Creating a file using FileOutputStream - GeeksforGeeks

22 Dec, 2016
FileOutputStream class belongs to byte stream and stores the data in the form of individual bytes. It can be used to create text files. A file represents storage of data on a second storage media like a hard disk or CD. Whether or not a file is available or may be created depends upon the underlying platform. Some platforms, in particular, allow a file to be opened for writing by only one FileOutputStream (or other file-writing objects) at a time. In such situations, the constructors in this class will fail if the file involved is already open.
FileOutputStream is meant for writing streams of raw bytes such as image data. For writing streams of characters, consider using FileWriter.
Important methods:
void close() : Closes this file output stream and releases any system resources associated with this stream.
protected void finalize() : Cleans up the connection to the file, and ensures that the close method of this file output stream is called when there are no more references to this stream.
void write(byte[] b) : Writes b.length bytes from the specified byte array to this file output stream.
void write(byte[] b, int off, int len) : Writes len bytes from the specified byte array starting at offset off to this file output stream.
void write(int b) : Writes the specified byte to this file output stream.
Following steps are to be followed to create a text file that stores some characters (or text):
Reading data: First of all, data should be read from the keyboard. For this purpose, associate the keyboard to some input stream class. The code for using DataInputSream class for reading data from the keyboard is as:DataInputStream dis =new DataInputStream(System.in);Here System.in represent the keyboard which is linked with DataInputStream objectSend data to OutputStream: Now , associate a file where the data is to be stored to some output stream. For this , take the help of FileOutputStream which can send data to the file. Attaching the file.txt to FileOutputStream can be done as:FileOutputStream fout=new FileOutputStream(“file.txt”);Reading data from DataInputStream: The next step is to read data from DataInputStream and write it into FileOutputStream . It means read data from dis object and write it into fout object, as shown here:ch=(char)dis.read();
fout.write(ch);Close the file: Finally, any file should be closed after performing input or output operations on it, else the data of the may be corrupted. Closing the file is done by closing the associated streams. For example, fout.close(): will close the FileOutputStream ,hence there is no way to write data into the file.
Reading data: First of all, data should be read from the keyboard. For this purpose, associate the keyboard to some input stream class. The code for using DataInputSream class for reading data from the keyboard is as:DataInputStream dis =new DataInputStream(System.in);Here System.in represent the keyboard which is linked with DataInputStream object
DataInputStream dis =new DataInputStream(System.in);
Here System.in represent the keyboard which is linked with DataInputStream object
Send data to OutputStream: Now , associate a file where the data is to be stored to some output stream. For this , take the help of FileOutputStream which can send data to the file. Attaching the file.txt to FileOutputStream can be done as:FileOutputStream fout=new FileOutputStream(“file.txt”);
FileOutputStream fout=new FileOutputStream(“file.txt”);
Reading data from DataInputStream: The next step is to read data from DataInputStream and write it into FileOutputStream . It means read data from dis object and write it into fout object, as shown here:ch=(char)dis.read();
fout.write(ch);
ch=(char)dis.read();
fout.write(ch);
Close the file: Finally, any file should be closed after performing input or output operations on it, else the data of the may be corrupted. Closing the file is done by closing the associated streams. For example, fout.close(): will close the FileOutputStream ,hence there is no way to write data into the file.
Implementation:
//Java program to demonstrate creating a text file using FileOutputStreamimport java.io.BufferedOutputStream;import java.io.DataInputStream;import java.io.FileOutputStream;import java.io.IOException;class Create_File{    public static void main(String[] args) throws IOException     {        //attach keyboard to DataInputStream        DataInputStream dis=new DataInputStream(System.in);          // attach file to FileOutputStream        FileOutputStream fout=new FileOutputStream("file.txt");          //attach FileOutputStream to BufferedOutputStream        BufferedOutputStream bout=new BufferedOutputStream(fout,1024);        System.out.println("Enter text (@ at the end):");        char ch;          //read characters from dis into ch. Then write them into bout.        //repeat this as long as the read character is not @        while((ch=(char)dis.read())!='@')        {            bout.write(ch);        }        //close the file        bout.close();    }}
If the Program is executed again, the old data of file.txt will be lost and any recent data is only stored in the file. If we don’t want to lose the previous data of the file, and just append the new data to the end of already existing data, and this can be done by writing true along with file name.
FileOutputStream fout=new FileOutputStream(“file.txt”,true);

Improving Efficiency using BufferedOutputStream
Normally, whenever we write data to a file using FileOutputStream as:
fout.write(ch);
Here, the FileOutputStream is invoked to write the characters into the file. Let us estimate the time it takes to read 100 characters from the keyboard and write all of them into a file.
Let us assume data is read from the keyboard into memory using DataInputStream and it takes 1 sec to read 1 character into memory and this character is written into the file by FileOutputStream by spending another 1 sec.
So for reading and writing a file will take 200 sec. This is wasting a lot of time. On the other hand, if Buffered classed are used, they provide a buffer which is first filled with characters from the buffer which can be at once written into the file. Buffered classes should be used in connection to other stream classes.
First, the DataInputStream reads data from the keyboard by spending 1 sec for each character. This character is written into the buffer. Thus, to read 100 characters into a buffer, it will take 100 second time. Now FileOutputStream will write the entire buffer in a single step. So, reading and writing 100 characters took 101 sec only. In the same way, reading classes are used for improving the speed of reading operation.  Attaching FileOutputStream to BufferedOutputStream as:BufferedOutputStream bout=new BufferedOutputStream(fout,1024);Here ,the buffer size is declared as 1024 bytes. If the buffer size is not specified , then a default size of 512 bytes is used
BufferedOutputStream bout=new BufferedOutputStream(fout,1024);
Here ,the buffer size is declared as 1024 bytes. If the buffer size is not specified , then a default size of 512 bytes is used
Important methods of BufferedOutputStream Class:
void flush() : Flushes this buffered output stream.
void write(byte[] b, int off, int len) : Writes len bytes from the specified byte array starting at offset off to this buffered output stream.
void write(int b) : Writes the specified byte to this buffered output stream.
Output:
C:\> javac Create_File.java
C:\> java Create_File
Enter text (@ at the end):
This is a program to create a file
@

C:/> type file.txt
This is a program to create a file

Related Articles:
CharacterStream vs ByteStream
File Class in Java
File handling in Java using FileWriter and FileReader
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