Enterprise Integration Solutions

134 Part II Message Endpoints

Using MSMQ Triggers to Respond to Messages

Most EI solutions that reside on the Windows platform will use Microsoft Mes-

sage Queuing (MSMQ) at some point. As mentioned, whenever possible, your

integration code should respond to events rather than query for changes. Having

a solution execute exactly one action in response to exactly one event is impor-

tant. Compared to polling, this method is significantly more efficient. Performing

an action on a server whenever a message arrives in a specified MSMQ queue

is often necessary. Even a task as simple as retrieving the message and deter-

mining how to use it is easily accomplished by using MSMQ triggers. In this

section, we will examine how to create and use an MSMQ trigger to execute

code on a machine.

Problem

In keeping with the best practice of using event-driven solutions instead of poll-

ing-driven ones, we want to execute a task whenever a message arrives in a spe-

cific queue without having to continually poll that queue. Ideally, we also want

to determine what code to run based on either the message header or content.

Solution

You can solve this problem by using MSMQ triggers. An MSMQ trigger is set up on

the box that manages the queue and is activated based on criteria you specify.

In the following example, it will be triggered any time a message shows up in

the specified queue. The first step is to add a rule for the trigger:

1. Locate and expand Message Queuing under Computer Management

in the Administrative Tools menu.

2. Expand Message Queuing Triggers.

3. Right-click Rules and select New. Then select Rule.

G06LS11

Chapter 6 File Endpoints 135

4. When the New Rule dialog box appears, enter a name and descrip-

tion for the rule. Then click Next.

G06LS12

5. Select the condition from the drop-down list, add the parameter, and

then click Add. Your new rule should appear in the Condition List box:

G06LS13

6. Click Next.

7. Enter the ProgID and method of the COM you want to trigger, or

select an .exe file to run.

8. Click Parameters. Select any parameters you want to add and click Add.

9. Click Finish.

136 Part II Message Endpoints

Your rule is now added. The next step is to attach your new rule to an

MSMQ trigger:

1. Right-click Triggers and select New. Then select Trigger. You should

see the following:

G06LS14

2. Type a trigger name and the queue name. Select Retrieval and click

Next. A dialog box similar to the following appears:

G06LS15

3. Select your rule in the left box and click Attach. Then click Finish.