transformer un string en Biginteger java

package com.mkyong;

import java.math.BigInteger;

public class JavaExample {

    public static void main(String[] args) {

        int n = 100;
        System.out.println(n);

        // convert int to Integer
        Integer integer = Integer.valueOf(n);
        System.out.println(integer);

        // convert int to BigInteger
        BigInteger bigInteger = BigInteger.valueOf(n);
        System.out.println(bigInteger);

        // convert Integer to BigInteger
        //BigInteger bigInteger2 = BigInteger.valueOf(integer); // works
        BigInteger bigInteger2 = BigInteger.valueOf(integer.intValue());
        System.out.println(bigInteger2);

    }

}foo = new String(bi.toByteArray());public BigInteger toBigInteger(String foo)
{
    return new BigInteger(foo.getBytes());
}

public String fromBigInteger(BigInteger bar)
{
    return new String(bar.toByteArray());
} 
package org.arpit.java2blog;
 
import java.math.BigInteger;
 
public class StringToBigIntegerMain {
 
	public static void main(String[] args) {
 
		String str="45";
		BigInteger bigIntegerStr=new BigInteger(str);
		System.out.println("Converted String to BigInteger: "+bigIntegerStr);
	}
}
 
String foo = "some text";
byte[] fooBytes = foo.getBytes();
BigInteger bi = new BigInteger(fooBytes);