why is bufferedwriter not writing in the file?

问题

Here is the code snippet.

read = new FileReader("trainfiles/"+filenames[i]);
                br = new BufferedReader(read);
                while((lines = br.readLine())!=null){
                    st = new StringTokenizer(lines);
                    while(st.hasMoreTokens()){
                        bw = new BufferedWriter(new FileWriter("files/file.txt"));
                        bw.write(st.nextToken());
                        bw.newLine();
                    }
                }

Edit: I am reading files from a directory. So, I need to open the reader in every loop. I have made some modification, but then also it is not writing to that file. Here is the code:

for(i=0;i==0;i++){
            if(filenames[i].matches(".*ham.*")){
                System.out.println("ham:"+filenames[i]);
                read = new FileReader("trainfiles/"+filenames[i]);
                br = new BufferedReader(read);
                while((lines = br.readLine())!=null){
                    st = new StringTokenizer(lines);
                    while(st.hasMoreTokens()){
                        System.out.println(st.nextToken());
                       bw.write(st.nextToken());
                    }
                }
                bw.close();
                br.close();

            }else{
                System.out.println("spam:"+filenames[i]);
            }
                        }

edit: I modified the code, but no success,

while((lines = br.readLine())!=null){
                    st = new StringTokenizer(lines);
                    bw = new BufferedWriter(new FileWriter("files/file.txt"));
                    while(st.hasMoreTokens()){
                        System.out.println(st.nextToken());
                       bw.write(st.nextToken());
                    }
                    bw.close();
                }

                br.close();

And i am getting this error: Exception in thread "main" java.util.NoSuchElementException at java.util.StringTokenizer.nextToken(StringTokenizer.java:332) at Test.main(Test.java:30)

edit: Thanks guys.. I figured it out. Actually I created an directory in eclipse and I did not refresh it to see the content. Its silly... anyways.thanks a lot

回答1:

You are creating the FileWritter inside the loop so you will always truncate the file in each cycle.
You forgot to close / flush the writter
But with some luck (terminating the program may cause the writter to flush) the file would contain the last word of your input file which I can only guess would be a new line and you probably missed when you opened up the file to check the content.

Your inner loop should be something like this:

try (BufferedWriter bw = new BufferedWriter(new FileWriter("file.txt"))) {
    while (st.hasMoreTokens()) {
        bw.write(st.nextToken());
        bw.newLine();
    }
}

回答2:

A couple of things:

You're creating a new FileWriter each time through the loop, which will truncate the file each time.
BufferedWriter is buffered, and you're never flushing the buffer. You need to either call bw.flush(), or even better, close the writer when done.

回答3:

Ideally you should use following Constructor to create FileWriter,

bw = new BufferedWriter(new FileWriter("files/file.txt",true));

Second parameter, true is for appending the new data. FileWriter will not truncate your previous write.

and your reader will be able to read proper data.

来源：https://stackoverflow.com/questions/4430143/why-is-bufferedwriter-not-writing-in-the-file

标签

java

bufferedwriter