Replacing a word in a text file

[preethi Ayyappan]

Hi,

I need to check for a particular word from an existing file and need to replace that word with new word.How should i do this? Now i can able to read that particular word from the existing file.But i dont know how to replace that particular word with new word.

Here is my code to read a particular word:

   
import java.io.*;
import java.lang.String;
class Fread
{
public static void main(String args[])
{

   try{
FileInputStream fstream = new FileInputStream("D:/eclipse/workspace/SpringExample1/bean.xml");
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
String value=null;
String value1=null;
while((strLine=br.readLine())!=null)
{
	System.out.print("success");
if (strLine.startsWith("<property")) 
{
value = strLine.substring(strLine.lastIndexOf("=")+1);   
System.out.println (value);
}  
 in.close();
 }catch (Exception e){

   e.printStackTrace();
 }
}
}
 

Please help me to do this.
Thanks>

[Rob Spoor]

Edit an existing file

[Fredrik Larsback]

Read the file into a StringBuilder, then use String replaceFirst(String regex,String replacement) to replace the word, then write the String back to the file.

[preethi Ayyappan]

Thanks for your responses.I have tried using Random access file first using the following code:

   
package com.vaannila;
import java.io.*;
 


public class ReadAccessFile{

    public static void main(String[] args) throws IOException{


      BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
   // System.out.print("Enter File name : ");
 //   String str = in.readLine();
 
   File file = new File("bean.xml");
    if(!file.exists())
{
 
     System.out.println("File does not exist.");
  
    System.exit(0);
 
   }
   
 try{
      //Open the file for both reading and writing
      RandomAccessFile rand = new RandomAccessFile(file,"rw"); 
      
     rand.seek(file.length());  //Seek to end of file
         rand.writeBytes("welcome");  //Write end of file 
 
      rand.close();
    
  System.out.println("Write Successfully");
  
  }
   
 

But the welcome is inserted at the end of the file.How could i replace the existing word say "Hello world" by "welcome"?

[Campbell Ritchie]

Can you replace things in a random access file like that? I thought they would have to be exactly the same length, but I might be mistaken.

[preethi Ayyappan]

I have tried to replace the value like the following:

 
package com.vaannila;


import java.io.*;
import java.lang.String;
import java.util.*;

class Fread
{
public static void main(String args[])
{

   try{
FileInputStream fstream = new FileInputStream("D:/eclipse/workspace/SpringExample1/bean.xml");
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
String value=null;
String value1=null;
while((strLine=br.readLine())!=null)
{
	//System.out.print("preetha");
//strLine=br.readLine();
if (strLine.startsWith("       <property")) 
{
value = strLine.substring(strLine.lastIndexOf("=")+1);   
System.out.println (value);

value1=value.replace(value, "hai");
//System.out.print("RAmya:"+value1);
String value2=strLine.replace(value, value1);
System.out.print("value2:"+value2);

}


}  
 in.close();
 }catch (Exception e){

   e.printStackTrace();
 }
}
}

   

Now my output is:

"Hello"></property>
value2: <property name="message" value=hai

But the value is not changed in the xml file.

Thanks>

[Rob Spoor]

Campbell Ritchie wrote:Can you replace things in a random access file like that? I thought they would have to be exactly the same length, but I might be mistaken.

You're not. Although you can shift bytes and if necessary truncate the RandomAccessFile, originally it only allows replacing bytes with the same number of bytes. It shouldn't be used for replacing characters at all because of encodings. That's why I posted the "editing an existing file" FAQ, because that's a better solution.

[David Newton]

sed.

[preethi Ayyappan]

Hi,

I have tried the following code to write the word in the xml file.But this code inserts the line in the file next to the existing line. But how can i delete the existing line?

   
import java.io.*;
class FileRead1
{
public static void main(String args[])
{
     try
      {      
        String line = null;
        BufferedReader br = new BufferedReader ( new FileReader ( "bean.xml" )  );
        PrintWriter pr = new PrintWriter ( new BufferedWriter ( new FileWriter ( "bean2.xml", false )  )  );      
             
        while  (  ( line = br.readLine (  )  )  != null )   {  
             pr.println ( line );
             if (line.startsWith("       <property"))
             {
        String     value = line.substring(line.lastIndexOf("=")+1);
        String value3=value.substring(1, 2);
             System.out.println (value3);
         String    value1=line.replace(value3, "1");
                   
             pr.write(value1);
             
             }
             
       
             
         }  
       
        br.close (  );            
        br = null;
           
        pr.close (  );
        pr = null;        
           
      }  catch  ( java.io.FileNotFoundException ex )   {  
        System.out.println ( "File '" + args [ 0 ]  + "' does not exist. " );      
      }  catch  ( java.io.IOException ex )   {  
        ex.printStackTrace (  );
      }

    //Read more: http://kickjava.com/1313.htm#ixzz0aa61qHyK

}
}

 

Actual xml file is bean.xml:

><?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/bean...s.xsd">
<bean id="helloWorld" class="com.vaannila.HelloWorld">
<property name="message" value="0"></property>
</bean>

</beans>

the newly created file is bean2.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/bean...s.xsd">
<bean id="helloWorld" class="com.vaannila.HelloWorld">
<property name="message" value="0"></property>
<property name="message" value="1"></property> </bean>

</beans>

How can i delete the old line

<property name="message" value="0"></property>

[Ulf Dittmer]

I'd advise to save yourself a lot of headaches and use a proper tool for the job: If you want to alter an XML file, that's what libraries like DOM, JDOM and XOM are for. Using string operations (or regular expressions or something else of that nature) on XML *will break* eventually when the file format changes in a way that the code doesn't foresee.

[preethi Ayyappan]

Thank you for your advise. To use DOM, should I download any jar file? I am not aware of DOM.Please assist me any samples or link to continue.

[Ulf Dittmer]

DOM is part of the JAXP API (which is the standard Java API for XML handling), and JAXP is part of the JRE, so you don't need to download or install anything. The XmlFaq contains links to numerous articles that should get you started.

The reason I mentioned other libraries like JDOM and XOM is that the DOM API, while perfectly functional, isn't specifically designed for Java -which JDOM and XOM are- so it is a bit awkward to work with.