I have this simple code that processes files in a designated folder.
processLog method throws IOException, when this happens I would like to exit (no need to continue processing rest of the files) but sadly I have to catch the exception locally.
try (Stream<Path> filePathStream = Files.walk(Paths.get(logs))){
filePathStream.forEach(filePath -> {
if (Files.isRegularFile(filePath)) {
processLog(filePath.toFile());
}
});
}
Any idea how I can break the loop? Thanks.
If you want to use a Stream specifically, you could do this:
import java.io.IOException;
import java.util.Arrays;
public class Eg {
public static void main(String[] args) {
int[] numbers = new int[] {1,2,3,4,5,6,7,8};
Arrays.stream(numbers).takeWhile(i -> process(i)).forEach(b ->{});
}
private static boolean process(int i) {
try {
if (i == 6) {
throw new IOException();
}
System.out.println("processed " + i);
return true;
} catch (IOException e) {
System.out.println("failed on " + i);
return false;
}
}
}
The final empty forEach is to force the Stream to be run. You could return a different type if there was something you wanted to do with the results of processing the files.
I think the easiest/cleanest solution is to convert the Stream to an Iterator. Then you can use a "normal" loop which can throw a checked exception. For example:
try (Stream<Path> filePathStream = Files.walk(Paths.get(logs))) {
// you can filter here instead of in an 'if' block later
Iterator<Path> itr = filePathStream.filter(Files::isRegularFile).iterator();
while (itr.hasNext()) {
processLog(itr.next().toFile());
}
} catch (IOException ex) {
// you've now stopped processing
// do something with 'ex'...
}
try (Stream<Path> filePathStream = Files.walk(Paths.get(logs))){
filePathStream.forEach(filePath -> {
if (Files.isRegularFile(filePath))
processLog(filePath.toFile());
});
}catch (IOException e){
e.printStackTrace();
}
Add just catch to get the exception, forEach will stop when processLog throw the Exception
My last answer was wrong.
Similar question has been asked before.
Related
I have to read a file in try block and later print it out. While the print method is working, the program is not running the method. How do I solve this? I can't keep it in the while loop.
Lexer.java
private boolean atEOF = false;
private SourceReader source;
public static void main(String args[]) {
Token token;
try {
Lexer lex = new Lexer(args[0]);
while(!(lex.atEOF)) {
token = lex.nextToken();
}
lex.source.printVec(); // WANT TO EXECUTE THIS METHOD
} catch (Exception e) {
System.out.println("usage: java lexer.Lexer filename.x");
System.exit(-1);
}
}
SourceReader.java
public void printVec() {
System.out.println("in the program");
for (String l : progVec) {
System.out.println(l);
}
}
How do I run printVec() after the while loop in Lexer.java?
I would simply declare the Lexer outside of the try-catch block then put the required Function at the first line of the catch part too.
Lexer lex;
try {
lex = new Lexer(args[0]);
while(!(lex.atEOF)) {
token = lex.nextToken();
}
lex.source.printVec();
} catch (Exception e) {
lex.source.printVec();
//... rest of code
}
I've created a Flowable (RxJava v3) that parses a file. I'd like it to support backpressure. This is important because the files can be quite large, and I don't want them to be loaded into memory at once. Here is my first attempt:
public Flowable<Byte> asFlowable(InputStream is) {
return Flowable.create(new FlowableOnSubscribe<Byte>() {
#Override
public void subscribe(FlowableEmitter<Byte> emitter) throws Exception {
try (DataInputStream inputStream = new DataInputStream(is)){
if (inputStream.readInt() != SOME_CONSTANT) {
throw new IllegalArgumentException("illegal file format");
}
if (inputStream.readInt() != SOME_OTHER_CONSTANT) {
throw new IllegalArgumentException("illegal file format");
}
final int numItems = inputStream.readInt();
for(int i = 0; i < numItems; i++) {
if(emitter.isCancelled()) {
return;
}
emitter.onNext(inputStream.readByte());
}
emitter.onComplete();
} catch (Exception e) {
emitter.onError(e);
}
}
}, BackpressureStrategy.BUFFER);
}
The reason I used Flowable.create instead of Flowable.generateis because I need to validate the file, and throw errors if some magic numbers at the beginning of the file are wrong or not found. This didn't fit well with the Flowable.generate lambdas (but if you know of a better way please post it).
Ok let's assume the cold Flowable supported backpressure. Now I'd like to process it in a console-like application.
Question:
I want to request a new Byte from the Flowable and print it to console each time the user presses space (similar to what more or less do in Linux). What would the best way of doing it? I intend to observe the flowable directly in the public static void main method, since I need to read and write using the console.
I've been reading the Backpressure section in RxJAva's Wiki and found this snippet:
someObservable.subscribe(new Subscriber<t>() {
#Override
public void onStart() {
request(1);
}
#Override
public void onCompleted() {
// gracefully handle sequence-complete
}
#Override
public void onError(Throwable e) {
// gracefully handle error
}
#Override
public void onNext(t n) {
// do something with the emitted item "n"
// request another item:
request(1);
}
});
But this confused me even more as the request method doesn't seem to exist in RxJava 3.
Use generate, blockingSubscribe and read a line from the console:
class State {
DataInputStream inputStream;
int count;
int i;
}
BufferedReader bin = new BufferedReader(new InputStreamReader(System.in));
Flowable.generate(() -> {
State s = new State();
s.inputStream = new DataInputStream(is);
try {
if (s.inputStream.readInt() != SOME_CONSTANT) {
throw new IllegalArgumentException("illegal file format");
}
if (s.inputStream.readInt() != SOME_OTHER_CONSTANT) {
throw new IllegalArgumentException("illegal file format");
}
s.count = s.inputStream.readInt();
} catch (IOException ex) {
s.inputStream.close();
throw ex;
}
return s;
}, (state, emitter) -> {
if (state.i < s.count) {
emitter.onNext(state.inputStream.readByte());
s.i++;
}
if (state.i >= s.count) {
emitter.onComplete();
}
}, state -> {
state.inputStream.close();
})
.subscribeOn(Schedulers.io())
.blockingSubscribe(b -> {
System.out.println(b);
bin.readLine();
}, Flowable.bufferSize());
I'm writing a program in order to keep track of DVDs in my library. I'm having trouble altering the text file that saves an added or removed DVD object from the arraylist. Whenever I call my save method, which is the one that overwrites the existing text file holding all the information, it will not change it whatsoever. My add and remove methods work fine but it's just the save method which overwrites the file that I'm reading from that will not work. The following code is what I was attempting to use to save the arraylist to the file. My filename is DVDCollection.txt and the boolean variable flag is a static variable used to check whether or not the code which adds or removes an object from the arraylist was reached.
public void save() {
try{
if(flag=true){
FileWriter instream = new FileWriter("DVDCollection.txt",false);
instream.close();
}else{
return;
}
}catch(IOException e){
System.out.println("The file could not be written to!");
}
}
If you are using java 8 or above it's as simple as:
List<String> lines = Arrays.asList("first line", "second line");
try {
Files.write(Paths.get("my-file.txt"), lines);
} catch (IOException e) {
//handle exception
}
Make sure you provide the right path!
Not sure, why this method should save an array list, as the actual code that writes to this file is missing. Here is simple test, let's start here:
import java.io.*;
import java.util.*;
public class FileSaveTest {
public static void main(String[] args) {
FileSaveTest test = new FileSaveTest();
test.fill();
test.save();
}
public void fill() {
arrayList.add("My disc 1");
arrayList.add("My disc 2");
arrayList.add("Another disc");
}
public void save() {
try {
if(flag) { // you dont need ==true
FileWriter instream = new FileWriter("DVDCollection.txt",false);
for (String entry : arrayList) {
instream.write(entry + "\n");
}
instream.close();
} else {
return;
}
} catch(IOException e) {
System.out.println("The file could not be written to!");
}
}
private ArrayList<String> arrayList = new ArrayList<>();
private static boolean flag = true;
}
Next, it's not very good, to close the file in such manner. If an exception occurs while writing, the file will not be closed. instream.close() should be put into the "finally" block. This block will be executed in any case, regardless of whether an exception occurred or the return keyword met:
public void save() {
Writer instream = null;
try {
if(flag) { // you dont need ==true
instream = new FileWriter("DVDCollection.txt",false);
for (String entry : arrayList) {
instream.write(entry + "\n");
}
} else {
return;
}
} catch(IOException e) {
System.out.println("The file could not be written to!");
} finally {
try {
if (instream != null)
instream.close();
} catch (IOException e) {
System.err.println("Exception during close");
}
}
}
Or, if you are using java 7, you can use try-with-resources syntax:
public void save() {
if(flag) { // you dont need ==true
try (Writer instream = new FileWriter("DVDCollection.txt",false)) {
for (String entry : arrayList)
instream.write(entry + "\n");
} catch(IOException e) {
System.out.println("The file could not be written to!");
}
} // you dont need "return else { return; }" anymore
}
This question already has answers here:
why does the catch block give an error with variable not initialized in Java
(7 answers)
Closed 6 years ago.
So, I'm working on a project that automates everything from character sheets to dice rolls for a table top RPG I like to play. I'm trying to store character data (character name, 2 arrays of stats, and 2 arrays of those stat values) that can be accessed at the start of executing the app. This has been very helpful so far.
However, I'd also like to display the name and stats so the user can confirm that this is the character data they want to use. And I'm having trouble displaying the data in a readable format. Here's my code (you'll find the problem I'm having toward the bottom, although if you see anything else that could be optimized along the way, I would appreciate any feedback :-)":
import java.io.*;
import javax.swing.JOptionPane;
public class fengShuiFiles implements Serializable {//start class
private FileOutputStream outFile;
private ObjectOutput objectWriter;
private FileInputStream inFile;
private ObjectInputStream objectReader;
public void WriteFile(String fileNameIn, String[] sArray1, String[] sArray2,
String[] sArray3, String[] sArray4) {
try {
outFile = new FileOutputStream(fileNameIn + ".txt", true);
objectWriter = new ObjectOutputStream(outFile);
objectWriter.writeObject(sArray1);
objectWriter.writeObject(sArray2);
objectWriter.writeObject(sArray3);
objectWriter.writeObject(sArray4);
} catch (IOException e) {
JOptionPane.showMessageDialog(null, "I/O occurred during a write operation\nFor more",
"information see console output.",
"Read File", JOptionPane.ERROR_MESSAGE);
e.printStackTrace();
} // End try/catch
} // End Open
//not sure if I'll need this. Keeping it for now just in case
//public void writeRecords(String textRecords)
//{
// outFile.close();
// pw.println(textRecords);
//} // End WriteRecords
public void ReadFile(String fileNamein) throws FileNotFoundException {
fengShuiFiles[] sArray1, sArray2, sArray3, sArray4;
try {
inFile = new FileInputStream(fileNamein + ".txt");
objectReader = new ObjectInputStream(inFile);
sArray1 = (fengShuiFiles[]) objectReader.readObject();
sArray2 = (fengShuiFiles[]) objectReader.readObject();
sArray3 = (fengShuiFiles[]) objectReader.readObject();
sArray4 = (fengShuiFiles[]) objectReader.readObject();
} catch (IOException | ClassNotFoundException e) {
JOptionPane.showMessageDialog(null, "I/O error occurred opening a",
"file\nFor more information see console output.",
"Read File", JOptionPane.ERROR_MESSAGE);
e.printStackTrace();
} // End try/catch
for (int x = 0; x < sArray1.length; x++) {
}
}
public void closeFile() {
try {
outFile.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} // End closeFile
}//end class
So, that sArray1.length in the for statement toward the bottom? It's coming up with an error message saying that sArray1 may not have been initialized. And I'm having trouble figuring out why, and how I can get that length so I can print out the arrays in a readable manner. Does anyone have any ideas? Thanks.
You need to initialize local variables. If an exception occurs, it's possible that some or all of the arrays aren't initialized and the compiler won't allow that.
The easiest way to get rid of the error is to initialize the arrays to null, but your program has a logic problem. You're catching the exceptions and continuing, even though there's no way your program can work correctly after that. You should instead throw the exceptions out of the readFile() method and then most likely exit the program. You could also continue as if the file didn't exist, but at least show a warning about it.
You always have to initialize variables in java. You do this in your try block, but if an exception occurs, the array will not have been initialized.
You can move the for loop to the try block:
public void ReadFile(String fileNamein) throws FileNotFoundException {
fengShuiFiles[] sArray1, sArray2, sArray3, sArray4;
try {
...
for(int x = 0; x < sArray1.length; x++) {
}
} catch (IOException | ClassNotFoundException e) {
...
} // End try/catch
}
Or use a default value to initialize the array in the catch block:
public void ReadFile(String fileNamein) throws FileNotFoundException {
fengShuiFiles[] sArray1, sArray2, sArray3, sArray4;
try {
...
} catch (IOException | ClassNotFoundException e) {
...
sArray1 = new fengShuiFiles[0]; // Some default value.
} // End try/catch
for(int x = 0; x < sArray1.length; x++) {
}
}
Something that might be more convenient though, is to return the read arrays, and do something with them in the calling method.
For instance:
public Optional<fengShuiFiles[][]> ReadFile(String fileNamein) throws FileNotFoundException {
try {
fengShuiFiles[] sArray1, sArray2, sArray3, sArray4;
// read the file
return Optional.of(new fenShuiFiles[][]{ sArray1, sArray2, sArray3, sArray4 });
} catch (IOException | ClassNotFoundException e) {
...
return OPtional.empty();
}
}
Then in some other method:
Optional<fengShuiFiles[][]> ret = ReadFile(...);
if(ret.isPresent()) {
for(fengShuiFiles[] arr : ret.get()) {
System.out.println(Arrays.toString(arr)); // Print here
}
}
I have to send a set of files to several computers through a certain port. The fact is that, each time that the method that sends the files is called, the destination data (address and port) is calculated. Therefore, using a loop that creates a thread for each method call, and surround the method call with a try-catch statement for a BindException to process the situation of the program trying to use a port which is already in use (different destination addresses may receive the message through the same port) telling the thread to wait some seconds and then restart to retry, and keep trying until the exception is not thrown (the shipping is successfully performed).
I didn't know why (although I could guess it when I first saw it), Netbeans warned me about that sleeping a Thread object inside a loop is not the best choice. Then I googled a bit for further information and found this link to another stackoverflow post, which looked so interesting (I had never heard of the ThreadPoolExecutor class). I've been reading both that link and the API in order to try to improve my program, but I'm not yet pretty sure about how am I supposed to apply that in my program. Could anybody give a helping hand on this please?
EDIT: The important code:
for (Iterator<String> it = ConnectionsPanel.list.getSelectedValuesList().iterator(); it.hasNext();) {
final String x = it.next();
new Thread() {
#Override
public void run() {
ConnectionsPanel.singleAddVideos(x);
}
}.start();
}
private static void singleAddVideos(String connName) {
String newVideosInfo = "";
for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
newVideosInfo = newVideosInfo.concat(it.next().toString());
}
try {
MassiveDesktopClient.sendMessage("hi", connName);
if (MassiveDesktopClient.receiveMessage(connName).matches("hello")) {
MassiveDesktopClient.sendMessage(newVideosInfo, connName);
}
} catch (BindException ex) {
MassiveDesktopClient.println("Attempted to use a port which is already being used. Waiting and retrying...", new Exception().getStackTrace()[0].getLineNumber());
try {
Thread.sleep(MassiveDesktopClient.PORT_BUSY_DELAY_SECONDS * 1000);
} catch (InterruptedException ex1) {
JOptionPane.showMessageDialog(null, ex1.toString(), "Error", JOptionPane.ERROR_MESSAGE);
}
ConnectionsPanel.singleAddVideos(connName);
return;
}
for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
try {
MassiveDesktopClient.sendFile(it.next().getAttribute("name"), connName);
} catch (BindException ex) {
MassiveDesktopClient.println("Attempted to use a port which is already being used. Waiting and retrying...", new Exception().getStackTrace()[0].getLineNumber());
try {
Thread.sleep(MassiveDesktopClient.PORT_BUSY_DELAY_SECONDS * 1000);
} catch (InterruptedException ex1) {
JOptionPane.showMessageDialog(null, ex1.toString(), "Error", JOptionPane.ERROR_MESSAGE);
}
ConnectionsPanel.singleAddVideos(connName);
return;
}
}
}
Your question is not very clear - I understand that you want to rerun your task until it succeeds (no BindException). To do that, you could:
try to run your code without catching the exception
capture the exception from the future
reschedule the task a bit later if it fails
A simplified code would be as below - add error messages and refine as needed:
public static void main(String[] args) throws Exception {
ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(corePoolSize);
final String x = "video";
Callable<Void> yourTask = new Callable<Void>() {
#Override
public Void call() throws BindException {
ConnectionsPanel.singleAddVideos(x);
return null;
}
};
Future f = scheduler.submit(yourTask);
boolean added = false; //it will retry until success
//you might use an int instead to retry
//n times only and avoid the risk of infinite loop
while (!added) {
try {
f.get();
added = true; //added set to true if no exception caught
} catch (ExecutionException e) {
if (e.getCause() instanceof BindException) {
scheduler.schedule(yourTask, 3, TimeUnit.SECONDS); //reschedule in 3 seconds
} else {
//another exception was thrown => handle it
}
}
}
}
public static class ConnectionsPanel {
private static void singleAddVideos(String connName) throws BindException {
String newVideosInfo = "";
for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
newVideosInfo = newVideosInfo.concat(it.next().toString());
}
MassiveDesktopClient.sendMessage("hi", connName);
if (MassiveDesktopClient.receiveMessage(connName).matches("hello")) {
MassiveDesktopClient.sendMessage(newVideosInfo, connName);
}
for (Iterator<Video> it = ConnectionsPanel.videosToSend.iterator(); it.hasNext();) {
MassiveDesktopClient.sendFile(it.next().getAttribute("name"), connName);
}
}
}