Java read multiple files simultaneously

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Software Engineering Stack Exchange is a question and answer site for professionals, academics, and students working within the systems development life cycle. It only takes a minute to sign up. I'm learning concurrency in Java and went over the tutorials on Oracle website.

While I have understood some of it, a greater portion eludes me.

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I was thinking of a hypothetical problem though it may or may not be a good case of using multiple threads where I have text files and I need to search for a particular word in all of them. If I implement a blocking queue, and I do not want to use a ThreadPool with an executor service:. What I have written may or may not make sense but I'm just a beginner and want to learn more about this as this problem has frequently appeared in programming interviews. Great question! I've written a small example it only uses 6 threads, but can easily be expanded to illustrate how you could read multiple files one thread to read each file and process the data with multiple threads.

So let's begin with the Controller which is basically just the director in charge of creating and managing the other threads. You'll notice that it gives each thread a reference to the queue which allows the threads to do their work - either adding items or removing items from the queue.

You'll also notice that it keeps two collections of threads - one for the producer threads and another for all of the threads. The producer thread collection is used to provide a way for the consumer threads to know whether they should continue to wait for more input. The collection holding all the threads is used to keep the controller from exiting before all producers and consumers have completed their work.

Next, here's the code for the Producer class that will be used to create all of the threads whose job it is to read a single file each. You'll see that the producer reads a specific file line by line and adds those lines to the queue as there is space available by making use of the put method.

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Finally, here is the Consumer class that will be responsible for reading data from the queue and processing it appropriately. Notice that this class does not use the take method. I wrote it this way so that the program would end after processing all the files.

If you want the consumers to stay alive you could replace poll with take along with a few other minor adjustments to the run method like handing the InterruptedException that might occur while waiting for take to return a value.

Here is some sample output from the program. Note that System. I hope this is helpful in illustrating how you could accomplish your task without using ExecutorService. Have fun! Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 3 years, 4 months ago. Active 1 year, 9 months ago. Viewed 17k times. If I implement a blocking queue, and I do not want to use a ThreadPool with an executor service: How should I go about solving this problem thinking algorithmically?

How should I do it if I want to implement the BlockingQueue with a multiple producers, multiple consumers model in mind wherein I have threads to put text file's contents in the BlockingQueue and another to take and search for a particular word in them?

Lii 4 4 silver badges 7 7 bronze badges.Given a set of files, I wanted to see how Python and Java would perform in both single- and multi- threaded environments. As a simple task, I chose to just count up the number of bytes in a given file by manually iterating over the bytes. Essentially—an intentionally non-optimal method of calculating the file size.

Java is usually faster than Python, but I was surprised to see that for this task, Python significantly faster. My test for this was to read approximately MB worth of data spread across 18 files on my MacBook Pro Intel i7 2. In Python, the code is much more concise. We use os. But if your using a rotational hard drive, reads are going to be moving only one head over the disk platter anyways, so creating all the threads just to get file size by reading files one byte at a time after forking a bunch of threads which is time consuming.

Thanks for the feedback! As you point out, there are much better ways to do that. Your email address will not be published.

List; import java. ArrayList; import java. IOException; import java. File; import java. FileReader; import java. FileInputStream; import java. Tagged on: concurrencyfileiojavaparallelperformancepython. Leave a Reply Cancel reply Your email address will not be published.It was introduced with the Java 1. NIO related questions are very popular in java interviews now-a-days.

In this post, I am showing a couple of ways to read a file from file system. So lets start them by first showing old famous approach first, so that we can see what really changed. It uses a BufferedReader object for reading. Another way can be using InputStream implementation. All above techniques will read the content of file and print it to console.

You can do whatever you want once you have read it. A family guy with fun loving nature. Love computers, programming and solving everyday problems.

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Will mappedbytebuffer is suggestible and how internally it will work without out of memory. It is size of the region to be mapped. It is not buffer size. Nice examples. When you close the reader it will close the file for you, theoretically you would miss the case when the reader throws an exception in the constructor after the file has opened, but I believe the only exceptions that could occur at that time would be things like out of memory and similar which would forcibly close down your JVM anyways.

java read multiple files simultaneously

I want to divide an xml file according to size using NIO. We can read char or byte only from buffer, so how can i check whether the xml file is proper or not. Brilliant question. I you get any solution, then please update me as well.

java read multiple files simultaneously

You are right. I must have forget to comment that line. Actually both methods are almost similar.Now i want to write to multiple files in the same code let us say 2 files. Do i need to define a new object other than fostream to write to another file out2. I will try to explain it through a code perhaps:.

You are confusing variables and objects. Variables just contain references pointers to an object. You create new FileWriter and BufferedWriter objects each time. Because you only use one at a time it's perfectly OK to re-use the same variables to refer to those objects. And if you're not using Java 7 then you should be!

I have a parent file containig data alongwith dates. I am trying to sort my data into 12 files, one for each month. Therefore i am trying to create 12 output stream objects for each file. I will read the data from the parent file and will keep on writing the data in the corresponding file using the given output stream object for that file. My code says: '.

java read multiple files simultaneously

This is always an option if nothing works out. Most of the people posting in this forum are newbies, so please don't worry about asking questions!

I am using the following code to write to the file out1. Answered by JamesCherrill 4, in a post from 6 Years Ago. Jump to Post. Edited 6 Years Ago by JamesCherrill. Where am i going wrong?

java read multiple files simultaneously

When you pass an array as a parameter you just use its name, you do not append a []. I am a newbie so please don't mind asking these kinds of doubts. Getting Started: Have something to contribute to this discussion? Please be thoughtful, detailed and courteous, and adhere to our posting rules. Edit Preview. H1 H2. Post Reply. Insert Code Block. Share Post. Permanent Link.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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Java read and write multi-threaded file example

In this code, FolderProcessor implements 1and DocProcessor implements 2. Is there any flaw in this implementation? My testing seems to show that 2 works and reduces time a lot, but 1 doesn't really reduce the processing time. This is why you're not seeing any benefits from parallelism; you're processing subfolders within the same thread! But even so, you'd be making a new ExecutorService each invocation; pool should be a class-level field:. After running some tests, I noticed that your path resolution is broken; the path separator isn't being added for subpaths!

You can use all the operating system's rules by switching to Path s:. While your current usage ensures that it is, you may want to put in a check down the line. Since we're missing the meat of the method the contents of the for loopit's hard to make too many recommendations. I am concerned with the shift in naming convention Java uses camelCaseand the lack of checking for errors in file creation. Also, you create a file and discard it as soon as you've made your checks, when you could save the FileWriter some work by passing it along.

I assumed you wanted the typo fixed. There's not much else to say about this class, since all the logic is either tied up in a class we can't see TextThread or omitted.

I will say that if you're running this method in parallel, you're going to be creating an ExecutorService for each invocation, possibly creating hundreds of threads. A shared ExecutorServicecould be static, but preferably a final instance variable would be a better solution. You probably want to use Executors. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Processing files in directories with multithreading Ask Question.

Asked 2 years, 9 months ago. Active 2 years, 9 months ago. Viewed 9k times. Active Oldest Votes. DocumentWriter Since we're missing the meat of the method the contents of the for loopit's hard to make too many recommendations. Other Notes You probably want to use Executors. What's the arrow?Forum: Threads and Synchronization.

Loading files in parallel using Threads. Niall Loughnane. Paul Clapham. I like Steve Luke. The limit usually comes with the throughput and read-heads on the disk s involved. If the files are all stored in a single disk, and that disk only has a single read-head then you will likely take longer to read using multiple threads than just one as there would be more time for the read-head spent seeking to a file required for a particular thread.

If you have the files on multiple hard disks, or the files are stored on a RAID with multiple disks and a controller that supports parallel reads, then you can take advantage of multiple threads. So depending on your scenario you might consider making the pool of threads available to the Executor configurable so you can tune the system to the available hardware. Hi, and thanks for your answers, what im trying to do is load files on a single PC CPU to load them faster, do you think this is possible?

The number of CPUs doesn't really matter, because from the point of view of a CPU, file access consists almost entirely of waiting for the disk to spin to the right position. So depending on what you do with the data from the file, it's quite likely that even if you could process files from different disks simultaneously you still wouldn't be CPU-bound. However what Steve said about reading multiple files in multiple threads tending to be less useful than you might think, that still applies.

You really won't know until you try it whether using multiple threads speeds things up. William Brogden. Also note that operating system buffering and disk drive electronics buffering sit between your program and the physical disk. Therefore, it is time to experiment! Why not write up your results and let us know what happened so future readers can learn. Men call me Jim. Women look past me to this tiny ad:. Boost this thread! When to use Hashmap synchronized as needed and when to use Concurrent hashmap?

XML Log perfromance. Processing large files.Challenge: Have you ever faced a problem wherein two processes are accessing the same file, one is reading it and the other one is writing in it and one of them mostly the reader process gives error that the file is in use by another process?

To read and write files, we make use of the FileStream Class. Next, there are Enumerators defined that contain specific flags, which we need to select appropriately in the constructor of FileStream Class, so that the FileStream Object will act accordingly. The Enumerators are: 1. Now, what to do in case you have two processes doing the write and read operations concurrently?? Next, what matters is the FileShare given to both the processes, you should give ReadWrite Share to both — The reader as well as the writer process — so that they are at the same level.

How to read data from multiple files and write to a single file using SequenceInputStream? - Java IO

Ok, enough of concept now, Lets look at some code. Sample Code:. I was thinking of writing this article since a long time, but did not write it because didnt want to make it a theoritical article.

And this guy gave me a superb piece of code that you see above. Well, I gotto say one thing for Yogesh that he is the fastest developer I have ever seen. Happy Concurrent File Accessing! Varun Shringarpure, a developer by passion and profession, staying updated with tools, technology and gadgets is his fashion. He has a decade of experience working on Sitecore and has been working on it since Sitecore 6.

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Views about Sitecore and Technology on this blog Sitecore Endeavor are my own. View all posts by Varun. I had forgotten how to open files in this mode and File. I searched the Web far and wide, to find out if i could access one single file with two apps one read and one writeand kept getting references to MS Access, How to open two excel files, etc.

Just wanted to let you both know, you made a difference to this amateur in Virginia! You are commenting using your WordPress. You are commenting using your Google account.

3 Ways to Read Files – Java NIO

You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. This site uses Akismet to reduce spam. Learn how your comment data is processed. Skip to content Challenge: Have you ever faced a problem wherein two processes are accessing the same file, one is reading it and the other one is writing in it and one of them mostly the reader process gives error that the file is in use by another process?

FileAccess Read — Gives read access to the file. ReadWrite — Gives both Read as well as Write access to the file. Write — Gives Write access to the file. FileMode Append — If the file exists, opens it, moves to the end of it and adds there, else creates a file. Create — Creates a new file. In case such a file already exists, then overwrites it.

In case such a file already exists, throws in IO Exception.


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