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Information Technology
06 Feb 2019

How to replace specific string in text file in java?

We are defining one method called modifyFile(). This method reads all the content of input text file into a String object, replaces the old string with new string and rewrites the new content back into the same file. It takes three arguments : Path of the file to be modified – filepath, string to be replaced – oldString and string to be replaced with – newString. Let’s see how this method works step by step.

Step 1 : Create a File object by passing the path of the file to be modified.

File fileToBeModified = new File(filePath)

Step 2 : Initialize oldContent with an empty string. This String object will hold all the old content of the input text file.

String oldContent = “”

Step 3 : Create BufferedReader object to read the input text file line by line.

BufferedReader reader = new BufferedReader(new FileReader(fileToBeModified))

Step 4 : Read all the lines of input text file one by one and append it to oldContent.

String line = reader.readLine();

 while (line != null) 
        oldContent = oldContent + line + System.lineSeparator();
        line = reader.readLine();

Step 5 : Replace all the occurrences of oldString with newString using replaceAll() method. You will get a newContent.

String newContent = oldContent.replaceAll(oldString, newString)

Step 6 : Now create FileWriter object to write newContent back into the input text file fileToBeModified.

FileWriter writer = new FileWriter(fileToBeModified)

Step 7 : Rewrite the fileToBeModified with newContent using write() method of FileWriter object.

Step 8 : Close the resources.