0 JAVA installation and Set Up

Installation and Set Up of JAVA in Windows and UNIX machines

Before we begin JAVA installation, some points on JAVA installation

• For executing Java Programs Java 2 SDK Version 1.4 or higher Version needs to be installed.
• Java 2 SDK Can be downloaded freely from http://java.sun.com
• IDEs for JAVA are Eclipse and Netbeans, and Eclipse can be downloaded freely and doesnot require installation

Setting Environment variables for Java
We need to set some Environmental variables.
• Environmental variable is a variable that describes the operating environment of the process
• Common environment variables describe the home directory, command search path etc.

Environment variables used by JVM

JAVA_HOME
This environment variable is pointing to the Java Installation directory. This environment variable is used to derive all other environment variables used by JVM

In Windows:
set JAVA_HOME=C:\ProgramFiles\JAVA\jdk1.4.3

In UNIX:
export JAVA_HOME=/var/usr/java

CLASSPATH
Path variable is used by OS to locate executable files

In Windows:
set PATH=%PATH%;%JAVA_HOME%\lib\tools.jar

In UNIX:
set PATH=$PATH:$JAVA_HOME/lib/tools.jar:.

Do the Environmental variable settings by typing the given commands in the Command Prompt and Type ‘javac’. It will display all the options of using javac as shown in the diagram. If it says bad command or file name then check the path setting.

Alternate way to set CLASSPATH

In Windows:
set PATH=%PATH%;%JAVA_HOME%\bin

In UNIX:
set PATH=$PATH:$JAVA_HOME/bin

• This approach helps in managing multiple versions of Java – Changing JAVA_HOME will reflect on CLASSPATH and PATH as well

0 How to set Environment variables for Java

How to set Environment variables for Java?

• Environmental variable is a variable that describes the operating environment of the process
• Common environment variables describe the home directory, command search path etc.

Environment variables used by JVM

JAVA_HOME
This environment variable is pointing to the Java Installation directory. This environment variable is used to derive all other environment variables used by JVM

In Windows:
set JAVA_HOME=C:\ProgramFiles\JAVA\jdk1.4.3

In UNIX:
export JAVA_HOME=/var/usr/java

CLASSPATH
Path variable is used by OS to locate executable files

In Windows:
set PATH=%PATH%;%JAVA_HOME%\lib\tools.jar

In UNIX:
set PATH=$PATH:$JAVA_HOME/lib/tools.jar:.

Do the Environmental variable settings by typing the given commands in the Command Prompt and Type ‘javac’. It will display all the options of using javac as shown in the diagram. If it says bad command or file name then check the path setting.

Alternate way to set CLASSPATH

In Windows:
set PATH=%PATH%;%JAVA_HOME%\bin

In UNIX:
set PATH=$PATH:$JAVA_HOME/bin

• This approach helps in managing multiple versions of Java – Changing JAVA_HOME will reflect on CLASSPATH and PATH as well.

0 How to get data from session Java

How to Extract data from session in Java?

Get the session

request.getSession

Extract data from session

session.getAttribute

• Do typecast and check for null
• If you cast to a generic type, use @SuppressWarnings

0 Challenges in Session Tracking Java

support for distributed Web applications

Load balancing used to send different requests to different machines. Sessions should still work even if different hosts are hit.

support for persistent sessions

Session data written to disk and reloaded when server is restarted(as long as browser stays open).
• Tomcat 5 supports this

0 CRUD operations in MySQL Database

CRUD operations

CRUD is the acronym for Create, Read, Update and Delete. Create, Read, Update and Delete (CRUD) are the 4 basic functions of a Database or persistent storage. CRUD refers to all of the major functions that need to be implemented in a RDBMS.
Each letter in the CRUD can be mapped to a standard SQL statement:

Create        INSERT
Read        SELECT
Update        UPDATE
Delete        DELETE

CRUD operations in MySQL Database

Insert Data Into MySQL Database Table

The INSERT INTO statement is used to add new records to a database table.

Syntax

It is possible to write the INSERT INTO statement in two forms.

The first form doesn't specify the column names where the data will be inserted, only their values:

INSERT INTO table_name
VALUES (value1, value2, value3,...)

The second form specifies both the column names and the values to be inserted:

INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...)

Select Data From MySQL Database Table

The SELECT statement is used to select data from a database.

Syntax

SELECT column_name(s)
FROM table_name

Update Data In MySQL Database Table

The UPDATE statement is used to update existing records in a table.

Syntax

UPDATE table_name
SET column1=value, column2=value2,...
WHERE some_column=some_value

Delete Data from MySQL Database Table

The DELETE FROM statement is used to delete records from a database table.

Syntax

DELETE FROM table_name
WHERE some_column = some_value