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JavaBatchReview > Servlets > Flashcards

Servlets Flashcards

1
Q

What is TCP/IP?

A
  • Stands for Transmission Control Protocol/Internet Protocol.
  • It is a communication protocol used to interconnect network devices on the internet.
  • It is a suite that encompasses a number of different protocols for different purpose and needs
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2
Q

What are the different content types?

A
  • Content types is also known MIME (Multipurpose Internet Mail Extension) Type
  • Commonly used content types:
    • text/html
    • text/plain
    • application/jar
    • application/pdf
    • images/jpeg
    • images/png
    • images/gif
    • audio/mp3
    • video/mp4
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3
Q

What is a servlet?

A

Servlet is a technology used to create web applications; it is used to respond to incoming requests.

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4
Q

What is the Lifecycle of a Servlet?

A
  • Servlet class is loaded
    • Loaded when the first request for the servlet is
      received by the web container
    • Load on startup
  • Servlet instance is created
    • Created after the servlet class is loaded.
    • Created only once in the servlet life cycle.
  • Init method is invoked
    • Web container calls the init method once after
      creating the servlet instance.
    • Used to initialize the servlet.
  • Service method is invoked
    • Called every time a request is received for the
      servlet
  • Destroy method is invoked
    • Called before removing the servlet instance from
      the service.
    • Used to clean up any resources
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5
Q

App Server vs Web Server

A
  • A Web server exclusively handles HTTP requests, whereas an application server serves business logic to application programs through any number of protocols.
  • Web server is responsible for serving static content over HTTP while Application server is responsible for serving dynamic content, managing EJB, lookup over JNDI, and application security.
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6
Q

What is XML?

A

Stands for extensible markup language

It defines set of rules for encoding documents in a format that is both human-readable and machine readable

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7
Q

What is Well-Formed XML?

A 
- Refers to an XML document that satisfies certain rules 
  specified by the W3C 
    - documents with correct syntax
- A Well-Formed XML requires that:
    - Content be defined
    - Content be delimited with beginning and end tag
    - Content be properly nested
    - There can be only one root tag
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8
Q

Element vs Attribute

A

Elements can be viewed as containers that stores text, elements, etc…
Attributes defines the property of an element

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9
Q

What is DTD?

A
  • DTD stands for Document Type Definition.
  • This defines the elements that may be included in the document, what attributes the elements have, and the ordering and nesting of the elements.
  • Documents validated against DTD is considered to be “Well-Formed” and “Valid”
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10
Q

What is an XML Schema?

A
  • Describe the structure of an XML document

- Provides a more powerful alternative to DTD

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11
Q

What is XSL?

A
  • Stands for Extensible Stylesheet Language
  • Describes how XML elements should be displayed
  • Consist of three parts:
    • XSLT - language for transforming XML documents
    • XPath - language for navigating in XML documents
    • XSL-FO - Used for formatting XML documents
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12
Q

What is XSLT?

A
  • Stands for Extensible Stylesheet Language Transformations
  • Used for transforming XML documents into other XML documents
    • Ex: HTML to XHTML
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13
Q

What is XPath?

A
  • Stands for XML Path Language
  • Used to navigate through elements and attributes in an
    XML document
  • Core component of XSLT
  • Defines part of the XML document
  • Provides powerful “path expressions”
  • Used to select node or list of nodes from an XML
    document
  • Provides library of standard functions for manipulating
    string, numbers, etc.
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14
Q

What is JAXB?

A
  • Stands for Java Architecture for XML Binding

- It is used to convert Java Object to XML and XML to Java Objects

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15
Q

What are the different types of XML parsing?

A
  • DOM parser
  • SAX parser
  • JDOM parser
  • StAX parser
  • XPath parser
  • DOM4J parser
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16
Q

What is Marshalling?

A

The process of transforming the memory representation of an object to a data format suitable for storage or transmission.

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17
Q

What is a Front Controller?

A

A design pattern that represents a single controller that handles all incoming requests.

18
Q

What is a Dispatcher?

A
  • Dispatcher is part of the Front Controller Design
    Pattern
  • It is responsible for view management and navigation
19
Q

What is MVC?

A
  • Represents Model, View, Controller
  • MVC is an architectural pattern that separates an
    application into three main components:
    • Model - all data related logic
    • View - all UI related logic
    • Controller - handles all business logic and incoming
      requests.
20
Q

What is the deployment descriptor?

A

A deployment descriptor describes how a component should be deployed.

21
Q

What are the important tags you need to include in the web.xml?

A
  • web-app
  • servlet, servlet-name, servlet-class
  • servlet-mapping, servlet-name, url-pattern
  • init-param, param-name, param-value
  • context-param, param-name, param-value
22
Q

What is the HttpServlet class? What methods does it provide?

A 
- It is a class that extends from the GenericServlet class 
  and provides Http specific methods
- Provided methods:
    - doGet
    - doPost
    - doPut
    - doDelete
    - service
23
Q

What is the flow of client-to-server using a servlet?

A

The client sends requests through HTTP over TCP/IP to the HTTP server. The servlet will receive the HTTP requests and return a response back to the client.

24
Q

What is a RequestDispatcher?

A
  • Is an interface that facilitates dispatching a requests to another resource.
  • The RequestDispatcher provides two methods:
    • Forward and Include
25
Q

Forward() vs Include()

A
  • Forward() - forwards a request from a servlet to another resource
  • Include() - includes the contents of a resource into the response
26
Q

Forward() vs SendRedirect()

A
  • Forward sends requests to other resources in the same server while SendRedirect sends requests to other resources in different servers
  • Forward is declared in the the RequestsDispatcher interface while SendRedirect is declared in HttpServletResponse
27
Q

Context-Param vs Init-Param

A

Init-param is only accessible to the servlet that it is declared in while context-param is accessible to all servlets

28
Q

Eager Loading vs Lazy Loading

A
  • Lazy loading - a servlet is not loaded when server is starting and load only when the servlet receives a request
  • Eager Loading - servlet loads while server is starting
    • A servlet can be set to load eagerly when you
      declare
29
Q

Servlet Context vs Servlet Config

A
  • Servlet Config - are specified only for a particular servlet and is used for initialization purpose
  • Servlet Context - are specified for the entire application and is accessible by all servlets within that application
30
Q

getParameter() vs getAttribute()

A

getParameter - returns the HTTP requests parameters passed from client to server
getAttribute - mostly for server-side usage only; filling a request with attributes that can be used within the same requests.

31
Q

URL vs URI vs URN

A
  • URL (Uniform Resource Locator) - identifies the location of the resource and how to access it
  • URI (Uniform Resource Identifier) - identifies a resource by name, location, or both
  • URN (Uniform Resource Name) - identifies a resource by name in a given namespace but does not specify how to obtain it
32
Q

Init, Service and Destroy, how many times do they execute?

A

The init and destroy method is called once

The service method is called for every requests the servlet receives

33
Q

How do I declare a Servlet?

A

extending HttpServlet

34
Q

How does the Servlet Container track sessions?

A

An HttpSession object can be created by invoking the requests getSession() method.
Sessions in servlets manage user sessions; used with JSPs and JSFs because they have views, meaning they serve as both the client and server; not with RESTful servlets

35
Q

What is the service method signature on GenericServlet?

A

Public abstract void service(ServletRequest req, ServletResponse res) throws ServletException, java.io.IOException.

36
Q

Service method in HttpServlet.

A

Protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException.

37
Q

How many versions of init does HttpServlet have?

A
  • 2 inits that are inherited from GenericServlet.
  • init()
  • init(ServletConfig config)
38
Q

Method signature doGet.

A

Protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException.

39
Q

How to maintain user state?

A
  • Cookies initialized when the user logs in.
  • Send the session id from the cookie in HTTP requests.
  • Access the HttpSession object from the request object using the getSession() method.
40
Q

Front Controller

A
  • A design pattern for full-stack applications.
  • Front-end sends a request to the back-end.
  • Back-end has a single servlet that is the request dispatcher it receives all requests.
  • When the dispatcher gets a request it consults the handler mapper which tells it by the request type url and other aspects what controller to send the request to.
  • The dispatcher sends it to the appropriate controller who uses a service to call a DAO.
  • The DAO sends a query to the database and receives the databases response which it sends back through the service.
  • The service returns it to the controller who passes it to the dispatcher.
  • If the request was for a page then the servlet would communicate with the view resolver to produce the correct view on the front-end.
  • The dispatcher writes a response with the data in it to the response stream to the front-end producing the view or passing the data for manipulation or display.
41
Q

What is a thread pool?

A
  • Object pools are used in java for storage of objects that we want to use dynamically.
  • The thread pool is one of these object pools
  • Object pools controls the lifecycle of its resources.
  • Many of the java.util.concurrent libraries use thread pools implementing thread pools of worker threads
  • Worker threads are separate objects from Runnable and Callable tasks and are usually used for multiple tasks.
42
Q

What are filters?

A

A filter in the context of java servlets is an object that performs filtering tasks on either the request to a resource or on the response from a resource. It’s used to limit input and output from a resource to only requests and responses fitting a set of rules defined by the filter.

JavaBatchReview (13 decks)

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