What is the best practice for reading property files in J2EE?

Question

I have several J2EE web applications running inside the same application server and I wanted to externalize the properties files that are inside the jars to a new directory to make these properties visible.

What is the recommended way to load these properties files?

Thanks.

Answer 1

Personally, I use the java.util.Properties Class and use the load() method to loadproperties.

InputStream inputStream  = MyProperties.class.getClassLoader().getResourceAsStream("file.properties");
this.properties = new Properties();
this.properties.load(inputStream);

Then I use the get() method to read properties as Strings.

I your properties files are outside your jar file, here are some useful tips to read it

http://lijinjoseji.wordpress.com/2007/09/14/reading-properties-file-from-outside-of-a-jar-file/

Answer 2

If you're using Spring, it's nice to abstract away in the code that there's even a properties file at all and use a PropertyPlaceHolderConfigurer. This allows you to externalize the properties from a BeanFactory definition to a standard Java properties file.

Example (ripped from the spring docs):

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <value>classpath:com/foo/jdbc.properties</value>
    </property>
</bean>

<bean id="dataSource" destroy-method="close"
      class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="${jdbc.driverClassName}"/>
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>

Answer 3

If you're using JBoss you can create a properties service file (named something-service.xml)

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE server>

<server>    
  <mbean code="org.jboss.varia.property.SystemPropertiesService" 
           name="jboss:type=Service,name=MySystemProperties">        
    <attribute name="Properties">
       property_a=value a
       property_b=value b
    </attribute>         
  </mbean>
</server>

Copy this to your deploy directory and the properties will be available with System.getProperty()

Answer 4

This link has some advice. You can either use ResourceBundle or do something like this:

// Assuming you are in a Servlet extending HttpServlet 
// This will look for a file called "/more/cowbell.properties" relative
// to your servlet Root Context
InputStream is = getServletContext().getResourceAsStream("/more/cowbell.properties");
Properties  p  = new Properties();
p.load(is);
is.close();

The recommended way for me will be to go with Spring, as another answer suggested.