Guice-JPA persistance.xml not reading placeholders from properties file

Question

I m using Guice-JPA module with hibernate to perform the DAO operations.

When hard coding the connection information in persistence.xml, everything works fine. but when I try to use properties file for connection parameters, persistence.xml just treats them as empty string and I get an exception.

here is my guice code and Persistense.xml.

    JpaPersistModule jpaModule = new JpaPersistModule("myModule");
    Properties properties = new Properties();
    try {
        properties.load(Bootstrap.class.getClassLoader().getResourceAsStream("appConfig.properties"));
    } catch (IOException e) {
        e.printStackTrace();
    }
    JpaPersistModule module = jpaModule.properties(properties);
    injector = Guice.createInjector(new ApplicationConfig(), module);
    PersistService persistService = injector.getInstance(PersistService.class);
    persistService.start();

After this code, I confirmed from the debugger that the properties object carry all the properties, so I m sure it read the properties file correctly.

here is the properties file and persistence.xml

hibernate.username=root

    <persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
    version="2.0">
   <persistence-unit name="24x7monitoring" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <properties>
        <property name="hibernate.show_sql" value="false" />
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/dbname"/>
        <property name="javax.persistence.jdbc.user" value="${hibernate.username}" />
        <property name="javax.persistence.jdbc.password" value="" />
        <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
        <property name="hibernate.hbm2ddl.auto" value="update"/>
    </properties>
</persistence-unit>

I get the following exception:

 Access denied for user ''@'localhost' to database 

Please advise on why properties files are not being read by the JPA module, knowing that it works fine without the placeholders..

Answer 1

You cannot use placeholders or replacement variables in persistence.xml like you are trying to do. The properties you pass to JpaPersistModule are an atlernative to defining <property> elements in persistence.xml.

For example instead of having this line in persitence.xml:

<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />

You can define the same property inside of your *.properties file:

javax.persistence.jdbc.driver=com.mysql.jdbc.Driver

So you should remove this invalid line:

<property name="javax.persistence.jdbc.user" value="${hibernate.username}" />

and add an entry like this in your properties file:

javax.persistence.jdbc.user=my_username