model \'mäd-l\ n: a pattern of something to be made
Intranet applications are like a corporate application suite. These include word processors, project planners, spreadsheets, and many other useful and productive applications. They encompass all departments and touch many types of data. But unlike the business productivity application suites available today, your intranet applications should all share a common foundation.
Creating a suite of applications from scratch is tedious and boring. Cutting and pasting code is easy, but that goes against all object-oriented programming practices. What is needed is a basic structure from which to build your applications. This foundation should be flexible, stable, and extensible.
This chapter introduces you to four standards that all of our applications share. These standards provide a flexible, stable, and extensible foundation for developing intranet applications. These four standards together produce a prototype or a model application that can be used as a base when developing applications.
On an intranet, the applications that are built share much of the same functionality. Sure they all do different things but they also do a lot of the same things. These commonalties should become the foundation for your intranet application framework. They are the base and are truly your application standards.
Our primary design goal is to provide a set of standard application features. These features create a familiar atmosphere for all your intranet applications. Familiarity provides users with a sense of comfort because they don't have to learn an entirely new program. Apple capitalized on this idea years ago when it introduced the Macintosh computer. If you learned how to use the Mac, then you knew how to run almost every Macintosh application written. It was the consistency and adherence to set standards that made this possible. Microsoft Windows has since capitalized on the same concept. The design presented here is not quite a Macintosh but what it provides is something similar: consistency.
The following four standard features are what we strive to provide in the model intranet application design:
Let's examine each goal individually, show an example, then point you in the right direction to find more information regarding each particular standard.
Using configuration parameters in programming can be a real hassle unless a stable foundation is in place. Generally you end up coding a new configuration scheme with each application. What we can create is a class that provides a solid method of getting configuration parameters. This method encompasses configuration files on disk and overridden parameters passed in by way of the command line of the application.
The configuration file in Listing 7.1 is an example of the kind of configuration files the applications have.
Listing 7.1. A sample configuration file.
# Configuration file for Employee Maintenance
WindowTitle=Employee Maintenance
server=tcp-loopback.world
user=munster
password=
At the start of the application, we read the configuration file
into memory. These parameters are merged with any configuration
parameters that are passed in by way of the command line. The
applications then need a consistent method of retrieving these
parameters from the configuration parameter storage area. We should
model the retrieval method after the method used in regular Java
applets.
| Note |
Chapter 8, "Utility Classes," discusses the ConfigProperties class which implements these design goals. |
For tracking problems during the development cycle and for error logging after your application has been deployed, a log file is just the ticket. A common log file is even better for all of your applications and users. A common log file is easily searched and filtered for errors. This standard logging mechanism is the first standard feature that we need to supply.
To facilitate such a log file, we need to create it on disk. The log file is appended to each time; it is never overwritten. If we overwrite the file, then information from a previous session can be lost. You know how annoying that can be.
But what if the disk log fails to open, or if it can't be written to? Well, we need a backup log. These failed log entries should go to the screen.
This screen logging facility produces the same log information
to a window, or using the System.out
facility. When an application fails to create a disk log, all
log output goes to the screen. Also, this screen log is used automatically
if no disk log is specified or if there is an error.
| Note |
System.out is a Java system object. It is an alias for the console in Windows. In UNIX it is an alias for stdout. |
The entries in the log file should follow a standard, one that is easy to view and search. This format should be used across all of your intranet applications, and possibly your non-intranet applications as well. This log file format should be simple enough so that other programs might even use it.
You might find in the future that you use a third-party network management tool that can monitor your intranet applications and their log files. These tools can be a lifesaver in a pinch, so why not think about their needs as well?
Therefore, the following log file format is what to go with as the design. It includes all the information needed in an easy-to-use format:
application|user|date|level|entry
where
application is the name of the application
user is the user who is running the application
date is the date of the log entry
level indicates the severity of the entry.
Six predefined levels are available: debug, informational, notice, warning, error, and fatal. Each is denoted in the log by the first letter in its name. D for debug, I for information, and so on.
Listing 7.2 shows some sample log entries.
Listing 7.2. Sample log entries.
Employee|960609|I|Application [Employee] started at Sun Jun 09 22:27:33 1996
Employee|960609|I|Port = 4333
Employee|960609|I|Server = mars.mcs.net
Employee|960609|I|Title = Employee Maintenance
Employee|960609|I|Application [Employee] ended at Sun Jun 09 22:28:38 1996
At startup, all of the intranet applications write several things to the log:
At shutdown, the application writes a corresponding entry to its
startup message. This is shown in Listing 7.2, also.
| Note |
Chapter 9, "Logging Classes," discusses the DiskLog and ScreenLog classes which implement these design goals. |
Connecting to databases with Java is a key point in your intranet
application design stage. Various methods are currently available.
Some are HTTP server extensions that return data in HTML format.
Others are non-portable system-dependent solutions. A more Java-like
option is JDBC.
| Note |
JDBC, along with other database connectivity options are covered in depth in Chapter 6, "Database Connectivity Options." |
It appears today that JDBC is the strongest supported database standard for Java. For this reason alone, JDBC is chosen as the database connectivity package for the intranet applications in this book. Using JDBC allows us to choose from almost any database and provides the flexibility to change databases when coding is complete.
To simplify database connectivity just a bit, we need to create a class that encapsulates the more monotonous aspects of connecting and disconnecting from a database server. This new class provides a connection strategy that is simple to use and easily extensible. This class also encapsulates much of the rudimentary JDBC initialization and cleanup. All we need to do is extend this class for each database we need to connect with.
Listing 7.3 shows how easy the class is to use.
Listing 7.3. How you should use your Database Connector Class.
// Make the connection...
if ( myConnector.connect( "munster", "hermy", "tcp-loopback.world" ) )
{
// Connection successful...
}
else
{
// Connection failed...
}
As you can see, the connect()
method is called with the connection parameters necessary to make
the connection. The exception handling is handled for you in the
class, returning nothing but a simple true
or false. This indicates
the connection state as well.
| Note |
Chapter 10, "Database Classes," discusses many database classes. One of them is the DBConnector class. This class implements many of these design goals. |
The final standard about the intranet applications is that they should have a consistent look and feel. This is achieved through the use of standard font, and a consistent layout of components.
Figure 7.1 illustrates the standard look and feel of the model intranet application. This application is the "Hello World" example presented in Chapter 11, "User Interface Classes."
Figure 7.1 : The standard intranet application look and feel.
Referring to Figure 7.1, you see the following standard application attributes:
You might notice that there is a menu shown in Figure 7.1; however,
no menu is shown as a standard look and feel. This menu varies
from application to application. It is not fair to impose a rigid
menu structure on applications that might not even need a menu.
Therefore, menus are not part of the application design.
| Note |
Chapter 11 discusses many classes which implement these design goals. |
There are several things about the source code in this book that might be different from other Java books that you have seen. A good percentage of the code styles here are simply done for readability. Here is a list of what I think is different and superior:
Let's go over each individually and show some examples.
The code in this book is laid out, or rather formatted, in a manner that might be different from other Java books that have been published. The format used in this book is my personal coding style for C and C++. I feel that this format is more readable and easier on the eyes and brain. My style differs in the ways described in the next few sections.
The original Java samples and source code that come with the JDK use what is known as the K&R style of code blocking. This style places the open parenthesis at the end of the statement that begins the block. Listing 7.4 is an example of K&R style.
Listing 7.4. The BadKitty class-K&R style.
public class BadKitty extends Kitty {
public BadKitty( int clawCount ) {
}
}
K&R stands for Kernigham (Brian) and Ritchie (Dennis), the creators of the C programming language. In their (in)famous book, The C Programming Language, this was the manner of code layout, hence the name.
In this book however, the parenthetical style used is that the braces match up in the same column. This style is easier to read and more clearly marks the blocks of code. Listing 7.5 illustrates this point.
Listing 7.5. The BadKitty class-Non-K&R style.
public class BadKitty extends Kitty
{
public BadKitty( int clawCount )
{
// Code goes here!
}
}
Whenever code is indented, tabs are used. Tabs keep code aligned and are portable between operating systems. The tab stops for the code in this book are every four spaces.
As you may or may not know, the compiler really doesn't care about spaces in your code. All white space and comments are stripped out before the actual compilation is done. Adding more spaces than necessary is another readability issue. Wherever possible, spaces are used. This might seem a bit lengthy. However, you will see the improvement. The following line of code uses no spacing:
blackBoxToUse=(myBlackBox==null)?defaultBlackBox:myBlackBox;
And this one spaces things out nicely:
blackBoxToUse = ( myBlackBox == null ) ? defaultBlackBox : myBlackBox;
Look how much more readable the second line is! You can quickly parse the line and understand what is going on. You don't spend time parsing.
In an effort to make the code more readable, all class and function declarations are split into two, three, or four lines. The number of lines depends on the number of elements that make up the statement. The rules are different between class and function declarations.
Class declarations in this book can appear on up to four lines and are in the following order:
[access] class
name
[extends super_class]
[implements interface]
Usually this declaration is made on a single line. However, by splitting it up into multiple lines you can immediately learn information about the class without even reading the declaration. Listing 7.6 illustrates the class declaration.
Listing 7.6. A beautiful class declaration.
public class
FileDate
extends Date
{
...
}
Functions are declared in much the same manner as classes. However, the function name is always on the second line, and all other information about the function is on the first line. Function declarations are always two lines long. The declarations are in the following format:
[access] return_type
function_name( arguments )
Listing 7.7 shows a complete function declaration using our described style.
Listing 7.7. A well-styled function declaration.
public String
toFileString()
{
String retString = "";
int m = 1 + getMonth();
int d = getDate();
int y = getYear() % 100;
if ( y < 10 )
retString += "0";
retString += y;
if ( m < 10 )
retString += "0";
retString += m;
if ( d < 10 )
retString += "0";
retString += d;
return( retString );
}
Comments are a sore issue with many programmers. A friend of mine (Hey Bill!) used to tell me that the only purpose comments serve are to amuse the compiler. In some cases, he might be right. However, to better document the code in this book, comments are everywhere. Generally the comments are restricted to a single line, right above the line of code to which it pertains. This is common practice.
In addition to the single line comments, I like to distinguish chunks of code from others with the use of a block header. It serves no purpose other than to segregate blocks of code visually. Listing 7.8 shows an example of such segregation.
Listing 7.8. Comments really do improve the readability of your code!
//****************************************************************************
//* Package &nb sp; *
//****************************************************************************
package jif.util;
//****************************************************************************
//* Imports &nb sp; *
//****************************************************************************
import java.util.Date;
//****************************************************************************
//* Date *
//****************************************************************************
/**
* An extension of the default Java Date.
*
* @see java.util.Date
*
* @version 1.00, 1 May 1996
* @author Jerry Ablan, [email protected]
*/
public class FileDate
extends Date
{
//****************************************************************************
//* toFileString &nbs p; *
//****************************************************************************
/**
* This method returns the date in a format suitable for using in
* file names. This format is YYMMDD, where YY is the year, MM is the
* month, and DD is the day.
*
* @see java.util.Date#toString
*/
public String
toFileString()
{
String retString = "";
int m = 1 + getMonth();
int d = getDate();
int y = getYear() % 100;
if ( y < 10 )
retString += "0";
retString += y;
if ( m < 10 )
retString += "0";
retString += m;
if ( d < 10 )
retString += "0";
retString += d;
return( retString );
}
}
Finally, there is code order. Again, some of the Java books published have different orders. The oddest order I've seen is that all class variable declarations are below all of the function declarations. This is quite odd, and not at all like any other programming language. I've tried to keep the coding style similar to C and C++ for clarity.
All the source code in this book lays out in the following order:
All class functions lay out in a similar manner:
Maintaining consistency throughout the code considerably improves readability.
This chapter introduces the four application design standards that are implemented in the next four chapters. These standards produce configuration processing, common logging, database connectivity, and consistent user interface. Through the use of these standards, the intranet application development will just fly by!
In the following chapters, the standards set forth in this chapter are implemented.