Version 1. To abstract over concrete database systems and vendor specific characteristics, the JDBC specification provides various classes and Service Provider Interfaces SPI that can be used for database interaction. Implementations are database specific and provided by the corresponding driver. Applications can rely on this mechanism to transparently access drivers and to stay independent from driver specific classes. Additionally, this mechanism helps to use common OSGi practices and to avoid class loading problems.
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- Definition at line 48 of file propagation-environment.
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How to create them, how they behave at runtime, how to reference other services, and so on. As there are multiple aspects with regards to component configuration I wanted to write a blog post that is dedicated to that topic, and here it is. After reading this blog post you should have a deeper understanding of how OSGi components can be configured.
With DS 1. Basically the property propagation is executed sequentially. Therefore it is even possible to override inline properties with properties from a properties file, if the properties file is specified after the inline properties. First I will explain how to specify Component Properties in different ways. I will use a simple example that inspects the properties in a life cycle method.
After that I will show some examples on the usage of properties of service references. You can add Component Properties to a declarative service component via the Component annotation property type element. Of course the same applies for Component Properties that are applied via Properties file, as they have an equal ranking. Run to see how to setup such a configuration. If you used the same property values as specified in the above example, you should see the welcome message printed out 3 times to the console.
It is for sure not a typical use case to inspect the inline specified properties at activation time. But it should give an idea on how to specify Component Properties statically inline via Component. Having these two facts in mind, there are not many use cases for this approach. IMHO this approach was intended to support client specific properties that are for example placed inside the bundle in the build process. Note: The destination is on the left side of the assignment and the source is on the right.
If only the source is specified that means no assignment , the file is added to the bundle root without the folder where it is included in the sources. For this we create a new component, although it would not be necessary, as we could also use one of the examples before remember that we could override the statically defined Component Properties dynamically via the Configuration Admin.
But I wanted to start with creating a new component, to have a class that can be directly compared with the previous ones. To specify properties via Configuration Admin it is not required to use any additional type element. You only need to know the configuration PID of the component to be able to provide a configuration object for it.
With regards to the Component Configuration this means, we need the configuration PID to be able to provide the configuration object for the component. If not specified explicitly it is the same as the component name, which is the fully qualified class name, if not explicitly set to another value. Via the configurationPolicy type element it is possible to configure the relationship between component and component configuration, e. The following values are available:.
If a configuration change happens at runtime, the SCR needs to take actions based on the configuration policy. To be able to react on a configuration change at runtime, a method to handle the modified life cycle can be implemented.
Using the DS annotations this can be done by using the Modified annotation, where the method parameters can be the same as for the other life cycle methods see the Getting Started Tutorial for further information on that.
Note: If you do not specify a modified life cycle method, the Component Configuration is deactivated and afterwards activated again with the new configuration object. This is true for the configuration policy require as well as for the configuration policy optional. Now create a component similar to the previous ones, that should only be satisfied if a configuration object is provided via the Configuration Admin.
If we now execute our example, we will see nothing new. The reason is of course that there is no configuration object yet provided by the Configuration Admin. Before we are able to do this we need to prepare our environment. Now we can create a Gogo Shell command that will be used to change a configuration object at runtime. Note: The ConfigurationAdmin reference is a static reference.
If you follow the example with Eclipse Neon you will probably see an error mentioning the missing unbind method. Either implement the unbind method for now or disable the error via Preferences. This is fixed with Eclipse Oxygen M2. These are necessary so the Apache Gogo Shell recognizes the component as a service that can be triggered by entering the corresponding values as a command to the console.
This shows the usage of Component Properties as additional meta-data that is examined by other components. Also note that we need to set the service type element, as only services can be referenced by other components. On executing the example you should notice that the AdminConfiguredComponent is not activated on startup, although it is an Immediate Component.
If you execute the command a second time with different parameters e. The reason for this is ConfigurationPolicy. Now you can play around with the implementation to get a better feeling. Note: To start from a clean state again you need to check the option Clear the configuration area before launching in the Settings tab of the Run configuration. Using the modified life cycle event enables to react on configuration changes inside the component itself.
To be able to react to configuration changes inside components that reference the service, the updated event method can be used. Now execute the example and call the configure command two times.
The result should look similar to this:. Calling the configure command the first time triggers the activation of the AdminConfiguredComponent , which then can be bound to the AdminReferencingComponent , which is satisfied and therefore can be activated afterwards. The second execution of the configure command triggers the modified life cycle event of the AdminConfiguredComponent and the updated event method of the AdminReferencingComponent. If you ask yourself why the AdminConfiguredComponent is still immediately activated, although we made it a service now, the answer is, because it is referenced by an Immediate Component.
This example is also helpful in getting a better understanding of the component life cycle. For example, if you remove the modified life cycle method from the AdminConfiguredComponent and call the configure command subsequently, both components get deactivated and activated, which results in new instances.
Modifying the Reference attributes will also lead to different results then. Change the cardinality , the policy and the policyOption to see the different behavior.
The correlation between cardinality , reference policy and reference policy option is explained in detail in the OSGi Compendium Specification table Some words about location binding here. The example above created a configuration object using the single parameter version of ConfigurationAdmin getConfiguration String.
The parameter specifies the PID for which a configuration object is requested or should be created. It then can not be consumed by other bundles. So the method is used to ensure that only the components inside the same bundle are affected. But there are also other cases where for example a configuration service in another bundle should be used to configure the components in all bundles of the application.
This can be done by creating an unbound configuration object using the two argument version of ConfigurationAdmin getConfiguration String, String. The first parameter is the PID and the second parameter specifies the bundle location string. If a configuration for the given PID already exists in the ConfigurationAdmin service, the location parameter will be ignored and the existing object will be returned.
But doing this introduces a dependency to the bundle that should be configured, which is typically not a good practice. Note that this could lead to issues if you have multiple services with the same PID in different bundles.
Multi-locations By using a multi-location binding, the configurations are dispatched to any target that has visibility to the configuration. A multi-location is specified with a leading question mark. Note: The multi-location name only has importance in case security is turned on and a ConfigurationPermission is specified. That means, it can not be used to restrict the targets based on the bundle symbolic name without security turned on.
Note: The Equinox DS implementation has some bugs with regards to location binding. Basically the location binding is ignored.
After restarting the IDE you are able to select org. Remember to remove org. For the org. Otherwise it will not be part of the resulting bundle. While we needed to add the Import-Package statement for org. So at that point there is no action necessary.
Only the launch configuration needs to be updated manually to include the Configuration Admin bundle. If you change a component class while the example is running, you will notice that the OSGi framework automatically restarts and the values set before via Configuration Admin are gone. A new feature added to the DS 1. The Component Property Type is specified as a custom annotation type, that contains property names, property types and default values.
Most of the examples found in the web show the definition of the annotation inside the component class. But of course it is also possible to create a public annotation in a separate file so it is reusable in multiple components. Note: If properties are needed that are not specified in the Component Property Type , you can have both as method arguments.
Since DS 1. Although the Component Property Type is defined as an annotation type, it is not used as an annotation. The reasons for choosing annotation types are:. As Component Property Types are intended to be type safe, an automatic conversion happens. This is also true for Component Properties that are specified via Java Properties files. To set configuration values via ConfigurationAdmin service you still need to operate on a Dictionary , which means you need to know the parameter names.
But of course on setting the values you are type safe. Another new feature in DS 1.
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Configuring OSGi Declarative Services | vogella blog
Version 1. To abstract over concrete database systems and vendor specific characteristics, the JDBC specification provides various classes and Service Provider Interfaces SPI that can be used for database interaction. Implementations are database specific and provided by the corresponding driver. Applications can rely on this mechanism to transparently access drivers and to stay independent from driver specific classes.
Additionally, this mechanism helps to use common OSGi practices and to avoid class loading problems. This specification uses a number of packages that are defined in Java SE 1. Lookup - Inspect available database drivers and provide means for driver access. Services - Uses a service model for getting the driver objects. Compatible - Minimize the amount of work needed to support this specification for existing drivers. Data Source Factory - Provides one of the different Data Sources that gives access to a database driver.
Application - The application that wants to access a relational database system. The classes and interfaces used in this specification come from the following packages:.
These packages have no associated version. It is assumed they come from the runtime environment. This specification is based on Java SE 1. Service properties are used to specify the database driver name, version, etc. These objects are then used by an application to interact with the relational database system in the standard way. The application can query the service registry for available Data Source Factory services. It can select particular drivers by filtering on the service properties.
This service based model is easy to use with dependency injection frameworks like Blueprint or Declarative Services. A Database Driver provides the connection between an Application and a particular database. Applications must be able to find the appropriate Database Driver.
The Database Driver must therefore register the Data Source Factory service with the following service properties:. This property is the primary key to find a driver's Data Source Factory.
It is not required that there is an actual class with this name. This property is informational. The version is not required to be an OSGi version, it should be treated as an opaque string. This version is likely not related to the package of the implementation class or its bundle. The previous properties are vendor-specific and are meant to further describe the Database Driver to the Application.
The Database Driver implementation bundle does not necessarily need to be the registrar of the Data Source Factory service. Any bundle can provide the Data Source Factory service and delegate to the appropriate driver specific implementation classes. This implies that the same driver can be registered multiple times. What happens to the objects created by the Data Source Factory service, and the objects they created, is undefined in this specification.
Database Drivers are not mandated to track the proper life cycle of these objects. A Database Driver must import the javax. The java. These packages are not normally versioned with OSGi version numbers. Bundles using the Data Source Factory must therefore ensure they get the proper imports, which is usually from the JRE.
Due to the lack of specified metadata, the deployer is responsible for ensuring this. Normally, the application needs access to specific drivers that match their needed relational database type. The service properties can be used to find the desired Database Driver. This model is well supported by dependency injection frameworks like Blueprint or Declarative Services. However, it can of course also be used with the basic service methods.
Which type of Connection provider that is actually required depends on the Application and the use case. For each type, the Data Source Factory service provides a method that returns the corresponding instance. Each method takes a Properties object as a parameter to pass a configuration to the Database Driver implementation. The configuration is driver-specific and can be used to specify the URL for the database and user credentials.
Common property names for these configuration properties are also defined in the DataSourceFactory interface. A Data Source Factory is not required to implement all of the factory methods.
If an implementation does not support a particular type then it must throw a SQL Exception. This specification does not provide a mechanism to depend on a Data Source Factory service that implements a particular factory method. The following code shows how a DataSource object could be created. The DataSourceFactory interface has several static fields that represent common property keys for the Properties instance. General properties are:. Which property keys and values are supported depends on the driver implementation.
Drivers can support additional custom configuration properties. A typical client would only use the DataSourceFactory. Containers generally offer connection pools and support XA transactions. To support containers, frameworks, or any client that wants to manage a pool, these Data Source types are included in the Data Source Factory service. Drivers are permitted to implement their own Data Source using an underlying connection pooling scheme.
This is driver-dependent and not related to the OSGi specifications. They are the same as what is defined for JDBC and the caller should know which properties make sense when passed to a given Data Source type.
If the driver does not support a given property with a given Data Source type then it can ignore it or it can throw an Exception. This specification depends on the JDBC specification for security. Bundles wishing to use this package must list the package in the Import-Package header of the bundle's manifest.
This package has two types of users: the consumers that use the API in this package and the providers that implement the API in this package.
Import-Package: org. A factory for JDBC connection factories. There are 3 preferred connection factories for getting JDBC connections: javax. DataSource , javax. ConnectionPoolDataSource , and javax. The "databaseName" property that DataSource clients should supply a value for when calling createDataSource Properties. The "description" property that DataSource clients should supply a value for when calling createDataSource Properties. The "networkProtocol" property that DataSource clients should supply a value for when calling createDataSource Properties.
The "password" property that DataSource clients should supply a value for when calling createDataSource Properties. The "url" property that DataSource clients should supply a value for when calling createDataSource Properties. The "user" property that DataSource clients should supply a value for when calling createDataSource Properties. Clients may filter or test this property to determine if the driver is suitable, or the desired one.
Returns A configured DataSource. Returns A configured Driver. DataSource javax. ConnectionPoolDataSource javax. XADataSource java. Options ConfigurationAttribute State EventType