SessionFactory NullPointerException - Spring Hibernate

I am beginner in Spring and I am trying to use Spring with an external properties file.

I encountered a NullpointerException for my sessionFactory

This in my applicationContext.xml :

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://ift.tt/GArMu6"
   xmlns:xsi="http://ift.tt/ra1lAU" xmlns:context="http://ift.tt/GArMu7"
   xmlns:tx="http://ift.tt/OGfeU2"
   xsi:schemaLocation="http://ift.tt/GArMu6 http://ift.tt/1jdM0fG
    http://ift.tt/OGfeU2 http://ift.tt/KC395X
    http://ift.tt/GArMu7 http://ift.tt/1ldEMZY">

<context:property-placeholder location="classpath:database.properties" />
<context:component-scan base-package="com.erm.monitoring" />

<tx:annotation-driven transaction-manager="hibernateTransactionManager" />

<bean class="org.springframework.jdbc.datasource.DriverManagerDataSource"
      id="dataSource">
    <property name="driverClassName" value="${database.driver}"></property>
    <property name="url" value="${database.url}"></property>
    <property name="username" value="${database.user}"></property>
    <property name="password" value="${database.password}"></property>
</bean>

<bean
    class="org.springframework.orm.hibernate4.LocalSessionFactoryBean"
    id="sessionFactory">
    <property name="dataSource" ref="dataSource"></property>
    <property name="hibernateProperties">
        <props>
            <prop key="hibernate.dialect">${hibernate.dialect}</prop>
            <prop key="connection.provider_class">${connection.provider_class}</prop>        
            <prop key="hibernate.c3p0.acquire_increment">${hibernate.c3p0.acquire_increment}</prop>
            <prop key="hibernate.c3p0.idle_test_period">${hibernate.c3p0.idle_test_period}</prop>
            <prop key="hibernate.c3p0.min_size">${hibernate.c3p0.min_size}</prop>
            <prop key="hibernate.c3p0.max_size">${hibernate.c3p0.max_size}</prop>
            <prop key="hibernate.c3p0.max_statements">${hibernate.c3p0.max_statements}</prop>
            <prop key="hibernate.c3p0.timeout">${hibernate.c3p0.timeout}</prop>
            <prop key="hibernate.c3p0.acquireRetryAttempts">${hibernate.c3p0.acquireRetryAttempts}</prop>
            <prop key="hibernate.c3p0.acquireRetryDelay">${hibernate.c3p0.acquireRetryDelay}</prop>
            <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>
            <prop key="hibernate.current_session_context_class">${hibernate.current_session_context_class}</prop>
            <prop key="hibernate.query.factory_class">${hibernate.query.factory_class}</prop>
        </props>
    </property>
</bean>

<bean class="org.springframework.orm.hibernate4.HibernateTransactionManager"
      id="hibernateTransactionManager">
    <property name="sessionFactory" ref="sessionFactory"></property>
</bean>

Here is my database.properties :

database.driver=oracle.jdbc.OracleDriver
database.url=jdbc:oracle:thin:@X:1521:X
database.user=X
database.password=X

hibernate.dialect=org.hibernate.dialect.Oracle10gDialect
connection.provider_class=org.hibernate.connection.C3P0ConnectionProvider
hibernate.c3p0.acquire_increment=1
hibernate.c3p0.idle_test_period=60
hibernate.c3p0.min_size=1
hibernate.c3p0.max_size=2
hibernate.c3p0.max_statements=50
hibernate.c3p0.timeout=0
hibernate.c3p0.acquireRetryAttempts=1
hibernate.c3p0.acquireRetryDelay=250
hibernate.show_sql=true
hibernate.current_session_context_class=thread
hibernate.query.factory_class=org.hibernate.hql.internal.classic.ClassicQueryTranslatorFactory

Finally this is my helper class :

public class MonitoringHelper implements Serializable {

private static final long serialVersionUID = 1L;

@Autowired
SessionFactory sessionFactory;

Session session;

public MonitoringHelper() {
}

public List getSourceApplication() {
    List<String> sourceList = null;
    List<SelectItem> sourceSelectItem = null;
    String query = "X";
    try {
        session = sessionFactory.openSession();
        Transaction tx = session.beginTransaction();
        sourceList = session.createSQLQuery(query).list();
        sourceSelectItem = this.convertStringToSelectItem(sourceList);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return sourceSelectItem;
}

Could you tell me why my sessionFactory is null knowing that I used an autowired on it ?

Thanks