream fos = null;
    ObjectOutputStream oos = null;
    try {
        fos = new FileOutputStream(nombre_archivo,true);
        oos = new ObjectOutputStream(fos);
        oos.writeObject(objeto);
        oos.flush();
        oos.reset();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (oos!=null) {
            try {
                oos.close();
                fos.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

}

answered by 18.05.2018 в 13:35

Build a UserControl based on a file (WPF) I can not extract the data from the "text" object of a json, I need to do it in java

score 0 · Accepted Answer

When writing a file with objects, a header is written at the beginning. If you write once and try to read there will be no failure. The program sees the header and will read everything perfectly. If you try to add something new to the file it will write after the existing one a new header. When you try to read it will use the first header and read the first value, but when you try to read the second one, written with another header, it will throw an error by corrupt header. Documentation about that error in the error method here

The solution to this problem is that every time you want to write something new you create a new first thing to do is create a reading and writing channel and read and write everything (without closing the writing channel) and when you reach the end write the new and then close the channels.

If you want to keep the file with objects, every time you want to write a new object, you will have to create a new file, copy all the existing objects and write the new ones without closing the writing channel.