Error: java.sql.SQLDataException,Invalid character string format for type int. I really don't understand?

I have a problem with my project. When i browse http://localhost:8080/user/form to fill information user

Then submit form to save user and automaticlly direct http://localhost:8080/user/list to display list User, but occur following error:

Hibernate: insert into userdat (age, birthday, gender, password, username) value s (?, ?, ?, ?, ?) Mar 27, 2016 8:30:17 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$Standar dWarningHandler logWarning WARN: SQL Warning Code: 10000, SQLState: 01J01 Mar 27, 2016 8:30:17 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$Standar dWarningHandler logWarning WARN: Database 'D:\PROJECTSPRING\userdb' not created, connection made to existin g database instead. Mar 27, 2016 8:30:17 AM org.hibernate.hql.internal.QueryTranslatorFactoryInitiat or initiateService INFO: HHH000397: Using ASTQueryTranslatorFactory Hibernate: select user0_.username as username1_0_, user0_.age as age2_0_, user0_ .birthday as birthday3_0_, user0_.gender as gender4_0_, user0_.password as passw ord5_0_ from userdat user0_ Mar 27, 2016 8:30:17 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExce ptions WARN: SQL Error: 20000, SQLState: 22018 Mar 27, 2016 8:30:17 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExce ptions ERROR: Invalid character string format for type int. [WARNING] org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.hibernate.exception.DataException: could not execute que ry

Caused by: org.hibernate.exception.DataException: could not execute query at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQL ExceptionTypeDelegate.java:52) at org.hibernate.exception.internal.StandardSQLExceptionConverter.conver t(StandardSQLExceptionConverter.java:42) at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlException Helper.java:111)

Caused by: java.sql.SQLDataException: Invalid character string format for type i nt. at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknow n Source) at org.apache.derby.impl.jdbc.Util.generateCsSQLException(Unknown Source ) at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException (Unknown Source)

Here file UserDaoImpl.java

@Repository
public class UserDaoImpl implements UserDao{
    @Autowired
    public LocalSessionFactoryBean sessionFactory;


    @Override
    public void save(User user) {
        // TODO Auto-generated method stub
        Session session = sessionFactory.getObject().openSession();
        session.save(user);
        session.flush();
        session.close();

    }

    @Override
    public void update(User user) {
        // TODO Auto-generated method stub

    }

    @Override
    public List<User> listUsers() {
        // TODO Auto-generated method stub
        Session session = sessionFactory.getObject().openSession();
        Query query = session.createQuery("from User");
        return (List<User>)query.list();
    }

Here file User.java

@Entity
@Table(name = "userdat",uniqueConstraints={@UniqueConstraint(columnNames="username")})
public class User {
    @Column(name = "gender", nullable = false)

    public Gender getGender() {
        return gender;
    }
    public void setGender(Gender gender) {
        this.gender = gender;
    }
    @Id
    @Column(name = "username", unique = true, nullable = false)
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    @Column(name = "password", nullable = false)
    public String getPassWord() {
        return passWord;
    }
    public void setPassWord(String passWord) {
        this.passWord = passWord;
    }
    @Column(name = "birthday", nullable = false)
    public Date getBirthDay() {
        return birthDay;
    }

    public void setBirthDay(Date birthDay) {
        this.birthDay = birthDay;
    }
    @Column(name="age", nullable = false)
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    private String userName;
    private String passWord;
    private Date birthDay;
    private Integer age;
    private Gender gender;


}

Here file Gender.java

public enum Gender {
    MALE("Male"),
    FEMALE("Female"),
    OTHER("Other");
    private String name;

    private Gender(String name) {
        this.name = name;
    }

    public String getGender(){
        return this.name;
    }
        }

Here Create Table in DB

public void createTable() throws SQLException{
        try {
            Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
            Connection connection = DriverManager.getConnection("jdbc:derby:D:/PROJECTSPRING/dbuser;create=true");
            createTableNotExist(connection,"userdat", "create table userdat"
                    + "(username varchar(1000) primary key,"
                    + "password varchar(1000),birthday date,"
                    + "age integer,gender varchar(100))");
//          createTableNotExist(connection,"subject","create table subject"
//                  + "(id bigint primary key generated always as identity(start with 1,increment by 1),"
//                  + "title varchar(1000),student integer,score integer)" );
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }