No, although it's useful because a lot of XML terminology and practice derives from two decades' experience of SGML.
Be aware that ‘knowing HTML’ is not the same as ‘understanding SGML’. Although HTML was written as an SGML application, browsers ignore most of it (which is why so many useful things don't work), so just because something is done a certain way in HTML browsers does not mean it's correct, least of all in XML.
SOURCE : www.referjava.com
Friday, February 9, 2007
Does XML replace HTML?
No. XML itself does not replace HTML. Instead, it provides an alternative which allows you to define your own set of markup elements. HTML is expected to remain in common use for some time to come, and the current version of HTML is in XML syntax. XML is designed to make the writing of DTDs much simpler than with full SGML.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
When should I use a CDATA Marked Section?
You should almost never need to use CDATA Sections. The CDATA mechanism was designed to let an author quote fragments of text containing markup characters (the open-angle-bracket and the ampersand), for example when documenting XML (this FAQ uses CDATA Sections quite a lot, for obvious reasons). A CDATA Section turns off markup recognition for the duration of the section (it gets turned on again only by the closing sequence of double end-square-brackets and a close-angle-bracket).
Consequently, nothing in a CDATA section can ever be recognised as anything to do with markup: it's just a string of opaque characters, and if you use an XML transformation language like XSLT, any markup characters in it will get turned into their character entity equivalents.
some text with <em>markup</em> in it.
In other words, CDATA Sections cannot preserve the embedded markup as markup. Normally this is exactly what you want because this technique was designed to let people do things like write documentation about markup. It was not designed to allow the passing of little chunks of (possibly invalid) unparsed HTML embedded inside your own XML through to a subsequent process—because that would risk invalidating the output.
As a result you cannot expect to keep markup untouched simply because it looked as if it was safely ‘hidden’ inside a CDATA section: it can't be used as a magic shield to preserve HTML markup for future use as markup, only as characters.
SOURCE : www.referjava.com
Consequently, nothing in a CDATA section can ever be recognised as anything to do with markup: it's just a string of opaque characters, and if you use an XML transformation language like XSLT, any markup characters in it will get turned into their character entity equivalents.
some text with <em>markup</em> in it.
In other words, CDATA Sections cannot preserve the embedded markup as markup. Normally this is exactly what you want because this technique was designed to let people do things like write documentation about markup. It was not designed to allow the passing of little chunks of (possibly invalid) unparsed HTML embedded inside your own XML through to a subsequent process—because that would risk invalidating the output.
As a result you cannot expect to keep markup untouched simply because it looked as if it was safely ‘hidden’ inside a CDATA section: it can't be used as a magic shield to preserve HTML markup for future use as markup, only as characters.
SOURCE : www.referjava.com
How do I include one XML file in another?
This works exactly the same as for SGML. First you declare the entity you want to include, and then you reference it by name
The one thing to make sure of is that the included file must not have an XML or DOCTYPE Declaration on it. If you've been using one for editing the fragment, remove it before using the file in this way.
SOURCE : www.referjava.com
The one thing to make sure of is that the included file must not have an XML or DOCTYPE Declaration on it. If you've been using one for editing the fragment, remove it before using the file in this way.
SOURCE : www.referjava.com
How do I control formatting and appearance?
In HTML, default styling was built into the browsers because the tagset of HTML was predefined and hardwired into browsers. In XML, where you can define your own tagset, browsers cannot possibly be expected to guess or know in advance what names you are going to use and what they will mean, so you need a stylesheet if you want to display formatted text.
Browsers which read XML will accept and use a CSS stylesheet at a minimum, but you can also use the more powerful XSLT stylesheet language to transform your XML into HTML—which browsers, of course, already know how to display (and that HTML can still use a CSS stylesheet). This way you get all the document management benefits of using XML, but you don't have to worry about your readers needing XML smarts in their browsers.
As with any system where files can be viewed at random by arbitrary users, the author cannot know what resources (such as fonts) are on the user's system, so the same care is needed as with HTML using fonts. To invoke a stylesheet from an XML file for standalone processing in the browser, include one of the stylesheet declarations:
SOURCE : www.referjava.com
Browsers which read XML will accept and use a CSS stylesheet at a minimum, but you can also use the more powerful XSLT stylesheet language to transform your XML into HTML—which browsers, of course, already know how to display (and that HTML can still use a CSS stylesheet). This way you get all the document management benefits of using XML, but you don't have to worry about your readers needing XML smarts in their browsers.
As with any system where files can be viewed at random by arbitrary users, the author cannot know what resources (such as fonts) are on the user's system, so the same care is needed as with HTML using fonts. To invoke a stylesheet from an XML file for standalone processing in the browser, include one of the stylesheet declarations:
SOURCE : www.referjava.com
How do I execute or run an XML file?
You can't and you don't. XML itself is not a programming language, so XML files don't ‘run’ or ‘execute’. XML is a markup specification language and XML files are just data: they sit there until you run a program which displays them (like a browser) or does some work with them (like a converter which writes the data in another format, or a database which reads the data), or modifies them (like an editor).
If you want to view or display an XML file, open it with an XML editor or an XML browser.
The water is muddied by XSL (both XSLT and XSL:FO) which use XML syntax to implement a declarative programming language. In these cases it is arguable that you can ‘execute’ XML code, by running a processing application like Saxon, which compiles the directives specified in XSLT files into Java bytecode to process XML.
SOURCE : www.referjava.com
If you want to view or display an XML file, open it with an XML editor or an XML browser.
The water is muddied by XSL (both XSLT and XSL:FO) which use XML syntax to implement a declarative programming language. In these cases it is arguable that you can ‘execute’ XML code, by running a processing application like Saxon, which compiles the directives specified in XSLT files into Java bytecode to process XML.
SOURCE : www.referjava.com
Can I use Java to create or manage XML files?
Yes, any programming language can be used to output data from any source in XML format. There is a growing number of front-ends and back-ends for programming environments and data management environments to automate this. Java is just the most popular one at the moment.
There is a large body of middleware (APIs) written in Java and other languages for managing data either in XML or with XML input or output.
SOURCE : www.referjava.com
There is a large body of middleware (APIs) written in Java and other languages for managing data either in XML or with XML input or output.
SOURCE : www.referjava.com
Can I use JavaScript, ActiveX, etc in XML files?
This will depend on what facilities your users' browsers implement. XML is about describing information; scripting languages and languages for embedded functionality are software which enables the information to be manipulated at the user's end, so these languages do not normally have any place in an XML file itself, but in stylesheets like XSL and CSS where they can be added to generated HTML.
XML itself provides a way to define the markup needed to implement scripting languages: as a neutral standard it neither encourages not discourages their use, and does not favour one language over another, so it is possible to use XML markup to store the program code, from where it can be retrieved by (for example) XSLT and re-expressed in a HTML script element.
Server-side script embedding, like PHP or ASP, can be used with the relevant server to modify the XML code on the fly, as the document is served, just as they can with HTML. Authors should be aware, however, that embedding server-side scripting may mean the file as stored is not valid XML: it only becomes valid when processed and served, so care must be taken when using validating editors or other software to handle or manage such files. A better solution may be to use an XML serving solution like Cocoon, AxKit, or PropelX.
SOURCE : www.referjava.com
XML itself provides a way to define the markup needed to implement scripting languages: as a neutral standard it neither encourages not discourages their use, and does not favour one language over another, so it is possible to use XML markup to store the program code, from where it can be retrieved by (for example) XSLT and re-expressed in a HTML script element.
Server-side script embedding, like PHP or ASP, can be used with the relevant server to modify the XML code on the fly, as the document is served, just as they can with HTML. Authors should be aware, however, that embedding server-side scripting may mean the file as stored is not valid XML: it only becomes valid when processed and served, so care must be taken when using validating editors or other software to handle or manage such files. A better solution may be to use an XML serving solution like Cocoon, AxKit, or PropelX.
SOURCE : www.referjava.com
Can I encode mathematics using XML?
Yes, if the document type you use provides for math, and your users' browsers are capable of rendering it. The mathematics-using community has developed the MathML Recommendation at the W3C, which is a native XML application suitable for embedding in other DTDs and Schemas.
It is also possible to make XML fragments from other DTDs, such as ISO 12083 Math, or OpenMath, or one of your own making. Browsers which display math embedded in SGML existed for many years (eg DynaText, Panorama, Multidoc Pro), and mainstream browsers are now rendering MathML. David Carlisle has produced a set of stylesheets for rendering MathML in browsers. It is also possible to use XSLT to convert XML math markup to LATEX for print (PDF) rendering, or to use XSL:FO.
Please note that XML is not itself a programming language, so concepts such as arithmetic and if-statements (if-then-else logic) are not meaningful in normal XML documents.
SOURCE : www.referjava.com
It is also possible to make XML fragments from other DTDs, such as ISO 12083 Math, or OpenMath, or one of your own making. Browsers which display math embedded in SGML existed for many years (eg DynaText, Panorama, Multidoc Pro), and mainstream browsers are now rendering MathML. David Carlisle has produced a set of stylesheets for rendering MathML in browsers. It is also possible to use XSLT to convert XML math markup to LATEX for print (PDF) rendering, or to use XSL:FO.
Please note that XML is not itself a programming language, so concepts such as arithmetic and if-statements (if-then-else logic) are not meaningful in normal XML documents.
SOURCE : www.referjava.com
How do I get XML into or out of my database?
Ask your database manufacturer: they all provide XML import and export modules to connect XML applications with databases. In some trivial cases there will be a 1:1 match between field names in the database table and element type names in the XML Schema or DTD, but in most cases some programming will be required to establish the desired match. This can usually be stored as a procedure so that subsequent uses are simply commands or calls with the relevant parameters.
In less trivial, but still simple, cases, you could export by writing a report routine that formats the output as an XML document by adding the relevant tags as literals before and after each data value; and you could import by writing an XSLT transformation that formatted the XML data as a load file in your database's preferred format.
SOURCE : www.referjava.com
In less trivial, but still simple, cases, you could export by writing a report routine that formats the output as an XML document by adding the relevant tags as literals before and after each data value; and you could import by writing an XSLT transformation that formatted the XML data as a load file in your database's preferred format.
SOURCE : www.referjava.com
Why do threads block on I/O?
Threads block on i/o (that is enters the waiting state) so that other threads may execute while the i/o Operation is performed.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What does it mean that a method or field is "static"?
Static variables and methods are instantiated only once per class. In other words they are class variables, not instance variables. If you change the value of a static variable in a particular object, the value of that variable changes for all instances of that class.
Static methods can be referenced with the name of the class rather than the name of a particular object of the class (though that works too). That's how library methods like System.out.println() work. out is a static field in the java.lang.System class.
SOURCE : www.referjava.com
Static methods can be referenced with the name of the class rather than the name of a particular object of the class (though that works too). That's how library methods like System.out.println() work. out is a static field in the java.lang.System class.
SOURCE : www.referjava.com
Why isn't there operator overloading?
Because C++ has proven by example that operator overloading makes code almost impossible to maintain. In fact there very nearly wasn't even method overloading in Java, but it was thought that this was too useful for some very basic methods like print(). Note that some of the classes like DataOutputStream have unoverloaded methods like writeInt() and writeByte().
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What are some alternatives to inheritance?
Delegation is an alternative to inheritance. Delegation means that you include an instance of another class as an instance variable, and forward messages to the instance. It is often safer than inheritance because it forces you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn't force you to accept all the methods of the super class: you can provide only the methods that really make sense. On the other hand, it makes you write more code, and it is harder to re-use (because it is not a subclass).
SOURCE : www.referjava.com
SOURCE : www.referjava.com
Can an Interface have an inner class?
Yes public interface abc { static int i=0; void dd(); class a1 { a1() { int j; System.out.println("in interfia"); }; public static void main(String a1[]) { System.out.println("in interfia"); } } }
SOURCE : www.referjava.com
SOURCE : www.referjava.com
Diffrence between JRE And JVM AND JDK
The "JDK" is the Java Development Kit. I.e., the JDK is bundle of software that you can use to develop Java based software. The "JRE" is the Java Runtime Environment. I.e., the JRE is an implementation of the Java Virtual Machine which actually executes Java programs. Typically, each JDK contains one (or more) JRE's along with the various development tools like the Java source compilers, bundling and deployment tools, debuggers, development libraries, etc.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
the diffrence between inner class and nested class?
When a class is defined within a scope od another class, then it becomes inner class.
If the access modifier of the inner class is static, then it becomes nested class.
SOURCE : www.referjava.com
If the access modifier of the inner class is static, then it becomes nested class.
SOURCE : www.referjava.com
the difference between an if statement and a switch statement?
The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
How does a try statement determine which catch clause should be used to handle an exception?
When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is the purpose of a statement block?
A statement block is used to organize a sequence of statements as a single statement group.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
The difference between the prefix and postfix forms of the ++ operator?
The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is numeric promotion?
Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What happens if a try-catch-finally statement does not have a catch clause to handle an exception that is thrown within the body of the try statement?
The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type.
The overriding method may not limit the access of the method it overrides.
The overriding method may not throw any exceptions that may not be thrown by the overridden method.
SOURCE : www.referjava.com
The overriding method may not limit the access of the method it overrides.
The overriding method may not throw any exceptions that may not be thrown by the overridden method.
SOURCE : www.referjava.com
What happens if an exception is not caught?
An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown
SOURCE : www.referjava.com
SOURCE : www.referjava.com
Following are the changes in CMP2.0
1)CMP entity beans are subclassed.
2)CMP entity beans have no declared fields.
3)CMP get/set methods are defined in the subclass.
4)CMP entity beans have an Abstract persisitence schema.
5)CMP entity beans have a query language.
6)CMP entity beans can have ejbSelect() methods
SOURCE : www.referjava.com
2)CMP entity beans have no declared fields.
3)CMP get/set methods are defined in the subclass.
4)CMP entity beans have an Abstract persisitence schema.
5)CMP entity beans have a query language.
6)CMP entity beans can have ejbSelect() methods
SOURCE : www.referjava.com
. What is the need of Remote and Home interface. Why cant it be in one
The home interface is your way to communicate with the container, that is who is responsable of creating, locating even removing one or more beans.The remote interface is your link to the bean, that will allow you to remotely access to all its methods and members.
At run time only we create remote object based on user input in create method(whether to access Wesley or x account)so it is not possible to know exactly user input and what remote object it want only at run time he gives input and based on user input remote object is created so we use Factory pattern while creating Remote object.so if we use Factory pattern we need two things either two class or interfac instance.
1, one instance takes input from user--- this is Home Interface instance
2, Based on input it returns an instance --- this Remote interface instance
RemotInt it1=homeint.create();
RemotInt it2=homeint.create(1,2);
RemotInt it3=homeint.create(1,2,5);
In above example based on user input one remote instance is returned from group of 3
so if we merge home and remote interface ,how will u bind JNDI name with (homeMergeRemote) object ,
only based on user input container creates Remote object so we cannot predict what input he gives and
based on input we create Remote object without object we cannot bind it with JNDI tree.
so we have separate Interface Home and Remote
Basic function of Homeobject is
1. To create Remote object simultaneously container will take bean instance from pool and associates with Remoteobject
2. To delete Remoteobject simultaneously container will disassociate bean instance from remote object, pull the bean instance back to the pool.
so home instance function is just like house keeping i.e creating ,locating,associating and deleteing the remote object.it has nothing do with bean instance or functionalty or business logic where as incase of Remoteobject it access the bean business logic Now it clear that we divide the work so we have two separate interface EJB Home and EJB Remote
SOURCE : www.referjava.com
At run time only we create remote object based on user input in create method(whether to access Wesley or x account)so it is not possible to know exactly user input and what remote object it want only at run time he gives input and based on user input remote object is created so we use Factory pattern while creating Remote object.so if we use Factory pattern we need two things either two class or interfac instance.
1, one instance takes input from user--- this is Home Interface instance
2, Based on input it returns an instance --- this Remote interface instance
RemotInt it1=homeint.create();
RemotInt it2=homeint.create(1,2);
RemotInt it3=homeint.create(1,2,5);
In above example based on user input one remote instance is returned from group of 3
so if we merge home and remote interface ,how will u bind JNDI name with (homeMergeRemote) object ,
only based on user input container creates Remote object so we cannot predict what input he gives and
based on input we create Remote object without object we cannot bind it with JNDI tree.
so we have separate Interface Home and Remote
Basic function of Homeobject is
1. To create Remote object simultaneously container will take bean instance from pool and associates with Remoteobject
2. To delete Remoteobject simultaneously container will disassociate bean instance from remote object, pull the bean instance back to the pool.
so home instance function is just like house keeping i.e creating ,locating,associating and deleteing the remote object.it has nothing do with bean instance or functionalty or business logic where as incase of Remoteobject it access the bean business logic Now it clear that we divide the work so we have two separate interface EJB Home and EJB Remote
SOURCE : www.referjava.com
What makes a Java class an enterprise bean?
An enterprise bean is composed of many parts, not just a single class. Essentially, an enterprise bean is constructed with a bean class, remote interface, home interface and deployment descriptor. These constituents are discussed below.
A bean class is the implementation class of the bean that defines its business, persistence, and passivation logic. The bean class implements either the javax.ejb.EntityBean or javax.ejb.SessionBean interface and runs inside the EJB container. Instances of the bean class service client request indirectly; instances of the bean class are not visible to the client.
The remote interface defines the business methods that will be visible to the client's that use the enterprise bean. The remote interface extends the javax.ejb.EJBObject interface and is implemented by a remote (distributed object) reference. Client applications interact with the enterprise bean through its remote
interface.
The home interface defines the create, delete (remove), and query methods for an enterprise bean type. The home interface extends the javax.ejb.EJBHome interface and is implemented by a remote (distributed object) reference. The client application will use the home interface to create beans, find existing beans, and remove specific beans.
The deployment descriptor is used to describe the enterprise bean's runtime behavior to the container. Among other things the deployment descriptor allows the transaction, persistence, and authorization security behavior of a bean to be defined using declarative attributes. This greatly simplifies the programming model when developing beans.
An enterprise bean represents the sum of all these parts (remote, home, bean class, and deployment descriptor) as one component. An enterprise bean is not an enterprise bean if any one of these parts is missing. A change to anyone of these parts -- changing even one attribute in the deployment descriptor for example -- creates an
entirely new enterprise bean.
SOURCE : www.referjava.com
A bean class is the implementation class of the bean that defines its business, persistence, and passivation logic. The bean class implements either the javax.ejb.EntityBean or javax.ejb.SessionBean interface and runs inside the EJB container. Instances of the bean class service client request indirectly; instances of the bean class are not visible to the client.
The remote interface defines the business methods that will be visible to the client's that use the enterprise bean. The remote interface extends the javax.ejb.EJBObject interface and is implemented by a remote (distributed object) reference. Client applications interact with the enterprise bean through its remote
interface.
The home interface defines the create, delete (remove), and query methods for an enterprise bean type. The home interface extends the javax.ejb.EJBHome interface and is implemented by a remote (distributed object) reference. The client application will use the home interface to create beans, find existing beans, and remove specific beans.
The deployment descriptor is used to describe the enterprise bean's runtime behavior to the container. Among other things the deployment descriptor allows the transaction, persistence, and authorization security behavior of a bean to be defined using declarative attributes. This greatly simplifies the programming model when developing beans.
An enterprise bean represents the sum of all these parts (remote, home, bean class, and deployment descriptor) as one component. An enterprise bean is not an enterprise bean if any one of these parts is missing. A change to anyone of these parts -- changing even one attribute in the deployment descriptor for example -- creates an
entirely new enterprise bean.
SOURCE : www.referjava.com
Why there is ejbActivate and ejbPassivate in SLSB when not used ?
Both Stateless and Stateful Session Bean implement javax.ejb.SessionBean and this would not be possible if stateless session bean is to remove ejbActivate and ejbPassivate from the interface.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
Two methods in a Primary Key class that should be implemented why?
The 2 methods are hashCode & equals.
These methods are required to compare the data of each row for uniqueness.
SOURCE : www.referjava.com
These methods are required to compare the data of each row for uniqueness.
SOURCE : www.referjava.com
How will use Where Clause in an CMP Bean ?
EJB2.0 introduced concept of EJB-QL to retrieve CMP beans. You can use WHERE clause in your EJB-QL and pass in parameters as part of findBy method parameters. Here is a sample ejb-ql which demonstrates a findBy method with EJB-QL having WHERE
clause.
hotelEJB
...
hotelSchemaName
...
...
findByCity
java.lang.String
hotelSchemaName AS h WHERE h.city = ?1]]>
...
...
SOURCE : www.referjava.com
clause.
...
...
hotelSchemaName AS h WHERE h.city = ?1]]>
...
...
SOURCE : www.referjava.com
What is the purpose of ejbRemove() in an Stateless Bean
To deallocate any resources. This method releases resources that were acquired within the ejbCreate and business methods.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What is Lazy Activation?
Lazy activation allows dynamic binding of object implementation into the registry. With lazy activation there is no need to bind the object with rmiregistry in the begining. When the server receives the first request from client it looks for the correct implementation and activates that object.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
Is session bean a coarse grained bean?
YES, session beans are coarse grained bean. Entity beans are fine grained beans.
Actually it depends on how you use them. You can have design in which even Session beans can behave as fine grained beans. One eg. of coarse gained session... Instead of accessing entity beans directly, many a times we use session beans as a wrapper over a number of entity beans in the system. If a business functionality requires access to say 10 entity beans, that functionality can be encapsulated in a single session bean. Thus making it what we say coarse grained. In this case, entity beans can be said as fine grained.
A fine grained entity bean directly mapped to one relational table. A coarse grained entity bean is larger and more complex, either because its attributes include values or lists from other tables, or because it has more sets of dependent objects. The coarse grained bean might be mapped to a single table or flat file.
SOURCE : www.referjava.com
Actually it depends on how you use them. You can have design in which even Session beans can behave as fine grained beans. One eg. of coarse gained session... Instead of accessing entity beans directly, many a times we use session beans as a wrapper over a number of entity beans in the system. If a business functionality requires access to say 10 entity beans, that functionality can be encapsulated in a single session bean. Thus making it what we say coarse grained. In this case, entity beans can be said as fine grained.
A fine grained entity bean directly mapped to one relational table. A coarse grained entity bean is larger and more complex, either because its attributes include values or lists from other tables, or because it has more sets of dependent objects. The coarse grained bean might be mapped to a single table or flat file.
SOURCE : www.referjava.com
Container-Managed vs Bean-Managed Persistence
1. speed. You can avoid some of the unnecessary container initialized databases calls, if you use BMP's
2. In CMP, the developer uses the deployment descriptor to tell the container which attributes of the entity bean to persist.
Bean-Managed persistence gives the developer explicit control of the management of a bean instance's state.
The main advantage of BMP is Database Acess Flexbility ,
LOng back i read that BMP has acts as an interface to complex legacy SQL databases via JDBC and also enterprise data sources such as CICS, MQ-Series e.t.c.,
Disadvantage of BMP is writing the hard program for all callback
methods by us ..
3. For example with BMP, it takes two SQL stements to load an entity bean. the first call- a finder method ( loading only the primary key ) and a second, during ejbLoad() to load the actual data. A collection of n BMP requires n+1 database calls to load that data.(one finder to find a collection of primary keys, and then n loads).
With CMP, the container can reduce the n+1 database calls to a single call, by performing one giant SELECT statement. You set this up using container specific flags."
You can refer "Matering Enterprise Java Beans" second edition Ed Roman.
The container cannot do the same sort of sql optimization for BMPs for the simple reason that the
container has no control over the sqls. One of the main disadvanteges of CMP is that you can'tcall Stored Procedure from CMP.
will go for BMP in the following cases:
1.My persistent data is in non-RDBMS and the EJB container does not
support this.
2.The database schema does not map exactly to Entity fields.
3.For better performance I would like to use Stored procedure.
4.I want to manage relationship between entities for which I need to
use BMP (This is solved by using EJB 2.0 but for preEJB 2.0...)
5.I have my data from different tables or databases.
SOURCE : www.referjava.com
2. In CMP, the developer uses the deployment descriptor to tell the container which attributes of the entity bean to persist.
Bean-Managed persistence gives the developer explicit control of the management of a bean instance's state.
The main advantage of BMP is Database Acess Flexbility ,
LOng back i read that BMP has acts as an interface to complex legacy SQL databases via JDBC and also enterprise data sources such as CICS, MQ-Series e.t.c.,
Disadvantage of BMP is writing the hard program for all callback
methods by us ..
3. For example with BMP, it takes two SQL stements to load an entity bean. the first call- a finder method ( loading only the primary key ) and a second, during ejbLoad() to load the actual data. A collection of n BMP requires n+1 database calls to load that data.(one finder to find a collection of primary keys, and then n loads).
With CMP, the container can reduce the n+1 database calls to a single call, by performing one giant SELECT statement. You set this up using container specific flags."
You can refer "Matering Enterprise Java Beans" second edition Ed Roman.
The container cannot do the same sort of sql optimization for BMPs for the simple reason that the
container has no control over the sqls. One of the main disadvanteges of CMP is that you can'tcall Stored Procedure from CMP.
will go for BMP in the following cases:
1.My persistent data is in non-RDBMS and the EJB container does not
support this.
2.The database schema does not map exactly to Entity fields.
3.For better performance I would like to use Stored procedure.
4.I want to manage relationship between entities for which I need to
use BMP (This is solved by using EJB 2.0 but for preEJB 2.0...)
5.I have my data from different tables or databases.
SOURCE : www.referjava.com
Entity beans and Entity beans Performance?
Entity beans are more costly then Session beans for one simple reason that Entity beans are special types of Session beans(Entity beans are build over session beans). One point to note is that Entity beans never store any state like statefull beans (They are database persistant and not memory persistant like StateFull beans). For every call or for any update or for any operation it will query the database. Now again there are two considerations in entity beans, CMP and BMP. A project coded using Session beans will any time perform better then BMP's. So the level of performance can be listed in the order of best to worse (in case of database operations)
1.Entity beans 2.BMPs 3.CMPs
U may consider this before u make any decision. In one of my project we had to drop the CMP design at the last moment because of the speed consideration. Entity type beans are ment as a better s/w design practice and not ment for a better performance. You should consider a tradeof, may be by using BMP's.
Entity beans www.referjava.com
1.Entity beans 2.BMPs 3.CMPs
U may consider this before u make any decision. In one of my project we had to drop the CMP design at the last moment because of the speed consideration. Entity type beans are ment as a better s/w design practice and not ment for a better performance. You should consider a tradeof, may be by using BMP's.
Entity beans www.referjava.com
Difference between javabeans and ejb?
JavaBeans components are small-grained application bits. You can use JavaBeans to assemble larger-grained components or to build entire applications. JavaBeans, however, are development components and are not deployable components. You typically do not deploy a JavaBean because a JavaBean is not a complete application; rather, JavaBeans help you construct larger software that is deployable. And because they cannot be deployed, JavaBeans do not need a runtime environment in which to live. JavaBeans do not need a container to instantiate
them, to destroy them, and to provide other services to them because the application itself is made up of JavaBeans. By way of comparison
The Enterprise JavaBeans (EJB) standard defines a component architecture for deployable components called enterprise beans. Enterprise beans are larger, coarser-grained application components that are ready to be deployed. They can be deployed as is, or they can be assembled with other components into larger application
systems. Deployable components must be deployed in a container that provides runtime services to the components, such as services to instantiate components as needed.
SOURCE : www.referjava.com
them, to destroy them, and to provide other services to them because the application itself is made up of JavaBeans. By way of comparison
The Enterprise JavaBeans (EJB) standard defines a component architecture for deployable components called enterprise beans. Enterprise beans are larger, coarser-grained application components that are ready to be deployed. They can be deployed as is, or they can be assembled with other components into larger application
systems. Deployable components must be deployed in a container that provides runtime services to the components, such as services to instantiate components as needed.
SOURCE : www.referjava.com
Web Server and Application Server
Webserver is for hosting ur webapplications (Servlets and jsps). Application
server is server which provides services like transactions, security,messaging, and other j2ee services like jndi etc to the application. Theapplications can be built using ejb which use all the declarative services,which minimizes the lines of code and reduces the application development time.
WebServer is a service or a daemon running at a given IP and a Port that is capable of accepting and responding to all HTTP events. It is created to understand the HTTP transfer protocol. The basic functionality of a WebServer is to accept a browser request for HTML pages and respond it with the resources in it. To completely understand a webserver, i will suggest, write your own webserver. Dont get scared. Writting a webserver using java is no big deal.
Creating your own WebServer
* Create a Server Socket using the ServerSocket class.
* Configure it to accept requests at a default HTTP port that is port 80.
* Once a connection is established and a request is send, read the HTTP header in the request.
* From the HTTP header, do normal parsing using StringTokenizer, and you can get the filename that is requested.
* Once u get the filename, open a filestream and read the file into some DataOutputStream object.
* Write this object over the open connection.
* Now Flush the data.
This is the most basic HTTP server that can be written in JAVA. I did this long time back, let me know if you require code, i ll try finding it in my old backups.
Over this basic functionality you can build a better and powefull WebServer.
For instance you can start with using threads to support more requests. You can set unset session id to track Sessions. You can Read the MIME type in the header to respond to various file formats like JPEG, MPEG, GIF etc. And other things. So now you understand what a web server is.
A WebServer is a service running on some remote machine that can communicate with your webBrowser and fetch you files using HTTP protocol.
And thats it, nothing more nothing less. For instance IIS and Apache are webServers. Though they do many other things then serving webpages. But that is not a part of a simple webServer.
Applicatin server.
Anything u know abt app servers minus the defn of the web server that i just stated is the job of an application server. An application server executes an application code written in some language and bundles the results in form of HTTP response, which can be send over wire by the HTTP Web Server. (Dont get confused). For instance IIS is a combination of both application server as well as web server. The webserver part is supposed to deal with the browser sending and receiving request and response objects using the HTTP protocol. The application server is responsible of doing all the processing work, executing scripts, accessing the database, bla bla.. Today's Application servers evolved long way back from there ancistors -> CGI or common gateway interface. Though CGI are not true app server as per todays defn of application servers, but it provides a backbone for the application technology that is build in the middleware.
So to make the discussion short, lets define application server
An Application server is a service or daemon running on some remote machine that communicates with the WebServer using HTTP protocol and hosts a range of services and applications. Not to explain, these services can be anything like ACLs, Object pooling, Transaction management, etc etc.
A noteworthy difference betn the two is webservers communicate with the Browser, where as app server communicate with the webServers. Here u can very well question "but y so" ?
The ans is simple. Let me give you one eg, and things will be clear.
In 1 of my project we had the following congifuration. We used the Weblogic server, providing its service at 7001 port. This is where our application(JSP, EJB, Servlets etc etc) was hosted. Then we had a IIS server providing service on 80 port. So if i connect http:\\www.mysite.com\index.html, the index.html page will be served directly by the IIS server. Now we had a configuration in IIS server which stated that all the application related requests be directed to the WebLogic server. So wheneveer IIS gets a request asking for *.jsp, *.class (say http:\\www.mysite.com\index.jsp) it gets routed to WebLogic app server. WL will get the request object, execute the script, create the response object and dump it back to IIS. IIS will wait till it receives a response from WL or till timeout occurs. On response it will just fwd it to the browser.
This architecture clearly differentiates the app server from the web server. Most of the app servers also bundle a webserver with them. That is, they behave as a single web+app server. So we dont understand the difference betwn the dual role. (above architecture is used in many scenarios, but detailed explaination is out of the scope of this discussion.)
One last thing. we can summarize by saying that serving files is the job of an webserver. And serving appliactions is the job of app server. Remember, we can access the application sevices without using the HTTP protocol. HTTP protocol was specifically created for web servers. If you have used WebLogic, there is something called as T3 services. This is the application protocol that gives you access directly to the app server services. We had an application that accessed WL directly using t3 to get the job done. (again detailed explaination of t3 or app protocols is out of the scope of this discussion).
SOURCE : www.referjava.com
server is server which provides services like transactions, security,messaging, and other j2ee services like jndi etc to the application. Theapplications can be built using ejb which use all the declarative services,which minimizes the lines of code and reduces the application development time.
WebServer is a service or a daemon running at a given IP and a Port that is capable of accepting and responding to all HTTP events. It is created to understand the HTTP transfer protocol. The basic functionality of a WebServer is to accept a browser request for HTML pages and respond it with the resources in it. To completely understand a webserver, i will suggest, write your own webserver. Dont get scared. Writting a webserver using java is no big deal.
Creating your own WebServer
* Create a Server Socket using the ServerSocket class.
* Configure it to accept requests at a default HTTP port that is port 80.
* Once a connection is established and a request is send, read the HTTP header in the request.
* From the HTTP header, do normal parsing using StringTokenizer, and you can get the filename that is requested.
* Once u get the filename, open a filestream and read the file into some DataOutputStream object.
* Write this object over the open connection.
* Now Flush the data.
This is the most basic HTTP server that can be written in JAVA. I did this long time back, let me know if you require code, i ll try finding it in my old backups.
Over this basic functionality you can build a better and powefull WebServer.
For instance you can start with using threads to support more requests. You can set unset session id to track Sessions. You can Read the MIME type in the header to respond to various file formats like JPEG, MPEG, GIF etc. And other things. So now you understand what a web server is.
A WebServer is a service running on some remote machine that can communicate with your webBrowser and fetch you files using HTTP protocol.
And thats it, nothing more nothing less. For instance IIS and Apache are webServers. Though they do many other things then serving webpages. But that is not a part of a simple webServer.
Applicatin server.
Anything u know abt app servers minus the defn of the web server that i just stated is the job of an application server. An application server executes an application code written in some language and bundles the results in form of HTTP response, which can be send over wire by the HTTP Web Server. (Dont get confused). For instance IIS is a combination of both application server as well as web server. The webserver part is supposed to deal with the browser sending and receiving request and response objects using the HTTP protocol. The application server is responsible of doing all the processing work, executing scripts, accessing the database, bla bla.. Today's Application servers evolved long way back from there ancistors -> CGI or common gateway interface. Though CGI are not true app server as per todays defn of application servers, but it provides a backbone for the application technology that is build in the middleware.
So to make the discussion short, lets define application server
An Application server is a service or daemon running on some remote machine that communicates with the WebServer using HTTP protocol and hosts a range of services and applications. Not to explain, these services can be anything like ACLs, Object pooling, Transaction management, etc etc.
A noteworthy difference betn the two is webservers communicate with the Browser, where as app server communicate with the webServers. Here u can very well question "but y so" ?
The ans is simple. Let me give you one eg, and things will be clear.
In 1 of my project we had the following congifuration. We used the Weblogic server, providing its service at 7001 port. This is where our application(JSP, EJB, Servlets etc etc) was hosted. Then we had a IIS server providing service on 80 port. So if i connect http:\\www.mysite.com\index.html, the index.html page will be served directly by the IIS server. Now we had a configuration in IIS server which stated that all the application related requests be directed to the WebLogic server. So wheneveer IIS gets a request asking for *.jsp, *.class (say http:\\www.mysite.com\index.jsp) it gets routed to WebLogic app server. WL will get the request object, execute the script, create the response object and dump it back to IIS. IIS will wait till it receives a response from WL or till timeout occurs. On response it will just fwd it to the browser.
This architecture clearly differentiates the app server from the web server. Most of the app servers also bundle a webserver with them. That is, they behave as a single web+app server. So we dont understand the difference betwn the dual role. (above architecture is used in many scenarios, but detailed explaination is out of the scope of this discussion.)
One last thing. we can summarize by saying that serving files is the job of an webserver. And serving appliactions is the job of app server. Remember, we can access the application sevices without using the HTTP protocol. HTTP protocol was specifically created for web servers. If you have used WebLogic, there is something called as T3 services. This is the application protocol that gives you access directly to the app server services. We had an application that accessed WL directly using t3 to get the job done. (again detailed explaination of t3 or app protocols is out of the scope of this discussion).
SOURCE : www.referjava.com
What is MultiPooling?
Muli pool is nothing but pool of connection pools. WEBLOGIC server provides multipool facility
SOURCE : www.referjava.com
SOURCE : www.referjava.com
What's a Naming System or Service?
A naming system associates names with addresses. A phone book is a perfect example of a naming system that associate people's names with phone numbers and addresses. Naming systems are used in computing to make it easier for user to locate and utilize software that is addressable. A software system that exposes a naming system to other software is called a naming service.
SOURCE : www.referjava.com
SOURCE : www.referjava.com
Subscribe to:
Posts (Atom)
