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Jayasanka
Name : Jayasanka Illangarathne (J)

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Message driven beans(MDB) and transaction attributes

"Message-driven beans may declare only the NOT_SUPPORTED or REQUIRED transaction attribute. The other transaction attributes don't make sense in message-driven beans because they apply to client-initiated transactions." Why ? MDB are called asynchronously. Therefore NEVER, SUPPORTS, REQUIRES_NEW transaction attributes are not make sense, because there isn't pre-existing transaction context for MDB. NEVER throws Exception if there is pre-existing transaction context, but that don't ever occur. If there is pre-existing transaction context, SUPPORTS will run in that transaction context. (But, there is NO such in MDB!) REQUIRES_NEW always run in new transaction context, but this behavior is always the same to REQUIRED. REQUIRED Vs. REQUIRES_NEW why are we allowed to use a REQUIRED , but not a REQUIRES_NEW? When we specify theh RequiresNew, it comes with an implicit understanding that if the client has a transaction, it needs to be suspended. i.e. the existence of a cl...
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What is serialVersionUID?

If a class implements Serializable interface, your IDE worn you to add serialVersionUID or it add automatically. This variable holds a private static final long and IDE automatically declared it to 1L. class SerializeMe implements Serializable { private static final long serialVersionUID = 1L; private String data; public SerializeMe (String data) { this.data = data; } public String getData() { return data; } } Field data represents some information stored in the class. Note that serialVersionUID is a static value, then it should not have been serialized. But why is this so impotent? public class SerialVersionUIDTester { public static void main(String [] args) throws Exception { File file = new File("out.ser"); FileOutputStream fos = new FileOutputStream(file); ObjectOutputStream oos = new ObjectOutputStream(fos); SerializeMe serializeMe = new SerializeMe("serialVersionUID is 1L"); ...
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Kill a Process

Unix > ps -ef | grep java > kill -9 PID Windows > netstat -ano | findstr 8100 TCP    0.0.0.0:8100           0.0.0.0:0              LISTENING       8732 TCP    [::]:8100              [::]:0                 LISTENING       8732 > taskkill /PID 8732 /F  SUCCESS: The process with PID 8732 has been terminated.
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