Javazoid

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Tag Resources

JSP Custom Tags
by Qusay H. Mahmoud

JSP taglibs: Better usability by design
by Noel J. Bergman

Core Servlets and JavaServer Pages
by Marty Hall

Testing under Tomcat 3.3
I tested the component under Tomcat 3.3 on both Redhat Linux 7.2 and Windows 2000. Here are some suggestions to do a quick test of the component in your environment.

Download and install Tomcat 3.3 from Apache.org

Create a directory under webapp called reportTag. Extract the source code for ReportWriter tag under this directory.

Configure a datasource. I tested using MySQL and Access. You can import the file called Resource.txt in the reportTag directory into you favorite database product. I also have two versions of web.xml -- one for Access; one for MySQL.

Make sure the datasource works by running the Datasource.jsp. This example does a simple "select * from resource" and does no Example formatting. If this JSP doesn't work, you may have a database connection problem.

Test the other jsps. When these are working, you have a working base for your own development.

ReportWriter JSP Tag

by Gervase Gallant
January 3, 2002

Recently, I have been working on a project where it was required to display grid-type data from database tables. Right now the words "Report Writer" kind of spring to mind, although, as it turned out, HTML tables could easily handle the data display and, actually, allowed for certain types of customization that you could hardly expect in a Report Writer product..

To solve the problem, particularly since the web application was deployed on a JSP 1.0 application server, I developed a Bean that would accept a brief number of parameters (a SELECT statement being the main one) and format the data by merging a ResultSet object with a number of pre-set HTML tags. .

Since the HTML was all constructed in Java code, I developed a scheme whereby the major formatting elements could be embedded in a property file which the Bean's formatter would read and apply. Of course, this goes against all the articles you will read about MVC architecture and divorcing the presentation layer from the Java database/business logic. However, in the circumstance, it did work and I was able to code everything pretty quickly..

Despite everything you will read today about putting together JSP presentation code with Java database/business logic, the major issue of the design I describe above is that it works well in one scenario: if the JSP developer is a seasoned Java pro. If the HTML template required a change, I could easily document the how-to. In fact, I believe that a large number of projects you will find today are just like mine: a group of JSP developers are really either Java pros or Java wannabes. Therefore, they have no problem tweaking the code.

However, when the JSP developer is not a Java developer, the whole thing falls down. And, in reality, I will admit that if JSP is going to grow as a means of connecting HTML to backend logic, we will start seeing more and more JSP developers that don't know and don't care..

Enter the tag library

Since about JSP 1.1, the use of tags mixed with HTML/JSP code has become a more attractive and fully-featured means of connecting the dots between layers of development. There are a number of web development products out there, like ColdFusion, that have already figured this one out. The developer passes in a brief, simple message and gets a whole bunch of functionality from some back-end API.

Unlike the UseBean tag that I applied for my project, tags are now able to read and pass along various application variables from the web.xml configuration file. Therefore, whereas my UseBean has to understand how to look up database connection info, this data can now be stored in the servlet application's web.xml and passed along to any layer that has access to the JSP's PageContext object.

Tags are also now capable of scanning portions of the HTML and handing it off to the tag layer. This is an important feature in my mind because in my original design, I would have liked to let the JSP developer give me a template file that actually was an HTML table. The goal: let the JSP side say "format the report like this table...".

Tags, tags, tags...

Using JSP 1.1 tag capability, I decided let the JSP side present a mock-up for the report right on the page in the form of an HTML table. The tag logic could then parse through the example table, figure out items like column headers and split the table into formatting segments and data segments. Then, as the tag code looped through the database ResultSet, the template could be chunked appropriately. To test the tag, I created tables in Dreamweaver, Websphere Studio and Netscape navigator. The example below -- which actually doesn't display too well in my Linux version of Netscape -- was created with Dreamweaver.

Check Box example :SOURCE CODE

<%@ taglib uri="../WEB-INF/jsp/javazoid.tld" prefix="j" %>
<j:reportwriter datasource="mysqlAtHome" sqlKey="select linkName,description, url from resource;" startRow="20" endRow="30" >

select	resource	description	url
	Yahoo mail	Internet http based mail provider	mail.yahoo.com

</j:reportwriter>:

Check Box example: THE RESULT

SELECT	RESOURCE	DESCRIPTION	URL
	Viewsource.dk	offers free java applets	13
	The Java Security Hotlist	When you have questions regarding Java and security	including Books
	JavaSofts JavaReel	This applications/applet showcase features a wide variety of current Java products. You can view all the products listed	or a breakdown of products by market category.
	Elliotte Rusty Harolds Cafe au Lait	Elliottes page of Java news and resources	10
	Dave Central Software Archive	Daves site offers an abundance of Java-related software tools and resources	databases
	JavaToys	This Java development resource center provides tons of useful links for Java developers	reference materials
	Java Game Park	If youre into gaming	which has more than 200 free games online. Whether youre an adventure fan or into sports
	The JavaBoutique	features downloadable Java development environment demos	how-to articles
	Automated Software Mart	Bayside Computing	Java applets
	The Applet Depot	This is the place to find applets such as Java poetry magnets. It also includes demos of other applets and the possibility of having a custom applet created just for you.	http://www.ericharshbarger.org/java/

There were a few problems with Visual designers. WebSphere Studio outputs upper-case HTML tags, while the other two products output lower case tags. Not a problem to the designer but a considerable nuisance to the parsing routine.

On the whole, it seemed that I could throw considerably sophisticated example tables at the tag and still get great results. Some features like banded reports (where the back color of one row contrasts sharply against the backcolor of it predecessor) are definitely do-able, but not in this version.

How to construct a JSP report

Assuming you have everything installed correctly (I will walk through this later...), the steps are straightforward:

Place the following at the top of the page: < %@ taglib uri="../WEB-INF/jsp/javazoid.tld" prefix="j" %> Note that the uri depends on where your JSP reside relative to the web app. If you place your page in a JSP folder under the web app, this uri will work. If you have a series of JSP folders, it might be easier to use an abosolute path.

Insert a tag like this one: where

j	is the variable referencing the tag prefix
reportwriter	is the tag name in the TLD file
datasource	is the string to indicate how to connect to the database using JDBC. In the web.xml file for my web app, I set up a number of variables like <context-param> <param-name> mysqlAtHome.jdbc.driver </param-name> <param-value> org.gjt.mm.mysql.Driver </param-value> </context-param> <context-param> <param-name> mysqlAtHome.jdbc.url </param-name> <param-value> jdbc:mysql://localhost:3306/javazoid </param-value> </context-param> <context-param> <param-name>mysqlAtHome.jdbc.user </param-name> <param-value>app </param-value> </context-param> <context-param> <param-name> mysqlAtHome.jdbc.password </param-name> <param-value>matthew </param-value> </context-param> <context-param> This feature allows you to support multiple databases from the web app. If you have only one data source, you might use "default" as a datasource name, i.e., "default.jdbc.driver".
sqlKey	is a tag to identify a SQL statement or is the SELECT statement itself. You can create a entry in web.xml like listAllResources select * from resource By entering "listAllResources" as the sqlKey, the tag knows how to find the correct SQL. I added this feature because I have worked on a number of projects with SQL embedded in many, many web pages and then seen panic when the database changed. If this feature isn't required, you can simply enter a SELECT statement in the sqlKey variable (however, you can't use stored procedures this way..yet).
startRow and endRow	are optional variable that you can set in the Web page only to indicate how many rows you want to see on the page. You probably should set the endRow variable to something reasonable, but if you don't, there is a default endRow of about 500. Sorry, I won't let you dump and entire database into the browser... Also, remember that the implementation of this feature is pretty basic. If, for some reason, you need to set the startRow at 50,000 and endRow at 50,020, you might want to look at how the source code implements this (in fact, you might wish to have a stored procedure handle this....)
debug	if set to true, outputs what I figure a developer needs to see from the tag component.

Insert an HTML table. You need a two-row table -- one row for the column headers; one row for the data. Format this table any way you like, but remember to insert some non-tag data on the second row. Make sure you create the same number of columns as the SQL statement requires. I have created a number of examples in the source jar <> that acompanies this package. If you don't insert a valid table, the component will ignore your design and format it in a plain-jane fashion. This feature was intended to support "functionality in a hurry". In this case you can insert something like "TABLE GOES HERE" between the tags.

End the tag with
</j:reportwriter>

Installing the component.

You need to understand how a JSP1.1/Servlet 2.2 web application works to install the component. But I will outline the steps assuming minimal knowledge.

I assume you have set up a directory in your "webapps" folder. I'll call it reportTag for now.

You need a WEB-INF folder under reportTag. This folder will have a web.xml file. See examples.

Store the taglib descriptor file, javazoid.tld, referenced in WEB-INF/jsp.

Place the reportwritertag.jar file (which contains only class files... you can find it in the WEB-INF/lib folder in the jar) in your WEB-INF/lib directory.

I am assuming here that your database drivers are already set up in the classpath. This seems to depend on how many apps reference the driver's jar file. For this experiment, you might want to make sure that the jar is in the classpath. If you see ClassNotFound errors, put it in the WEB-INF/lib directory directory.
Copyright (c) 2002, Gervase Gallant gervasegallant@yahoo.com