read content of text file which is in jar

[naveen yadav]

hi ranchers ,

i have a jar file jkl.jar which have a text file in it named as poi.txt.

is there any way i can read and alter the content of text file poi.txt ( which is in jar)

this is attempt i have made

import java.io.*;
import java.util.*;

public class FileUtils{

  public static List<String> readTextFromJar(String s) {
    InputStream is = null;
    BufferedReader br = null;
    String line;
    ArrayList<String> list = new ArrayList<String>();

    try { 
			  is = FileUtils.class.getResourceAsStream(s);
			  br = new BufferedReader(new InputStreamReader(is));
			  while (null != (line = br.readLine())) {
			  
				 list.add(line);
			  }
    }
    catch (Exception e) 
	{
      e.printStackTrace();
    }
    finally {
				  try {
					if (br != null) br.close();
					if (is != null) is.close();
				  }
				catch (IOException e) {
						e.printStackTrace();
				}
    }//finally
    return list;
  }

  public static void main(String args[]) throws IOException{
    List<String> list = FileUtils.readTextFromJar("jkl.jar");
    Iterator<String> it = list.iterator();
    while(it.hasNext()) {
      System.out.println(it.next());
    }
	}
	}

It prints the Special Unicode character ?

[Paul Clapham]

No, you can't alter resources which are stored in a jar file.

[Rob Spoor]

And you're trying to read the JAR file as if it is a text file, while you should access the text file within the JAR file. You can use JarFile for that.

[Paul Clapham]

No, observe this code:

is = FileUtils.class.getResourceAsStream(s);

It assumes the jar file is in the classpath and reads the text file from that jar, assuming that all the details are got right.

[Rob Spoor]

But s is "jkl.jar", not "poi.txt".

[Paul Clapham]

Hence why I said "assuming that all the details are got right".

[naveen yadav]

now i have added jkl.jar in CLASSPATH and here is code

In this piece of code I have got the reference of poi.txt file which is in jar

Enumeration enm  = jf.entries();
File txtFileObj = null;
String txtFileObjPath = null;
String txtFile = null;

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

JarFile jf = new JarFile("jkl.jar");
while(enm.hasMoreElements() ){
		Object obj = enm.nextElement();
		System.out.println(obj); //entries in jar
		
		String entryName = obj.toString();
		
		//find if there is any text file (poi.txt)
		if(entryName.endsWith("txt")){
			txtFile = entryName	;             //poi.txt
			txtFileObj = new File(txtFile);   // object ref of "poi.txt"
			
			txtFileObjPath = txtFileObj.getCanonicalPath(); 
			System.out.println(txtFileObjPath); //E;\codes\poit.xt
			}
		else
		System.out.println("Not.txt file in jkl.jar");
}//while


//=============more code 

up to now i have txtFile holding name of poi.txt file and file obj reference to it in txtFileObj

Next step is to read the poi.txt

method 1 : It throws IOException saying stream closed in Line 2

InputStream fis = UsingJarFile.class.getResourceAsStream(txtFile);
BufferedInputStream br = new BufferedInputStream(fis);
int i = 0;
while(br.read()!=-1)
{
System.out.println(i);

}

method 2 :it throws IOException FileNotFoundException

FileInputStream is = new FileInputStream(txtFileObj);

while(true){
int i =is.read();
System.out.println(i);
if(i==-1)
break;

}

i have reference of poi.txt now what is problem here ?

[Rob Spoor]

You can't use java.io.File with files inside ZIP or JAR files. Instead you should use the methods of JarFile:

JarFile jf = new JarFile("jkl.jar"); // you can actually also use ZipFile as you don't need any of JarFile's added methods
ZipEntry entry = jf.getEntry("poi.txt"); // direct access to the entry
if (entry != null)
{
    InputStream in = jf.getInputStream(entry);
    // now use and close in
}

[naveen yadav]

Rob Spoor wrote:You can't use java.io.File with files inside ZIP or JAR files. Instead you should use the methods of JarFile:

thanks Rob.

But how can one alter the poi.txt(in jar) there is no such method like getOutputStream() method in JarFile or ZipEntry .Is that possible, help me with a hint, if possible.

[Rob Spoor]

You cannot. No program can directly edit files inside ZIP / JAR files. That's because editing one file may cause the entire structure of the ZIP / JAR file to be modified.
Some programs appear they can edit files inside ZIP / JAR files, but they actually recreate the ZIP / JAR file when they store the edited files.

[naveen yadav]

here is my attempt to create a jar file problematically. i have a txt file as users.txt and want it to be bundled in a jar file called admin.jar

String txtFile = "user.txt";
BufferedInputStream bi = new BufferedInputStream(new FileInputStream(txtFile));

Manifest mf = new Manifest(bi);
JarOutputStream jos = new JarOutputStream(new FileOutputStream("admin.jar"), mf);

JarEntry je = new JarEntry(txtFile );
jos.putNextEntry(je);

byte[] buf = new byte[1024];
int anz;
     
while ((anz = bi.read(buf)) != -1) {
  jos.write(buf, 0, anz);
}

what details am i missing ?