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| Java WMQ Exits using AOP |
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Message
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| JLRowe |
 Posted: Thu Jun 17, 2004 10:27 am Post subject: Java WMQ Exits using AOP |
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Yatiri
Joined: 25 May 2002
Posts: 664
Location: South East London
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An interesting question came up the other day, someone wanted to perform encyption of MQ messages, by encrypting them before they are placed on the queue and into persitent storage. A set of wrapper classes would do the job, but J2EE and message driven beans would ignore them. The easiest solution would be API exits written in java if such a thing existed. We could write MQPUT and MQGET exits in C and port them and support on each platform. Or, we could purchase a product, but again it would have to be supported on each different platform.
The other way is to used AOP, and specifically AspectJ which is the eclipse based AOP project for java. AOP excels at this kind of problem, we have some classes that we want to augment with additional functionality. Specifically, we want to intercept mqput and mqget calls, as they are in transit so we can get the message, encrypt it, then put it back and continue with the method call without having to change the code of the caller and callee.
This is the base java class PutTest, which simply places a message on the queue TEST1 on queue manager Development:
| Code: |
package test;
import com.ibm.mq.*;
public class PutTest {
public static void main(String[] args) {
System.out.println("Start...");
try {
MQQueueManager mqQueueManager = new MQQueueManager("Development");
MQQueue queue = mqQueueManager.accessQueue("TEST1", MQC.MQOO_OUTPUT);
MQMessage message = new MQMessage ();
message.writeString("pre-scrambled content");
System.out.println("Just before put()...");
queue.put(message);
System.out.println("Just after put()...");
queue.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
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If we run this code, we get the following result and our message in the queue:
| Code: |
Start...
Just before put()...
Just after put()...
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This is our code that intercepts the mqput call:
| Code: |
package test;
import com.ibm.mq.*;
/**
* Aspect MessageEncryption : An aspect to ensure our MQ messages are encrypted, by intercepting calls to mqput()
*/
public aspect MessageEncryption {
/**
* Static method to encrypt/decrypt a string by reversing the String
*/
static String encryptString(String in) {
StringBuffer encryptedText = (new StringBuffer(in)).reverse();
return encryptedText.toString();
}
/**
* This pointcut callPointCut() represents all the places in the code where
* the method MQQueue.put is executed in the all classes
*/
pointcut mqPutPointcut(): execution(void MQQueue.put(MQMessage));
/**
* Our advice runs just before the called method (MQQueue.put) is executed
*/
before(): mqPutPointcut()
{
System.out.println("In advice... before():mqPutPointcut");
// get an array of objects that are being passed in the method call
Object[] pointcutArguments = thisJoinPoint.getArgs();
// there is only one object being passed, thats the first one, the MQMessage
MQMessage message = (MQMessage)pointcutArguments[0];
// encrypt the contents of message
try {
message.seek(0);
String clearText = message.readString(message.getMessageLength());
// reverse clearText to encryptedText
String encryptedText = encryptString(clearText);
// update the message text to be encrypted
message.clearMessage();
message.writeString(encryptedText.toString());
message.format = MQC.MQFMT_STRING;
// tell us what happened
System.out.println("Got a reference to the MQMessage and encrypted it...");
} catch (java.io.IOException e) {
e.printStackTrace();
}
System.out.println("Leaving advice... before():mqPutPointcut");
}
}
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To compile the aspect, we have to do a few things. Our pointcut is right in the middle of the IBM WMQ class libraries. So, we have to pass the IBM libraries through the AspectJ compiler, allowing our advise to be weaved into the bytecode.
Our PutTest class then runs with these aspects weaved in:
| Code: |
Start...
Just before put()...
In advice... before():mqPutPointcut
Got a reference to the MQMessage and encrypted it...
Leaving advice... before():mqPutPointcut
Just after put()...
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This time the advice has been woven into the java bytecode, and allows us to intercept the MQQueue.put(MQMessage) method, obtain a reference to the MQMessage as it is being passed from method-to-method, encrypt the message and return from the advise allowing the put method to continue with our newly encrypted message. |
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