Hibernate entity design with a Currency class

Question

I have a class Currency, where I want to store business logic for working with currencies:

public class Currency implements Comparable<Currency> {
 public static final int NAME_MAX_STRING_LENGTH = 50;
 public static final int ISO_CODE_STRING_LENGTH = 3;
 public static final int SYMBOL_STRING_LENGTH = 1;
 public static final int COMMENTS_MAX_STRING_LENGTH = 100;
 private String name;
 private String isoCode;
 private String symbol;
 private String comments;
 public Currency(String name, String isoCode, String symbol, String comments) {
 setName(name);
 setIsoCode(isoCode);
 setSymbol(symbol);
 setComments(comments);
 }
 public String getIsoCode() {
 return isoCode;
 }
 public String getName() {
 return name;
 }
 public String getSymbol() {
 return symbol;
 }
 public String getComments() {
 return comments;
 }
 public void setIsoCode(String isoCode) {
 if (isoCode == null) {
 throw new ArgumentIsNullException("isoCode");
 }
 if (isoCode.length() != ISO_CODE_STRING_LENGTH) {
 throw new IllegalArgumentException(
 "ISO code should be consisted of 3 letters.");
 }
 if (!isoCode.matches(defineRegularExpressionForIsoCode())) {
 throw new IllegalArgumentException("ISO code is not valid.");
 }
 this.isoCode = isoCode;
 }
 public void setName(String name) {
 if (name == null) {
 throw new ArgumentIsNullException("name");
 }
 if (name.length() > NAME_MAX_STRING_LENGTH) {
 StringBuilder exceptionMessageBuilder = new StringBuilder();
 exceptionMessageBuilder
 .append("Length of name's string can not be more than ");
 exceptionMessageBuilder.append(NAME_MAX_STRING_LENGTH);
 exceptionMessageBuilder.append(" symbols.");
 throw new IllegalArgumentException(
 exceptionMessageBuilder.toString());
 }
 this.name = name;
 }
 public void setSymbol(String symbol) {
 if (symbol == null) {
 throw new ArgumentIsNullException("symbol");
 }
 if (symbol.length() != SYMBOL_STRING_LENGTH) {
 throw new IllegalArgumentException(
 "Currency's symbol should be exactly one character.");
 }
 this.symbol = symbol;
 }
 public void setComments(String comments) {
 if (comments != null && comments.length() > COMMENTS_MAX_STRING_LENGTH) {
 StringBuilder exceptionMessageBuilder = new StringBuilder();
 exceptionMessageBuilder
 .append("Length of comments' string can not be more than ");
 exceptionMessageBuilder.append(COMMENTS_MAX_STRING_LENGTH);
 exceptionMessageBuilder.append(" symbols.");
 throw new IllegalArgumentException(
 exceptionMessageBuilder.toString());
 }
 this.comments = comments;
 }
 private String defineRegularExpressionForIsoCode() {
 return "^[A-Z][A-Z][A-Z]$";
 }
 @Override
 public int compareTo(Currency currency) {
 return this.getIsoCode().compareTo(currency.getIsoCode());
 }
 @Override
 public int hashCode() {
 final int prime = 31;
 int result = 1;
 result =
 prime * result + ((comments == null) ? 0 : comments.hashCode());
 result = prime * result + ((isoCode == null) ? 0 : isoCode.hashCode());
 result = prime * result + ((name == null) ? 0 : name.hashCode());
 result = prime * result + ((symbol == null) ? 0 : symbol.hashCode());
 return result;
 }
 @Override
 public boolean equals(Object obj) {
 if (this == obj)
 return true;
 if (obj == null)
 return false;
 if (getClass() != obj.getClass())
 return false;
 Currency other = (Currency) obj;
 if (comments == null) {
 if (other.comments != null)
 return false;
 } else if (!comments.equals(other.comments))
 return false;
 if (isoCode == null) {
 if (other.isoCode != null)
 return false;
 } else if (!isoCode.equals(other.isoCode))
 return false;
 if (name == null) {
 if (other.name != null)
 return false;
 } else if (!name.equals(other.name))
 return false;
 if (symbol == null) {
 if (other.symbol != null)
 return false;
 } else if (!symbol.equals(other.symbol))
 return false;
 return true;
 }
}

CurrencyEntity interface:

public interface CurrencyEntity {
 void setName(String name);
 String getName();
 void setIsoCode(String isoCode);
 String getIsoCode();
 void setSymbol(String symbol);
 String getSymbol();
 void setComments(String comments);
 String getComments();
}

which CurrencyEntityAtJpa implements for working with Hibernate:

@Entity
@Table(name = "currencies")
public class CurrencyEntityAtJpa implements CurrencyEntity {
 public static final int NAME_MAX_STRING_LENGTH =
 Currency.NAME_MAX_STRING_LENGTH;
 public static final int ISO_CODE_STRING_LENGTH =
 Currency.ISO_CODE_STRING_LENGTH;
 public static final int SYMBOL_STRING_LENGTH =
 Currency.SYMBOL_STRING_LENGTH;
 public static final int COMMENTS_MAX_STRING_LENGTH =
 Currency.COMMENTS_MAX_STRING_LENGTH;
 private Currency currency;
 private long id;
 public CurrencyEntityAtJpa() {
 setCurrency(new Currency("Invalid currency", "INV", "I", null));
 }
 public CurrencyEntityAtJpa(String name, String isoCode, String symbol,
 String comments) {
 setCurrency(new Currency(name, isoCode, symbol, comments));
 }
 public CurrencyEntityAtJpa(Currency currency) {
 this(currency.getName(), currency.getIsoCode(), currency.getSymbol(),
 currency.getComments());
 }
 @Transient
 public Currency getCurrency() {
 return currency;
 }
 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 @Column
 public long getId() {
 return id;
 }
 @Override
 @Column(name = "iso_code", nullable = false, length = ISO_CODE_STRING_LENGTH)
 public String getIsoCode() {
 return getCurrency().getIsoCode();
 }
 @Override
 @Column(name = "name", nullable = false, length = NAME_MAX_STRING_LENGTH)
 public String getName() {
 return getCurrency().getName();
 }
 @Override
 @Column(name = "symbol", nullable = false, length = SYMBOL_STRING_LENGTH)
 public String getSymbol() {
 return getCurrency().getSymbol();
 }
 @Override
 @Column(name = "comments", nullable = true, length = COMMENTS_MAX_STRING_LENGTH)
 public String getComments() {
 return getCurrency().getComments();
 }
 private void setCurrency(Currency currency) {
 this.currency = currency;
 }
 public void setId(long id) {
 this.id = id;
 }
 @Override
 public void setIsoCode(String isoCode) {
 getCurrency().setIsoCode(isoCode);
 }
 @Override
 public void setName(String name) {
 getCurrency().setName(name);
 }
 @Override
 public void setSymbol(String symbol) {
 getCurrency().setSymbol(symbol);
 }
 @Override
 public void setComments(String comments) {
 getCurrency().setComments(comments);
 }
 @Override
 public int hashCode() {
 return getCurrency().hashCode();
 }
 @Override
 public boolean equals(Object obj) {
 if (obj == null) {
 return false;
 }
 if (!(obj instanceof CurrencyEntityAtJpa)) {
 throw new IllegalArgumentException(obj.toString()
 + " is not CurrencyEntityAtJPA object.");
 }
 return getCurrency().equals(((CurrencyEntityAtJpa) obj).getCurrency());
 }
}

Is this a good design for Hibernate entity where I want to separate business logic and classes which work with database?

Answer 1

I don't see too much of an advantage in separating like this. Especially when considering Basic Java Persistence API Best Practices, Access Fields Rather Than Properties:

I prefer to specify object-relational mapping by annotating entity fields directly, rather than annotating get/set methods (properties), for several reasons.