struts interview questions

1.What is MVC?

Model-View-Controller (MVC) is a design pattern put together to help control change. MVC decouples interface from business logic and data.

• Model : The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller.


• View: The view provides the presentation of the model. It is the look of the application. The view can access the model getters, but it has no knowledge of the setters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur.


• Controller:The controller reacts to the user input. It creates and sets the model.

2.What is a framework?

A framework is made up of the set of classes which allow us to use a library in a best possible way for a specific requirement.

3.What is Struts framework?

Struts framework is an open-source framework for developing the web applications in Java EE, based on MVC-2 architecture. It uses and extends the Java Servlet API. Struts is robust architecture and can be used for the development of application of any size. Struts framework makes it much easier to design scalable, reliable Web applications with Java.

4.What are the components of Struts?

Struts components can be categorize into Model, View and Controller:

• Model: Components like business logic /business processes and data are the part of model.
• View: HTML, JSP are the view components.
• Controller: Action Servlet of Struts is part of Controller components which works as front controller to handle all the requests.

5.What are the core classes of the Struts Framework?

Struts is a set of cooperating classes, servlets, and JSP tags that make up a reusable MVC 2 design.

• JavaBeans components for managing application state and behavior.
• Event-driven development (via listeners as in traditional GUI development).
• Pages that represent MVC-style views; pages reference view roots via the JSF component tree.

6.What is ActionServlet?

ActionServlet is a simple servlet which is the backbone of all Struts applications. It is the main Controller component that handles client requests and determines which Action will process each received request. It serves as an Action factory – creating specific Action classes based on user’s request.

7.What is role of ActionServlet?

ActionServlet performs the role of Controller:

• Process user requests
• Determine what the user is trying to achieve according to the request
• Pull data from the model (if necessary) to be given to the appropriate view,
• Select the proper view to respond to the user
• Delegates most of this grunt work to Action classes
• Is responsible for initialization and clean-up of resources

8.What is the ActionForm?

ActionForm is javabean which represents the form inputs containing the request parameters from the View referencing the Action bean.

9.What are the important methods of ActionForm?

The important methods of ActionForm are : validate() & reset().

10.Describe validate() and reset() methods ?

validate() : Used to validate properties after they have been populated; Called before FormBean is handed to Action. Returns a collection of ActionError as ActionErrors. Following is the method signature for the validate() method.

public ActionErrors validate(ActionMapping mapping,HttpServletRequest request)

reset(): reset() method is called by Struts Framework with each request that uses the defined ActionForm. The purpose of this method is to reset all of the ActionForm's data members prior to the new request values being set.

public void reset() {}

11.What is ActionMapping?

Action mapping contains all the deployment information for a particular Action bean. This class is to determine where the results of the Action will be sent once its processing is complete.

12.How is the Action Mapping specified ?

We can specify the action mapping in the configuration file called struts-config.xml. Struts framework creates ActionMapping object from configuration element of struts-config.xml file

  path="/submit"

	type="submit.SubmitAction"

        name="submitForm"

        input="/submit.jsp"

        scope="request"

        validate="true">

  name="success" path="/success.jsp"/>

  name="failure" path="/error.jsp"/>

13.What is role of Action Class?

An Action Class performs a role of an adapter between the contents of an incoming HTTP request and the corresponding business logic that should be executed to process this request.

14.In which method of Action class the business logic is executed ?

In the execute() method of Action class the business logic is executed.

public ActionForward execute(

	    ActionMapping mapping,

             ActionForm form,

             HttpServletRequest request,

             HttpServletResponse response)

          throws Exception ;

execute() method of Action class:

• Perform the processing required to deal with this request
• Update the server-side objects (Scope variables) that will be used to create the next page of the user interface
• Return an appropriate ActionForward object

15.What design patterns are used in Struts?

Struts is based on model 2 MVC (Model-View-Controller) architecture. Struts controller uses the command design pattern and the action classes use the adapter design pattern. The process() method of the RequestProcessor uses the template method design pattern. Struts also implement the following J2EE design patterns.

• Service to Worker
• Dispatcher View
• Composite View (Struts Tiles)
• Front Controller
• View Helper
• Synchronizer Token

16.Can we have more than one struts-config.xml file for a single Struts application?

Yes, we can have more than one struts-config.xml for a single Struts application. They can be configured as follows:

>actionservlet-name>      

 

	org.apache.struts.action.ActionServlet

 



 config

 

    /WEB-INF/struts-config.xml,             

    /WEB-INF/struts-admin.xml,

    /WEB-INF/struts-config-forms.xml         

 



.....

17.What is the directory structure of Struts application?

The directory structure of Struts application :

18.What is the difference between session scope and request scope when saving formbean ?

when the scope is request,the values of formbean would be available for the current request.
when the scope is session,the values of formbean would be available throughout the session.

19.What are the important tags of struts-config.xml ?

The five important sections are:

20.What are the different kinds of actions in Struts?

The different kinds of actions in Struts are:

• ForwardAction
• IncludeAction
• DispatchAction
• LookupDispatchAction
• SwitchAction

21.What is DispatchAction?

The DispatchAction class is used to group related actions into one class. Using this class, you can have a method for each logical action compared than a single execute method. The DispatchAction dispatches to one of the logical actions represented by the methods. It picks a method to invoke based on an incoming request parameter. The value of the incoming parameter is the name of the method that the DispatchAction will invoke.

22.How to use DispatchAction?

To use the DispatchAction, follow these steps :

• Create a class that extends DispatchAction (instead of Action)
• In a new class, add a method for every function you need to perform on the service – The method has the same signature as the execute() method of an Action class.
• Do not override execute() method – Because DispatchAction class itself provides execute() method.
• Add an entry to struts-config.xml

DispatchAction Example »

23.What is the use of ForwardAction?

The ForwardAction class is useful when you’re trying to integrate Struts into an existing application that uses Servlets to perform business logic functions. You can use this class to take advantage of the Struts controller and its functionality, without having to rewrite the existing Servlets. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page. By using this predefined action, you don’t have to write your own Action class. You just have to set up the struts-config file properly to use ForwardAction.

24.What is IncludeAction?

The IncludeAction class is useful when you want to integrate Struts into an application that uses Servlets. Use the IncludeAction class to include another resource in the response to the request being processed.

25.What is the difference between ForwardAction and IncludeAction?

The difference is that you need to use the IncludeAction only if the action is going to be included by another action or jsp. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page.

26.What is LookupDispatchAction?

The LookupDispatchAction is a subclass of DispatchAction. It does a reverse lookup on the resource bundle to get the key and then gets the method whose name is associated with the key into the Resource Bundle.

27.What is the use of LookupDispatchAction?

LookupDispatchAction is useful if the method name in the Action is not driven by its name in the front end, but by the Locale independent key into the resource bundle. Since the key is always the same, the LookupDispatchAction shields your application from the side effects of I18N.

28.What is difference between LookupDispatchAction and DispatchAction?

The difference between LookupDispatchAction and DispatchAction is that the actual method that gets called in LookupDispatchAction is based on a lookup of a key value instead of specifying the method name directly.

29.What is SwitchAction?

The SwitchAction class provides a means to switch from a resource in one module to another resource in a different module. SwitchAction is useful only if you have multiple modules in your Struts application. The SwitchAction class can be used as is, without extending.

30.What if element has declaration with same name as global forward?

In this case the global forward is not used. Instead the element’s takes precendence.

31.What is DynaActionForm?

A specialized subclass of ActionForm that allows the creation of form beans with dynamic sets of properties (configured in configuration file), without requiring the developer to create a Java class for each type of form bean.

32.What are the steps need to use DynaActionForm?

Using a DynaActionForm instead of a custom subclass of ActionForm is relatively straightforward. You need to make changes in two places:

• In struts-config.xml: change your to be an org.apache.struts.action.DynaActionForm instead of some subclass of ActionForm

 name="loginForm"type="org.apache.struts.action.DynaActionForm" >

     name="userName" type="java.lang.String"/>

     name="password" type="java.lang.String" />

• In your Action subclass that uses your form bean:
  • import org.apache.struts.action.DynaActionForm
  • downcast the ActionForm parameter in execute() to a DynaActionForm
  • access the form fields with get(field) rather than getField()

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;

import org.apache.struts.action.ActionForm;

import org.apache.struts.action.ActionForward;

import org.apache.struts.action.ActionMapping;

import org.apache.struts.action.ActionMessage;

import org.apache.struts.action.ActionMessages;





import org.apache.struts.action.DynaActionForm;



public class DynaActionFormExample extends Action {

public ActionForward execute(ActionMapping mapping, ActionForm form,

  HttpServletRequest request, HttpServletResponse response)

            throws Exception {            

 DynaActionForm loginForm = (DynaActionForm) form;

                ActionMessages errors = new ActionMessages();       

        if (((String) loginForm.get("userName")).equals("")) {

            errors.add("userName", new ActionMessage(

                            "error.userName.required"));

        }

        if (((String) loginForm.get("password")).equals("")) {

            errors.add("password", new ActionMessage(

                            "error.password.required"));

        }

        ...........

33.How to display validation errors on jsp page?

tag displays all the errors. iterates over ActionErrors request attribute.

34.What are the various Struts tag libraries?

The various Struts tag libraries are:

• HTML Tags
• Bean Tags
• Logic Tags
• Template Tags
• Nested Tags
• Tiles Tags

35.What is the use of ?

repeats the nested body content of this tag over a specified collection.

 id="customer" name="customers">

   




  
 
 

     
 name="customer" property="firstName"/>
 
     
 name="customer" property="lastName"/>
     
 name="customer" property="address"/>
  

 

36.What are differences between and

: is used to retrive keyed values from resource bundle. It also supports the ability to include parameters that can be substituted for defined placeholders in the retrieved string.

key="prompt.customer.firstname"/>

: is used to retrieve and print the value of the bean property. has no body.

 name="customer" property="firstName"/>

37.How the exceptions are handled in struts?

Exceptions in Struts are handled in two ways:

• Programmatic exception handling :
Explicit try/catch blocks in any code that can throw exception. It works well when custom value (i.e., of variable) needed when error occurs.


• Declarative exception handling :You can either define handling tags in your struts-config.xml or define the exception handling tags within tag. It works well when custom page needed when error occurs. This approach applies only to exceptions thrown by Actions.

 key="some.key"

           type="java.lang.NullPointerException"

           path="/WEB-INF/errors/null.jsp"/>

or

 key="some.key" 

          type="package.SomeException"

          path="/WEB-INF/somepage.jsp"/>

38.What is difference between ActionForm and DynaActionForm?

• An ActionForm represents an HTML form that the user interacts with over one or more pages. You will provide properties to hold the state of the form with getters and setters to access them. Whereas, using DynaActionForm there is no need of providing properties to hold the state. Instead these properties and their type are declared in the struts-config.xml
  
• The DynaActionForm bloats up the Struts config file with the xml based definition. This gets annoying as the Struts Config file grow larger.
  
• The DynaActionForm is not strongly typed as the ActionForm. This means there is no compile time checking for the form fields. Detecting them at runtime is painful and makes you go through redeployment.
  
• ActionForm can be cleanly organized in packages as against the flat organization in the Struts Config file.
  
• ActionForm were designed to act as a Firewall between HTTP and the Action classes, i.e. isolate and encapsulate the HTTP request parameters from direct use in Actions. With DynaActionForm, the property access is no different than using request.getParameter( .. ).
  

39.How can we make message resources definitions file available to the Struts framework environment?

We can make message resources definitions file (properties file) available to Struts framework environment by adding this file to struts-config.xml.

 parameter="com.login.struts.ApplicationResources"/>

40.What is the life cycle of ActionForm?

The lifecycle of ActionForm invoked by the RequestProcessor is as follows:

• Retrieve or Create Form Bean associated with Action
• "Store" FormBean in appropriate scope (request or session)
• Reset the properties of the FormBean
• Populate the properties of the FormBean
• Validate the properties of the FormBean
• Pass FormBean to Action

JDBC Driver Types

JDBC drivers are divided into four types or levels. The different types of jdbc drivers are:

Type 1: JDBC-ODBC Bridge driver (Bridge)
Type 2: Native-API/partly Java driver (Native)
Type 3: AllJava/Net-protocol driver (Middleware)
Type 4: All Java/Native-protocol driver (Pure)

Type 1 JDBC Driver

JDBC-ODBC Bridge driver

The Type 1 driver translates all JDBC calls into ODBC calls and sends them to the ODBC driver. ODBC is a generic API. The JDBC-ODBC Bridge driver is recommended only for experimental use or when no other alternative is available.

Type 1: JDBC-ODBC Bridge

Advantage

The JDBC-ODBC Bridge allows access to almost any database, since the database's ODBC drivers are already available.

Disadvantages

1. Since the Bridge driver is not written fully in Java, Type 1 drivers are not portable.
2. A performance issue is seen as a JDBC call goes through the bridge to the ODBC driver, then to the database, and this applies even in the reverse process. They are the slowest of all driver types.
3. The client system requires the ODBC Installation to use the driver.
4. Not good for the Web.

import java.sql.*;

public class AccessDAO {

 private Connection con;
 private Statement st;
   private static final String url="jdbc:odbc:MyAccessDB";
 private static final String className="sun.jdbc.odbc.JdbcOdbcDriver";
 private static final String user="";
 private static final String pass="";

 AccessDAO()throws Exception {


 Class.forName(className);
  con = DriverManager.getConnection(url, user, pass);
  st = con.createStatement();

  //do whatever database processing is required
 }
}

Type 2 JDBC Driver

Native-API/partly Java driver

The distinctive characteristic of type 2 jdbc drivers are that Type 2 drivers convert JDBC calls into database-specific calls i.e. this driver is specific to a particular database. Some distinctive characteristic of type 2 jdbc drivers are shown below. Example: Oracle will have oracle native api.

Type 2: Native api/ Partly Java Driver

Advantage

The distinctive characteristic of type 2 jdbc drivers are that they are typically offer better performance than the JDBC-ODBC Bridge as the layers of communication (tiers) are less than that of Type
1 and also it uses Native api which is Database specific.

Disadvantage

1. Native API must be installed in the Client System and hence type 2 drivers cannot be used for the Internet.
2. Like Type 1 drivers, it’s not written in Java Language which forms a portability issue.
3. If we change the Database we have to change the native api as it is specific to a database
4. Mostly obsolete now
5. Usually not thread safe.

Type 3 JDBC Driver

All Java/Net-protocol driver

Type 3 database requests are passed through the network to the middle-tier server. The middle-tier then translates the request to the database. If the middle-tier server can in turn use Type1, Type 2 or Type 4 drivers.

Type 3: All Java/ Net-Protocol Driver

Advantage

1. This driver is server-based, so there is no need for any vendor database library to be present on client machines.
2. This driver is fully written in Java and hence Portable. It is suitable for the web.
3. There are many opportunities to optimize portability, performance, and scalability.
4. The net protocol can be designed to make the client JDBC driver very small and fast to load.
5. The type 3 driver typically provides support for features such as caching (connections, query results, and so on), load balancing, and advanced
system administration such as logging and auditing.
6. This driver is very flexible allows access to multiple databases using one driver.
7. They are the most efficient amongst all driver types.

Disadvantage

It requires another server application to install and maintain. Traversing the recordset may take longer, since the data comes through the backend server.

Type 4 JDBC Driver

Native-protocol/all-Java driver

The Type 4 uses java networking libraries to communicate directly with the database server.

Type 4: Native-protocol/all-Java driver

Advantage

1. The major benefit of using a type 4 jdbc drivers are that they are completely written in Java to achieve platform independence and eliminate deployment administration issues. It is most suitable for the web.
2. Number of translation layers is very less i.e. type 4 JDBC drivers don't have to translate database requests to ODBC or a native connectivity interface or to pass the request on to another server, performance is typically quite good.
3. You don’t need to install special software on the client or server. Further, these drivers can be downloaded dynamically.

Disadvantage

With type 4 drivers, the user needs a different driver for each database.

EX::http://www.cs.wright.edu/~schung/cs801/JDBC.pdf

in this pdf book we weill get some examples

JDBC Driver Types

JDBC drivers are divided into four types or levels. The different types of jdbc drivers are:

Type 1: JDBC-ODBC Bridge driver (Bridge)
Type 2: Native-API/partly Java driver (Native)
Type 3: AllJava/Net-protocol driver (Middleware)
Type 4: All Java/Native-protocol driver (Pure)

Type 1 JDBC Driver

JDBC-ODBC Bridge driver

The Type 1 driver translates all JDBC calls into ODBC calls and sends them to the ODBC driver. ODBC is a generic API. The JDBC-ODBC Bridge driver is recommended only for experimental use or when no other alternative is available.

Type 1: JDBC-ODBC Bridge

Advantage

The JDBC-ODBC Bridge allows access to almost any database, since the database's ODBC drivers are already available.

Disadvantages

1. Since the Bridge driver is not written fully in Java, Type 1 drivers are not portable.
2. A performance issue is seen as a JDBC call goes through the bridge to the ODBC driver, then to the database, and this applies even in the reverse process. They are the slowest of all driver types.
3. The client system requires the ODBC Installation to use the driver.
4. Not good for the Web.

Type 2 JDBC Driver

Native-API/partly Java driver

The distinctive characteristic of type 2 jdbc drivers are that Type 2 drivers convert JDBC calls into database-specific calls i.e. this driver is specific to a particular database. Some distinctive characteristic of type 2 jdbc drivers are shown below. Example: Oracle will have oracle native api.

Type 2: Native api/ Partly Java Driver

Advantage

The distinctive characteristic of type 2 jdbc drivers are that they are typically offer better performance than the JDBC-ODBC Bridge as the layers of communication (tiers) are less than that of Type
1 and also it uses Native api which is Database specific.

Disadvantage

1. Native API must be installed in the Client System and hence type 2 drivers cannot be used for the Internet.
2. Like Type 1 drivers, it’s not written in Java Language which forms a portability issue.
3. If we change the Database we have to change the native api as it is specific to a database
4. Mostly obsolete now
5. Usually not thread safe.

Type 3 JDBC Driver

All Java/Net-protocol driver

Type 3 database requests are passed through the network to the middle-tier server. The middle-tier then translates the request to the database. If the middle-tier server can in turn use Type1, Type 2 or Type 4 drivers.

Type 3: All Java/ Net-Protocol Driver

Advantage

1. This driver is server-based, so there is no need for any vendor database library to be present on client machines.
2. This driver is fully written in Java and hence Portable. It is suitable for the web.
3. There are many opportunities to optimize portability, performance, and scalability.
4. The net protocol can be designed to make the client JDBC driver very small and fast to load.
5. The type 3 driver typically provides support for features such as caching (connections, query results, and so on), load balancing, and advanced
system administration such as logging and auditing.
6. This driver is very flexible allows access to multiple databases using one driver.
7. They are the most efficient amongst all driver types.

Disadvantage

It requires another server application to install and maintain. Traversing the recordset may take longer, since the data comes through the backend server.

Type 4 JDBC Driver

Native-protocol/all-Java driver

The Type 4 uses java networking libraries to communicate directly with the database server.

Type 4: Native-protocol/all-Java driver

Advantage

1. The major benefit of using a type 4 jdbc drivers are that they are completely written in Java to achieve platform independence and eliminate deployment administration issues. It is most suitable for the web.
2. Number of translation layers is very less i.e. type 4 JDBC drivers don't have to translate database requests to ODBC or a native connectivity interface or to pass the request on to another server, performance is typically quite good.
3. You don’t need to install special software on the client or server. Further, these drivers can be downloaded dynamically.

Disadvantage

With type 4 drivers, the user needs a different driver for each database.

JDBC interview questions and answers

1. What are the steps involved in establishing a JDBC connection? This action involves two steps: loading the JDBC driver and making the connection.
2. How can you load the drivers?
   Loading the driver or drivers you want to use is very simple and involves just one line of code. If, for example, you want to use the JDBC-ODBC Bridge driver, the following code will load it:

   Class.forName(”sun.jdbc.odbc.JdbcOdbcDriver”);

   Your driver documentation will give you the class name to use. For instance, if the class name is jdbc.DriverXYZ, you would load the driver with the following line of code:

   Class.forName(”jdbc.DriverXYZ”);

3. What will Class.forName do while loading drivers? It is used to create an instance of a driver and register it with the
   DriverManager. When you have loaded a driver, it is available for making a connection with a DBMS.
4. How can you make the connection? To establish a connection you need to have the appropriate driver connect to the DBMS.
   The following line of code illustrates the general idea:

   String url = “jdbc:odbc:Fred”;
   Connection con = DriverManager.getConnection(url, “Fernanda”, “J8?);

5. How can you create JDBC statements and what are they?
   A Statement object is what sends your SQL statement to the DBMS. You simply create a Statement object and then execute it, supplying the appropriate execute method with the SQL statement you want to send. For a SELECT statement, the method to use is executeQuery. For statements that create or modify tables, the method to use is executeUpdate. It takes an instance of an active connection to create a Statement object. In the following example, we use our Connection object con to create the Statement object

   Statement stmt = con.createStatement();

6. How can you retrieve data from the ResultSet?
   JDBC returns results in a ResultSet object, so we need to declare an instance of the class ResultSet to hold our results. The following code demonstrates declaring the ResultSet object rs.

   ResultSet rs = stmt.executeQuery(”SELECT COF_NAME, PRICE FROM COFFEES”);
   String s = rs.getString(”COF_NAME”);

   The method getString is invoked on the ResultSet object rs, so getString() will retrieve (get) the value stored in the column COF_NAME in the current row of rs.

7. What are the different types of Statements?
   Regular statement (use createStatement method), prepared statement (use prepareStatement method) and callable statement (use prepareCall)
8. How can you use PreparedStatement? This special type of statement is derived from class Statement.If you need a
   Statement object to execute many times, it will normally make sense to use a PreparedStatement object instead. The advantage to this is that in most cases, this SQL statement will be sent to the DBMS right away, where it will be compiled. As a result, the PreparedStatement object contains not just an SQL statement, but an SQL statement that has been precompiled. This means that when the PreparedStatement is executed, the DBMS can just run the PreparedStatement’s SQL statement without having to compile it first.

   PreparedStatement updateSales =
   con.prepareStatement("UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?");
   

9. What does setAutoCommit do?
   When a connection is created, it is in auto-commit mode. This means that each individual SQL statement is treated as a transaction and will be automatically committed right after it is executed. The way to allow two or more statements to be grouped into a transaction is to disable auto-commit mode:

   con.setAutoCommit(false);

   Once auto-commit mode is disabled, no SQL statements will be committed until you call the method commit explicitly.

   con.setAutoCommit(false);
   PreparedStatement updateSales =
   con.prepareStatement( "UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?");
   updateSales.setInt(1, 50); updateSales.setString(2, "Colombian");
   updateSales.executeUpdate();
   PreparedStatement updateTotal =
   con.prepareStatement("UPDATE COFFEES SET TOTAL = TOTAL + ? WHERE COF_NAME LIKE ?");
   updateTotal.setInt(1, 50);
   updateTotal.setString(2, "Colombian");
   updateTotal.executeUpdate();
   con.commit();
   con.setAutoCommit(true);
   

10. How do you call a stored procedure from JDBC?
    The first step is to create a CallableStatement object. As with Statement an and PreparedStatement objects, this is done with an open
    Connection object. A CallableStatement object contains a call to a stored procedure.

     CallableStatement cs = con.prepareCall("{call SHOW_SUPPLIERS}");
    ResultSet rs = cs.executeQuery();
    

11. How do I retrieve warnings?
    SQLWarning objects are a subclass of SQLException that deal with database access warnings. Warnings do not stop the execution of an
    application, as exceptions do; they simply alert the user that something did not happen as planned. A warning can be reported on a
    Connection object, a Statement object (including PreparedStatement and CallableStatement objects), or a ResultSet object. Each of these
    classes has a getWarnings method, which you must invoke in order to see the first warning reported on the calling object:

    SQLWarning warning = stmt.getWarnings();
    if (warning != null)
    {
    System.out.println("n---Warning---n");
    while (warning != null)
    {
     System.out.println("Message: " + warning.getMessage());
     System.out.println("SQLState: " + warning.getSQLState());
     System.out.print("Vendor error code: ");
     System.out.println(warning.getErrorCode());
     System.out.println("");
     warning = warning.getNextWarning();
    }
    }
    

12. How can you move the cursor in scrollable result sets?
    One of the new features in the JDBC 2.0 API is the ability to move a result set’s cursor backward as well as forward. There are also methods that let you move the cursor to a particular row and check the position of the cursor.

    Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY);
    ResultSet srs = stmt.executeQuery(”SELECT COF_NAME, PRICE FROM COFFEES”);

    The first argument is one of three constants added to the ResultSet API to indicate the type of a ResultSet object: TYPE_FORWARD_ONLY, TYPE_SCROLL_INSENSITIVE , and TYPE_SCROLL_SENSITIVE. The second argument is one of two ResultSet constants for specifying whether a result set is read-only or updatable: CONCUR_READ_ONLY and CONCUR_UPDATABLE. The point to remember here is that if you specify a type, you must also specify whether it is read-only or updatable. Also, you must specify the type first, and because both parameters are of type int , the compiler will not complain if you switch the order. Specifying the constant TYPE_FORWARD_ONLY creates a nonscrollable result set, that is, one in which the cursor moves only forward. If you do not specify any constants for the type and updatability of a ResultSet object, you will automatically get one that is TYPE_FORWARD_ONLY and CONCUR_READ_ONLY.

13. What’s the difference between TYPE_SCROLL_INSENSITIVE , and TYPE_SCROLL_SENSITIVE?
    You will get a scrollable ResultSet object if you specify one of these ResultSet constants.The difference between the two has to do with whether a result set reflects changes that are made to it while it is open and whether certain methods can be called to detect these changes. Generally speaking, a result set that is TYPE_SCROLL_INSENSITIVE does not reflect changes made while it is still open and one that is TYPE_SCROLL_SENSITIVE does. All three types of result sets will make changes visible if they are closed and then reopened:

    Statement stmt =
    con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
    ResultSet srs =
    stmt.executeQuery("SELECT COF_NAME, PRICE FROM COFFEES");
    srs.afterLast();
    while (srs.previous())
    {
    String name = srs.getString("COF_NAME");
    float price = srs.getFloat("PRICE");
    System.out.println(name + " " + price);
    }
    

14. How to Make Updates to Updatable Result Sets?
    Another new feature in the JDBC 2.0 API is the ability to update rows in a result set using methods in the Java programming language rather than having to send an SQL command. But before you can take advantage of this capability, you need to create a ResultSet object that is updatable. In order to do this, you supply the ResultSet constant CONCUR_UPDATABLE to the createStatement method.

15. Difference between statement and prepared statement


A Statement compiles (into a database internal format) and executes a
SQL command all at once from a String, with all values hard-coded. For
example:

Statement stmt = cxn.createStatement(); // no command yet

At the time of the query the String provides everything hard coded:

ResultSet rset = // define and execute command
stmt.executeQuery( "SELECT * FROM mytable WHERE id = '12354'" );

A PreparedStatement (note the letter case) pre-compiles a SQL command
from a String upon its creation. The String may have placeholder
parameters for some values, each marked by a question mark (?). By query
execution time the code must provide a value for each parameter. Thus:

PreparedStatement pstmt = // precompile command at creation
cxn.prepareStatement( "SELECT * FROM mytable WHERE id = ?" );

By the time of the query there must be a value set for the 'id' column:

pstmt.setString( 1, "12354" ); // set parameter 1, a String
ResultSet rset = // command already defined
pstmt.executeQuery();

A (non-Prepared) Statement is compiled at every execution. A
PreparedStatement is compiled once, then executed from that compiled
format even if there are dynamic parameters. (One certainly can make a
PreparedStatement with hard-coded values.) If a command will execute
multiple times, perhaps with different dynamic values, the
PreparedStatement will be much faster over time.

Also, a PreparedStatement is immune to certain SQL insertion exploits
that could compromise a database. (The Statement can be made immune,
but it requires conscious thought.


A Statement is a static SQL statement. It does not support SQL parameters.
A PreparedStatement is a more dynamic SQL statement. The SQL doesn't
change, but it supports SQL parameters so you can execute the same query
in different ways (different filters for example).

The Waterfall Software Life Cycle Model

http://www.cs.toronto.edu/~sme/CSC444F/slides/L04-Lifecycles.pdf

Comparison of Struts 1 and Struts 2

Let us see the basic difference between Struts 1 and 2 framework.

1. Unlike Struts 1, Struts 2 does not need to implement Action class. The Action in Struts 2 is a POJO object. Thus making it easy to unit test the code.
2. Struts 1 Actions are singletons and must be thread-safe since there will only be one instance of a class to handle all requests for that Action. Struts 2 Action objects are instantiated for each request, so there are no thread-safety issues.
3. Struts 1 Actions have dependencies on the servlet API since the HttpServletRequest and HttpServletResponse is passed to the execute method when an Action is invoked. Struts 2 Actions are not coupled to a container. Most often the servlet contexts are represented as simple Maps, allowing Actions to be tested in isolation.
4. Struts 1 uses an ActionForm object to capture input. Like Actions, all ActionForms must extend a base class. Since other JavaBeans cannot be used as ActionForms, developers often create redundant classes to capture input. Struts 2 uses Action properties as input properties, eliminating the need for a second input object. Input properties may be rich object types which may have their own properties.
5. Struts 1 integrates with JSTL, so it uses the JSTL EL. The EL has basic object graph traversal, but relatively weak collection and indexed property support. Struts 2 can use JSTL, but the framework also supports a more powerful and flexible expression language called “Object Graph Notation Language” (OGNL).
6. Struts 1 uses the standard JSP mechanism for binding objects into the page context for access. Struts 2 uses a “ValueStack” technology so that the taglibs can access values without coupling your view to the object type it is rendering.
7. Struts 1 supports separate Request Processors (lifecycles) for each module, but all the Actions in the module must share the same lifecycle. Struts 2 supports creating different lifecycles on a per Action basis via Interceptor Stacks. Custom stacks can be created and used with different Actions, as needed.

PREVIEW_JAVA_J2EE_BOOK

http://www.lulu.com/items/volume_9/192000/192463/3/preview/PREVIEW_JAVA_J2EE_BOOK.pdf