表person对应的model类：

@Entity
@Table(name = "person")
public class Person {
    @Id
    @GeneratedValue
    private Long id;
    private Integer age;
    private String name;
    @Column(name = "nick_name")
    private String nickName;
    private String company;
    private Date birthday;
    
    // getter and setter
}

数据库访问PersonRepository类：

public interface PersonRepository extends JpaRepository<Person, Long>, JpaSpecificationExecutor<Person> {
}

查询年龄小于等于20的人。

public List<Person> findAll(SearchRequest request) {
    Specification<Person> specification = new Specifications<Person>()
            .le(Object.nonNull(request.getAge()), "age", 20)
            .build();

    return personRepository.findAll(specification); 
}