Renewing the dynamic IP from ISP

Got this error for broadband connection from reliance : "Connection has limited connectivity or no connection" when starting up the system. To solve this problem we need to release the existing IP and get a new IP. To do the same,
1. execute from cmd prompt : ipconfig/release
2. then, ipconfig/renew (no space between ipconfig and renew).

EJB Lookup

1. When deploying EJB, it has a name(if specified using annotation : @Stateless(name="SessionEJB") or if descriptor: <ejb-name>SessionEJB</ejb-name>.

2. This EJB deployed to OC4J. Now to do a lookup for this EJB, we can use either ApplicationClientInitialContextFactory or RMIInitialContextFactory.

3. In case of RMIInitialContextFactory, no need of application-client.xml and the context lookup will be : new InitialContext.lookup("SessionEJB").

4. In case of ApplicationClientInitialContextFactory, we need application-client.xml. It has to introduce the ejb refrence going to be used in code as:

<application-client 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/application-client_1_4.xsd" version="1.4" xmlns="http://java.sun.com/xml/ns/j2ee">
<display-name>InterceptorTest-app-client</display-name>
<ejb-ref>
<ejb-ref-name>ejb/SessionEJB</ejb-ref-name>
<ejb-ref-type>Session</ejb-ref-type>
<remote>myEJB.SessionEJB</remote>
<ejb-link>SessionEJB</ejb-link>
</ejb-ref>
</application-client>

5. Here, ejb-link is used to link to the actual bean. Now, in the client code we use the ejb-ref-name for lookup as:

new InitialContext().lookup("java:comp/env/ejb/SessionEJB");

MDB deployment in OC4J

1. Create the MDB(normal java class with @MessageDriven annotation). Set the ActivationConfigs.

@MessageDriven(
activationConfig = {
@ActivationConfigProperty(propertyName="connectionFactoryJndiName", propertyValue="jms/TopicConnectionFactory"),
@ActivationConfigProperty(propertyName="destinationName",
propertyValue="jms/demoTopic"),
@ActivationConfigProperty(propertyName="destinationType", propertyValue="javax.jms.Topic"),
@ActivationConfigProperty(propertyName="messageSelector", propertyValue="RECIPIENT = 'MDB'") } )

2. Create EJB jar deployment profile(MDBServer.deploy) for the above MDB and deploy it to OC4J server(application name = MDBServer)

3. In same project, create the MDBClient. Inject the resources @Resource(name="jms/demoQueue") and @Resource(name="jms/TopicConnectionFactory"). Use connectionFactory and create connection, then session, message and send the message using producer.

4. In Jdeveloper create jndi.properties file with:

java.naming.factory.initial= oracle.j2ee.naming.ApplicationClientInitialContextFactory
java.naming.provider.url=ormi://localhost:23791/MDBServer
java.naming.security.principal=oc4jadmin
java.naming.security.credentials=welcome

5. Create client Jar deployment profile from Jdeveloper. This creates application-client.xml. Modify application-client.xml and add following lines for the resource reference entries(Make sure to mention the main class file name in descriptor creation)

<application-client 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/application-client_1_4.xsd" version="1.4" xmlns="http://java.sun.com/xml/ns/j2ee">
<display-name>MDB1-app-client</display-name>
<resource-env-ref>
<resource-env-ref-name>jms/demoTopic</resource-env-ref-name>
<resource-env-ref-type>javax.jms.Topic</resource-env-ref-type>
</resource-env-ref>
<resource-env-ref>
<resource-env-ref-name>jms/TopicConnectionFactory </resource-env-ref-name>
<resource-env-ref-type>javax.jms.TopicConnectionFactory </resource-env-ref-type>
</resource-env-ref>
</application-client>

6. Deploy the deployment profile MDBClient.deploy to MDBClient.jar.

7. From command prompt containing the jar file, set class path and run :

D:\installs\JdevStudio10131\jdev\mywork\MDB\MDB1\deploy>set CLASSPATH =.\;D:\installs\oc4j\j2ee\home\oc4jclient.jar;D:\installs\oc4j\j2ee\home\lib\javax77.jar;

D:\installs\JdevStudio10131\jdev\mywork\MDB\MDB1\deploy>java oracle.oc4j.appclient.AppClientContainer MDBClient.jar

Output from the application server log will contain:

06/12/24 20:26:44 onMessage() - Message[ID:Oc4jJMS.Message.krishnamoorthy.64e0c3
ab:10fb4f6b670:-8000.4]

onMessage method of the MDB just does a system.out.println(message)

Note: Without creating jar of client files and if I directly run using:

D:\installs\JdevStudio10131\jdev\mywork\MDB\MDB1\classes>java -Djava.naming.factory.initial=oracle.j2ee.naming.ApplicationClientInitialContextFactory -Djava.naming.provider.url=ormi://localhost:23791/MDBServer -Djava.naming.security.principal=oc4jadmin -Djava.naming.security.credentials=welcome myJMSClient.TestJMSClient

I get

Exception in thread "main" java.lang.NullPointerException
at myJMSClient.TestJMSClient.main(TestJMSClient.java:22)

So, should a JMS client be run always using AppClientContainer as :

java oracle.oc4j.appclient.AppClientContainer MDBClient.jar

Running EJB Client Standalone

HelloWorld.java

package myEJB;

import javax.ejb.Remote;

@Remote
public interface HelloWorld {
public String sayHello(String name);
}

HelloWorldBean.java

package myEJB;

import javax.ejb.Stateless;

@Stateless
public class HelloWorldBean implements HelloWorld {
private int count;

public String sayHello(String name) {
count++;
System.out.println("sayHello method from Bean ");
return "Hello " + name + " Count : " + count;
}
}

Compile the classes and run in embedded oc4j of jdeveloper. Or create a ejb jar deployment profile and deploy it to standalone oc4j server. Deployment name is the application name in the standalone oc4j. Let us say application is HelloWorldDeploy. Ear file contains jar file and META-INF. Inside META-INF is the application.xml containing the name of ejb module jar file. Jar file contains the interface and bean classes. After deploying, create a test client as follows:

HelloWorldClient.java

package myEJB;

import java.util.Hashtable;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;

public class HelloWorldClient {
public static void main(String [] args) {
try {
final Context context = new InitialContext();
HelloWorld helloWorld = (HelloWorld)context.lookup("java:comp/env/ejb/HelloWorldBean");
// Call any of the Remote methods below to access the EJB
System.out.println(helloWorld.sayHello( "Krishna" ));
} catch (Exception ex) {
ex.printStackTrace();
}
}
}

To invoke ejb method from command line:

D:\work\MyWork\ejb\ejb3>set CLASSPATH=D:\installs\JdevStudio10131\j2ee\home\oc4jclient.jar;.\;

D:\work\MyWork\ejb\ejb3>java -Djava.naming.factory.initial=oracle.j2ee.naming.Ap
plicationClientInitialContextFactory -Djava.naming.provider.url=ormi://localhost
:23791/HelloWorldDeploy -Djava.naming.security.principal=oc4jadmin -Djava.naming
.security.credentials=welcome myEJB.HelloWorldClient

Output is : Hello Krishna Count : 1

Transaction Isolation Level

Good link for getting a refresh on the isolation level: http://www.oracle.com/technology/oramag/oracle/05-nov/o65asktom.html
Oracle supports READ COMMITTED and SERIALIZABLE. Oracle doesn't allow dirty reads(READ UNCOMMITTED). It allows a third isolation level which is READ ONLY. No insert, update, delete can be done in this mode.

RMI tutorial on SUN

1. Start the rmiregistry at the default port 1099. (rmiregistry.exe)

2. Start the Local Http server for delivering class files between server-RMI and RMI-Client.

D:\work\MyWork\rmi\suntutorial>java examples.classServer.ClassFileServer 1185 D:\work\MyWork\rmi\suntutorial

3. Then start the ComputeEngine server using :

D:\work\MyWork\rmi\suntutorial>java -cp .\;compute.jar -Djava.rmi.server.codebase=http://pc-krsethur-in:1185/ -Djava.rmi.server.hostname=pc-krsethur-in -Djava.security.policy=D:\work\MyWork\rmi\suntutorial\server.policy engine.ComputeEngine

4. Remove the client files from the suntutorial folder and place it in a folder named test under this suntutorial so that RMI will get the files using http from the client(thus, the above classpath doesn't include the client classes).

5. server.policy should have the line

grant {
permission java.net.SocketPermission "*:*", "listen,accept,connect";
};

for the binding of remote object to the registry(1099).

6. Now run the client as

D:\work\MyWork\rmi\suntutorial\test>java -cp .\;..\compute.jar; -Djava.rmi.server.codebase=http://pc-krsethur-in:1185/test/ -Djava.security.policy=D:\work\MyWork\rmi\suntutorial\client.policy client.ComputePi pc-krsethur-in 45

Output
3.141592653589793238462643383279502884197169399

7. Client.policy should have similar line above(5)

8. here -Djava.rmi.server.codebase=http://pc-krsethur-in:1185/test/ will be set because during client execution, we call executeTask on the proxy remote object. The remote object running in the RMI runtime will delegate to the task object. Now, the task object is still not present in the RMI runtime and will give class not found exception. To prevent that we set the codebase to http://pc-krsethur-in:1185/test/. Here pc-krsethur-in:1185 will deliver files present under D:\work\MyWork\rmi\suntutorial. However, the task class is present in D:\work\MyWork\rmi\suntutorial\test folder. Hence, we append the test/ in the URL for the codebase. Our local file server will serve the classes from D:\work\MyWork\rmi\suntutorial\test for RMI runtime during client execution. Similarly, when the server was started, during binding of remote object, the interface classes(Compute.class and Task.class) for the RMI runtime was served by -Djava.rmi.server.codebase=http://pc-krsethur-in:1185/.

9. After a single execution of both server and client, the classes(Compute.class and Task.class) for the server execution and the class(Task.class) from client execution will be present in the RMI runtime and hence if the local file server is stopped at this time and the server is aborted and restarted, it will work fine without any error about class not found. Similarly if the client is run now also, the client will work fine, because the Task.class is already loaded in the RMI runtime.

10. Now if we stop the rmiregistry.exe(thus all the classes loaded in RMI runtime are gone) and restart the rmiregistry and then start the server or client(with the local file server stopped), they will fail with class not found exception.

Mapping URL to servlet

• Request URI = context path + servlet path + path info


• Context Path and Servlet Path start with a / but do not end with it.

Identifying Servlet Path

1. Exact match of URI to any servlet mapping. In this case, entire match is servlet path and path info is null


2. Recursive match the longest path by stepping down the request URI path tree to a directory at a time, using / character as a path separator.


3. last node of request URI contains extension and there exists servlet that handles request for that extension,


4. forward to default servlet. If no default servlet, send an error message

My Notes for SCWCD

1. Browser sends web request when
   - user clicks on the hyperlink
   - form post
   - enters address in address bar and press enter


2. For form data in POST method, enctype attribute should be set as multipart-formdata


3. Difference between GET and POST on : resource type, type of data,amount of data,visibility and caching


4. Signature of method doXXXX is protected void and it throws ServletException, IOException


5. ServletRequest defines getParameter(String Name), getParameterValues(String Name) and getParameterNames() which return String, String[] and Enumeration respectively.


6. HttpServletRequest defines getHeader(String Name), getHeaders(String Name) and getHeaderNames() which return String, Enumeration and Enumeration respectively.


7. getWriter on ServletResponse returns PrintWriter object and getOutputStream returns ServletOutputStream(extends OutputStream).


8. Call to setContentType for setting the mimetype should be done on response object before getWriter or getOutputStream is invoked.


9. Either getWriter or getOutputStream should be called. Mixing will result in IllegalStateException


10. setHeader on response object sets the header. setIntHeader and setDateHeader similar functions. addHeader, addIntHeader and addDateHeader sets new value for same header if already exists. containsHeader which returns boolean returns true if the header is already set.


11. Common headers are : Date, Expires, Last-Modified and Refresh


12. sendRedirect on response object does a browser redirect. Calling redirect after response is committed (calling flush on writer) will cause IllegalStateException


13. sendError(int errorcode) will send the error code in response header so that browser can display appropriate message(or web server sends appropriate contents).


14. ServletContainer loads and instantiates servlet by calling Class.forName(...).new Instance(). To do this there should be a public constructor with no arguments. Having a default class with no constructor or a public class with some constructor having arguments(no default constructor) will error when accessed by client with 500 status.


15. Two init methods. one takes ServletConfig and the other none. Overriding the one which takes parameter requires a call to super.init to store the config object. instead the GenericServlet's init method which takes parameter makes a call to the no argument init method. So, overriding the no argument init method takes care of everything. To get servletconfig in no arg method call, getServletConfig()


16. Servlet not initialized at startup to reduce the startup time. However if large initialization is done then the first request for servlet will take long time. To prevent this servlet can be preinitialized at startup by the element in descriptor.


17. ServletConfig class has getInitParameter and getInitParameterNames which return String and Enumeration respectively. It has getServletContext and getServletName methods.


18. getResource on ServletContext return java.net.URL. call openStream on URL to get InputStream. Instead call getResourceAsStream to directly get Stream corresponding to resource.


19. Limitation of getResource is that any URL for any active resource cannot be passed. This will result in security loophole. getResource on jsp file returns the source code of jsp and not the executed output.

Oracle Collections

Good Link for on Oracle collection : http://sheikyerbouti.developpez.com/collections/collections.htm