I have two classes (writeArray and readArray) which should write an array of {10, 20, 30} and print it in a demo class but it only prints out 10, with no 20 or 30, and I don't understand if it isn't reading the whole array or if there's an issue with my demo code.
Here's the array class:
import java.io.*;
public class FileArray{
public static void writeArray(){
String fileName = "file.bin";
int[] array = {10, 20, 30};
try{
FileOutputStream fileOs = new FileOutputStream(fileName);
DataOutputStream os = new DataOutputStream(fileOs);
for (int i = 0; i < 3; i++)
os.writeInt(array[i]);
os.close();
fileOs.close();
}
catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e){
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void readArray(){
String fileName = "file.bin";
int[] array1;
try{
FileInputStream fileIs = new FileInputStream(fileName);
DataInputStream is = new DataInputStream(fileIs);
System.out.println(is.readInt());
is.close();
fileIs.close();
}
catch (FileNotFoundException e){
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e){
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Here is the display class:
public class FileArrayDemo {
public static void main(String[] args){
FileArray write = new FileArray();
write.writeArray();
System.out.println("Done writing. Now reading.");
FileArray read = new FileArray();
read.readArray();
}
}
You're only reading a single int. Instead, you should loop until you reach EOF:
while (true) {
try {
System.out.println(is.readInt());
} catch (EOFException e) {
// Reached the end of the file, break out the loop
break;
}
}
just add the for loop you used in your write method with your
System.out.println(is.readInt());
Related
After implementing the suggestions I was given on my last post, I now have a working piece of code without any error messages, but my code will still only print the first object from my file. I would be grateful for any suggestions.
import java.io.*;
import java.util.*;
public class Mainclass {
public static void main(String[] args) {
InputStream is;
try {
is = new FileInputStream("or.rtf");
ObjectInputStream ois;
try {
int l = 1;
ois = new ObjectInputStream(is);
while (l > 0) {
try {
Stone p = (Stone) ois.readObject();
System.out.println(p);
} catch(Exception e) {
if(e instanceof EOFException) {
l--;
System.err.println();
} else if(e instanceof FileNotFoundException) {
l--;
System.err.println(e);
} else {
System.err.println(e);
}
}
}
ois.close();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
} catch (FileNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
Code to save objects to a file:
import java.io.*;
import java.util.*;
public class Saver {
public static void main(String[] args) {
ArrayList<Stone> objects = new ArrayList<Stone>();
objects.add(new Stone("Max",50,90));
objects.add(new Stone("Fiona",30,60));
objects.add(new Stone("Sam",20,30));
for (int i = 0; i < objects.size(); i++ ) {
try {
OutputStream os = new FileOutputStream("qt.rtf");
ObjectOutputStream oos = new ObjectOutputStream(os);
oos.writeObject(objects.get(i));
System.out.println(i);
oos.close();
} catch (IOException e) {
System.err.println(e);
}
}
}
}
I implemented the println(i) to check whether the code was even executed in a loop.
Change the scope of ObjectOutputStream and FileOutputStream.
public static void main(String[] args) {
ArrayList<Stone> objects = new ArrayList<Stone>();
objects.add(new Stone("Max",50,90));
objects.add(new Stone("Fiona",30,60));
objects.add(new Stone("Sam",20,30));
try {
OutputStream os = new FileOutputStream("qt.rtf");
ObjectOutputStream oos = new ObjectOutputStream(os);
for (int i = 0; i < objects.size(); i++ ) {
oos.writeObject(objects.get(i));
System.out.println(i);
}
oos.close();
} catch (IOException e) {
System.err.println(e);
}
}
}
You are also not reading from the same file you created or.rtf and qr.rtf.
I am working on my first server project for school and I am receiving a NoSuchElementException when reaching the code below in my client. From my understanding, the way I have written it, the scanner should be waiting for the server to send back a string. Instead it seems to be jumping right to the exception. In the server code (second below) I have the output that is supposed to return all strings in an array. My goal is to have the client print all of the strings in the text area (status).
static void runClient() {
Socket client = null;
PrintWriter output = null;
Scanner input = null;
try {
client = new Socket("localhost", 5007);
input = new Scanner(client.getInputStream());
output = new PrintWriter(client.getOutputStream());
output.println(game);
output.println(numberOfPicks);
output.flush();
pStr("Data Sent");
while (true) {
pStr("Waiting for Server");
status.appendText(input.nextLine());
if (!input.hasNext())
break;
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
input.close();
} catch (Exception e) {
}
try {
output.close();
} catch (Exception e) {
}
try {
client.close();
} catch (Exception e) {
}
}
}
private static void pStr(String string) {
System.out.println(string);
}
}
PARTIAL SERVER CODE BELOW
public void run() {
PrintWriter output = null;
Scanner input = null;
try {
// Get input and output streams.]
input = new Scanner(connection.getInputStream());
output = new PrintWriter(connection.getOutputStream());
String game;
int quickPicks;
try {
game = input.nextLine();
quickPicks = Integer.parseInt(input.nextLine());
switch (game) {
case "PowerBall":
ansStr = new pickNumbers(game, quickPicks, 69, 26).getQuickPicks();
break;
case "MegaMillions":
ansStr = new pickNumbers(game, quickPicks, 70, 25).getQuickPicks();
break;
case "Lucky4Life":
ansStr = new pickNumbers(game, quickPicks, 48, 18).getQuickPicks();
break;
default:
throw new RuntimeException("Incorrect Game");
}
} catch (Exception e) {
output.println(e.getMessage());
}
for (int i = 0; i < ansStr.length; i++) {
output.println(ansStr[i]);
//output.flush();
}
} catch (Exception e) {
pStr(e.getMessage());
} finally {
try {
input.close();
} catch (Exception e) {
}
try {
output.close();
} catch (Exception e) {
}
try {
connection.close();
} catch (Exception e) {
}
}
}
}
How about nesting status.appendText(input.nextLine()); in a test for hasNextLine e.g:
if(input.hasNextLine()){
status.appendText(input.nextLine());
}
cur file does not seem to be deleted and temp file does not get renamed.
private class editClassListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
File temp = new File("courseTemp.bin");
File cur = new File("course.bin");
ArrayList<Course> courses = new ArrayList<Course>();
int count = 0;
try {
FileInputStream fin = new FileInputStream(cur);
while(true)
{
try
{
ObjectInputStream oin = new ObjectInputStream(fin);
Course c = (Course) oin.readObject();
courses.add(c);
}catch (EOFException eofException){
break;
} catch (IOException e1) {
e1.printStackTrace();
} catch (ClassNotFoundException e1) {
e1.printStackTrace();
}
}
while(count < courses.size())
{
if(enterCourseID.getText().equals(courses.get(count).getCourseID()))
{
courses.get(count).setDescription(enterCourseDescription.getText());
courses.get(count).setSemester((String) semesterBox.getSelectedItem());
courses.get(count).setYear(yearBox.getSelectedIndex());
}
}
temp.renameTo(cur);
cur.delete();
temp.delete();
fin.close();
FileOutputStream fos = new FileOutputStream(temp);
courses.trimToSize();
count = 0;
while(count < courses.size())
{
ObjectOutputStream oop = new ObjectOutputStream(fos);
oop.writeObject(courses.get(count));
count++;
}
} catch (FileNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
Both File.delete() and File.renameTo() do not throw an Exception but instead return false if the underlying OS-operation cannot be executed. Reasons for that are dependant on your system, but include among others:
The file you are trying to rename/delete is in use (i. e. open streams)
The file is protected by the OS (insufficient rights)
In case of renaming: A file with the new name already exists
In your case, at least the first point is true. You should be fine by simply closing your FileInputStream fin before trying to delete cur. As for the renaming, you might need to delete cur first before renaming temp.
As an aside, the Utility Class java.nio.file.Files offers methods (move()&delete()) for renaming and deleting, which throw an IOException, if the operation fails, with the cause of failure in the error message.
Trying to learn about Jackson some, so I'm writing a simple program that reads a file/creates one to store some JSON in it. From the Jackson website I figured out how to read and write from the file, but in the case of my rudimentary program, i'd like to append as well. I'm basically trying to store a list of shopping lists. There is a shopping list object which has store name, amd items for that store.
The trouble is that I cannot figure a way to append another entry to the end of the file (in JSON format). Here is what I am working with so far, you can ignore the first bit it's just a silly console scanner asking for input:
public class JacksonExample {
static ObjectMapper mapper = new ObjectMapper();
static File file = new File("C:/Users/stephen.protzman/Desktop/user.json");
static List<ShoppingList> master = new ArrayList<ShoppingList>();
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
boolean running = true;
while (running) {
System.out.println("[ 1 ] Add a new shopping list");
System.out.println("[ 2 ] View all shopping lists");
System.out.println("[ 3 ] Save all shopping lists");
int choice = Integer.parseInt(in.nextLine());
switch (choice) {
case 1:
getNewList();
case 2:
display();
case 3:
running = false;
}
}
in.close();
}
public static void getNewList() {
boolean more = true;
String store, temp;
List<String> items = new ArrayList<String>();
Scanner s = new Scanner(System.in);
System.out.println("Enter the store: ");
store = s.nextLine();
System.out.println("Enter each item [If done type 'DONE'] :");
while (more) {
temp = s.nextLine();
if (temp != null) {
if (temp.toUpperCase().equals("DONE")) {
more = false;
} else {
items.add(temp);
}
}
}
save(store, items);
s.close();
}
public static void display() {
try {
ShoppingList list = mapper.readValue(file, ShoppingList.class);
System.out.println(mapper.defaultPrettyPrintingWriter()
.writeValueAsString(list));
} catch (JsonParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JsonMappingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void save(String store, List<String> items) {
//load in old one
try {
ShoppingList list = mapper.readValue(file, ShoppingList.class);
System.out.println(mapper.defaultPrettyPrintingWriter()
.writeValueAsString(list));
} catch (JsonParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JsonMappingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//add to end of older list
ShoppingList tempList = new ShoppingList();
tempList.setStore(store);
tempList.setItems(items);
master.add(tempList);
try {
mapper.writeValue(file, master);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
I want to keep using ObjectMapper (considering im trying to learn Jackson) I just havent found a way to append yet is all. Any ideas?
To append content, you need to use Streaming API to create JsonGenerator; and then you can give this generator to ObjectMapper to write to. So something like:
JsonGenerator g = mapper.getFactory().createGenerator(outputStream);
mapper.writeValue(g, valueToWrite);
// and more
g.close();
Below method can be used to write objects into a json file in append mode. it first reads your existing json file and adds new java objects to JSON file.
public static void appendWriteToJson() {
ObjectMapper mapper = new ObjectMapper();
try {
// Object to JSON in file
JsonDaoImpl js = new JsonDaoImpl();
URL resourceUrl = js.getClass().getResource("/data/actionbean.json");
System.out.println(resourceUrl);
File file = new File(resourceUrl.toURI());
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(file, true))); // append mode file writer
mapper.writeValue(out, DummyBeanObject);
} catch (Exception e) {
e.printStackTrace();
}
}
hello dear colleagues,
I have a Garden class in which I serialize and deserialize multiple Plant class objects. The serializing is working but the deserializing is not working if a want to assign it to calling variable in the mein static method.
public void searilizePlant(ArrayList<Plant> _plants) {
try {
FileOutputStream fileOut = new FileOutputStream(fileName);
ObjectOutputStream out = new ObjectOutputStream(fileOut);
for (int i = 0; i < _plants.size(); i++) {
out.writeObject(_plants.get(i));
}
out.close();
fileOut.close();
} catch (IOException ex) {
}
}
deserializing code:
public ArrayList<Plant> desearilizePlant() {
ArrayList<Plant> plants = new ArrayList<Plant>();
Plant _plant = null;
try {
ObjectInputStream in = new ObjectInputStream(new FileInputStream(fileName));
Object object = in.readObject();
// _plant = (Plant) object;
// TODO: ITERATE OVER THE WHOLE STREAM
while (object != null) {
plants.add((Plant) object);
object = in.readObject();
}
in.close();
} catch (IOException i) {
return null;
} catch (ClassNotFoundException c) {
System.out.println("Employee class not found");
return null;
}
return plants;
}
My invoking code:
ArrayList<Plant> plants = new ArrayList<Plant>();
plants.add(plant1);
Garden garden = new Garden();
garden.searilizePlant(plants);
// THIS IS THE PROBLEM HERE
ArrayList<Plant> dp = new ArrayList<Plant>();
dp = garden.desearilizePlant();
edit
I got a null Pointer exception
The solution of #NilsH is working fine, thanks!
How about serializing the entire list instead? There's no need to serialize each individual object in a list.
public void searilizePlant(ArrayList<Plant> _plants) {
try {
FileOutputStream fileOut = new FileOutputStream(fileName);
ObjectOutputStream out = new ObjectOutputStream(fileOut);
out.writeObject(_plants);
out.close();
fileOut.close();
} catch (IOException ex) {
}
}
public List<Plant> deserializePlant() {
List<Plants> plants = null;
try {
ObjectInputStream in = new ObjectInputStream(new FileInputStream(fileName));
plants = in.readObject();
in.close();
}
catch(Exception e) {}
return plants;
}
If that does not solve your problem, please post more details about your error.
It may not always be feasible to deserialize a whole list of objects (e.g., due to memory issues). In that case try:
ObjectInputStream in = new ObjectInputStream(new FileInputStream(
filename));
while (true) {
try {
MyObject o = (MyObject) in.readObject();
// Do something with the object
} catch (EOFException e) {
break;
}
}
in.close();
Or using the Java SE 7 try-with-resources statement:
try (ObjectInputStream in = new ObjectInputStream(new FileInputStream(
filename))) {
while (true) {
MyObject o = (MyObject) in.readObject();
// Do something with the object
}
} catch (EOFException e) {
return;
}
If you serialize it to an array linear list, you can cast it back to an array linear list when deserializing it -- all other methods failed for me:
import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
public class Program
{
public static void writeToFile(String fileName, Object obj, Boolean appendToFile) throws Exception
{
FileOutputStream fs = null;
ObjectOutputStream os = null;
try
{
fs = new FileOutputStream(fileName);
os = new ObjectOutputStream(fs);
//ObjectOutputStream.writeObject(object) inherently writes binary
os.writeObject(obj); //this does not use .toString() & if you did, the read in would fail
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
try
{
os.close();
fs.close();
}
catch(Exception e)
{
//if this fails, it's probably open, so just do nothing
}
}
}
#SuppressWarnings("unchecked")
public static ArrayList<Person> readFromFile(String fileName)
{
FileInputStream fi = null;
ObjectInputStream os = null;
ArrayList<Person> peopleList = null;
try
{
fi = new FileInputStream(fileName);
os = new ObjectInputStream(fi);
peopleList = ((ArrayList<Person>)os.readObject());
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
catch(EOFException e)
{
e.printStackTrace();
}
catch(ClassNotFoundException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
catch(Exception e)
{
e.printStackTrace();
}
finally
{
try
{
os.close();
fi.close();
}
catch(Exception e)
{
//if this fails, it's probably open, so just do nothing
}
}
return peopleList;
}
public static void main(String[] args)
{
Person[] people = { new Person(1, 39, "Coleson"), new Person(2, 37, "May") };
ArrayList<Person> peopleList = new ArrayList<Person>(Arrays.asList(people));
System.out.println("Trying to write serializable object array: ");
for(Person p : people)
{
System.out.println(p);
}
System.out.println(" to binary file");
try
{
//writeToFile("output.bin", people, false); //serializes to file either way
writeToFile("output.bin", peopleList, false); //but only successfully read back in using single cast
} // peopleList = (ArrayList<Person>)os.readObject();
// Person[] people = (Person[])os.readObject(); did not work
// trying to read one at a time did not work either (not even the 1st object)
catch (Exception e)
{
e.printStackTrace();
}
System.out.println("\r\n");
System.out.println("Trying to read object from file. ");
ArrayList<Person> foundPeople = null;
try
{
foundPeople = readFromFile("input.bin");
}
catch (Exception e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
if (foundPeople == null)
{
System.out.println("got null, hummm...");
}
else
{
System.out.println("found: ");
for(int i = 0; i < foundPeople.size(); i++)
{
System.out.println(foundPeople.get(i));
}
//System.out.println(foundPeople); //implicitly calls .toString()
}
}
}