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
Related
So I have a working ObjectOutputStream in a method that I start by calling the method in main. I need to then read the file it created and print out all 5 objects in it. Right now I'm only printing out the first object.
public static AccountSerializable serializReadObject() throws ClassNotFoundException, IOException {
AccountSerializable read = null;
try { // Create an input stream for file accounts.ser
ObjectInputStream input = new ObjectInputStream(new FileInputStream("accounts.ser"));
read = (AccountSerializable) input.readObject();
input.close();
} catch (IOException i) {
throw i;
}catch(ClassNotFoundException c){
throw c;
}
return read;
}
public static void main(String[] args) {
try {
System.out.println(serializReadObject());
} catch (ClassNotFoundException | IOException e) {
System.out.println("Class not found");
e.printStackTrace();
}
}
I've tried to throw
boolean eof = false;
while(!eof){
try{
//read data
}catch(EOFException e){
eof = true;
}
}
in serializReadObject To loop it and I've also tried to instead catch it in main but I keep getting an error stating "Unreachable catch block for EOFException it is already handled by the catch block"
I then tried to take away the IOException and just put EOFEception but alas it keeps forcing me to surround my read with IOException. Is there another way to loop this with EOF?
You're only getting the first object because your opening and closing the stream on each call. There are many ways to achieve what you want. One way is to use a List<AccountSerializable>:
public static List<AccountSerializable> serializeReadObjects() throws IOException, ClassNotFoundException {
// create an input stream for file accounts.ser
// this line will throw an IOException if something goes wrong
// we don't need to catch it in this method though
ObjectInputStream input = new ObjectInputStream(new FileInputStream("accounts.ser"));
// create list to hold read in accounts
List<AccountSerializable> accounts = new ArrayList<>();
// keep reading until EOFException is thrown
boolean keepReading = true;
while(keepReading) {
try {
// read in serialized account
AccountSerializable read = (AccountSerializable) input.readObject();
// add read in serialized account to the list
accounts.add(read);
} catch(EOFException eofe) {
// we are at the end of file, so stop reading
keepReading = false;
input.close();
} catch(IOException ioe) {
// input stream error other than EOF, not sure what to do
input.close();
throw ioe;
} catch(ClassNotFoundException cnfe) {
// not sure what to do in this case, so close input
input.close();
throw cnfe;
}
}
return accounts;
}
public static void main(String[] args) {
List<AccountSerializable> accounts = null;
try {
// get list of read in accounts
accounts = serializeReadObjects();
} catch (ClassNotFoundException | IOException e) {
e.printStackTrace();
}
// iterate over list of read in accounts and output them to stdout
for(AccountSerializable account : accounts) {
System.out.println(account);
}
}
Can somebody tell me what am I doing wrong in the below java code ? It doesn't compile and gives me compilation error.
import java.io.*;
public class ShowFile {
public static void main(String[] args) {
int i;
FileInputStream Fin;
try {
Fin = new FileInputStream("C:\\Users\\cbr\\Desktop\\test.txt");
} catch (FileNotFoundException exp) {
System.out.println("exception caught" + exp);
}
try {
do {
i = Fin.read();
System.out.print((char) i);
} while (i != -1);
} catch (IOException exp) {
System.out.println("Exception caught" + exp);
}
finally {
try {
Fin.close();
} catch (IOException exp) {
System.out.println("Exception caught" + exp);
}
}
}
}
while the below code compiles. You can see both initialization are within try block.
import java.io.*;
class ShowFile2 {
public static void main(String args[]) {
int i;
FileInputStream fin;
// First make sure that a file has been specified.
try {
fin = new FileInputStream("C:\\Users\\cbr\\Desktop\\test.txt");
} catch (FileNotFoundException exc) {
System.out.println("File Not Found");
return;
}
try {
// read bytes until EOF is encountered
do {
i = fin.read();
if (i != -1) {
System.out.print((char) i);
}
} while (i != -1);
} catch (IOException exc) {
System.out.println("Error reading file.");
}
try {
fin.close();
} catch (IOException exc) {
System.out.println("Error closing file.");
}
}
}
The problem is, that if new FileInputStream("C:\\Users\\cbr\\Desktop\\test.txt"); throws an exception, your variable will not be initialized in the second part of your method. This is not allowed. Object members will be initialized to null when the object is created, but this is not the case for local variables: they must be initialized explicitly.
A quick fix (but read on for a better fix) would be to initialize your variable (to null) when you are defining it:
FileInputStream fin = null;
This will solve your compilation error, however, you will get NullPointerExceptions when an exception is thrown in the first catch block.
A better solution is to put your error handling logic in the same place: if creating the FileInputStream fails, you don't want to read bytes from it anyway. So you can use a single try-catch block:
try {
fin = new FileInputStream("C:\\Users\\cbr\\Desktop\\test.txt");
// Read bytes from fin.
...
} catch (IOException e) {
// handle exception
...
}
Final advice: to make sure that your input stream is closed in all circumstances, you can use a try-with-resources block:
try (fin = new FileInputStream("C:\\Users\\cbr\\Desktop\\test.txt")) {
// Read bytes from fin.
...
} catch (IOException e) {
// handle exception
...
}
It does compile because the ShowFile2 class contains return in the catch block: this will ensure that the variable fin will be always initialized.
In the first class you caught the exception and you continue the execution of your program.
I'm trying to close a RandomAccessFile but resource remain busy.
Code:
public boolean isOpen(RandomAccessFile f) {
try {
f.length() ;
return true ;
}
catch (IOException e) {
return false ;
}
}
this.rfmFile = new File(filePath);
try {
this.rfmRandomAccessFile = new RandomAccessFile(rfmFile, "rws");
} catch(Exception e){
}finally{
this.rfmRandomAccessFile.close();
}
while(!isOpen(this.rfmRandomAccessFile));
log.debug("I Finally Closed this RAF");
Log is not showed and thread goes in loop.
When I try to access to my resource from shell it gives me "Device or Resource busy".
The only way to access is kill java process.
When you are trying to access the RandomAccessFile length(), method, it is already closed and thus you cannot access it anymore.
You probably want to use the length() method of File. Your loop cannot work as the RandomAccessFile was already closed.
But I must admit I am clueless on the low level reason why rfmRandomAccessFile would not really be closed. It could be a side effect of your strange loop trying to get the size of a closed file.
[edit:]Could not reproduce your issue with the following piece of code:
package com.company;
import java.io.*;
public class Main {
public static void main(String[] args) {
File file = new File("foobar.txt");
RandomAccessFile randomAccessFile = null;
try {
randomAccessFile = new RandomAccessFile(file, "rws");
randomAccessFile.write(new byte[]{'f'});
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(randomAccessFile !=null){
try {
randomAccessFile.close();
} catch (IOException e) {
//doh!
}
}
}
FileReader reader = null;
try {
reader = new FileReader(file);
char read = (char) reader.read();
System.out.println("what was written: "+read);
System.out.println("file size: "+file.length());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(reader !=null){
try {
reader.close();
} catch (IOException e) {
//doh!
}
}
}
}
}
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?
Due to my company's policy of using Eclipse and using Eclipse's code-autofix, the following code pattern appears excessively in the codebase:
InputStream is = null;
try {
is = url.openConnection().getInputStream();
// .....
} catch (IOException e) {
// handle error
} finally {
if (is != null) {
try {
is.close();
} catch (IOException e) {
// handle error
}
}
}
IMO it's extremely fugly and hard to read, especially the portion within the finally block (is there really a need to catch 2 instances of IOException?). Is there anyway to streamline the code such that it looks cleaner?
Why do anything? It's working code. It's correct.
Leave it be.
First, about using IOUtils - may worth a shot telling your supervisors that the very application-server / Java runtime environment they might use, uses IOUtils and similar libraries itself. so in essence you're not introducing new components to your architecture.
Second, no, not really. There isn't really any way around it other than writing your own utility that will immitate IOUtils' closeQuietly method.
public class Util {
public static void closeStream(inputStream is) {
if (is != null) {
try {
is.close();
} catch (IOException e) {
// log something
}
}
}
Now your code is
InputStream is = null;
try {
is = url.openConnection().getInputStream();
// .....
} catch (IOException e) {
// handle error
} finally {
Util.closeStream(is);
}
Not a lot else to do as the IOException in the catch might have some specific processing.
See this question, use the closeQuietly() solution.
InputStream is = null;
try {
is = url.openConnection().getInputStream();
// .....
} catch (IOException e) {
// handle error
} finally {
IoUtils.closeQuietly(is);
}
// stolen from the cited question above
public class IoUtils {
public static closeQuietly (Closeable closeable) {
try {
closeable.close();
} catch (IOException logAndContinue) {
...
}
}
}
Or wait for JDK7's ARM blocks.
You could define something like this somewhere:
private static interface InputStreamCallback {
public void doIt(InputStream is) throws IOException;
}
private void with(InputStreamCallback cb) {
InputStream is = null;
// Creational code. Possibly adding an argument
try {
cb.doIt(is);
} catch (IOException e) {
// handle error or rethrow.
// If rethrow add throws to method spec.
} finally {
if (is != null) {
try {
is.close();
} catch (IOException e) {
// handle error or rethrow.
}
}
}
}
And invoke your code like this:
with(new InputStreamCallback() {
#Override
public void doIt(InputStream is) throws IOException {
is = url.openConnection().getInputStream();
// .....
}
});
If you declare with method static in a helper class, then you could even do an import static of it.
There's a drawback. You need to declare url final.
EDIT: creational code is not the point. You can arrange it in several ways. The callback is the point. You could isolate what you need to do there.