JSR-303注释字段vs Getter

当使用JSR-303注释执行bean验证时,注释字段和getter之间有什么区别?

是否建议一种方法优于另一种方法?

字段上的批注

public class Person {

  @NotBlank
  private String firstName;

  public String getFirstName() {
    return firstName;
  }

  public String setFirstName(String firstName) {
    this.firstName = firstName;
  }
}

getter上的批注

public class Person {

  private String firstName;

  @NotBlank
  public String getFirstName() {
    return firstName;
  }

  public String setFirstName(String firstName) {
    this.firstName = firstName;
  }
}