What are Java Server Pages?

JavaServer Pages (JSPs)
JavaServer Pages (JSPs) are based on the concept of server-side parsing. A JavaServer Page is an HTML page with Java statements embedded in it. The JSP specification defines certain special tags that can be embedded within the HTML page. In a normal working scenario, the JSP pages are parsed by a JSP compiler within the application server and converted into a Java servlet with the generated code embedded within the Java servlet as a set of Java statements. The generated Java servlet is then compiled as a normal servlet and loaded into the Java servlet container. The Java servlet is then used to process the user requests.

The JSP specification defines the following set of tags that can be used by application component providers:

• Directive tag— A directive tag embedded in a JSP is used to issue directives to the JSP compiler that compiles the JSP.
• Declaration tag— A declaration tag can be used by the application component provider to define variables or methods that need to be put outside the service() method of the final generated Java servlet.
• Expression tag— In order to use Java values or variables directly in the JSP, you can use the expression tag.
• Scriptlet tag— The scriptlet tag is the most important tag in the JSP specification because it enables the actual embedding of Java code within an HTML page. An application component provider can write entire processing routines within the scriptlet tags.
• Custom tag— The final set of tags that the JavaServer Page specification defines is the embedding of custom tags. Because the JSP compiler cannot process these tags on its own, a special set of classes called the JSP tag library must be built by the application component provider to support the processing of the custom tags.

Testing with JUnit

Testing with JUnit

JUnit is an open source testing framework that comes with Eclipse and other IDEs. You can create JUnit-based classes in the same project as other classes, and use this JUnit code to test the other classes in your project. Using JUnit in this way, you can construct a set of standard tests for everyone working on an application, and if they change the application's code, all they'll need is a few clicks to verify that the application still passes the standard set of tests.

JUnit is designed to test your code, and it's made up of assertion methods that can test various conditions. Here they are:

assertEquals(a, b)

Tests if a is equal to b (a and b are either primitive values or must have an equals method for comparison purposes)

assertFalse(a)

Tests if a is false, where a is a Boolean value

assertNotNull(a)

Tests if a is not null, where a is either an object or null

assertNotSame(a, b)

Tests if a and b both do not refer to the identical object

assertNull(a)

Tests if a is null, where a is either an object or null

assertSame(a, b)

Tests if a and b both refer to the identical object

assertTrue(a)

Tests if a is true, where a is a Boolean value

You construct JUnit tests using these methods; when you run a JUnit application, it opens its own view to give you an immediate indication of which tests have passed and which have failed.

What is Struts?

What is Struts?
Struts Frame work is the implementation of Model-View-Controller (MVC) design pattern for the JSP. Struts is maintained as a part of Apache Jakarta project and is open source. Struts Framework is suited for the application of any size. Latest version of struts can be downloaded from http://jakarta.apache.org/. We are using jakarta-struts-1.1 and jakarta-tomcat-5.0.4 for this tutorial.

What is Model-View-Controller (MVC) Architecture?
Model-View-Controller architecture is all about dividing application components into three different categories Model, View and the Controller. Components of the MVC architecture has unique responsibility and each component is independent of the other component. Changes in one component will have no or less impact on other component. Responsibilities of the components are:
Model: Model is responsible for providing the data from the database and saving the data into the data store. All the business logic are implemented in the Model. Data entered by the user through View are check in the model before saving into the database. Data access, Data validation and the data saving logic are part of Model.
View: View represents the user view of the application and is responsible for taking the input from the user, dispatching the request to the controller and then receiving response from the controller and displaying the result to the user. HTML, JSPs, Custom Tag Libraries and Resources files are the part of view component.
Controller: Controller is intermediary between Model and View. Controller is responsible for receiving the request from client. Once request is received from client it executes the appropriate business logic from the Model and then produce the output to the user using the View component. ActionServlet, Action, ActionForm and struts-config.xml are the part of Controller.

Precedence and Associativity Rules for Operators in Java

Precedence and Associativity Rules for Operators
Precedence and associativity rules are necessary for deterministic evaluation of expressions.

• The operators are shown with decreasing precedence from the top of the table.
• Operators within the same row have the same precedence.
• Parentheses, ( ), can be used to override precedence and associativity.
• The unary operators, which require one operand, include the postfix increment (++) and decrement (--) operators from the first row, all the prefix operators (+, -, ++, --, ~, !) in the second row, and the prefix operators (object creation operator new, cast operator (type)) in the third row.
• The conditional operator (? :) is ternary, that is, requires three operands.
• All operators not listed above as unary or ternary, are binary, that is, require two operands.
• All binary operators, except for the relational and assignment operators, associate from left to right. The relational operators are nonassociative.
• Except for unary postfix increment and decrement operators, all unary operators, all assignment operators, and the ternary conditional operator associate from right to left.

Precedence rules are used to determine which operator should be applied first if there are two operators with different precedence, and these follow each other in the expression. In such a case, the operator with the highest precedence is applied first.
2 + 3 * 4 is evaluated as 2 + (3 * 4) (with the result 14) since * has higher precedence than +.

Associativity rules are used to determine which operator should be applied first if there are two operators with the same precedence, and these follow each other in the expression.
Left associativity implies grouping from left to right, Right associativity implies grouping from right to left.