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BigInteger x = new BigInteger("530500452766");
String s = x.toString();  // valid character data
byte[] byteArray = s.getBytes();
String ns = new String(byteArray);  
x = new BigInteger(ns); 

Compliant Solution (Java 8)

While Java does not provide a Charset that guarantees lossless encoding of byte data, there are many other solutions for safely converting an arbitrary byte array into a string and back. Java 8 provides the java.util.Base64 class which provides encoders and decoders for the Base64 encoding scheme. This compliant solution uses Base64 to safely convert the number to a string and back without corruption of data.

BigInteger x = new BigInteger("530500452766");
byte[] byteArray = x.toByteArray();
String s = Base64.getEncoder().encodeToString( byteArray);
byteArray = Base64.getDecoder().decode(s);
x = new BigInteger(byteArray);

Risk Assessment

Storing numeric data as a string is likely to result in a loss of data integrity.

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