Category Archives: Java

relative vs absolute path

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The path with reference to root directory is called absolute. The path with reference to current directory is called relative.

Completely relative:

 <img src="kitten.png"/>

Absolute in all respects: 

<img src="http://www.foo.com/images/kitten.png">
Posted in JSP.

Passing value in URL

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TestController.java

@RequestMapping(value="/Control2/{personId}")		
public String TestMe(@PathVariable("personId") Long personIdVal)
{
  System.out.println(personIdVal);
  return "hello";
}

Input

http://localhost:8089/Test2/Control1/Control2/152

Output

152

How Spring MVC Works

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Spring MVC uses 2 design Patterns Internally

  1. Front Controller
  2. MVC

How Spring MVC Handles Request

  1. Receive the request from client
  2. Consult Handle Mapper to decide which controller processes the request
  3. Dispatch the request to the controller
  4. Controller processes the request and returns the logical view name and model back to DispatcherServlet
  5. Consult View Resolver for appropriate View for the logical view name from Controller
  6. Pass the model to View implementation for rendering
  7. View renders the model and returns the result to DispatcherServlet
  8. Return the rendered result from view to the client

MappingHandler
DispatcherServlet uses MappingHandler to find out which controller is right one for this request.There are many MappingHandler implementations which uses different strategies to map the request to Controller. By default DispatcherServlet will use BeanNameUrlHandlerMapping and DefaultAnnotationHandlerMapping.

public interface HandlerMapping 
{
      HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}

ViewResolver
With the help of ViewResolver strategy object DispatcherServlet can find out physical view from the logical view name. Similar to MappingHandler there are also many different strategies for resolving the view based on the different view technologies. Most commonly used implementation of ViewResolver is InternalResourceViewResolver. 

public interface ViewResolver 
{
      View resolveViewName(String viewName, Locale locale) throws Exception;
}

Spring Project Setup – XML Configuration

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Creating a Preconfigured MVC Project
web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

	<!-- The definition of the Root Spring Container shared by all Servlets and Filters -->
	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/spring/root-context.xml</param-value>
	</context-param>
	
	<!-- Creates the Spring Container shared by all Servlets and Filters -->
	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>

	<!-- Processes application requests -->
	<servlet>
		<servlet-name>appServlet</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>/WEB-INF/spring/appServlet/servlet-context.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>
		
	<servlet-mapping>
		<servlet-name>appServlet</servlet-name>
		<url-pattern>/</url-pattern>
	</servlet-mapping>

</web-app>
  1. DispatcherServlet is the first servlet which gets called when you run Preconfigured MVC Project
  2. servlet-context.xml in init param of DispatcherServlet get run for other initialization of internal beans
  3. Apart from servlet-context.xml the other xml file that gets called is root-context.xml in a separate context

Test.java

package com.mugil.spring;

import java.util.Locale;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class Test
{	
	@RequestMapping(value = "/", method = RequestMethod.GET)
	public String testMethod(Locale locale, Model model) 
	{	
		model.addAttribute("testMsg", "Hi There" );		
		return "home";
	}
}

home.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page session="false" %>
<html>
<head>
	<title>Home</title>
</head>
<body>
<h1>
	${testMsg}  
</h1>
</body>
</html>

Output(http://localhost:8089/spring/)

Hi There

servlet-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/mvc"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:beans="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
		http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
	<annotation-driven />
	<resources mapping="/resources/**" location="/resources/" />
	<beans:bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
		<beans:property name="prefix" value="/WEB-INF/views/" />
		<beans:property name="suffix" value=".jsp" />
	</beans:bean>

	<context:component-scan base-package="com.mugil.spring" />
</beans:beans>
  1. context:component-scan base-package defines the base location in which the controller to be found
  2. beans:property name=”prefix” defines the folder in which jsp should be found
  3. beans:property name=”suffix” defines the valid prefix
  4. Based on the return type of testMethod method the jsp page name is recognized. In our case it is home.jsp

Choosing Controllers based on Form Inputs

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hello.java

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form name="frmTest" id="frmTest" method="post">		
	<select name="cboArea">
		<option value="Teynampet">Teynampet</option>
		<option value="TNagar">TNagar</option>
		<option value="Adyar">Adyar</option>
	</select>		
	<input type="checkbox" name="cboAgree" value="I Agree"/>I Agree		
	<input type="submit" name="btnSubmit" value="Submit"/>		
</form>
</body>
</html>

TestController.java

package com.mugil.controls;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
@RequestMapping("/Control1")
public class TestController 
{	
	@RequestMapping("/Control2")		
	public String TestMe()
	{
		return "hello";
	}

	@RequestMapping(value="/Control2", method=RequestMethod.POST)
	public String TestMe2()
	{
		System.out.println("Hi there");
		return "hello";
	}

	@RequestMapping(value="/Control2", method=RequestMethod.POST, params={"cboArea=TNagar", "cboAgree"})
	public String TestMe3()
	{
		System.out.println("I am in TNagar");
		return "hello";
	}
}

Binding Form elements with Bean Values

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add_person.jsp

<body>
  <form name="frmTest" id="frmTest" method="post" action="/Test2/Control1/displayPerson">
    <input type="text" name="Name" />I Agree
	<select name="Location">
  	  <option value="Teynampet">Teynampet</option>
	  <option value="TNagar">TNagar</option>
	  <option value="Adyar">Adyar</option>
	</select>
    <input type="checkbox" name="cboAgree" value="I Agree"/>I Agree		
    <input type="submit" name="btnSubmit" value="Submit"/>		
  </form>
</body>

Person.java

public class Person 
{
	private String Name;
	private String Location;	
	
	public String getName() {
		return Name;
	}
	public void setName(String name) {
		Name = name;
	}
	public String getLocation() {
		return Location;
	}
	public void setLocation(String location) {
		Location = location;
	}

        @Override
	public String toString() 
        {
	  return "Person [Name=" + Name + ", Location=" + Location + "]";
	}
}

TestController .java

@Controller
@RequestMapping("/Control1")
public class TestController 
{
	@RequestMapping(value="/displayPerson", method=RequestMethod.POST)
	public String TestMe4(@ModelAttribute Person person)
	{
		System.out.println(person); 
		return "add_person";
	}
}

Output

Person [Name=Mac, Location=TNagar]

Accessing Bean Values

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TestController.java

@RequestMapping(value="/Control2", method=RequestMethod.POST)
public String TestMe2(Model model)
{
  Person objPerson = new Person();
  objPerson.setName("Mugil");
  objPerson.setAddress("Sample Address");
  objPerson.setAge("27");

  model.addAttribute("objPerson", objPerson);
  return "display";
}

display.jsp

Person Name : ${objPerson.name}
Person Location : ${objPerson.location}
Person Age : ${objPerson.age}
Person Address : ${objPerson.address}

public class Person 
{
 private String Name;
 private String Location;
 private String Age;
 private String Address;

 public String getName() {
	return Name;
 }
 public void setName(String name) {
	Name = name;
 }
 public String getLocation() {
	return Location;
 }
 public void setLocation(String location) {
	Location = location;
 }

 .
 .
 .
}

How to Design Spring MVC for View Page

  1. Have a isSuccess attribute in the bean
  2. Use when and choose to decide whether to form element or form value based on the value set in the isSuccess
  3. When isSuccess is set to true the show the form Value or show the form element else display the form element
  4. When adding a new values in through the form the bean would be set to isSuccess true
  5. Next time when the page gets loaded the form values filled before the click of the submit will be displayed a s form values.

How to access the bean values where the bean has sub bean

class Student
{
 String Name;
 Address houseAddress;
 .
 .
}

For accessing values in Student bean the form elements should be

path=Name value="${student.Name}"

For accessing values in Student Address bean the form elements should be

path=Address.houseAddress value="${Student.Address.StreetName}"

Servlet Config and Servlet Context

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ServletConfig

  1. ServletConfig is one of the pre-defined interface.
  2. ServletConfig object is used for developing flexible servlets.
  3. ServletConfig objct exist one per servlet program.
  4. An object of ServletConfig created by the container during its initialization phase.
  5. An object of ServletConfig is available to the servlet during its execution, once the servlet execution is completed, automatically ServletConfig interface object will be removed by the container.
  6. An object of ServletConfig interface contains details at web.xml, of a particular servlet.
  7. The moment when we are using an object of ServletConfig, we need to configure the web.xml by writing tag under tag of web.xml.
  8. When ever compiler executes init() mehod then the ServletConfig will be created in general.
  9. An object of ServletConfig contain the data in the form of key,value pairs, here the keys represents init param names and values are its values, which are represented in the web.xml file

How to Get ServletConfig Object into Servelt
Method1

ServletConfig conf = getServletConfig();

Method2
ServletConfig object will be available in init() method of the servlet.

public void init(ServletConfig config)
{
// …………………
}

How to Retrieve Data from ServletConfig Interface Object

public String getInitParameter(“param name”);
public Enumeration getInitParameterNames();

web.xml

<web-app> 
  <servlet>
     <servlet-name>onServletConfig</servlet-name>
     <servlet-class>java4s.OnServletConfig</servlet-class> 
     <init-param>
        <param-name> n1 </param-name>
        <param-value> 100 </param-value>
     </init-param>
    .
    .
</web-app>

Test.java

ServletConfig conf=getServletConfig(); 
String s1=conf.getInitParameter("n1");

ServletContext
An object of ServletContext is created by the web container at time of deploying the project. This object can be used to get configuration information from web.xml file. There is only one ServletContext object per web application.

Methods of ServletContext interface

  1. public String getInitParameter(String name):Returns the parameter value for the specified parameter name.
  2. public Enumeration getInitParameterNames():Returns the names of the context’s initialization parameters.
  3. public void setAttribute(String name,Object object):sets the given object in the application scope.
  4. public Object getAttribute(String name):Returns the attribute for the specified name.
  5. public Enumeration getInitParameterNames():Returns the names of the context’s initialization parameters as an Enumeration of String objects.

web.xml

    <web-app>  
     ......  
          
      <context-param>  
        <param-name>parametername</param-name>  
        <param-value>parametervalue</param-value>  
      </context-param>  
     ......  
    </web-app>

Test.java

  ServletContext context=getServletContext();    

  //Getting the value of the initialization parameter and printing it  
  String driverName=context.getInitParameter("parametername");

Basic Controllers

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Simple Controller Example
TestController.java

package com.mugil.controls;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
@RequestMapping("/Control1")
public class TestController 
{	
  @RequestMapping("/Control2")	
  public String TestMe()
  {
    return "hello";
  }
}

hello.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
   Hi Dear!
</body>
</html>

Java Programs

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Fibonacci(without using recursion)

public class Test
{
  public static void main(String[] args)
  {
     int a=0 , b=0 , c=1;
     System.out.println(a);
     System.out.println(b);

     for(int i=0;i<15;i++)
     {
        a=b;
        b=c;
        c=a+b;
        System.out.println(c);
     }
   }
}

Fibonacci(using recursion)

7

Reverse array without Temp Array

public static int[] reverseArrayWithoutTempArray(int[] array) 
{
    int i = 0, j = array.length - 1;
 
    for (i = 0; i < array.length / 2; i++, j--) 
    {
        int temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
    return array;
}

Iterate random integer array and print the values greater than the current value

class Main 
{
 static void printNGE(int arr[]) 
 {
  int highestVal = 0, i, j;

  for (i = 0; i < arr.length; i++) 
  {
       if (arr[i] > highestVal) 
       {
        System.out.println(arr[i]);
        highestVal = arr[i];
       }
  }
 }

 public static void main(String args[]) 
 {
  int arr[]= {11, 13, 21, 3, 45};
  printNGE(arr);
 }
}

Inheritance program with Class and Interface.Find and print the Area and Perimeter for Rectangle,Square and Circle

  1. Interface Shape
  2. Rectangle class implements Shape
  3. Circle class extends Rectangle
interface Shape 
{
 void input();
 void area();
}

class Circle implements Shape 
{
 int r = 0;
 double pi = 3.14, ar = 0;
 
 @Override
 public void input() 
 {
  r = 5;
 }
 
 @Override
 public void area() 
 {
  ar = pi * r * r;
  System.out.println("Area of circle:" + ar);
 }
}

class Rectangle extends Circle 
{
 int l = 0, b = 0;
 double ar;

 public void input() 
 {
  super.input();
  l = 6;
  b = 4;
 }

 public void area() 
 {
  super.area();
  ar = l * b;
  System.out.println("Area of rectangle:" + ar);
 }
}

public class Demo 
{
 public static void main(String[] args) 
 {
  Rectangle obj = new Rectangle();
  obj.input();
  obj.area();
 }
}

Area of circle:78.5
Area of rectangle:24.0