Chapter 2 - Client-Server Systems

Question 1

What is a database?

Answer 1

• collection of data
• links between entries
• accessible from many perspectives

Question 2

6 advantages of a database

Answer 2

• Easy to share info
• see relationships
• avoid data duplication
• easier to enforce data security
• easier to enforce data integrity
• transaction friendly

Question 3

2 types of database

Answer 3

Relational

Object Oriented

Question 4

Describe Relational Database

Answer 4

Tables with mathematical relationships.
Rows=records
Columns=attributes

Question 5

What is a foreign key?

Answer 5

A foreign key in this table is a primary key in that table

Question 6

What does Java need in order to connect to a DBMS?

Answer 6

A driver (eg JDBC)

Question 7

Statements vs prepared statements

Answer 7

Prepared statements are

• prepared long before execution
• compiled at the DB, not at the client
• safer from code injection

Question 8

3 Layers of basic multi tier system (MVC)

Answer 8

• • VIEW (the browsers/clients)
• • CONTROL (the server)
• • MODEL (DBMS/database)

Question 9

What is the purpose of the CONTROLLER layer in a multi tier system?

Answer 9

Handles DB (SQL) transactions.

• load balancing
• concurrency control
• security
• logic & control

Question 10

What protocols are used between the VIEW and CONTOLLER layer in a multitier system?

Answer 10

http - used between browser clients and server

Question 11

What protocols are used between the CONTROLLER and MODEL layers in a multitier system?

Answer 11

SQL (between server and DBMS)

Question 12

3 Advantages of Multitier Systems

Answer 12

• scale ability
• Reduce network congestion
• Flexibility (eg languages)

Question 13

give 2 database models

Answer 13

Relational and Object-Oriented

Question 14

What is a candidate key in a DB table?

Answer 14

a collection of attributes (column values) which can uniquely identify a single record

Question 15

What is a primary key?

Answer 15

A candidate key made up of only one attribute… that attribute is the primary key

Question 16

What is a foreign key?

Answer 16

when a record in one table refers to a primary key from another table, the primary key is called a foreign key

Question 17

Give 6 advantages of databases

Answer 17

• easy sharing of info btwn processes
• can see relationships between data
• avoids data duplication
• easier to enforce security
• easier to enforce integrity
• transaction-friendly

Question 18

What are the 4 steps Java goes through to communicate with a DB?

Answer 18

1. Load Driver
2. Connect
3. Create Statement object & execute
4. Access results in ResultSet

Question 19

give the code to load a DB driver

Answer 19

String driver = “com.mysql.jdbc.Driver”;

Class.forName(driver);

Question 20

give 2 lines of code to make the connection with a DB

Answer 20

String url = “jdbc:mysql//server-name:port/context-root

Connection connection = DriverManager.getConnection(url, “user”, “pwrd”);

Question 21

Give a little code to go through a ResultSet:

Answer 21

ResultSet results = //execute statement here
while( results.next() ) {
String str = results.getString(“column-name);
Date bDay = results.getDate(1); // used row number

Question 22

Create, set and execute prepared statement to get 2 values.

Answer 22

PreparedStatement prep = connection.prepareStatement(“SELECT attribute1 FROM table WHERE strAttr=? AND dateAttr=?”);

prep. setString(1, “name”);
prep. setString(2, myBDay);

ResultSet rs = prep.executeQuery();

Question 23

Create, set and execute prepared statement to write a value.

Answer 23

PreparedStatement prep = connection.prepareStatement(“UPDATE table SET attribute=? WHERE primKeyAttribute=?”);

prep. setString(1, “name”);
prep. setInt(2, id);

ResultSet rs = prep.executeUpdate();

Question 24

What are the three tiers of a multi-tier architecture?

Answer 24

Client
domain / application Server
Database server

Question 25

3 advantages of multi-tier systems

Answer 25

- scaleability - reduce network congestion - flexibility

Question 26

4 main actions of a server tier

Answer 26

- read data sent by client (usually http) - process data - prepare results - send results back to client

Question 27

list 6 servlet methods

Answer 27

- init - service - doGet - doPost - doPut - destroy

Question 28

describe the "service" method of a servlet

Answer 28

Called by server in a new thread on receipt of http request. checks HTTP method type and calls doXxx, as required. SHOULD NOT BE OVERRIDDEN

Question 29

``` create a GET form in a url with the following attributes: firstname is John lastname is Smith server is localhost context root is servlet/FormProcessor port is 8080 ```

Answer 29

http://localhost:8080/servlet/FormProcessor?firstname=John&lastname=Smith

Question 30

How can session information be achieved if the client does not allow the use of cookies?

Answer 30

Use URL rewriting

Question 31

what are the four scopes of session bean?

Answer 31

- page - request - session - application

Question 32

what are the access limitations of a session bean with a scope of "page"

Answer 32

can be accessed from PageContext by that JSP only during the current request

Question 33

what are the access limitations of a session bean with a scope of "request"

Answer 33

Can be accessed from the ServletRequest object by any JSP or Servlet during the current request

Question 34

what are the access limitations of a session bean with a scope of "session"

Answer 34

Can be accessed from the HttpSession object for the rest of the client session

Question 35

what are the access limitations of a session bean with a scope of "application"

Answer 35

Can be accessed from ServletContext object by all JSP and Servlets

Question 36

What are the three states of an EJB?

Answer 36

@Stateful @Stateless @Singleton

Question 37

Give two types of EJB

Answer 37

session bean and | message-driven bean

Question 38

purpose of EJBs

Answer 38

To hold the business logic of a multi-tier application, as opposed to the website and client interfacing logic

Question 39

How are EJBs handled by the application server?

Answer 39

They are created in an EJB container, and the application server creates and deletes them as needed. Note, there is only ever one instance of a Singleton bean

Question 40

Server Tier provides CGI. | What is CDI & what are its 3 main functions?

Answer 40

Common Gateway Interface, handles client requests and responses: - handle http requests and responses - manage sessions (eg URL encoding and cookies) - fetch & prepare results