Java Program to Append a String in an Existing File

12 Dec, 2021
In Java, we can append a string in an existing file using FileWriter which has an option to open a file in append mode. Java FileWriter class is used to write character-oriented data to a file. It is a character-oriented class that is used for file handling in Java. Unlike FileOutputStream class, we don’t need to convert the string into a byte array because it provides a method to write a string directly. 
Note: The buffer size may be specified, or the default size may be used. A Writer sends its output immediately to the underlying character or byte stream.
Let us see constructors used  later on adhering towards as usual methods of this class 
Constructor: FileWriter(File file, boolean append): 
It Constructs a FileWriter object given a File object in append mode. Now let us toggle onto methods of this class which is invoked here and play a crucial role in appending a string in an existing file as follows:
Method 1: write()
This method writes a portion of a String
Syntax:
void write(String s,int off,int len);
Return Type: Void 
Parameters: 
Input string
int off
String length
Method 2: close()
This method closes the stream after flushing it.
Return Type: Void 
Example 
Java
// Java Program to Append a String to the// End of a File // Importing input output classesimport java.io.*; // Main classclass GeeksforGeeks {     // Method 1    // TO append string into a file    public static void appendStrToFile(String fileName,                                       String str)    {        // Try block to check for exceptions        try {             // Open given file in append mode by creating an            // object of BufferedWriter class            BufferedWriter out = new BufferedWriter(                new FileWriter(fileName, true));             // Writing on output stream            out.write(str);            // Closing the connection            out.close();        }         // Catch block to handle the exceptions        catch (IOException e) {             // Display message when exception occurs            System.out.println("exception occurred" + e);        }    }     // Method 2    // main driver method    public static void main(String[] args) throws Exception    {        // Creating a sample file with some random text        String fileName = "Geek.txt";         // Try block to check for exceptions        try {             // Again operating same operations by passing            // file as            // parameter to read it            BufferedWriter out = new BufferedWriter(                new FileWriter(fileName));             // Writing on. file            out.write("Hello World:\n");             // Closing file connections            out.close();        }         // Catch block to handle exceptions        catch (IOException e) {             // Display message when error occurs            System.out.println("Exception Occurred" + e);        }         // Now appendinggiven str to above        // created file        String str = "This is GeeksforGeeks";         // Calling the above method        appendStrToFile(fileName, str);         // Let us print modified file        try {            BufferedReader in = new BufferedReader(                new FileReader("Geek.txt"));             String mystring;             // TIll there is content in string            // condition holds true            while ((mystring = in.readLine()) != null) {                System.out.println(mystring);            }        }         // Catch block to handle IO exceptions        catch (IOException e) {            System.out.println("Exception Occurred" + e);        }    }}
Output:
solankimayank
prachisoda1234
singghakshay
anikakapoor
java-file-handling
Java-String-Programs
Java
Java Programs
Java
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Object Oriented Programming (OOPs) Concept in Java
How to iterate any Map in Java
Interfaces in Java
HashMap in Java with Examples
Stream In Java
Initializing a List in Java
Java Programming Examples
Convert a String to Character Array in Java
Convert Double to Integer in Java
Implementing a Linked List in Java using Class