Below Few Java interview question asked at MNC software company
1. How can you count active sessions by using listeners in JAVA.
we can do it by using HttpSessionListener for that you can create a session count class implementing HttpSessionListener interface. Our listener object will be called every time a session is created or destroyed by the server. You can find more information about HttpSessionListener at When do I use HttpSessionListener?.
Code example,
we have MySessionCounter.java that implements HttpSessionListener interface. We implement sessionCreated() and sessionDestroyed() methods, the sessionCreated() method will be called by the server every time a session is created and the sessionDestroyed() method will be called every time a session is invalidated or destroyed.
To receive notification events, the implementation class MySessionCounter must be configured in the deployment descriptor for the web application. add <listener> section into our /WEB-INF/web.xml file:
<!-- Listeners --> <listener> <listener-class>com.xyzws.web.utils.MySessionCounter</listener-class> </listener>
For show in JSP
the following JSP code shows the total active session:
<%@ page import="com.xyzws.utils.MySessionCounter"%><html>... Active Sessions : <%= MySessionCounter.getActiveSessions() %>...</html>
2) what is XML schema and it tags??
Definition
An XML Schema defines and describes certain types of XML data by using the XML Schema definition language (XSD). XML Schema elements (elements, attributes, types, and groups) are used to define the valid structure, valid data content, and relationships of certain types of XML data. XML Schemas can also provide default values for attributes, and elements.
XML Schema has contains below :
The xs:schema declaration indicates that this is a schema and that the xs: prefix will be used before schema items.
The xmlns:xs="http://www.w3.org/2001/XMLSchema" declaration indicates that all tags in this schema should be interpreted according to the default namespace of the World Wide Web Consortium (W3C), which was created in 2001.
The targetnamespace declaration names this schema as XMLSchema1.xsd and indicates its default location, which will be in a default URI (universal resource identifier) on your development server called tempuri.org.
When you create a schema with the XML Designer, the version and namespace statements are automatically added for you. You might modify the contents of these two declarations in some cases. For example, if you want to use a tag prefix other than "XS," you would need to define the default namespace for that tag in addition to the XS tag prefix.
A complex type called "addressType" is defined that will contain five elements of various data types. Note that each of the elements it contains is a simple, named type.
Example
How to write XML schema of below requirments
The final element in the purchaseOrder, Item, contains a facet called maxOccurs. Facets set limits on the type of content a simple type can contain. maxOccurs is used to constrain how many times an element can occur in the documents created from this schema. By default, maxOccurs is equal to one. In this case, setting it to unbounded indicates that the Item element can reoccur as many times as needed.
1. How can you count active sessions by using listeners in JAVA.
we can do it by using HttpSessionListener for that you can create a session count class implementing HttpSessionListener interface. Our listener object will be called every time a session is created or destroyed by the server. You can find more information about HttpSessionListener at When do I use HttpSessionListener?.
Code example,
we have MySessionCounter.java that implements HttpSessionListener interface. We implement sessionCreated() and sessionDestroyed() methods, the sessionCreated() method will be called by the server every time a session is created and the sessionDestroyed() method will be called every time a session is invalidated or destroyed.
package com.xyzws.web.utils;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionEvent;
public class MySessionCounter implements HttpSessionListener {
private static int activeSessions = 0;
public void sessionCreated(HttpSessionEvent se) {
activeSessions++;
}
public void sessionDestroyed(HttpSessionEvent se) {
if(activeSessions > 0)
activeSessions--;
}
public static int getActiveSessions() {
return activeSessions;
}
}
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionEvent;
public class MySessionCounter implements HttpSessionListener {
private static int activeSessions = 0;
public void sessionCreated(HttpSessionEvent se) {
activeSessions++;
}
public void sessionDestroyed(HttpSessionEvent se) {
if(activeSessions > 0)
activeSessions--;
}
public static int getActiveSessions() {
return activeSessions;
}
}
To receive notification events, the implementation class MySessionCounter must be configured in the deployment descriptor for the web application. add <listener> section into our /WEB-INF/web.xml file:
<!-- Listeners --> <listener> <listener-class>com.xyzws.web.utils.MySessionCounter</listener-class> </listener>
For show in JSP
the following JSP code shows the total active session:
<%@ page import="com.xyzws.utils.MySessionCounter"%><html>... Active Sessions : <%= MySessionCounter.getActiveSessions() %>...</html>
Definition
An XML Schema defines and describes certain types of XML data by using the XML Schema definition language (XSD). XML Schema elements (elements, attributes, types, and groups) are used to define the valid structure, valid data content, and relationships of certain types of XML data. XML Schemas can also provide default values for attributes, and elements.
XML Schema has contains below :
- The first statement, <?xml version="1.0" encoding="utf-8"?>, specifies the version of XML in use.
- The second statement consists of several parts:
The xs:schema declaration indicates that this is a schema and that the xs: prefix will be used before schema items.
The xmlns:xs="http://www.w3.org/2001/XMLSchema" declaration indicates that all tags in this schema should be interpreted according to the default namespace of the World Wide Web Consortium (W3C), which was created in 2001.
The targetnamespace declaration names this schema as XMLSchema1.xsd and indicates its default location, which will be in a default URI (universal resource identifier) on your development server called tempuri.org.
When you create a schema with the XML Designer, the version and namespace statements are automatically added for you. You might modify the contents of these two declarations in some cases. For example, if you want to use a tag prefix other than "XS," you would need to define the default namespace for that tag in addition to the XS tag prefix.
A complex type called "addressType" is defined that will contain five elements of various data types. Note that each of the elements it contains is a simple, named type.
Example
How to write XML schema of below requirments
The final element in the purchaseOrder, Item, contains a facet called maxOccurs. Facets set limits on the type of content a simple type can contain. maxOccurs is used to constrain how many times an element can occur in the documents created from this schema. By default, maxOccurs is equal to one. In this case, setting it to unbounded indicates that the Item element can reoccur as many times as needed.
<?xml version="1.0" encoding="utf-8"?>
<xs:schema targetNamespace="http://tempuri.org/XMLSchema1.xsd" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:complexType name="addressType">
<xs:sequence>
<xs:element name="street1" type="xs:string"/>
<xs:element name="street2" type="xs:string"/>
<xs:element name="city" type="xs:string"/>
<xs:element name="state" type="xs:string"/>
<xs:element name="zip" type="xs:integer"/>
</xs:sequence>
</xs:complexType>
<xs:element name="purchaseOrder">
<xs:complexType>
<xs:sequence>
<xs:element name="shipTo" type="addressType" />
<xs:element name="billTo" type="addressType" />
<xs:element name="shipDate" type="xs:date" />
<xs:element name="item" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
