This question already has answers here:
Appending to an ObjectOutputStream
(6 answers)
Closed 5 years ago.
I have a program utilizing the memento design pattern and want to save the state of each object into a file using serialization and return the object back. The problem is that I get a "java.io.StreamCorruptedException: invalid type code: AC" exception due to corrupt headers. I looked at Appending to an ObjectOutputStream and tried to implement the class but still can't get the program to work properly. Multiple objects should be saved in a file and the user passes a string into a function which should match part of the object's string representation.
public class Caretaker implements Serializable {
public void addMemento(Memento m) {
try {
// write object to file
FileOutputStream fos = new FileOutputStream("ConeOutput1.txt", true);
BufferedOutputStream outputBuffer = new BufferedOutputStream(fos);
AppendableObjectOutputStream objectStream = new AppendableObjectOutputStream(outputBuffer);
objectStream.writeObject(m);
objectStream.reset();
objectStream.close();
}
catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public Memento getMemento(String temp) {
try {
Memento result = null;
FileInputStream fis = new FileInputStream("ConeOutput1.txt");
ObjectInputStream ois = new ObjectInputStream(fis);
result = (Memento) ois.readObject();
while (result != null) {
Matcher m = Pattern.compile(temp).matcher(result.toString());
if (m.find()) {
return result;
}
else {
result = (Memento) ois.readObject();
}
ois.close();
}
}
catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return null;
}
}
public class AppendableObjectOutputStream extends ObjectOutputStream {
public AppendableObjectOutputStream(OutputStream out) throws IOException {
super(out);
}
#Override
protected void writeStreamHeader() throws IOException {}
}
You should only use the appending ObjectOutputStream if the file already exists with data in it. If the file is new it needs the object stream header.
Related
I'm working on appending objects to a binary file. My file is:
File f=new File("person.dat");
I'm getting an error (java.io.StreamCorruptedException: invalid stream header: 79737200) when I attempt to open the binary file. As far as I can tell the program writes the data just fine, but as soon as I try reading from it, I get the above error. Any help is appreciated!
My Code to write:
AppendObjectOutputStream out = null;
try {
out = new AppendObjectOutputStream(new FileOutputStream(f, true));
out.writeObject(new Student(name, age));
out.flush();
}
catch (Exception ex) {
ex.printStackTrace();
}
finally {
out.close();
}
My class for making appendable:
public class AppendObjectOutputStream extends ObjectOutputStream {
public AppendObjectOutputStream(OutputStream out) throws IOException {
super(out);
}
#Override
protected void writeStreamHeader() throws IOException {
reset();
}
}
My partial code for reading and adding objects to an ArrayList:
Course course = new Course();
Student st = null;
ObjectInputStream in = null;
try {
in = new ObjectInputStream(new FileInputStream("person.dat"));
try
{
while (true)
{
st = (Student) in.readObject();
course.addAccount(st); //adds student object to an ArrayList in
//class Course
}
}
catch (EOFException ex) {
}
}
catch (Exception ex) {
ex.printStackTrace();
} finally {
in.close();
}
UPDATE:
Current code to read but its not printing anything to screen:
try(ObjectInputStream ois = new ObjectInputStream(
new BufferedInputStream(Files.newInputStream(f))))
{
while (ois.available() > 0)
{
st = (Student) ois.readObject();
studentlist.addAccount(st);
System.out.println(st.getStudentNumber());
}
}
catch (Exception ex)
{
ex.printStackTrace();
}
This is how I write to file:
Path f = Paths.get("person.dat");
try (ObjectOutputStream oos = new ObjectOutputStream(
new BufferedOutputStream(Files.newOutputStream(f, StandardOpenOption.APPEND))))
{
oos.writeObject(new Student(name,age));
}
catch(Exception ex)
{
ex.printStackTrace();
}
Rather than trying to fix your utility classes, I suggest to use the standard classes of the NIO.2 File API.
Try something like (untested):
Path personDataFilePath = Paths.get("person.dat");
// or Java 11:
// Path personDataFilePath = Path.of("person.dat");
try (ObjectOutputStream oos = new ObjectOutputStream(new BufferedOutputStream(Files.newOutputStream(personDataFilePath, StandardOpenOption.APPEND)))){
oos.writeObject(new Student(name,age));
} catch (IOException ex) {
// do some error handling here
}
and to read the file, something like (untested):
List<Student> students = new ArrayList<>();
try (ObjectInputStream ois = new ObjectInputStream(new BufferedInputStream(Files.newInputStream(personDataFilePath)))){
while (ois.available() > 0){
students.add((Student) ois.readObject());
}
} catch (IOException ex) {
// do some error handling here
}
I have modified the code to work around making a file "appendable". I write a single arraylist object to the file (the arraylist holds a list of student objects). When I want to add a student, I read the object (arraylist) from the file, add my new student to the arraylist and write the arraylist back to the file. It is now working and my file does not have an append format.
I am trying to create a new .ser file to store objects if there is not one already present. When this is ran, it throws an EOFException. What exactly is an EOFException and is this method correctly written to create and read a .ser file? Thanks for any feedback.
public void readDatabase() throws IOException {
File dataFile = new File("database.ser");
// If data file does not exist, create it.
if (!dataFile.exists()) {
System.out.println("database.ser does not exist, creating one now . . .");
// if the file doesn't exists, create it
dataFile.createNewFile();
return; // No need to try to read anything from an empty file, so return.
}
ObjectInputStream objectinputstream = null;
boolean cont = true;
try {
FileInputStream streamIn = new FileInputStream(dataFile);
objectinputstream = new ObjectInputStream(streamIn);
while (cont) {
Item obj = null;
try {
obj = (Item) objectinputstream.readObject();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
if (obj != null)
itemList.add(obj);
else
cont = false;
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (objectinputstream != null) {
objectinputstream.close();
}
}
}
EOFException:
java.io.EOFException
at java.base/java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2758)
at java.base/java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputStream.java:3253)
at java.base/java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:866)
at java.base/java.io.ObjectInputStream.<init>(ObjectInputStream.java:343)
at hardwarestore.HardwareStore.readDatabase(HardwareStore.java:254)
at hardwarestore.HardwareStore.<init>(HardwareStore.java:33)
at hardwarestore.MainApp.<init>(MainApp.java:24)
at hardwarestore.MainApp.main(MainApp.java:259)
EOFException stands for:
End of File Exception
This typically occurs when you try to read data from a file where the FileReader has reached the end of the file. In other words, no more data to read.
You should catch the exception and close your stream. as it indicates that you have read all the objects in the file. Referring to the answer in this question:
while (true) {
try {
// Read the next object from the stream. If there is none, the
// EOFException will be thrown.
Item obj = (Item) objectinputstream.readObject();
itemList.add(obj);
} catch (EOFException e) {
// If there are no more objects to read, return what we have.
return contactMap;
} finally {
// Close the stream.
in.close();
}
}
I have a problem with reading objects from file Java.
file is anarraylist<projet>
This is the code of saving objects :
try {
FileOutputStream fileOut = new FileOutputStream("les projets.txt", true);
ObjectOutputStream out = new ObjectOutputStream(fileOut);
for (projet a : file) {
out.writeObject(a);
}
out.close();
} catch (Exception e) {
e.printStackTrace();
}
And this is the code of reading objects from file ::
try {
FileInputStream fileIn = new FileInputStream("les projets.txt");
ObjectInputStream in = new ObjectInputStream(fileIn);
while (in.available() > 0){
projet c = (projet) in.readObject();
b.add(c);
}
choisir = new JList(b.toArray());
in.close();
} catch (Exception e) {
e.printStackTrace();
}
Writing is working properly. The problem is the reading... it does not read any object (projet) What could be the problem?
As mentioned by EJP in comment and this SO post . if you are planning to write multiple objects in a single file you should write custom ObjectOutputStream , because the while writing second or nth object header information the file will get corrupt.
As suggested by EJP write as ArrayList , since ArrayList is already Serializable you should not have issue. as
out.writeObject(file) and read it back as ArrayList b = (ArrayList) in.readObject();
for some reason if you cant write it as ArrayList. create custome ObjectOutStream as
class MyObjectOutputStream extends ObjectOutputStream {
public MyObjectOutputStream(OutputStream os) throws IOException {
super(os);
}
#Override
protected void writeStreamHeader() {}
}
and change your writeObject as
try {
FileOutputStream fileOut= new FileOutputStream("les_projets.txt",true);
MyObjectOutputStream out = new MyObjectOutputStream(fileOut );
for (projet a : file) {
out.writeObject(a);
}
out.close();
}
catch(Exception e)
{e.printStackTrace();
}
and change your readObject as
ObjectInputStream in = null;
try {
FileInputStream fileIn = new FileInputStream("C:\\temp\\les_projets1.txt");
in = new ObjectInputStream(fileIn );
while(true) {
try{
projet c = (projet) in.readObject();
b.add(c);
}catch(EOFException ex){
// end of file case
break;
}
}
}catch (Exception ex){
ex.printStackTrace();
}finally{
try {
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I am trying to store my ArrayList between runtimes. So when I enter items into the ArrayList then close the program down and then open it back up and try to search the item I put in it will still be there.
I have tried MySQL and XML but I cannot figure it out. If you could please direct me in the direction of an easy way to store ArrayList that would be amazing.
Edit:
I am trying to serialize this ArrayList:
static ArrayList<Product> Chart=new ArrayList<Product>();
with these objects:
double Total;
String name;
double quantity;
String unit;
double ProductPrice;
Look into object serialization, it sounds like exactly what you want
What is object serialization?
This allows you to write a Java object to a file and read it back in later.
Here is an example. It also zips up the file, although you don't have to do that. You can also use the stream to write to a MYSQL blob instead of a file.
public static <T> void writeToGZIP(String filename, T obj) {
ObjectOutputStream os = null;
try {
os = new ObjectOutputStream(new GZIPOutputStream(new FileOutputStream(filename)));
os.writeObject(obj);
System.out.println("Object written to " + filename);
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (os != null) { os.flush(); os.close(); }
} catch (IOException e) {
e.printStackTrace();
}
}
}
#SuppressWarnings("unchecked")
public static <T> T readFromGZIP(String filename, T obj) {
ObjectInputStream ois = null;
try {
ois = new ObjectInputStream(new GZIPInputStream(new FileInputStream(filename)));
obj = (T) ois.readObject();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if( ois != null ) ois.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return obj;
}
ObjectOutputStream and ObjectInputStream
I want to write a method that reads an object from a binary file but I want to generalize it using generics.
I have this code:
#SuppressWarnings ("unchecked")
public static <T> T readFromBinaryFile (String filename){
T obj = null;
if (FileUtils.existsFile (filename)){
ObjectInputStream ois = null;
try{
ois = new ObjectInputStream (new FileInputStream (filename));
obj = (T)ois.readObject ();
}catch (IOException e){
Debug.out (e);
}catch (ClassNotFoundException e){
Debug.out (e);
}finally{
try{
if (ois != null) ois.close();
}catch (IOException e){
Debug.out (e);
}
}
}
return obj;
}
When I execute it I get a ClassCastException. I don't know anything about templates in java so any information will be apreciated. I've read something related to erasure, compile-time and execution-time but I don't understand very well why I get this ClassCastException.
Thanks.
EDIT: I call the method like this:
FileUtils.readFromBinaryFile (filename); (Without "")
Are there templates in Java? Just use Object instead of T. In Java everything derives from Object at the base, so you don't want T obj but Object obj.
A ClassCastException means the type you read didn't match the type you were expecting (and cast to) I suggest you see which object you are read in a debugger (or a log message) and compare it with what you are expecting.
You're calling your method wrong.
Just do it this way:
FileUtils.readFromBinaryFile (filename);
What you're calling is so-called generic method.
"We don't have to pass an actual type argument to a generic method. The compiler infers the type argument for us, based on the types of the actual arguments. It will generally infer the most specific type argument that will make the call type-correct." source
EDIT:
I've tried your example and it works (I had actually comment some lines)
private static String filename = "number.serialized";
public static void main(String[] args) {
Double d = 3.14;
writeToBinary(d, filename);
Double readD = readFromBinaryFile(filename);
System.out.println(readD);
}
#SuppressWarnings ("unchecked")
public static <T> T readFromBinaryFile(String filename) {
T obj = null;
File file = new File(filename);
if (file.exists()) {
ObjectInputStream ois = null;
try {
ois = new ObjectInputStream(new FileInputStream(filename));
obj = (T)ois.readObject();
} catch (IOException e) {
} catch (ClassNotFoundException e) {
} finally {
try {
if (ois != null)
ois.close();
} catch (IOException e) {
}
}
}
return obj;
}
public static <T> void writeToBinary(T obj, String filename)
{
try {
FileOutputStream fis = new FileOutputStream(filename);
ObjectOutputStream oos = new ObjectOutputStream(fis);
oos.writeObject(obj);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}