Lab Test Revision

8/11/2019 Lab Test Revision

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Lab Test Revision

Week 7 Supplementary Class


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JSP BASICS


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JSP Basics

Scriplet Code is inserted in service

method.

Expression Expression is evaluated and

placed in output.

PageDirective

(import)

import parts of a packagenamespace into the local

scope of a Java class.

Declaration Instance variable/method of

translated servlet class

Comment Documentation for yourself


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Implicit Variables

Name Class Description

request javax.servlet.http.HttpServletRequest Represents the request that triggers

the processing of the current page

response javax.servlet.http.HttpServletResponse Contains information created by the

JSP to be send back to the client

out Subclass of Writer

(javax.servlet.jsp.JspWriter)

Used to output information to the

client


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Form Processing

welcome.html

A simple form

Enter your name:


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Form Processing

greet.jsp


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Form Processing Summary

Method

request.getParameter(String name) Returns the value of a request

parameter as a String, or null if the

parameter does not exist

request.getParameterValues(Stringname)

Returns an array of String objectscontaining all of the values the given

request parameter has, or null if the

parameter does not exist.


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MORE JSP


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Forwarding Request (Internal)

// JSP tag (part of HTML)

//another way - part of scriptlet ()

RequestDispatcher dispatcher =

request.getRequestDispatcher("");

dispatcher.forward(request, response);

Servlet/JSP

Servlet/JSP

Servlet Engine

1.HTTP Request

3.HTTP Response

2.Hands over control

Br

ow

ser


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Redirecting Response (External)

// part of scriptlet ()

response.sendRedirect("");

Servlet Engine B

Servlet Engine A

Servlet/JSP

Servlet/JSP

1.HTTP Request

2.HTTP Response (I have moved to )

Br

ow

ser

3.HTTP Request

4.HTTP Response


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Internal Forwarding vs. External Redirecting

Internal Forwarding External Redirecting

Is a new HTTP Request

created?

No, it is the same HTTP

Request. The control of

processing is handed

over to anotherresource.

Yes, a new HTTP

Request is created.

Will the URL that the

client sees change?

No Yes


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Question!

page1.jsp

RequestDispatcher dispatcher =

request.getRequestDispatcher(p

age2.jsp");

String temp = Hello World;

request.addAttribute(temp,

temp);

dispatcher.forward(request,

response);

page2.jsp

String retrieved = (String)

request.getAttribute(temp);

What will be the value in

retrieved?


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Question!

page1.jsp

String temp = Hello World;

request.addAttribute(temp,

temp);response.sendRedirect(page2.js

p);

page2.jsp

String retrieved = (String)

request.getAttribute(temp);

What will be the value in

retrieved?


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Implicit Variables

Name Class Description

request javax.servlet.http.HttpServletRequest Represents the request that triggers

the processing of the current page

response Javax.servlet.http.HttpServletResponse Contains information created by the

JSP to be send back to the client

out Subclass of Writer

(javax.servlet.jsp.JspWriter)

Use to output information to the

client

session Javax.servlet.http.HttpSession Allows you to access the client's

session data, managed by the server


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Methods of HttpSession

Method

setAttribute(String name, Object

value)

Binds an object to this session, using

the name specified.

*Helpful for loginremoveAttribute(String name) Removes the object bound with the

specified name from this session.

*Helpful for logout

setMaxInactiveInterval(int interval) Sets the timeout intervalinvalidate() Invalids and removes the session


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JSP Include Action Tag

content.jsp


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Include Directive

content jsp

Xxxxxxxxxxxxxxxxxxxxx

xxxxxxxxxxxxxx

xxxxxxxxxxxxxx

-----------------------------------

--------------

header.jspcontent.jsp

translation

Xxxxxxxxxxxxxx---------------------xxxxxxxxxxxxxx

Source(content_jsp.java)

compilation

101010110101010101010101010101010101010101

0101010

Page Servlet(content_jsp.class)

Content of header.jsp


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JSP Page Composition Summary

JSP Include Action Tag Include Directive

How is the compilation

done?

The separate pages are

compiled separately.

The content of the page

that is included is added

into the page which

includes it and so, they

are compiled together.

What happens if there is

an error in one of the

pages?

The other page will still

be loaded.

The other page will not

be loaded as they are

compiled together.


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SERVLET


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Steps to Write a Basic HTTP Servlet

Step 1: Subclass from HttpServlet

Step 2: Override doGet and/or doPost method

Step 3: Specify the content type

Step 4: Get a PrintWriter object Step 5: Write data to the client

Step 6: Close the Writer


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Step 1: Subclass from HttpServlet

importjava.io.*;

importjavax.servlet.*;

importjavax.servlet.http.*;

public classHelloWorldServlet extendsHttpServlet {

public void doGet(HttpServletRequest request,HttpServletResponse response)

throwsServletException, IOException {

response.setContentType("text/html");

PrintWriter out = response.getWriter();

out.println("");

out.println("");out.println("Hello World");

out.println("");

out.close();

}

}


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Step 2: Override doGet and/or doPost method

importjava.io.*;








out.println("");


out.println("");

out.close();

}

}


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Step 3: Specify the content type

importjava.io.*;








out.println("");


out.println("");

out.close();

}

}


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Step 4: Get a PrintWriter object

importjava.io.*;








out.println("");


out.println("");

out.close();

}

}


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Step 5: Write data to the client

importjava.io.*;








out.println("");


out.println("");

out.close();

}

}


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Step 6: Close the Writer

importjava.io.*;








out.println("");


out.println("");

out.close();

}

}


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Handling Form Data


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HTTP GET vs. HTTP POST

HTTP GET HTTP POST

Where is the form data? It is contained in the

URL of the HTTP request

It is contained in the

body of the HTTP

request

What is the URL on the

browser?

http://localhost:8080/N

ameServlet?fullname=L

ee

http://localhost:8080/N

ameServlet

When do you use it? If you want to expose

the parameter values.

E.g. when doing a search

If you want to hide the

parameter values.

E.g. Login


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Configuring Servlet

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

import javax.servlet.annotation.WebServlet;

@WebServlet("/display)public class NameServlet extends HttpServlet {

public void doPost(HttpServletRequest request,

HttpServletResponse response)

throws ServletException, IOException {

// ...

}

}

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