I use SimpleXML to save a simple POJO into XML file and then read it back. I follow this tutorial. The file is successfully created, but the reading part is just simply not working. It throws the second exception which comes from serializer.read.
Room room = new Room("1");
Serializer serializer = new Persister();
try {
File ff = new File("room.xml");
serializer.write(room, ff);
} catch (FileNotFoundException e) {
System.out.println("FileNotFoundException\n");
} catch (Exception e) {
System.out.println("Exception from serializer.write\n");
}
try {
File ffi = new File("room.xml");
Room aroom = serializer.read(Room.class, ffi);
System.out.println("RoomName: " + aroom.getRid() + "\n");
} catch (FileNotFoundException e) {
System.out.println("FileNotFoundException\n");
} catch (Exception e) {
System.out.println("Exception from serializer.read\n");
}
Any hint?
Make sure you have a default constructor in Room.
public Room(){
}
Alternatively, make sure your constructor looks like this:
public Room(#Attribute(name="rid") String rid){
this.rid = rid;
}
Related
something is really messed up. I've got a ".ser" document in the assets folder, which stores an ArrayList of Objetcs. In an android application, I want to read this objects. There are a lot of posts related to this issue, however none of them could solve my problem. The strange part is, when I am using similar code in non - android context / "normal" java, it works properly. Here, the last line throws a NullPointerException - What is going wrong?
public void getData() {
ArrayList<MyClass> output= null;
InputStream is = null;
ObjectInputStream ois = null;
try{
is = this.getAssets().open("data.ser");
ois = new ObjectInputStream(is);
output = (ArrayList<MyClass>)ois.readObject();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
try {
ois.close();
} catch (IOException e) {
e.printStackTrace();
}
}
Log.d("TAG", output.get(0).getId());
}
I would create a class and place the array within a single object:
public class ListObjects implements Serializable {
List<MyClass> listMyClass = new ArrayList<>();
public ListObjects(){
}
public List<MyClass> getListMyClass() {
return listMyClass;
}
public void setListMyClass(List<MyClass> listMyClass) {
this.listMyClass = listMyClass;
}
}
I had a similar problem. And it was because the name of the package in the java app was not called the same as the package name in android. And therefore I did not recognize them as equal objects. This is how I do it:
public static Object fromData(byte[] data) {
ObjectInputStream ois = null;
Object object = null;
try {
ois = new ObjectInputStream(
new ByteArrayInputStream(data));
object = ois.readObject();
} catch (Exception ex) {
Logger.getLogger(ModeloApp.class.getName()).log(Level.SEVERE, null, ex);
} finally {
try {
ois.close();
} catch (Exception ex) {
Logger.getLogger(ModeloApp.class.getName()).log(Level.SEVERE, null, ex);
}
}
return object;
}
This question already has answers here:
java.io.FileNotFoundException when creating FileInputStream
(2 answers)
Closed 6 years ago.
For my application I want to use a Map to act as a database. To save and load a map, I am writing/reading it to/from database.ser using this 2 methods:
private synchronized void saveDB() {
try {
fileOut = new FileOutputStream(db);
out = new ObjectOutputStream(fileOut);
out.writeObject(accounts);
fileOut.close();
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
#SuppressWarnings("unchecked")
private void loadDB() {
try {
fileIn = new FileInputStream(db);
in = new ObjectInputStream(fileIn); // that is where error is produced if fileIn is empty
accounts = (Map<String, Client>) in.readObject();
in.close();
fileIn.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I want to load into Map when application starts, so I invoke method in constructor like this:
protected DriveatorImpl() {
accounts = new ConcurrentHashMap<String, Client>();
db = new File("C:/Users/eduar/git/Multy-Threaded-Bank-System/Bank-Services/database.ser");
// also, any suggestions how can I make path to a file more flexible in case I want to run Server side of an app on different machine?
if (!db.exists()) {
try {
db.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}
loadDB(); // loads database when server start
}
I am aware of what causing an error, but I don't know what should I change in my design to avoid ObjectInputStream constructor receiving empty stream!
Any suggestions on what I can do differently?
Edit: I want to note that in fresh application run database.ser is empty since there was no entries made into Map yet.
Thank You!
First why the EOFExcpetion occur?
There are no contents in file or file is empty and you tried to read file.
You can avoid the EOFException for an empty file by checking file content length if it is less than or equal to zero means file is empty. another way to check if file is empty
Some code change and it worked for me.
#SuppressWarnings("unchecked")
private void loadDB() {
try {
if (db.length() <= 0) {
// if statement evaluates to true even if file doesn't exists
saveDB(); // save to a file an empty map
// if file doesn't exist, it creates a new one
// call loadDB inside constructor
}
FileInputStream fileIn = new FileInputStream(db);
ObjectInputStream in = new ObjectInputStream(fileIn); // that is where error is produced if fileIn is empty
in.readObject();
in.close();
fileIn.close();
System.out.println(accounts);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
Get rid of the file.exists()/file.createNewFile() crap. All it is doing for you is masking the original FileNotFoundException problem, and turning into a thoroughly predictable EOFException because of trying to construct an ObjectInputStream around an empty stream. Handle the original problem. Don't just move it, or turn it into something else.
I am using Jackcess API in my Eclipse plugin project. I added jackcess-2.1.0.jar file under resources/lib. I included the jar under my Binary build and in build.properties. I successfully make a connection using connection string but my DatabaseBuilder.open() call is not executing. My code is
public void run() {
try {
File tempTarget = File.createTempFile("eap-mirror", "eap");
try {
this.source = DriverManager.getConnection(EaDbStringParser.eaDbStringToJdbc(sourceString));
this.source.setReadOnly(true);
try {
FileUtils.copyFile(new File(templateFileString), tempTarget);
} catch (IOException e) {
e.printStackTrace();
}
// Changes
try {
this.target = DatabaseBuilder.open(tempTarget);
} catch (IOException e) {
e.printStackTrace();
}
Collection<String> tables = selectTables(source);
long time = System.currentTimeMillis();
for (String tableName : tables) {
long tTime = System.currentTimeMillis();
Table table = target.getTable(tableName);
System.out.print("Mirroring table " + tableName + "...");
table.setOverrideAutonumber(true);
copyTable(table, source, target);
System.out.println(" took "+ (System.currentTimeMillis() - tTime));
}
System.out.println("Done. Overall time: "+ (System.currentTimeMillis() - time));
System.out.println("done");
} catch (SQLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
// More Code here
} catch (IOException e1) {
}
}
When I run the class in debug mode and I reach DatabaseBuilder.open call it fails.
Here is my project structure:
Can anyone tell me the possible reason for it ?
The .open method of DatabaseBuilder expects to open an existing well-formed Access database file. The .createTempFile method of java.io.File creates a 0-byte file. So, the code
File dbFile;
try {
dbFile = File.createTempFile("eap-mirror", "eap");
try (Database db = DatabaseBuilder.open(dbFile)) {
System.out.println(db.getFileFormat());
} catch (IOException ioe) {
ioe.printStackTrace(System.out);
}
} catch (Exception e) {
e.printStackTrace(System.out);
} finally {
System.out.println("Finally...");
}
will cause Jackcess to throw
java.io.IOException: Empty database file
when it tries to do DatabaseBuilder.open(dbFile).
Instead, you should DatabaseBuilder.create to convert the 0-byte file into a real Access database file like this
File dbFile;
try {
dbFile = File.createTempFile("eap-mirror", ".accdb");
dbFile.deleteOnExit();
try (Database db = DatabaseBuilder.create(Database.FileFormat.V2010, dbFile)) {
System.out.println(db.getFileFormat());
} catch (IOException ioe) {
ioe.printStackTrace(System.out);
}
} catch (Exception e) {
e.printStackTrace(System.out);
} finally {
System.out.println("Finally...");
}
I have a program that needs to load data at launch. The data comes from a serialized object. I have a method loadData(), which is called upon construction of the Data class. Sometimes, (I.e. after a loss of saveData, or on first program launch on a new system), the file can be empty. (The file will exist though, the method ensures that).
When I try to run the program, I recieve an EOFException. So, in the method, I try to catch it, and just print a line to the console explaining what happened and return to the caller of the method. (so, upon return, the program will think loadData() is complete and has returned. However, it still crashes throwing the exception without printing a line to the console or anything. It is like it is totally ignoring the catch I have in place.
CODE:
protected void loadData()
{
// Gets/creates file object.
saveFileObject = new File("savedata.ser");
if(!saveFileObject.exists())
{
try
{
saveFileObject.createNewFile();
}
catch(IOException e)
{
System.out.println("Uh oh...");
e.printStackTrace();
}
}
// Create file input stream
try
{
fileIn = new FileInputStream(saveFileObject);
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
// Create object input stream
try
{
inputStream = new ObjectInputStream(fileIn);
}
catch(IOException e)
{
e.printStackTrace();
}
// Try to deserialize
try
{
parts = (ArrayList<Part>)inputStream.readObject();
}
catch(EOFException e)
{
System.out.println("EOFException thrown! Attempting to recover!");
return;
}
catch(ClassNotFoundException e)
{
e.printStackTrace();
}
catch(IOException e)
{
e.printStackTrace();
}
// close input stream
try
{
inputStream.close();
}
catch(IOException e)
{
e.printStackTrace();
}
}
Any help please?
Try writing your code like :
protected void loadData() {
// Gets/creates file object.
saveFileObject = new File("savedata.ser");
try {
if (!saveFileObject.exists()) {
saveFileObject.createNewFile();
}
// Create file input stream
fileIn = new FileInputStream(saveFileObject);
// Create object input stream
inputStream = new ObjectInputStream(fileIn);
// Try to deserialize
parts = (ArrayList<Part>) inputStream.readObject();
// close input stream
inputStream.close();
} catch (EOFException e) {
System.out.println("EOFException thrown! Attempting to recover!");
} catch (IOException e) {
System.out.println("Uh oh...");
e.printStackTrace();
}
}
Also note that EOFException is a sub-class of IOException
How about making one try and then making catches respectively like here?
I'm a beginner still, and currently learning about handling exceptions. The exercise in my book I'm trying to figure out tells me to add a Finally block to close out the file I opened, and I don't understand what I'm doing wrong. Keep in mind the file name and path are fake but here is what I have:
public static String readLineWithFinally()
{
System.out.println("Starting readLineWithFinally method.");
RandomAccessFile in = new RandomAccessFile("products.ran", "r");
try
{
String s = in.readLine();
return s;
}
catch (IOException e)
{
System.out.println(e.toString());
return null;
}
finally
{
try
{
in.close();
}
catch (Exception e)
{
System.out.println("Generic Error Message");
}
}
}
To add on to Taylor Hx's answer, you can take advantage of Java 7's try-with-resources construct to avoid having to use finally altogether in your case.
public static String readLineWithFinally() {
System.out.println("Starting readLineWithFinally method.");
try (RandomAccessFile in = new RandomAccessFile("products.ran", "r")) {
return in.readLine();
} catch (IOException e) {
System.out.println(e.toString());
return null;
}
}
You'll also want to be certain that your usage is consistent with what the API mandates for RandomAccessFile.
The code that you posted shouldn't compile, as RandomFile(String, String) can possibly throw FileNotFoundException. As such, we must include it in the try block.
System.out.println("Starting readLineWithFinally method.");
RandomAccessFile in = null;
try {
in = new RandomAccessFile("products.ran", "r");
String s = in.readLine();
return s;
} catch (IOException e) {
System.out.println(e.toString());
return null;
} finally {
try {
if(in != null) {
in.close();
}
} catch (Exception e) {
System.out.println("Generic Error Message");
}
}
Keep in mind the file name and path are fake but here is what I have:
That is why you will have a FileNotFoundException while creating RandomAccessFile("products.ran", "r") with read access mode "r".
From the documentation: RandomAccessFile(String name, String mode)
This constructor throws a FileNotFoundException if the mode is
"r" but the given string does not denote an existing regular file,
or if the mode begins with "rw" but the given string does not denote
an existing, writable regular file and a new regular file of that name
cannot be created, or if some other error occurs while opening or
creating the file