Develop Reference

Why are two try-catch blocks required for opening and reading a file?

I am trying to read a file but it is asking for two try-catch blocks, one for opening a file and another for reading its content. Why is this required?
String line = null;
try {
File file = new File("F:\\Mobile Extractor.txt");
BufferedReader reader = new BufferedReader(new FileReader(file));
while((line=reader.readLine())!=null) {
System.out.println(line);
}
reader.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

Consider using finally block for avoiding memory leaks and closing the streams if you are using versions before 7. From Java 7 on wards you can use try with resources is the best practice
String line = null;
File file = new File("F:\\Mobile Extractor.txt");
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(file));
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if(reader!=null){
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
Try-with-Resources:
String line = null;
File file = new File("F:\\Mobile Extractor.txt");
try(BufferedReader reader = new BufferedReader(new FileReader(file));) {
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
The declaration statement appears within parentheses immediately after the try keyword. The class BufferedReader, in Java SE 7 and later, implements the interface java.lang.AutoCloseable. Because the BufferedReader instance is declared in a try-with-resource statement, it will be closed regardless of whether the try statement completes normally or abruptly (as a result of the method BufferedReader.readLine throwing an IOException).

Try java8, you will not require anything. You can simply do it like this.
import java.nio.file.Files;
import java.nio.file.Paths;
Files.lines(Paths.get(path))
.filter(l -> l.contains(searchWord)).forEach(System.out::println);

The try-catch block is required for IOException.
It will check for the contents available in the file. If there are no contents, then IOException would be thrown else the contents will be displayed.
It should be like:
String line = null;
try {
File file = new File("F:\\Mobile Extractor.txt");
BufferedReader reader = new BufferedReader(new FileReader(file));
try {
while((line=reader.readLine())!=null)
{
System.out.println(line);
}
} catch(IOException ex)
{
System.out.println(ex.getMessage());
}
reader.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

Why is this not reading in?

I know I'm not doing something correctly. I know the file needs to be Serializable to read a text file.
I've got implements Serializable on the main class. But my readText and my writeText aren't converting.
Nothing is coming in when I read and when I write out the file is not text.
public static ArrayList<String> readText() {
ArrayList<String> read = new ArrayList<String>();
Frame f = new Frame();
FileDialog foBox = new FileDialog(f, "Reading serialized file",
FileDialog.LOAD);
foBox.setVisible(true);
String foName = foBox.getFile();
String dirPath = foBox.getDirectory();
File inFile = new File(dirPath + foName);
BufferedReader in = null;
ObjectInputStream OIS = null;
try {
in = new BufferedReader(new FileReader(inFile));
} catch (FileNotFoundException e1) {
e1.printStackTrace();
}
String line = null;
try {
line = in.readLine();
} catch (IOException e1) {
e1.printStackTrace();
while (line != null) {
try {
FileInputStream IS = new FileInputStream(inFile);
OIS = new ObjectInputStream(IS);
inFile = (File) OIS.readObject();
} catch (IOException io) {
io.printStackTrace();
System.out.println("An IO Exception occurred");
}
catch (ClassNotFoundException cnf) {
cnf.printStackTrace(); // great for debugging!
System.out.println("An IO Exception occurred");
} finally
{
try {
OIS.close();
} catch (Exception e) {
}
}
}
}
return read;
}
public static void writeText(ArrayList<String> file) {
ArrayList<String> write = new ArrayList<String>();
Frame f = new Frame();
FileDialog foBox = new FileDialog(f, "Saving customer file",
FileDialog.SAVE);
foBox.setVisible(true);
String foName = foBox.getFile();
String dirPath = foBox.getDirectory();
File outFile = new File(dirPath + foName);
PrintWriter out = null;
try {
out = new PrintWriter(new BufferedWriter(new FileWriter(outFile)));
for (int i = 0; i < write.size(); i++) {
String w = write.get(i);
out.println(file.toString());
}
}
catch (IOException io) {
System.out.println("An IO Exception occurred");
io.printStackTrace();
} finally {
try {
out.close();
} catch (Exception e) {
}
}
}

Nothing is coming in
You're never calling read.add(line) and you're attempting to read the file within an infinite loop inside of the catch block, which is only entered if you are not able to read the file.
Just use one try block, meaning try to open and read the file at once, otherwise, there's no reason to continue trying to read the file if it's not able to be opened
List<String> read = new ArrayList<>();
try (BufferedReader br = new BufferedReader(new FileReader(inFile)) {
String line = null;
while ((line = in.readLine()) != null) {
read.add(line); // need this
}
} catch (Exception e) {
e.printStackTrace();
}
return read;
Now, whatever you're doing with this serialized object stuff, that's completely separate, and it isn't the file or your main class that needs set to Serializable, it's whatever object you would have used a writeObject method on. However, you're reading and writing String objects, which are already Serializable.
when I write out the file is not text
Not sure what you mean by not text, but if you followed the above code, you'll get exactly what was in the initial file... Anyway, you do not need a write list variable.
You must use the individual lines of ArrayList<String> file parameter instead, but not file.toString()
for (String line:file) {
out.println(line);
}
out.close(); // always close your files and writers

Trying to Continue the program when it returns file not found exception in java

I i am able to read the lines from csv and download the images from url when the url is not having the image it is showing file not found exception in middle of the program i want to continue the program with out terminating.
public static void main(String[] args) throws IOException {
InputStream inputStream = null;
OutputStream outputStream = null;
try {
BufferedReader br = new BufferedReader(new FileReader("D:\\imgdwnld\\file.csv"));
String line = br.readLine();
while ((line = br.readLine()) !=null){
URL url = new URL(line);
inputStream = url.openStream();
outputStream = new FileOutputStream("D:\\imgdwnld\\" +
line.substring(line.lastIndexOf("/")));
byte[] buffer = new byte[2048];
int length;
while ((length = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, length);
}
}
} catch (MalformedURLException e) {
System.out.println("MalformedURLException :- " + e.getMessage());
} catch (FileNotFoundException e) {
System.out.println("FileNotFoundException :- " + e.getMessage());
} catch (IOException e) {
System.out.println("IOException :- " + e.getMessage());
} finally {
try {
inputStream.close();
outputStream.close();
} catch (IOException e) {
System.out.println("Finally IOException :- " + e.getMessage());
}
}
}

This is the relevant outline of your code:
try {
...
while ((line = br.readLine()) !=null) {
... process each CSV line ...
}
} catch (IOException e) {
... handle it ...
}
At the place where you catch the exception you have already broken out of the main loop. Change the code to have this outline:
while ((line = br.readLine()) !=null) {
try {
... process one CSV line ...
} catch (IOException e) {
... handle it, the loop will proceed with the next line
}
}

You need to remove the "return" instruction from the corresponding catch (or maybe from the whole code). In your case, the instruction allows to "exit" the main method so the rest of instruction (those after the return statement) won't be executed.
Another tip is to separate this instructions in blocs. For example, if reading the CSV and the Img are not bound, you may need to encapsulate each treatment in an individual try-catch block. When parsing/reading the CSV file fails, your code may continue fetching the image.

Write Integer Value to a File and Read it

I got a Follower-check function in my twitch.bot and i need a read/write solution for it.
It should do the following:
Read an given Number(int) out of the file
Write a new Number to the file and delete the old one
Create the file if it doesnt exist
(the File needs only to store 1 number)
So how can i do this?
right now, i got a String Reader and as soon as i read it i parse it into an INT but i only got errors so i think it doesnt work that way so im searching an option for writing/reading the int already without parsing it from a string.
import java.io.*;
public class FollowerChecker {
public static StringBuilder sb;
static String readFile(String fileName) throws IOException {
BufferedReader br = new BufferedReader(new FileReader(fileName));
try {
sb = new StringBuilder();
String line = br.readLine();
while (line != null) {
sb.append(line);
sb.append("\n");
line = br.readLine();
}
return sb.toString();
} finally {
br.close();
}
}
public static void Writer() {
FileWriter fw = null;
try {
fw = new FileWriter("donottouch.txt");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
StringWriter sw = new StringWriter();
sw.write(TwitchStatus.totalfollows);
try {
fw.write(sw.toString());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
fw.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

It appears to be way more complicated than it should be. If you just want to write a number without parsing it as text you can do this.
BTW You may as well use a long as it will use the same disk space and store more range.
public static void writeLong(String filename, long number) throws IOException {
try (DataOutputStream dos = new DataOutputStream(new FileOutputStream(filename))) {
dos.writeLong(number);
}
}
public static long readLong(String filename, long valueIfNotFound) {
if (!new File(filename).canRead()) return valueIfNotFound;
try (DataInputStream dis = new DataInputStream(new FieInputStream(filename))) {
return dis.readLong();
} catch (IOException ignored) {
return valueIfNotFound;
}
}

Java: Read/Write a File and more

I made a Class with 2 Methods which should handle either Writing in a file or reading from it.
Ive came up with something like this:
package YBot;
import java.io.*;
public class FollowerChecker {
public static StringBuilder sb;
static String readFile(String fileName) throws IOException {
BufferedReader br = new BufferedReader(new FileReader(fileName));
try {
sb = new StringBuilder();
String line = br.readLine();
while (line != null) {
sb.append(line);
sb.append("\n");
line = br.readLine();
}
return sb.toString();
} finally {
br.close();
}
}
public static void Writer() {
FileWriter fw = null;
try {
fw = new FileWriter("donottouch.txt");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
StringWriter sw = new StringWriter();
sw.write(TwitchStatus.totalfollows);
try {
fw.write(sw.toString());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
fw.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Now My Question is:
How can i add the function to create the "donottouch.txt" file if it doesnt exist already or if its empty to write "0" in it? when my program starts it will read the file for a number and later, if the number is changed it will rewrite it. so it would be the best that as soon it trys to read and its not there, it creates it right then and reread it. hope some1 can give me any examples =)

Here is how I handled it:
public static boolean checkIfExists(String path) {
if (!new File(path).exists()) {
return false;
} else {
return true;
}
}
public static String readFile(String file) throws IOException {
BufferedReader reader = new BufferedReader(new FileReader (file));
String line;
StringBuilder sb = new StringBuilder();
while( ( line = reader.readLine() ) != null) {
sb.append( line );
}
reader.close();
return sb.toString();
}
public static void writeFile(String path) throws FileNotFoundException,
UnsupportedEncodingException {
PrintWriter writer = new PrintWriter(path, "UTF-8");
writer.println("0");
writer.close();
return;
}
public static void main(String args[]) {
/*Gets absolute path to your project folder, assuming that is where
* you are storing this text file. Otherwise hard code your path
* accordingly.
*/
File file = new File("");
String fileGet = file.getAbsolutePath();
StringBuilder sb = new StringBuilder();
String path = sb.append(fileGet.toString() + "/donottouch.txt").toString();
String result=null;
if(!checkIfExists(path)) {
try {
writeFile(path);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
System.out.println("File created: 'donottouch.txt'");
} else {
try {
result = readFile(path);
} catch (IOException e) {
e.printStackTrace();
}
if( result.length() == 0 ) {
try {
writeFile(path);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
System.out.println("File amended: 'donottouch.txt'");
}
System.out.println("File exists: 'donottouch.txt'");
}
}
Obviously I created a main class and did all of this outside of a class, unlike you, but it should be very simple to integrate. It is predicated on the presumption that you are storing your "donottouch.txt" in the source file of the project, however you can easily change the piece of code that grabs your absolute path to the hardcoded path of the folder in which you are looking. Hope this helps!