NullPointerException Insert JDBC Spring

[Gerard Geded]

Hello Everyone,

I'm triying to insert user with jdbc template and spring , but when I called the method for insert User, I have a JavaNullPointerException, I don't know why, I tried lot of things but it still doesn't work.

Look at my code please :

applicationContext.xml :

 <bean id="myDataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
 
    <property name="jndiName" value="jdbc/userDb"/>
     
  </bean>

<bean class="com.example.UserDB" id="user">
        <property name="dataSource" ref="myDataSource"/>

UserDB.java :

public class UserDB{


    protected JdbcTemplate jdbcTemplate;
    
    public void setDataSource(DataSource dataSource) {
        jdbcTemplate = new JdbcTemplate(dataSource);
    }

      public void insertNewUser(String username){

        jdbcTemplate.update( connection -> {
            PreparedStatement ps = connection.prepareStatement(sqlUserInsert, new String[]{"id"});
            int i =1;
            ps.setString(i++, username);
        
            return ps;});

    }

}

And  below my class where I call the method insertNewUser(); :

UserDB userDB= new UserDB();

userDB.insertNewUser

And I have this error :

java.lang.NullPointerException
    at com.example.UserDB.insertNewUser

Anyone has idea please ?

Thanks

[Campbell Ritchie]

Welcome to the Ranch

Why are you initialising your template in a setXXX() method rather than the constructor or similar? That will mean the field will point to null until the setXXX() method is called, and you cannot be certain that users will ever call that method. I presume, but I am not certain, that the connection has been initialised.
What int value do you expect to pass to the setString() method in line 15?

[Gerard Geded]

Campbell Ritchie wrote:Welcome to the Ranch

Why are you initialising your template in a setXXX() method rather than the constructor or similar? That will mean the field will point to null until the setXXX() method is called, and you cannot be certain that users will ever call that method. I presume, but I am not certain, that the connection has been initialised.
What int value do you expect to pass to the setString() method in line 15?

Hi Ritchie,

I'm not sure to understand what do you mean,

the method  setXXX() is called in application Context i'm presume,

And in line 15 in setString() , it's not a int, it's a string username.

[Campbell Ritchie]

But line 15 takes an int as ist first parameter, obviously to set the index in the prepared statement. What did you intend the index to be?
Don't presume somebody will call that method. If setDataSource() isn't called, the template object won't be created and cannot be used in line 12. Force them to initialise it. If you can't set the user name via the constructor, test whether the data source has been initialised by line 11 and throw an illegal state exception (or a checked exception of some sort) if it hasn't. And write some documentation comments to make it clear to users. If they ignore the comments, you can tell them off.public UserDB(DataSource dataSource) {    jdbcTemplate = new JdbcTemplate(dataSource); }If that is the only constructor you write, users must initialise the template. Why is the template field marked protected? That is tempting other code to change it, without your knowing about it.