Monday, July 16, 2012

doGet() and doPost()



In doGet Method the parameters are appended to the URL and sent along with header information

In doPost, parameters are sent in separate line in the body

Maximum size of data that can be sent using doget is 240 bytes

There is no maximum size for data

Parameters are not encrypted

Parameters are encrypted

DoGet method generally is used to query or to get some information from the server

Dopost is generally used to update or post some information to the server

DoGet is faster if we set the response content length since the same connection is used. Thus increasing the performance

DoPost is slower compared to doGet since doPost does not write the content length

DoGet should be idempotent. i.e. doget should be able to be repeated safely many times

This method does not need to be idempotent. Operations requested through POST can have side effects for which the user can be held accountable, for example, updating stored data or buying items online.

DoGet should be safe without any side effects for which user is held responsible

This method does not need to be either s

Wednesday, July 11, 2012

Database Connection Pooling in Tomcat

Database Connection Pooling in Tomcat 

tomcat-connection-poolingDatabase Connection Pooling is a great technique used by lot of application servers to optimize the performance. Database Connection creation is a costly task thus it impacts the performance of application. Hence lot of application server creates a database connection pool which are pre initiated db connections that can be leverage to increase performance.

Apache Tomcat also provide a way of creating DB Connection Pool. Let us see an example to implement DB Connection Pooling in Apache Tomcat server. We will create a sample web application with a servlet that will get the db connection from tomcat db connection pool and fetch the data using a query. We will use Eclipse as our development environment. This is not a prerequisite i.e. you may want to use any IDE to create this example.

Step 1: Create Dynamic Web Project in Eclipse

Create a Dynamic Web Project in Eclipse by selecting:
File -> New -> Project… ->Dynamic Web Project.

Step 2: Create context.xml

Apache Tomcat allow the applications to define the resource used by the web application in a file called context.xml (from Tomcat 5.x version onwards). We will create a file context.xml under META-INFdirectory.
Copy following content in the context.xml file.

    <?xml version="1.0" encoding="UTF-8"?>  <Context>  	<!-- Specify a JDBC datasource -->  	<Resource name="jdbc/testdb" auth="Container"  		type="javax.sql.DataSource" username="DB_USERNAME" password="DB_PASSWORD"  		driverClassName="oracle.jdbc.driver.OracleDriver"  		url="jdbc:oracle:thin:@xxx:1525:dbname"  		maxActive="10" maxIdle="4" />    </Context>  

In above code snippet, we have specify a database connection pool. The name of the resource isjdbc/testdb. We will use this name in our application to get the data connection. Also we specify db username and password and connection URL of database. Note that I am using Oracle as the database for this example. You may want to change this Driver class with any of other DB Providers (like MySQL Driver Class).

Step 3: Create Test Servlet and WEB xml entry

Create a file called I have created this file under package: net.viralpatel.servlet. Copy following code into it.

package net.viralpatel.servlet;    import;  import java.sql.Connection;  import java.sql.ResultSet;  import java.sql.SQLException;  import java.sql.Statement;    import javax.naming.Context;  import javax.naming.InitialContext;  import javax.naming.NamingException;  import javax.servlet.ServletException;  import javax.servlet.http.HttpServlet;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse;  import javax.sql.DataSource;    public class TestServlet extends HttpServlet {  	  	private DataSource dataSource;  	private Connection connection;  	private Statement statement;  	  	public void init() throws ServletException {  		try {  			// Get DataSource  			Context initContext  = new InitialContext();  			Context envContext  = (Context)initContext.lookup("java:/comp/env");  			dataSource = (DataSource)envContext.lookup("jdbc/testdb");    			  		} catch (NamingException e) {  			e.printStackTrace();  		}  	}    	public void doGet(HttpServletRequest req, HttpServletResponse resp)  			throws ServletException, IOException {  		  		ResultSet resultSet = null;  		try {  			// Get Connection and Statement  			connection = dataSource.getConnection();  			statement = connection.createStatement();  			String query = "SELECT * FROM STUDENT";  			resultSet = statement.executeQuery(query);  			while ( {  				System.out.println(resultSet.getString(1) + resultSet.getString(2) + resultSet.getString(3));  			}  		} catch (SQLException e) {  			e.printStackTrace();  		}finally {  			try { if(null!=resultSet)resultSet.close();} catch (SQLException e)   			{e.printStackTrace();}  			try { if(null!=statement)statement.close();} catch (SQLException e)   			{e.printStackTrace();}  			try { if(null!=connection)connection.close();} catch (SQLException e)   			{e.printStackTrace();}  		}  	}  }  

In the above code we initiated the datasource using InitialContext lookup:

    Context initContext  = new InitialContext();  Context envContext  = (Context)initContext.lookup("java:/comp/env");  dataSource = (DataSource)envContext.lookup("jdbc/testdb");  

Create test servlet mapping in the web.xml file (deployment descriptor) of the web application. The web.xml file will look like:

<?xml version="1.0" encoding="UTF-8"?>  <web-app id="WebApp_ID" version="2.4"  	xmlns=""  	xmlns:xsi=""  	xsi:schemaLocation="">  	<display-name>TomcatConnectionPooling</display-name>  	<welcome-file-list>  		<welcome-file>index.jsp</welcome-file>  	</welcome-file-list>    	<servlet>  		<servlet-name>TestServlet</servlet-name>  		<servlet-class>  			net.viralpatel.servlet.TestServlet  		</servlet-class>  	</servlet>  	<servlet-mapping>  		<servlet-name>TestServlet</servlet-name>  		<url-pattern>/servlet/test</url-pattern>  	</servlet-mapping>  </web-app>  

Now Run the web application in Tomcat using Eclipse (Alt + Shift + X, R). You will be able to see the result of the query executed.
Thus this way we can create a database pool in Tomcat and get the connections from it.

Sunday, July 1, 2012

Struts 1 Vs Struts 2

Feature Struts 1Struts 2
Action classesStruts 1 requires Action classes to extend an abstract base class. A common problem in Struts 1 is programming to abstract classes instead of interfaces. An Struts 2 Action may implement an Action interface, along with other interfaces to enable optional and custom services. Struts 2 provides a base ActionSupport class to implement commonly used interfaces. Albeit, the Action interface is not required. Any POJO object with a execute signature can be used as an Struts 2 Action object.
Threading Model 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. The singleton strategy places restrictions on what can be done with Struts 1 Actions and requires extra care to develop. Action resources must be thread-safe or synchronized. Struts 2 Action objects are instantiated for each request, so there are no thread-safety issues. (In practice, servlet containers generate many throw-away objects per request, and one more object does not impose a performance penalty or impact garbage collection.)
Servlet Dependency 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. Struts 2 Actions can still access the original request and response, if required. However, other architectural elements reduce or eliminate the need to access the HttpServetRequest or HttpServletResponse directly.
Testability A major hurdle to testing Struts 1 Actions is that the execute method exposes the Servlet API. A third-party extension, Struts TestCase, offers a set of mock object for Struts 1. Struts 2 Actions can be tested by instantiating the Action, setting properties, and invoking methods. Dependency Injection support also makes testing simpler.
Harvesting InputStruts 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. DynaBeans can used as an alternative to creating conventional ActionForm classes, but, here too, developers may be redescribing existing JavaBeans. 
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. The Action properties can be accessed from the web page via the taglibs. Struts 2 also supports the ActionForm pattern, as well as POJO form objects and POJO Actions. Rich object types, including business or domain objects, can be used as input/output objects. The ModelDriven feature simplifies taglb references to POJO input objects. 
Expression Language 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).
Binding values into viewsStruts 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. The ValueStack strategy allows reuse of views across a range of types which may have the same property name but different property types. 
Type Conversion Struts 1 ActionForm properties are usually all Strings. Struts 1 uses Commons-Beanutils for type conversion. Converters are per-class, and not configurable per instance. Struts 2 uses OGNL for type conversion. The framework includes converters for basic and common object types and primitives.
ValidationStruts 1 supports manual validation via a validate method on the ActionForm, or through an extension to the Commons Validator. Classes can have different validation contexts for the same class, but cannot chain to validations on sub-objects. Struts 2 supports manual validation via the validate method and the XWork Validation framework. The Xwork Validation Framework supports chaining validation into sub-properties using the validations defined for the properties class type and the validation context.
Control Of Action Execution 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.