Philip Grove wrote: Reading multiple files regardless of format is perfectly doable, you just have to make sure not to overwrite "old" data when reading new files.
Using StringTokenizer is strongly discouraged, it's a legacy class retained for compatability reasons. Look into the split methods of String or the java. While regular expressions might be difficult at first, and more so in Java as they don't use the standard POSIX syntax, it's a very powerful tool. If you want a object doing the splitting, then look at the Scanner class of the java. Forum: Java in General.
Reading multiple CSV files. Akil Kumar. The purpose behind this is to create a mock dataset for the client. Is it possible to read multiple CSV files and update the client with different data sets?
Right now I use buffered reader and file reader to read the file and String Tokenizer to read the individual tokens within the file. Can anyone tell if the above scenario is possible? Philip Grove. I like Reading multiple files regardless of format is perfectly doable, you just have to make sure not to overwrite "old" data when reading new files.
Joe Areeda. The different tokenizers are fine if the data is simple but if you're dealing with spreadsheets or databases it can get complicated. What are concerned about? It's not what your program can do, it's what your users do with the program. Hello, Thanks for the reply.
I have the following code to read the CSV file. Can you explain what you are saying with some code sample? Do you want loop through all files? My delimiter in this case is space " ".
Ulf Dittmer. I generally advise to use one of the numerous available CSV libraries instead of rolling your own see the AccessingFileFormats page for a list of such libraries.
CSV has features that will break the code you posted. Hey, sticks and stones baby.Burette set usage
And maybe a wee mention of my stuff:. Boost this thread! Transpose matrix. Appending two Multidimensional Arrays together. Reading different file extensions.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.Watery cm bfp
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.
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!67 Java - How to read content of multiple files using SequenceInputStream in java - by Sanjay Gupta
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. 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.
Code Review Stack Exchange is a question and answer site for peer programmer code reviews. It only takes a minute to sign up. 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.
How to Run Multiple Threads Concurrently in Java? ExecutorService Approach
What's the arrow? Also, where is the Runnable? Maybe there is a little syntax error in the code? Please double check. It is complaining the processFolder 's arguments.
It compiles and runs fine. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
Post as a guest Name.Forum Rules. Remember Me? What's New? Results 1 to 12 of Thread: about FileReader and BufferedReader - to read multiple files. For each file, they have their unique data. Every data is in String datatype. I want to get all the data value for all files by writing all filenames lines by lines file My problem is, i want to get every value data from every files and not the file names. Can somebody help me? I hope my text is clear enough because i'm not good in english writing. This is my code; Java Code:.
Your just printing what you are reading in from the first file. Yes, you need to actually read the files once you have their names as ZMan says.Tesla battery investor day 2020
You don't necessarily need to put them into an array though. Java Code:. Originally Posted by pbrockway2. Show us the code you're running, because that shouldn't happen with the code above. Originally Posted by Tolls. Look at pbrockway2's code again. Especially the second BufferedReader That error means it cannot find that file. Since you say that the base file contains a list of filenames that exist, then it clearly doesn't. Replies: 2 Last Post:PM. How to read multiple ZipEntry using single InputStream?
By prasannadavid in forum New To Java. Replies: 5 Last Post:PM. Replies: 1 Last Post:PM. Replies: 4 Last Post:PM.Forum: Threads and Synchronization.
Loading files in parallel using Threads. Niall Loughnane.
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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.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.Nivolas vermelle mappy
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: '. 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 and write multi-threaded file example
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.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.
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