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Examples of gateway patterns include: Security gateway This rather specific example of a gateway pattern offloads all non-standard security processing from the main infrastructure and will execute authentication, authorisation and possibly audit before calling the true destination. In this mode there is almost always a trusted link between the gateway and other parts of the ESB so that the security model required for those other parts of the ESB can be simplified.

Security gateways may reside in a different security zone to the rest of the ESB and would provide connectivity to external clients.

This pattern would support a wide range of incoming security protocols while simplifying security in other ESB components. Service connector The gateway pattern can provide the simplest possible way of connecting a number of existing services into an ESB when introduced as part of an enterprise architecture based on service oriented principles. The gateway introduces a point of control in the enterprise architecture and can bring a range of ad hoc services under the control of a service registry and associated governance but without the need to develop individual mediation flows for each service.

Messages enter the gateway and are routed onwards to an end provider, to a provider facade or to a further mediation flow. These standard content independent mediations are developed once in the gateway and can be applied to all incoming messages. These mediations may include any or all of validation, logging, audit, authentication and authorization. They may be applied universally or selectively based on the gateway properties, lookup based on request data or on data within the incoming request normally in headers.

Examples of such "applications" would include routing and transformation services, logging services etc. This may extend a single underlying messaging infrastructure or provide a bridge between different products and technologies.

Adapters may be used to provide access to applications or services which do not have an in-built messaging capability. Figure 5. Message-based integration patterns View image at full size Functionally the message-based patterns in some regards correspond to the service virtualization patterns.

However, there is a key difference in how we might think about them. In a message oriented model we are typically much more focused around the data that is flowing through the system and the set of actions that are to be applied to this in-flight data; that is, we have more of a producer-to-consumer view. Whilst not an absolute distinction this thinking may influence the context in which we seekto apply each pattern.

Some specific examples follow: Message router The message router pattern can be used to provide a strong level of decoupling between applications or services which need to exchange data by enabling data sent from one application to be routed to one of several potential target applications based on various conditions.

Context-based routers select an appropriate target based on the identity of the sender or on some aspect of the data carried in a protocol header. Content-based routers make a selection based on the content of the message payload.

Load-based routers use information about the application load on the various target systems. Message translator The message translator pattern allows data from one application to be mapped into the data format required by another application without either application being aware that such mapping is needed or taking place.

This pattern covers anything from direct mapping to highly complex transformations possibly involving lookups and cross references. Messaging bridge The messaging bridge pattern maps data from one transport mechanism to another without modifying the format or content of the message payload.

An implementation of this pattern must also handle the mapping between the different addressing schemes which might be used by the separate messaging systems. A frequent example of the use of this pattern is the bridging between JMS implementations from different vendors. Message aggregator The message aggregator pattern addresses the need to take multiple messages from one or more applications and merge them into a single piece of data to be propagated as a new message.

The inbound messages may come from independent applications or may be asynchronous response messages from a set of applications which received requests from an implementation of the message splitter pattern described below. An implementation of this pattern may simply concatenate the individual source messages or may incorporate some more sophisticated set of data mapping capabilities.

It must also be able to handle the failure of an expected inbound message to arrive within a prescribed time period and the subsequent late arrival of this message. Message splitter The message splitter pattern extracts subsets of a message which are then sent as separate messages to multiple target applications. A set of mapping rules define how the original inbound message is to be broken apart into constituent pieces. When such requests are being routed to a further system or systems there will be a requirement to correlate any response messages to the original request.

File processing An ESB may provide a managed execution environment for the processing of files either locally or using an FTP protocol. Figure 6. Some examples of this patterns and its use are: File Record Processor This pattern processes each record in an input file and accumulates the resulting processed records in one or more "transitory" target files which will be moved to target directories on completion.

This pattern supports the need to provide processing of batch files containing end of interval transactions. This might be the transfer of accumulated transactions for a day where the source and target systems cannot support transactional interfaces, or might be the transfer of transactions which are expected to occur at a particular time. Record Batcher This pattern receives data in service requests, messages or through adapters and after processing generates records to transitory files which are moved to target on completion.

It supports interactions between newer systems and legacy systems which support only batch interfaces. This might be the first step in a move towards a more service oriented architecture or perhaps the integration of a batch system acquired by acquisition into a more transactional environment.

This pattern also supports the need to accumulate data for overnight runs which might cover invoicing, billing, issue of contracts and related documents and renewal reminders. File record Distributor This pattern breaks a file down into records and uses each record to make a service call, or pass a message to one or more systems with a transactional interface.

A typical use of this pattern would be the processing EDI files which contain a number of transactions of different types to be routed and processed individually. This approach may also be taken to update systems with reference data especially where timing of such updates is not critical as in the case of updates with a given start date. Figure 7. Event-driven integration patterns Some examples of this patterns and its use are: Event Distributor This pattern provides for distribution of events with appropriate classification by "topic" and associated data to multiple interested parties who register their need to be informed about subsets of published events based on a tag "the topic" or data associated with each event.

Data is published to a publication point on the ESB and distributed from that publication point to all subscribers who have registered for that information.

Events published to a publication point may represent change of status, with the latest status available to all subscribers whether new or requesting a refresh.

Alternatively events may represent a stream of data with each "event" being distributed and then deleted. Event Filter This pattern provides for processing of events interactions entering the ESB to filter and transform them into a stream of significant events which are passed to an event engine.

This may be a event processing engine for detection of complex events or may be to a system which monitors business events, for example a dashboard application.

This pattern supports a one-way communication and is acting purely as a pre-processor to the event engine. A particular specialisation of this pattern would be the provision of entry points for data from a variety of sensors, actuators and adapters.

Event Extractor This pattern monitors interactions across the ESB and processes them to extract and pass relevant events to the event processing engine. Event Reactor This pattern is like the preceding pattern in that it acts as a pre-processor for an event engine. However this pattern supports a synchronous interaction with the event engine and may receive a response which indicates that the latest event has triggered a complex event.

The ESB flow may then react to that event by, for example, raising an alert to targets which need to act when such an event occurs. Operational aspects The aspect-oriented connectivity features of the bus include the interaction styles and security models described in subsequent sections together with various standard service management functions or utilities which will typically include such things as: validation.


Top 10 Best practice and Pattern books for the intermediate to advanced programmers

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