How to Read in a Random File Java

Random access file is a special kind of file in Java that allows non-sequential or random admission to any location in the file. This means you don't demand to showtime from 1st line if you want to read line number 10, yous can directly become to line 10 and read. Information technology's similar to the array information structure, Simply like you lot can access any chemical element in the assortment by alphabetize you can read any content from the file past using a file pointer. A random-access file actually behaves like a large array of bytes stored in the file system and that's why information technology's very useful for low latency applications which need some kind of persistence e.k. in front end role trading application and Set Engine, you tin use random access file to shop FIX sequence numbers or all open orders.

This will be handy when you recover from the crash and you need to build your in-retention enshroud to the land just before the crash.  RandomAccessFile provides you the ability to read and write into whatever random access file. When you lot read content from a file, y'all start with the current location of the file arrow, and the arrow is moved forrad past how many bytes are read.

Similarly, when you write information into the random access file, it starts writing from the current location of the file pointer and so advances the file pointer past the number of files written. Random access is achieved by setting a file pointer to whatever arbitrary location using theseek() method.

You can also get the current location by calling thegetFilePointer() method. In that location are ii master ways to read and write information into RandomAccessFile, either you can use Channel similarSeekableByteChannel and ByteBuffer class from Java NIO, this allows you to read information from file to byte buffer or write data from byte buffer to random admission file.

Alternatively you lot tin can besides use various read() and write() method from RandomAccessFile likereadBoolean(), readInt(), readLine() or readUTF().  This is a 2-part Java IO tutorial, in this part, we will learn how to read and write String from RandomAccess file in Java without using Java NIO channels, and in the next part, nosotros will larn how to read bytes using ByteBuffer and Channel API.

And, If you are new to the Java world then I as well recommend you go throughThe Complete Java MasterClasson Udemy to acquire Coffee in a better and more structured fashion. This is ane of the best and upwardly-to-date courses to learn Java online.

How to Read/Write into Random Access File

In order to write data into random access file, you get-go need to create an instance of RandomAccessFile form in reading and write mode. You can do this by passing "rw" as the mode to the constructor. One time y'all accept washed that y'all can either use SeekableByteChannel or seek() method to fix the pointer to a location where y'all desire to write data.

You tin either write bytes using ByteBuffer and Java NIO Channel API or you can write int, float, string, or any other Java data type by using corresponding writeInt(), writeFloat(), and writeUTF() methods.

All these methods are defined in coffee.io.RandomAccessFile class in the Java IO package. When y'all write data that exceeds the current size of the file caused random access file to be extended. For reading data from random access, you can either open up the file into theread-but mode or read write mode.

Just like writing, you lot tin can also perform reading either by using Aqueduct API and ByteBuffer class ( you should if you are using Java NIO ) or traditional methods defined in RandomAccessFile in Coffee. Only like you lot accept different write methods to write different data types yous too take corresponding read methods to read them dorsum.

In society to read from a random location, y'all can use seek() method to set the file pointer to a particular location in the file. Past the way, if the stop of the file is reached before your program reads the desired number of bytes, an EOFException will be thrown. If whatsoever byte cannot be read due to whatsoever other reason then IOException will be thrown.

RandomAccessFile Example in Java

Following is our sample Java program to demonstrate how you can read or write String from a RandomAccessFile. The file name is "sample.store" which will be created in the current directory, usually in your projection directory if yous are using Eclipse IDE.

We have two utility methods to read String from random access file and write a string into a file, both methods take an int location to demonstrate random read and random write operation. In club to write and read String, we will exist using thewriteUTF() and readUTF() method, which reads String in modified UTF-8 format.

Though in this program, I have closed file in the try block, you should e'er do that in a finally block with an additional try block, or better utilize try-with-resource statement from Coffee 7. I will bear witness y'all how you can practise that in the side by side part of this tutorial when we will larn to read and writing byte arrays using ByteBuffer and SeekableByteChannel course.

          import          coffee.io.FileNotFoundException;          import          coffee.io.IOException;          import          java.io.RandomAccessFile;          import          java.nio.ByteBuffer;          import          java.nio.channels.FileChannel;          /** * Java Program to read and write UTF String on RandomAccessFile in Coffee. * *            @author            Javin Paul */          public          class          RandomAccessFileDemo{          public          static          void          main(Cord          args[]) {          String          data          =          "KitKat (four.4 - 4.4.2)";         writeToRandomAccessFile("sample.store", 100, data);          System          .out.println("String written into RandomAccessFile                               from Coffee Plan : "          +          data);          Cord          fromFile          =          readFromRandomAccessFile("sample.store", 100);          System          .out.println("String read from RandomAccessFile in Coffee : "                    +          fromFile);      }          /*      * Utility method to read from RandomAccessFile in Coffee      */          public          static          String          readFromRandomAccessFile(String          file,          int          position) {          Cord          tape          =          cipher;          effort          {          RandomAccessFile          fileStore          =          new          RandomAccessFile(file,          "rw");          // moves file arrow to position specified          fileStore.seek(position);          // reading String from RandomAccessFile          record          =          fileStore.readUTF();              fileStore.shut();          }          grab          (IOException          e) {             e.printStackTrace();         }          return          record;     }          /*     * Utility method for writing into RandomAccessFile in Java     */          public          static          void          writeToRandomAccessFile(String          file,          int          position,          Cord          record) {          attempt          {          RandomAccessFile          fileStore          =          new          RandomAccessFile(file,          "rw");          // moves file pointer to position specified          fileStore.seek(position);          // writing Cord to RandomAccessFile          fileStore.writeUTF(record);              fileStore.close();          }          catch          (IOException          east) {             e.printStackTrace();         }     } }          Output          :          String          written into          RandomAccessFile          from          Coffee          Program          :          KitKat          (4.four          -          4.iv.two)          String          read from          RandomAccessFile          in          Coffee          :          KitKat          (4.4          -          4.four.2)

That's all nearly how to read and write from RandomAccessFile in Java.  Y'all would be surprised that this class is available from JDK ane.0 itself.  It is indeed a very useful class from traditional Java IO API, which was the merely source of doing high-speed IO before Coffee NIO came with the memory-mapped file.

If y'all like this Java IO tutorial and are hungry for more than checkout following tutorials :

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Thank you for reading this Java RandomAccess tutorial so far. If you like this Java NIO tutorial and case so please share information technology with your friends and colleagues. If you have any questions or feedback, please driblet a note.

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Source: https://javarevisited.blogspot.com/2015/02/randomaccessfile-example-in-java-read-write-String.html

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