File Update In Java

We are examining how to update txt – Csv and JSON files in Java with examples.

Table Of Content-

Java File Update – Txt

In java file update, we can replace any word in a txt file at its first occurrence by using the replace() method from the String methods:

Example: 

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import java.io.*;public class Main {
public static void main(String[] args) {
try {
// Read the file into a String
FileReader fr = new FileReader("FirstFile.txt");
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace("Hey", "Greetings");// Write the modified content back to the file
FileWriter fw = new FileWriter("FirstFile.txt");
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
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The same goal can also be achieved by creating a method once and calling it as many time as we want:

Example: 

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import java.io.*;public class Main {public static void replace_word(String match_word,String new_word){
try {
// Read the file into a String
FileReader fr = new FileReader("FirstFile.txt");
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace(match_word,new_word);// Write the modified content back to the file
FileWriter fw = new FileWriter("FirstFile.txt");
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}}
public static void main(String[] args) {
replace_word("Greetings","Hello User");
}
}
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Correspondingly, We can Also replace all the same words in a txt file by matching it with any specific String, using the replaceAll() method from Java Strings.

Example: 

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import java.io.*;public class Main {
public static void main(String[] args) {
try {
// Read the file into a String
FileReader fr = new FileReader("FirstFile.txt");
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replaceAll("we", "you");// Write the modified content back to the file
FileWriter fw = new FileWriter("FirstFile.txt");
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
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In the similar way, we can also create a method to match a string and replace all the corresponding words from the file.

Here we have created a method named replace_word_multiple_times() to replace multiple words in a txt file:

Example: 

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import java.io.*;public class Main {
public static void replace_word_multiple_times(String file_name,String word_match,String new_word){
try {// Read the file into a String
FileReader fr = new FileReader(file_name);
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace(word_match,new_word);// Write the modified content back to the file
FileWriter fw = new FileWriter(file_name);
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}}
public static void main(String[] args) {
replace_word_multiple_times("FirstFile.txt","you","We");
}
}
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Java File Update – CSV

We can also update the content of the .csv file as shown in the examples below.

To modify a word at its first occurrence follow the example below:

Example: 

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import java.io.*;public class Main {
public static void main(String[] args) {
try {
// Read the file into a String
FileReader fr = new FileReader("NewFile.csv");
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace("writing", "declaring");// Write the modified content back to the file
FileWriter fw = new FileWriter("NewFile.csv");
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
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Correspondingly, we can also modify all the same words in a .csv file after matching them all:

Example: 

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import java.io.*;public class Main {
public static void main(String[] args) {
try {
// Read the file into a String
FileReader fr = new FileReader("NewFile.csv");
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replaceAll("we", "you");// Write the modified content back to the file
FileWriter fw = new FileWriter("NewFile.csv");
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
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Now, to do this work more efficiently, let’s make methods named replace_word_multiple_times() and replace_word_single_time() as shown below:

Example: 

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import java.io.*;public class Main {
public static void replace_word_multiple_times(String file_name,String word_match,String new_word) {
try {// Read the file into a String
FileReader fr = new FileReader(file_name);
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace(word_match, new_word);// Write the modified content back to the file
FileWriter fw = new FileWriter(file_name);
fw.write(replace_word);
fw.close();
System.out.println("Replacing all words after matching File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
public static void replace_word_single_time(String file_name,String word_match,String new_word){
try {// Read the file into a String
FileReader fr = new FileReader(file_name);
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace(word_match,new_word);// Write the modified content back to the file
FileWriter fw = new FileWriter(file_name);
fw.write(replace_word);
fw.close();
System.out.println("Word changed at first occurrence File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}}
public static void main(String[] args) {replace_word_single_time("NewFile.csv","Hey","Hey learner ");
replace_word_multiple_times("NewFile.csv","you","We");
}
}
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Java File Update – JSON

We can also update the data of the .json file as shown in the examples below.

To modify a word at its first occurrence follow the example below:

Example: 

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import java.io.*;public class Main {
public static void main(String[] args) {
try {
// Read the file into a String
FileReader fr = new FileReader("NewFile.json");
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace("Java Programming Language", "Java Programming");// Write the modified content back to the file
FileWriter fw = new FileWriter("NewFile.json");
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
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Correspondingly, we can also modify multiple words in a .json file after matching them and then replacing them using replaceAll() method :

Example: 

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import java.io.*;public class Main {
public static void main(String[] args) {
try {
// Read the file into a String
FileReader fr = new FileReader("NewFile.json");
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replaceAll("Java", "_Java_");// Write the modified content back to the file
FileWriter fw = new FileWriter("NewFile.json");
fw.write(replace_word);
fw.close();
System.out.println("File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
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Here, we have create two different methods – One for updating first match word occurrence and second for all match words in a JSON file:

Example: 

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import java.io.*;public class Main {
public static void replace_word_multiple_times(String file_name,String word_match,String new_word) {
try {// Read the file into a String
FileReader fr = new FileReader(file_name);
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace(word_match, new_word);// Write the modified content back to the file
FileWriter fw = new FileWriter(file_name);
fw.write(replace_word);
fw.close();
System.out.println("Replacing all words after matching File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}
}
public static void replace_word_single_time(String file_name,String word_match,String new_word){
try {// Read the file into a String
FileReader fr = new FileReader(file_name);
BufferedReader mrx = new BufferedReader(fr); // helps in efficient reading of data from a file
StringBuilder ample = new StringBuilder(); // less time is taken to read the file
String line;
while ((line = mrx.readLine()) != null) {
ample.append(line);
ample.append(System.lineSeparator());
}
String replace_word = ample.toString();
mrx.close();
fr.close();// Replace the specific word with the new word
replace_word = replace_word.replace(word_match,new_word);// Write the modified content back to the file
FileWriter fw = new FileWriter(file_name);
fw.write(replace_word);
fw.close();
System.out.println("Word changed at first occurrence File updated successfully.");
} catch (IOException e) {
e.printStackTrace();
}}
public static void main(String[] args) {replace_word_single_time("NewFile.json","Developer","Java Developer");
replace_word_multiple_times("NewFile.json","_Java_","Java");
}
}
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Now you know how to update Txt, JSON and Csv files in Java.

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