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The Java EE 6 Tutorial, Volume I

Chapter 28 Resource Connections

JavaTM EE components can access a wide variety of resources, including databases, mail sessions, Java Message Service objects, and URLs. The Java EE 6 platform provides mechanisms that allow you to access all these resources in a similar manner. This chapter describes how to get connections to several types of resources.

The following topics are addressed here:

Resources and JNDI Naming

In a distributed application, components need to access other components and resources such as databases. For example, a servlet might invoke remote methods on an enterprise bean that retrieves information from a database. In the Java EE platform, the Java Naming and Directory InterfaceTM (JNDI) naming service enables components to locate other components and resources.

A resource is a program object that provides connections to systems, such as database servers and messaging systems. (A Java DataBase Connectivity (JDBCTM) resource is sometimes referred to as a data source.) Each resource object is identified by a unique, people-friendly name, called the JNDI name.

For example, the JNDI name of the JDBC resource for the Java DB database that is shipped with Sun GlassFishTM Enterprise Server v3 (Enterprise Server) is jdbc/__default.

An administrator creates resources in a JNDI namespace. In the Enterprise Server, you can use either the Administration Console or the asadmin command to create resources. Applications then use annotations to inject the resources. If an application uses resource injection, the Enterprise Server invokes the JNDI API, and the application is not required to do so. However, it is also possible for an application to locate resources by making direct calls to the JNDI API.

A resource object and its JNDI name are bound together by the naming and directory service. To create a new resource, a new name-object binding is entered into the JNDI namespace. You inject resources by using the @Resource annotation in an application.

You can use a deployment descriptor to override the resource mapping that you specify in an annotation. Using a deployment descriptor allows you to change an application by repackaging it, rather than by both recompiling the source files and repackaging. However, for most applications, a deployment descriptor is not necessary.

DataSource Objects and Connection Pools

To store, organize, and retrieve data, most applications use a relational database. Java EE 6 components may access relational databases through the JDBC API. For information on this API, see http://java.sun.com/javase/technologies/database/.

In the JDBC API, databases are accessed by using DataSource objects. A DataSource has a set of properties that identify and describe the real world data source that it represents. These properties include information such as the location of the database server, the name of the database, the network protocol to use to communicate with the server, and so on. In the Sun GlassFish Enterprise Server, a data source is called a JDBC resource.

Applications access a data source using a connection, and a DataSource object can be thought of as a factory for connections to the particular data source that the DataSource instance represents. In a basic DataSource implementation, a call to the getConnection method returns a connection object that is a physical connection to the data source.

If a DataSource object is registered with a JNDI naming service, an application can use the JNDI API to access that DataSource object, which can then be used to connect to the data source it represents.

DataSource objects that implement connection pooling also produce a connection to the particular data source that the DataSource class represents. The connection object that the getConnection method returns is a handle to a PooledConnection object rather than being a physical connection. An application uses the connection object in the same way that it uses a connection. Connection pooling has no effect on application code except that a pooled connection, like all connections, should always be explicitly closed. When an application closes a connection that is pooled, the connection is returned to a pool of reusable connections. The next time getConnection is called, a handle to one of these pooled connections will be returned if one is available. Because connection pooling avoids creating a new physical connection every time one is requested, applications can run significantly faster.

A JDBC connection pool is a group of reusable connections for a particular database. Because creating each new physical connection is time consuming, the server maintains a pool of available connections to increase performance. When an application requests a connection, it obtains one from the pool. When an application closes a connection, the connection is returned to the pool.

Applications that use the Persistence API specify the DataSource object they are using in the jta-data-source element of the persistence.xml file.

<jta-data-source>jdbc/MyOrderDB</jta-data-source>

This is typically the only reference to a JDBC object for a persistence unit. The application code does not refer to any JDBC objects.

Resource Injection

The javax.annotation.Resource annotation is used to declare a reference to a resource. @Resource can decorate a class, a field, or a method. The container will inject the resource referred to by @Resource into the component either at runtime or when the component is initialized, depending on whether field/method injection or class injection is used. With field and method-based injection, the container will inject the resource when the application is initialized. For class-based injection, the resource is looked up by the application at runtime.

@Resource has the following elements:

The name element is the JNDI name of the resource, and is optional for field- and method-based injection. For field-based injection, the default name is the field name qualified by the class name. For method-based injection, the default name is the JavaBeansTM property name based on the method qualified by the class name. The name element must be specified for class-based injection.

The type of resource is determined by one of the following:

For class-based injection, the type element is required.

The authenticationType element is used only for connection factory resources, such as the resources of a connector (also called the resource adapter or data source). This element can be set to one of the javax.annotation.Resource.AuthenticationType enumerated type values: CONTAINER, the default, and APPLICATION.

The shareable element is used only for Object Resource Broker (ORB) instance resources or connection factory resource. It indicates whether the resource can be shared between this component and other components, and may be set to true, the default, or false.

The mappedName element is a non-portable, implementation-specific name to which the resource should be mapped. Because the name element, when specified or defaulted, is local only to the application, many Java EE servers provide a way of referring to resources across the application server. This is done by setting the mappedName element. Use of the mappedName element is non-portable across Java EE server implementations.

The description element is the description of the resource, typically in the default language of the system on which the application is deployed. It is used to help identify resources, and to help application developers choose the correct resource.

Field-Based Injection

To use field-based resource injection, declare a field and decorate it with the @Resource annotation. The container will infer the name and type of the resource if the name and type elements are not specified. If you do specify the type element, it must match the field’s type declaration.

package com.example;

public class SomeClass {
    @Resource
    private javax.sql.DataSource myDB;
...
}

In the code above, the container infers the name of the resource based on the class name and the field name: com.example.SomeClass/myDB. The inferred type is javax.sql.DataSource.class.

package com.example;

public class SomeClass {
    @Resource(name="customerDB")
    private javax.sql.DataSource myDB;
...
}

In the code above, the JNDI name is customerDB, and the inferred type is javax.sql.DataSource.class.

Method-Based Injection

To use method-based injection, declare a setter method and decorate it with the @Resource annotation. The container will infer the name and type of the resource if the name and type elements are not specified. The setter method must follow the JavaBeans conventions for property names: the method name must begin with set, have a void return type, and only one parameter. If you do specify the type element, it must match the field’s type declaration.

package com.example;

public class SomeClass {

    private javax.sql.DataSource myDB;
...
    @Resource
    private void setMyDB(javax.sql.DataSource ds) {
        myDB = ds;
    }
...
}

In the code above, the container infers the name of the resource based on the class name and the field name: com.example.SomeClass/myDB. The inferred type is javax.sql.DataSource.class.

package com.example;

public class SomeClass {

    private javax.sql.DataSource myDB;
...
    @Resource(name="customerDB")
    private void setMyDB(javax.sql.DataSource ds) {
        myDB = ds;
    }
...
}

In the code above, the JNDI name is customerDB, and the inferred type is javax.sql.DataSource.class.

Class-Based Injection

To use class-based injection, decorate the class with a @Resource annotation, and set the required name and type elements.

@Resource(name="myMessageQueue",
                type="javax.jms.ConnectionFactory")
public class SomeMessageBean {
...
}

Declaring Multiple Resources

The @Resources annotation is used to group together multiple @Resource declarations for class-based injection.

@Resources({
    @Resource(name="myMessageQueue",
                    type="javax.jms.ConnectionFactory"),
    @Resource(name="myMailSession",
                    type="javax.mail.Session")
})
public class SomeMessageBean {
...
}

The code above shows the @Resources annotation containing two @Resource declarations. One is a Java Message Service (JMS) message queue, and the other is a JavaMailTM session.

Resource Adapters

A resource adapter is a Java EE component that implements the Java EE Connector Architecture for a specific Enterprise Information System (EIS). Examples of EISs include Enterprise Resource Planning (ERP), mainframe transaction processing (TP), and database systems. As illustrated in Figure 35-1, the resource adapter facilitates communication between a Java EE application and an EIS.

Resource Adapter Contracts

Stored in a Resource Adapter Archive (RAR) file, a resource adapter can be deployed on any Java EE server, much like a Java EE application. An RAR file may be contained in an Enterprise Archive (EAR) file, or it may exist as a separate file.

A resource adapter is analogous to a JDBC driver. Both provide a standard API through which an application can access a resource that is outside the Java EE server. For a resource adapter, the target system is an EIS; for a JDBC driver, it is a DBMS. Resource adapters and JDBC drivers are rarely created by application developers. In most cases, both types of software are built by vendors that sell products such as tools, servers, or integration software.

Resource Adapter Contracts

The resource adapter mediates communication between the Java EE server and the EIS by means of contracts. The application contract defines the API through which a Java EE component such as an enterprise bean accesses the EIS. This API is the only view that the component has of the EIS. The system contracts link the resource adapter to important services that are managed by the Java EE server. The resource adapter itself and its system contracts are transparent to the Java EE component.

Management Contracts

The Java EE Connector Architecture defines system contracts that enable resource adapter life cycle and thread management.

Life cycle Management

The Connector Architecture specifies a life cycle management contract that allows an application server to manage the life cycle of a resource adapter. This contract provides a mechanism for the application server to bootstrap a resource adapter instance during the deployment or application server startup. It also provides a means for the application server to notify the resource adapter instance when it is undeployed or when an orderly shutdown of the application server takes place.

Work Management Contract

The Connector Architecture work management contract ensures that resource adapters use threads in the proper, recommended manner. It also enables an application server to manage threads for resource adapters.

Resource adapters that improperly use threads can jeopardize the entire application server environment. For example, a resource adapter might create too many threads or it might not properly release threads it has created. Poor thread handling inhibits application server shutdown. It also impacts the application server's performance because creating and destroying threads are expensive operations.

The work management contract establishes a means for the application server to pool and reuse threads, similar to pooling and reusing connections. By adhering to this contract, the resource adapter does not have to manage threads itself. Instead, the resource adapter has the application server create and provide needed threads. When the resource adapter is finished with a given thread, it returns the thread to the application server. The application server manages the thread: It can return the thread to a pool and reuse it later, or it can destroy the thread. Handling threads in this manner results in increased application server performance and more efficient use of resources.

In addition to moving thread management to the application server, the Connector Architecture provides a flexible model for a resource adapter that uses threads:

With the latter two approaches, the submitting thread and the work thread may execute simultaneously or independently from each other. For these approaches, the contract specifies a listener mechanism to notify the resource adapter that the thread has completed its operation. The resource adapter can also specify the execution context for the thread, and the work management contract controls the context in which the thread executes.

Generic Work Context Contract

A generic work context contract enables a resource adapter to control the contexts in which the Work instances submitted by it are executed by the application server's WorkManager. A Generic Work context mechanism also enables an application server to support new message inflow and delivery schemes. It also provides a richer contextual Work execution environment to the resource adapter while still maintaining control over concurrent behavior in a managed environment.

The Generic Work Context contract standardizes the following contexts: Transaction Context and Security Context.

Transaction Context

The transaction context between the resource adapter and the application server leverages the Generic Work Context mechanism by describing a standard WorkContext, the TransactionContext. It represents the standard interface that a resource adapter can use to propagate transaction context information from the EIS to the application server.

Security Context

The security context between the resource adapter and the application server leverages the Generic Work Context mechanism by describing a standard WorkContext, the SecurityContext, that can be provided by the resource adapter while submitting a Work for execution.

The SecurityContext provides a portable mechanism for the resource adapter to pass security context information to the application server. This work context enables an EIS or resource adapter to flow-in security context information while submitting a Work to a WorkContext for execution.

Work Security Map

A work security map matches EIS identities to the application server domain's identities.

Hints Context

The propagation of Quality of Service hints to a WorkManager for the execution of a Work instance is standardized through the HintsContext class. It provides a mechanism for the resource adapter to pass quality-of-service metadata to the WorkManager during the submission of a Work instance. The application server can use the specified hints to control the execution of the Work instance.

Outbound Contracts

The Connector Architecture defines system-level contracts between an application server and an EIS that enable outbound connectivity to an EIS: connection management, transaction management, and security.

Connection Management Contract

The connection management contract supports connection pooling, a technique that enhances application performance and scalability. Connection pooling is transparent to the application, which simply obtains a connection to the EIS.

Transaction Management Contract

The Connector Architecture supports the concept of transactions - a number of operations that must be committed together or not at all for the data to remain consistent and to maintain data integrity.

A local transaction is limited in scope to a single EIS system, and the EIS resource manager itself manages such transaction. An XA transaction or global transaction can span multiple resource managers. This form of transaction requires transaction coordination by an external transaction manager, typically bundled with an application server. A transaction manager uses a two-phase commit protocol to manage a transaction that spans multiple resource managers or EISs. It uses one-phase commit optimization if only one resource manager is participating in an XA transaction.

The Connector Architecture defines a transaction management contract between an application server and a resource adapter . The transaction management contract extends the connection management contract and provides support for management of both local and XA transactions. These contracts enable an application server to provide the infrastructure and runtime environment for transaction management. Application components rely on this transaction infrastructure to support the component-level transaction model.

An application server is required to support all three levels of transactions:

Security Management Contract

The security management contract provides mechanisms for authentication, authorization, and secure communication between a Java EE server and an EIS to protect the information in the EIS.

Inbound Contracts

The Java EE Connector Architecture defines system contracts between a Java EE server and an EIS that enable inbound connectivity from the EIS: pluggability contracts for message providers and contracts for importing transactions.

Messaging Contracts

To enable external systems to connect to a Java EE application server, the Connector Architecture extends the capabilities of message-driven beans to handle messages from any message provider. That is, message-driven beans are no longer limited to handling JMS messages. Instead, EISs and message providers can plug any message provider, including their own custom or proprietary message providers, into a Java EE server.

To provide this feature, a message provider or an EIS resource adapter implements the messaging contract, which details APIs for message handling and message delivery. A conforming resource adapter is assured of the ability to send messages from any provider to a message-driven bean, and it also can be plugged into a Java EE server in a standard manner.

Transaction Inflow

The Connector Architecture supports importing transactions from an EIS to a Java EE server. The architecture specifies how to propagate the transaction context from the EIS. For example, a transaction can be started by the EIS, such as the Customer Information Control System (CICS). Within the same CICS transaction, a connection can be made through a resource adapter to an enterprise bean on the application server. The enterprise bean does its work under the CICS transaction context and commits within that transaction context.

The Connector Architecture also specifies how the container participates in transaction completion and how it handles crash recovery to ensure that data integrity is not lost.

Metadata Annotations

Java EE Connector Architecture 1.6 introduces a set of annotations to minimize the need for deployment descriptors.

The specification allows a resource adapter to be developed in mixed-mode form, that is the ability for a resource adapter developer to use both metadata annotations and deployment descriptors in applications. An application assembler or deployer may use the deployment descriptor to override the metadata annotations specified by the resource adapter developer.

A new attribute, metadata-complete, is introduced in the Connector 1.6 deployment descriptor (the ra.xml file). The metadata-complete attribute defines whether the deployment descriptor for the resource adapter module is complete, or whether the class files available to the module and packaged with the resource adapter need to be examined for annotations that specify deployment information.

For the complete list of annotations and JavaBeans components introduced in Java EE 6, see http://jcp.org/en/jsr/detail?id=322.

Replacing Deployment Descriptors With Metadata Annotations

The use of annotations reduces or completely eliminates the need to deal with a deployment descriptor in many cases. The use of annotations also reduces the need to keep the deployment descriptor synchronized with changes to source code.

The following examples provide sample deployment descriptors and equivalent annotations.

Example 1: @Connector Annotation

The following deployment descriptor defines a connector:

<connector xmlns "http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/connector_1_6.xsd" 
version="1.6">
<description>Sample adapter using the JavaMail API</description>
<display-name>InboundResourceAdapter</display-name>
<icon></icon>
<vendor-name>Sun Microsystems, Inc</vendor-name>

<eis-type>MAIL</eis-type>
<resourceadapter-version>1.0</resourceadapter-version>
...
...
...
<authentication-mechanism>
	<authentication-mechanism-type>BasicPassword</authentication-mechanism-type>
<credential-interface>javax.resource.spi.security.PasswordCredential</credential-interface>
</authentication-mechanism>
<reauthentication-support>false</reauthentication-support>
...
...
</connector>

The equivalent metadata annotation is as follows:

@Connector(
description = "Sample adapter using the JavaMail API",
   displayName = "InboundResourceAdapter",
   vendorName = "Sun Microsystems, Inc.",
    eisType = "MAIL",
    version = "1.0",
   authMechanisms = {
                @AuthenticationMechanism(
          authMechanism = "BasicPassword",
credentialInterface = AuthenticationMechanism.CredentialInterface.PasswordCredential
                )
        }

/*
 // Since the following attribute values denote the default values of the annotation,
 // they need not be specified explicitly

 transactionSupport = TransactionSupport.TransactionSupportLevel.NoTransaction,
    reauthenticationSupport = false
*/
)

public class ResourceAdapterImpl 
implements ResourceAdapter, java.io.Serializable
{
...
...
}

Example 2: @ConnectionDefinition Annotation

The following deployment descriptor snippet describes a connection definition:

<connection-definition>
<managedconnectionfactory-class>
samples.mailra.ra.outbound.ManagedConnectionFactoryImpl
</managedconnectionfactory-class>
<config-property><config-property-name>serverName</config-property-name>
<config-property-type>java.lang.String</config-property-type>
<config-property-value>UnknownHostName</config-property-value>

...
...
<connectionfactory-interface>samples.mailra.api.JavaMailConnectionFactory</connectionfactory-interface>
<connectionfactory-impl-class>samples.mailra.ra.outbound.JavaMailConnectionFactoryImpl</connectionfactory-impl-class>
<connection-interface>samples.mailra.api.JavaMailConnection</connection-interface>
<credential-interface>javax.resource.spi.security.PasswordCredential</credential-interface>
<connection-impl-class>samples.mailra.ra.outbound.JavaMailConnectionImpl</connection-impl-class>
</connectiondefinition>

The equivalent metadata annotation is as follows:

@ConnectionDefinition(
        connectionFactory = 
samples.mailra..api.JavaMailConnectionFactory.class,
        connectionFactoryImpl = 
samples.mailra.ra.outbound.JavaMailConnectionFactoryImpl.class,
        connection = samples.connectors.mailconnector.api.JavaMailConnection.class,
        connectionImpl = 
samples.mailra..ra.outbound.JavaMailConnectionImpl.class
)
public class ManagedConnectionFactoryImpl implements
    ManagedConnectionFactory, Serializable
{
...
...
 @ConfigProperty(
          defaultValue = "UnknownHostName"
    )
    public void setServerName(String serverName)
    {
       ...
    }

}

Example 3: @Activation Annotation

The following deployment descriptor snippet describes the messaging capabilities of a resource adapter:

<messageadapter>
<messagelistener>
<messagelistener-type>samples.mailra.api.JavaMailMessageListener</messagelistener-type>
<activationspec>
<activationspec-class>samples.mailra.ra.inbound.ActivationSpecImpl</activationspec-class>
required-config-property>
	<config-property-name>serverName</config-property-name>
</required-config-property>
<required-config-property>
	<config-property-name>userName</config-property-value>
</required-config-property>
<required-config-property>
	<config-property-name>password</config-property-value>
</required-config-property>
<required-config-property>
<config-property-name>folderName</config-property-value>
</required-config-property>
<required-config-property>
<description>Normally imap or pop3</description>
<config-property-name>protocol</config-property-name>
<config-property-value>IMAP</config-property-value>
</required-config-property>
</activationspec>
</messagelistener>
</messageadapter>

The equivalent metadata annotation is as follows:

@Activation(
        messageListeners = {samples.mailra.api.JavaMailMessageListener.class}

)
public class ActivationSpecImpl implements javax.resource.spi.ActivationSpec,
                                           java.io.Serializable
{
...
 @ConfigProperty()
    // serverName property value
    private String serverName = new String("");

    @ConfigProperty()
    // userName property value
    private String userName = new String("");

    @ConfigProperty()
    // password property value
    private String password = new String("");

    @ConfigProperty()
    // folderName property value
    private String folderName = new String("Inbox");

    // protocol property value
    // Normally imap or pop3
    @ConfigProperty(
            description = "Normally imap or pop3"
    )
    private String protocol = new String("imap");


...
...
}

Common Client Interface

This section describes how components use the Connector Architecture Common Client Interface (CCI) API and a resource adapter to access data from an EIS.

Defined by the Java EE Connector Architecture specification, the CCI defines a set of interfaces and classes whose methods allow a client to perform typical data access operations. The CCI interfaces and classes are as follows:

A client or application component that uses the CCI to interact with an underlying EIS does so in a prescribed manner. The component must establish a connection to the EIS's resource manager, and it does so using the ConnectionFactory. The Connection object represents the actual connection to the EIS and is used for subsequent interactions with the EIS.

The component performs its interactions with the EIS, such as accessing data from a specific table, using an Interaction object. The application component defines the Interaction object using an InteractionSpec object. When the application component reads data from the EIS (such as from database tables) or writes to those tables, it does so using a particular type of Record instance: either a MappedRecord, an IndexedRecord, or a ResultSet instance. Just as the ConnectionFactory creates Connection instances, a RecordFactory creates Record instances.

Note, too, that a client application that relies on a CCI resource adapter is very much like any other Java EE client that uses enterprise bean methods.

Further Information about Resources

For more information about resources and annotations, see: