1.1. What is J2EE architecture?Distributed (Clustered) àApp serversMulti-tiered àdifferent container in one App server Component & Container based1.2. Why we use APP server?web server/app server:∙web server: presentation logic only (can be changed to support business logic layer with plugin) ∙app server/middleware/platform: presentation logic && business logicAPP server:∙It is J2EE compatible middleware∙It is pure java-based, so it can run on top of Unix OS, and it is more stable and secure.∙J2EE App is app which is running on top of J2EE App serverBenefit of using J2EE app server/platform：∙Do not reinvent the wheel/do not start from the scratch∙Reuse all of the app server’s services1.3. Why the Sun’s java & j2ee become morecompetitive?第二章1.1. What is presentation logic?∙the server/waiter is the presentation layer(view, and control in MVC),∙the server can act as a view and control in the MVC(pass to different roles, cook or bartender).∙In J2EE app, the JSP as view, and the servlet as control1.2. Why to use Java Bean and Taglib in the JSP? Use a JavaBean when:∙to be primarily encapsulating data(data from the form), rather than business logic.∙to modularize your Java code for reuse in something other than JSP.∙to minimize the chance of having the Web/HTML designers inadvertently modify your Java code.Use custom tag libraries when:∙You have relatively simple business logic that you do want to make available for use by Webdevelopers. For example, you can create a login module for your Web application that the HTML designers can include in every page requiring a user login.??∙You want to do pre- and post-processing of content for tasks such as personalization or content management. Personalization might include special tags that look up a user's information. Content management would enable you to create special tags to load data from your content repository.Or(总结)∙In the final analysis, much of what you can do with JavaBeans you can also do with custom tag libraries.∙the deciding factor is the preference of the developer. 第三章1.1. What is business logic?∙the cook is the business logic layer∙The cook can also classified as Head cook && Helper cook∙The Head cook isàbusiness process controlàcontrol in MVC∙Helper cook à business dataàpersistencelayeràrelated to DB∙In J2EE app, the session bean as control, and the entity bean as ORM∙There is model between the Servlet && Session bean∙Business Logic layer is consisted of Business process control & Business data access∙Similar to the cook in the restaurant example(how to cook KongPao Chicken, what is the rule/business logic to cook KongPao Chicken? )∙Business logic is used for operations such as funds transfers, product orders, and so forth.∙Business logic is a rule that the business follows in a particular situation.1.2. Differentiate between Session bean and Entity bean?∙In the restaurant example,–the Session Beans is similar to the head cook–the Entity Beans is similar to the helper cook ∙For the business logic layer–We divide the business logic layer into 2 separate layers–the Session Beans represent the business process(control) part of business logic–the Entity Beans represent the business data part of business logic∙helper cook’s time should be occupied as short as possible in order to protect the Refrigerator/DB ∙1.3. Differentiate among Session bean, Entity bean and MDB?∙In both entity beans and session beans,a syn programming model is used. Clients makerequests to the EJB and wait for work to be completed on their behalf.∙MDBs introduce an asyn processing paradigm to enterprise Java applications. Tasks can be queued and made available for processing when resources are available.∙Using MDBs, the EJB is not attached to a client.Instead, it is attached to a message queue or topic.When a message arrives, a method on the EJB is executed.∙Use MDBs when your applicationrequires asyn processing for tasks such as sending email responses or tabulating the winners of this month's lottery.1.4. Differentiate between stateful Session bean and stateless Session bean? differentiate from the code?∙Stateless beans receive requests via RMI?? but do not keep any data associated with the client they are serving internally. //all the bean are same ∙Stateful beans, on the other hand, keep data specific to the client they are serving. //all the bean are not sameCode difference:∙In the stateless programming, no info about the client/invoker is included inside the object.∙Every instance is same∙In the stateful programming, info about the client/invoker is included inside the object.∙Every instance is NOT same∙Entity Bean Components?∙ a home interface,∙remote interface,∙bean class,∙primary key class,∙deployment descriptors.1.5. Differentiate between CMP and BMP entity bean ? differentiate from the code?∙CMP(Container-Managed Persistent) Entity Bean–Container offers defined DB’s Operation, like DB’s read/write.∙BMP(Bean-Managed Persistent) Entity Bean–User defined DB’s Operation, like DB’s read/write.CMP Entity Bean Concept∙Instead of writing cumbersome JDBC code, the CMP bean writer provides only the business logic and deployment descriptors.∙CMP can offer the developer faster development time and better performance than BMP entity beans.∙The CMP entity bean class is abstract. This enables the EJB container to implement persistence logic bygenerating a class that extends the bean class.Pro and Con of CMP∙CMP make the bean code independent from the database mapping. Therefore, more reusable.???∙CMP requires vender’s mapping tools to define how the bean’s fields map to the database.∙Legacy System or complicated join is not easy to map ∙More DB-independent, and more DB schema independentPro and Con of BMP∙BMP has flexibility in manage the persistence.(database, table, join, legacy system)∙BMP requires more work, more understanding of EJB theory.∙BMP is more database dependence, and database schema dependence.第四章1.1. Why is it necessary to use JNDI in the J2EE Application?（What is JNDI?）∙JNDI is the Java standard for the “centralregistry” (catalog) of naming and directory services.(registry & retrieval )∙In the case of WebLogic Server clustering, JNDI is also used as the shared naming service across the entire cluster.∙J2EE components can access a wide variety of resources, including databases, Mail sessions, Java Message Service objects, JAXR connection factories, and URLs, and EJBs.∙The J2EE platform provides mechanisms that allow you to access all these resources in a similar manner. (Conclusion)∙RMI and JNDI are core services offered by the WebLogic Server to enable scalable distributed applications.∙While RMI and JNDI make distributed programming much easier, it is important to understand the many failure cases in networked applications.∙Also noted that: distributed is network-dependent, and also time and resource consuming, it should be avoided if possible.∙Core J2EE services such as EJB and JMS are built ontop of RMI and JNDI.1.2. Why to use the JDBC connection pooling?There are a number of reasons to pool connections to the database:∙Creating a new connection for every individual client that visits your site is very expensive.∙You do not need to hard-code details such as the database management system (DBMS) password in your application. This is particularly beneficial in the case of J2EE services such as JavaServer Pages (JSPs), which typically store the source code with the application .(good for future maintenance) ∙You can change the database system you are using without changing your application code.Databases are most effective when the number of incoming connections is limited. With connection pooling, you can limit the number of connections to your DBMS.1.3. When do you think it is necessary to use JTA? The JTA is similar to the Java Exception Handing in some way?∙JTA–JTA is used when the possible roll back might be happening–In JTA, code that might rollback is put between transaction begin && commit block∙Exception–Exception is used if the possible exception might be happening–In Exception, code that might have exception happening is put between try && catch block1.4. Compare RMI and EJB?∙EJB and its relation with RMI, EJB is built on top of the RMI1.5. Why to use JMS? What is JMS’s relationship with MDB?∙JMS is to asynchronously process the client’s request in order to improve the performance in both client side and server side∙JMS queues messages and can deliver them asynchronously: Messaging need not take place inreal time; and messages can be sent and consumed at different times(Relation)∙In the J2EE app, the msg producer usually originally come from the Servlet, and the asyn consumer usually is a MDB, which is Message Driven Bean.1.6. Compare IMAP and POP3?∙In contrast, IMAP enables users to access their mail from the mail server, but without expectations that they immediately delete those messages. Using IMAP, the user's mail is stored on the mail server and is displayed by an IMAP email client, such as Netscape Communicator or Microsoft Outlook.∙Because IMAP does not store messages on the user's local machine, individuals using IMAP can move from client machine to client machine, with uninterrupted access to new and archived messages.∙POP3 stores mail for the user on the server. The user's mail client connects to the mail server and retrieves messages on behalf of the user.∙In most cases, enterprises using POP3 expect users to download their messages and then delete them from the mail server.1.7. What is JAAS?∙Java authorization & authentication service∙JAAS is a security framework (based on AOP) which the J2EE App server provided to the application component. (compare to Acegi in Spring Framework) ∙With the security framework, the app developer does not have to connect the web layer to the DB backend in order to verify the user’s identification.∙JAAS allow 600 users for each application1.8. Difference between programmatic and declarative security?∙Declarative security is preferred where possible because there is a better separation between the application code and the security constraints.∙Programmatic security is used by security-aware applications when declarative security alone is not sufficient.。
