使用SessionFactory时，Hibernate中出现奇怪的NumberFormatException

Question

[It may be useful to see my related, yet distinct, question from earlier today here Hibernate Schema Export in Eclipse .]

I have the following Java class

package com.examscam.model;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;

@Entity
public class User {
    private Long id;
    private String password;

    @Id
    @GeneratedValue
    public Long getId() {
        return id;
    }

    public String getPassword() {
        return password;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public static void main(String[] args) {
        AnnotationConfiguration config = new AnnotationConfiguration();
        config.addAnnotatedClass(User.class);
        config.configure();
//      new SchemaExport(config).create(true, true);

        SessionFactory factory = config.buildSessionFactory();
        Session session = factory.getCurrentSession();
        session.beginTransaction();

        User u = new User();        
        u.setPassword("abc123");

        session.saveOrUpdate(u);
        session.getTransaction().commit();

        System.out.println("Done.");
    }
}

I have a (MySQL) database and have created the User table with the code

create table User (id integer not null auto_increment, password varchar(255), primary key (id))

However, when I try running this code, I am given the following stack trace

Exception in thread "main" java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
    at java.lang.Integer.parseInt(Integer.java:470)
    at java.lang.Integer.valueOf(Integer.java:554)
    at org.hibernate.util.PropertiesHelper.getInteger(PropertiesHelper.java:37)
    at org.hibernate.connection.DriverManagerConnectionProvider.configure(DriverManagerConnectionProvider.java:47)
    at org.hibernate.connection.ConnectionProviderFactory.newConnectionProvider(ConnectionProviderFactory.java:124)
    at org.hibernate.connection.ConnectionProviderFactory.newConnectionProvider(ConnectionProviderFactory.java:56)
    at org.hibernate.cfg.SettingsFactory.createConnectionProvider(SettingsFactory.java:414)
    at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:62)
    at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:2009)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1292)
    at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:859)
    at com.examscam.model.User.main(User.java:40)

Line 40 of the User class is

    SessionFactory factory = config.buildSessionFactory();

Does anyone have any idea why this is happening? I am not entering an empty String anywhere on that line and I have copied the code exactly from the book. I have no doubt that the book is correct; my questions is more along the lines of 'Can anyone think of any reason (errors in xml files, classpath ordering issues, files not being in the correct directories etc) why this behaviour would occur?'.

An answer to this question might also help solve the issue in the link at the very top of this page with exporting the schema.

Thanks, Conor.

Answer 1

So I believe I've solved this problem which ended up being two problems. First, there was another older copy of hibernate in the classpath. This older version was requiring config elements that no longer were required, leading to the NumberFormatException as it was trying to parse an empty string into an int for the missing transaction isolation config element.

After fixing that, we started to see a NullPointerException on this line of code:

Environment.class.getClassLoader().getResourceAsStream(stripped);

Looking at that line of code, the only thing that could have been throwing the NPE was the getClassLoader call, but how could that ever be null? As it turns out getClassLoader can return null if the class loader being returned is the boot class loader. I asked Conor to check if he had put hibernate into the boot class path and it turns out that he did. Removing it from the boot class fixed the issue.

So two lessons here:

1. Manage your class path carefully. Know what's on it and keep it as trim as possible. The less 3rd party libs the better.
2. Don't ever put stuff on the boot class path. If you decide to ignore this rule, understand what the potential implications are so you're not stuck chasing issues like this.

Answer 2

The database id column datatype is integer, but entity class's id datatype is long, not sure whether this is the problem. But it is worth giving a try to changed the datatype of entity's id to int.