Title: Application Resources
# Resources
TomEE provides a simple but powerful way to define resources that can be injected into managed components inside your application, or looked up via JNDI. To use a resource, it needs to be defined in the `tomee.xml` configuration file, a `resources.xml` file within an application, or as a system property. Defining a resource in `tomee.xml` will make it available server-wide, whereas defining the resource within a `resources.xml` file makes it available to a specific application.
As a simple example, a JMS queue can be defined within `tomee.xml` with the following configuration.
Once the resource has been defined, the server will create an instance of the resource during startup, and it will be available to be injected into managed components using the `@Resource` annotation, as shown below. The `name` attribute on the `@Resource` annotation should match the `id` attribute on the `Resource` tag.
public class JmsClient {
@Resource(name="MyQueue")
private Queue queue;
public void sendMessage() {
// implementation here...
}
}
As an alternative to defining a resource in XML, resources can also be defined using system properties:
MyQueue = new://Resource?type=javax.jms.Queue
Resources, or attributes for resources specified using system properties will override definitions specified in `tomee.xml`.
Server-wide resources can be looked up in JNDI under the following name: openejb:Resources/resource id.
# Defining Resources
The `` tag has a number of attributes, and a resource may also have a number of fields that can be configured by adding properties to the body of the `Resource` tag.
For example, a DataSource resource needs a JDBC driver, URL, username and password to be able to connect to a database. That would be configured with the following syntax. Notice the key/value pair syntax for the properties within the `` tag.
JdbcDriver com.mysql.jdbc.Driver
JdbcUrl jdbc:mysql://localhost/test
UserName test
Password password
Specifying the key/value pairs specific to a Resource can also be done when defining the resource via system properties. This is done be specifying an additional property for each key/value pair, using the resource ID as a prefix: `.=`. The system properties equivalent of the resource above is:
p.setProperty("DB", "new://Resource?type=DataSource");
p.setProperty("DB.JdbcDriver", "com.mysql.jdbc.Driver");
p.setProperty("DB,JdbcUrl", "jdbc:mysql://localhost/test");
p.setProperty("DB.UserName", "test");
p.setProperty("DB.Password", "password");
The `` tag has a number of attributes which control the way that the resource get created.
* type
A type that TomEE knows. The type is associated with a provider that knows how to create that type, and also any default properties that the resource should have if they are not specified in the resource definition. See service-jar.xml for an example set of service providers that come with TomEE.
* provider
Explicitly specifies a provider to create the resource, using defaults for any properties not specified.
* class-name
The fully qualified class that creates the resource. This might the resource class itself, which is created by calling the constructor, or a factory class that provides a specific factory method to create the resource.
* factory-name
The name of the method to call to create the resource. If this is not specified, the constructor for the class specified by class-name will be used.
* constructor
Specifies a comma separated list of constructor arguments. These can be other services, or attributes on the resource itself.
# Custom resources
TomEE allows you to define resources using your own Java classes, and these can also be injected into managed components in the same way as known resource types are.
So the following simple resource
public class Configuration {
private String url;
private String username;
private int poolSize;
// getters and setters
}
Can be defined in `tomee.xml` using the following configuration (note the `class-name` attribute):
url http://localhost
username tomee
poolSize 20
This resource must be available in TomEE's system classpath - i.e. it must be defined in a .jar within the `lib/` directory.
# Field and properties
As shown above, a resource class can define a number of fields, and TomEE will attempt to apply the values from the resource definition onto those fields.
As an alternative to this, you can also add a properties field as shown below, and this will have any used properties from the resource configuration set added to it. So as an alternative to the above code, you could do:
public class Configuration {
private Properties properties;
public Properties getProperties() {
return properties;
}
public void setProperties(final Properties properties) {
this.properties = properties;
}
}
Using the same resource definition:
url http://localhost
username tomee
poolSize 20
the url, username and poolSize values will now be available in the properties field, so for example, the username property could be accessed via properties.getProperty("username");
# Application resources
Resources can also be defined within an application, and optionally use classes from the application's classpath. To define resources in a .war file, include a `WEB-INF/resources.xml`. For an ejb-jar module, use `META-INF/resources.xml`.
The format of `resources.xml` uses the same `` tag as `tomee.xml`. One key difference is the root element of the XML is `` and not ``.
url http://localhost
username tomee
poolSize 20
This mechanism allows you to package your custom resources within your application, alongside your application code, rather than requiring a .jar file in the `lib/` directory.
Application resources are bound in JNDI under openejb:Resource/appname/resource id.
# Additional resource properties
Resources are typically discovered, created, and bound to JNDI very early on in the deployment process, as other components depend on them. This may lead to problems where the final classpath for the application has not yet been determined, and therefore TomEE is unable to load your custom resource.
The following properties can be used to change this behavior.
* Lazy
This is a boolean value, which when true, creates a proxy that defers the actual instantiation of the resource until the first time it is looked up from JNDI. This can be useful if the resource's classpath until the application is started (see below), or to improve startup time by not fully initializing resources that might not be used.
* UseAppClassLoader
This boolean value forces a lazily instantiated resource to use the application classloader, instead of the classloader available when the resources were first processed.
* InitializeAfterDeployment
This boolean setting forces a resource created with the Lazy property to be instantiated once the application has started, as opposed to waiting for it to be looked up. Use this flag if you require the resource to be loaded, irrespective of whether it is injected into a managed component or manually looked up.
By default, all of these settings are `false`, unless TomEE encounters a custom application resource that cannot be instantiated until the application has started. In this case, it will set these three flags to `true`, unless the `Lazy` flag has been explicitly set.
# Initializing resources
## constructor
By default, if no factory-name attribute and no constructor attribute is specified on the `Resource`, TomEE will instantiate the resource using its no-arg constructor. If you wish to pass constructor arguments, specify the arguments as a comma separated list:
url http://localhost
username tomee
poolSize 20
## factory-name method
In some circumstances, it may be desirable to add some additional logic to the creation process, or to use a factory pattern to create resources. TomEE also provides this facility via the `factory-name` method. The `factory-name` attribute on the resource can reference any no argument method that returns an object on the class specified in the `class-name` attribute.
For example:
public class Factory {
private Properties properties;
public Object create() {
MyResource resource = new MyResource();
// some custom logic here, maybe using this.properties
return resource;
}
public Properties getProperties() {
return properties;
}
public void setProperties(final Properties properties) {
this.properties = properties;
}
}
UserName tomee
## @PostConstruct / @PreDestroy
As an alternative to using a factory method or a constructor, you can use @PostConstruct and @PreDestroy methods within your resource class (note that you cannot use this within a different factory class) to manage any additional creation or cleanup activities. TomEE will automatically call these methods when the application is started and destroyed. Using @PostConstruct will effectively force a lazily loaded resource to be instantiated when the application is starting - in the same way that the `InitializeAfterDeployment` property does.
public class MyClass {
private Properties properties;
public Properties getProperties() {
return properties;
}
public void setProperties(final Properties properties) {
this.properties = properties;
}
@PostConstruct
public void postConstruct() throws MBeanRegistrationException {
// some custom initialization
}
}
}
# Examples
The following examples demonstrate including custom resources within your application:
* resources-jmx-example
* resources-declared-in-webapp