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!
}
}
}
}
}
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;
}
I need to pass some Bitmaps from one activity to another, and, since the size limit of the Bundle won't let me pass these images (even using a byte array*), I thought that I could use a getter method between these Activities.
-But, since I'm still not a master in Android (Java), I don't know if that would make any difference, and, if it does, what should I watch out for when using it.
the byte array did reduce the total size(at about 60%), but it still wasn't enough
scaling down is a way out, but just in case any other solution works
save your object in a file
private void saveDataToFile() {
FileOutputStream fileOutputStream = null;
try {
fileOutputStream = getContext().openFileOutput("fileName", Context.MODE_PRIVATE);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (NullPointerException e) {
}
ObjectOutputStream objectOutputStream = null;
try {
objectOutputStream = new ObjectOutputStream(fileOutputStream);
} catch (IOException e) {
e.printStackTrace();
} catch (NullPointerException e) {
}
try {
if (objectOutputStream != null) {
objectOutputStream.writeObject(yourObject); //which data u want to save
}
} catch (IOException e) {
e.printStackTrace();
}
try {
if (objectOutputStream != null) {
objectOutputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
Retrieve the object from another activity
private void getDataFromFile() {
FileInputStream fileInputStream = null;
try {
fileInputStream = getContext().openFileInput("fileName");
} catch (FileNotFoundException e) {
e.printStackTrace();
return;
}
ObjectInputStream objectInputStream = null;
try {
objectInputStream = new ObjectInputStream(fileInputStream);
} catch (IOException |NullPointerException e) {
e.printStackTrace();
}
try {
yourObject = (ObjectClass) objectInputStream.readObject();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
try {
objectInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
Pass through Uri by writing getter method in POJO class
If you want to use getter setter, just create URI of your bitmap and pass to setter method in POJO class and then retrieve using getter method of POJO class.
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 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
I have following code :
// Read properties file.
Properties properties = new Properties();
try {
properties.load(new FileInputStream("filename.properties"));
} catch (FileNotFoundException e) {
system.out.println("FileNotFound");
}catch (IOException e) {
system.out.println("IOEXCeption");
}
Is it required to close the FileInputStream? If yes, how do I do that? I am getting a bad practice error in my code checklist . Asking it to put finally block.
You must the close the FileInputStream, as the Properties instance will not. From the Properties.load() javadoc:
The specified stream remains open after this method returns.
Store the FileInputStream in a separate variable, declared outside of the try and add a finally block that closes the FileInputStream if it was opened:
Properties properties = new Properties();
FileInputStream fis = null;
try {
fis = new FileInputStream("filename.properties");
properties.load(fis);
} catch (FileNotFoundException e) {
system.out.println("FileNotFound");
} catch (IOException e) {
system.out.println("IOEXCeption");
} finally {
if (null != fis)
{
try
{
fis.close();
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
Use try-with-resources since Java 7:
final Properties properties = new Properties();
try (final FileInputStream fis =
new FileInputStream("filename.properties"))
{
properties.load(fis);
} catch (FileNotFoundException e) {
System.out.println("FileNotFound: " + e.getMessage());
} catch (IOException e) {
System.out.println("IOEXCeption: " + e.getMessage());
}
You should always close your streams, and doing it in the finally block is a good practice. The reason for this is that the finally block always gets executed, and you want to make sure that the stream is always closed, even if Something Bad happens.
FileInputStream inStream = null;
try {
inStream = new FileInputStream("filename.properties");
properties.load(inStream);
} catch (FileNotFoundException e) {
System.out.println("FileNotFound");
} catch (IOException e) {
System.out.println("IOEXCeption");
} finally {
try {
inStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
If you are using Java 7, this becomes much easier, since a new try-with syntax was introduced. Then you can write like this:
try(FileInputStream inStream = new FileInputStream("filename.properties")){
properties.load(inStream);
} catch (FileNotFoundException e) {
System.out.println("FileNotFound");
} catch (IOException e) {
System.out.println("IOEXCeption");
}
and the stream is closed automatically.
here is an example:
public class PropertiesHelper {
public static Properties loadFromFile(String file) throws IOException {
Properties properties = new Properties();
FileInputStream stream = new FileInputStream(file);
try {
properties.load(stream);
} finally {
stream.close();
}
return properties;
}
}
You can use Lombok #Cleanup to do it simply.
http://projectlombok.org/features/Cleanup.html
Properties properties = new Properties();
try {
#Cleanup FileInputStream myFis = new FileInputStream("filename.properties");
properties.load(myFis);
} catch (FileNotFoundException e) {
System.out.println("FileNotFound");
}catch (IOException e) {
System.out.println("IOEXCeption");
}
Or, only if your are using Java 7, there is the "try with resource" new feature.
http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
Properties properties = new Properties();
try (FileInputStream myFis = new FileInputStream("filename.properties")) {
properties.load(myFis);
} catch (FileNotFoundException e) {
System.out.println("FileNotFound");
}catch (IOException e) {
System.out.println("IOEXCeption");
}