TomEE and more advanced resource configuration


TomEE 2 got two new interesting features (in particular in enterprises) to configure resources: default placeholder values and properties-provider.

Placeholder

TomEE supports placeholding in resources, for instance:

<Resource id="...">
  JdbcUrl = ${my.url}
  JdbcDriver = ${my.driver}
</Resource>

This is great but what happen if my.url or my.driver is not specified? You get the url my.url. You can of course set the real/test url:

<Resource id="...">
  JdbcUrl = ${jdbc:h2:mem:xx}
  JdbcDriver = ${my.driver}
</Resource>

but then you need to set -Djdbc:h2:mem:xx=jdbc:mysql://localhost:3306/xx which is a bit weird (in particular if you didn’t develop the application).

To avoid it we activated default values in placeholders with the separator (configurable) “:-“:

<Resource id="...">
  JdbcUrl = ${my.url:-jdbc:h2:mem:xx}
  JdbcDriver = ${my.driver}
  MinIdle = ${my.minIdle:-3}
</Resource>

This makes the configuration more readable :).

PS: if you want to use a simple “:” instead of “:-” which was choosen to be aligned with commons-lang3 default, just set as system property openejb.placeholder.delimiter to ‘:’

Properties provider

Resource properties values are set from resource properties. Main issue is in enterprises you often have a system to read/store them (Database, NoSQL, …..).

To allow to integrate with it you can now set properties-provider attribute on resources:

<Resource id="..." properties-provider="com.foo.MyPropertiesReader" />

For known types (DataSource for instance) default values will still be provided but all properties are overwritten by MyPropertiesReader.

MyPropertiesReader can either implements org.apache.openejb.api.resource.PropertiesResourceProvider or just defines a provides method returning Properties.

Another interesting thing is this provider can be configured with properties of the resource or get injected all properties if it has a setProperties(Properties) method.

Here is a sample:

public class MyPropertiesReader {
    private Properties properties;
    private String resourceCompanyId;

    public void setProperties(final Properties p) {
        this.p = p;
    }

    public Properties provides() {
        // change properties reading what you need using resourceCompanyId
        properties.remove("resourceCompanyId"); // not a resource config, remove it
        return properties;
    }
}

and the configuration could be:

<Resource id="myResource" properties-provider="com.foo.MyPropertiesReader">
   resourceCompanyId = 141186
   resourceAttribute = value
</Resource>
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