Using custom tags - not a "how to do my homework" question.

Question

Hi, I havn't done a heap of JSP and I'm experimenting with custom tags. I understand this may be elementary to some. I also expect there is probably some ready-to-go libary out there that would do this for me, I just wanted to do it from scratch, mostly as a learning exercise.
So I've got a servlet which runs a query, and sends two arrays of objects to a JSP, one is an array of column headings, the other is an array of arrays representing the rows of data.
The intention of the JSP is simply to display the data in a table.
I guess one question I have is:
What is the best way to apply styles to my table? Obviously I don't want to have to recompile the tag code to add/change styles. Is the best way to do it is to have another property of the tag that accepts the name of a style class?
So when I place the tag in my JSP it will looks like <test:report-table headings="..." rows="..." style="blue"/> and in the tag code it will look something like out.write("<table class=\" + classname + \"");I appreciate any comments on how good/bad my code/theory is. Any recomended additions/omissions?
The tag in the JSP looks like this.
        <test:report-table
            headings="<%= (Object[])request.getAttribute(\"columns\")%>"
            rows="<%= (Object[])request.getAttribute(\"rows\")%>"
        />The tag class looks like this.
bar.foo.test;
import java.io.IOException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;
public class ReportTable extends TagSupport
    private Object[] headings;
    public Object[] getHeadings() { return headings; }
    public void setHeadings(Object[] o) { this.headings = o; }
    private Object[] rows;
    public Object[] getRows() { return rows; }
    public void setRows(Object[] o) { this.rows = o; }
    public int doStartTag()
        JspWriter out = pageContext.getOut();
        try
            out.write("<table>");
            out.write("<tr>");
            for (int i = 0; i < headings.length; i++ )
                out.write("<td>" + headings[i] + "</td>");
            out.write("</tr>");
            for (int i = 0; i < rows.length; i++)
                out.write("<tr>");
                Object[] row = (Object[])rows;
for (int j = 0; j < row.length; j++)
out.write("<td>" + row[j] + "</td>");
out.write("</tr>");
out.write("</table>");
catch (IOException e)
e.printStackTrace();
return 0;
The tag definition in my tld looks like this
    <tag>
        <name>report-table</name>
        <tagclass>bar.foo.ReportTable</tagclass>
        <bodycontent>empty</bodycontent>
        <info> Report Table </info>
        <attribute>
            <name>headings</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
            <type>java.util.Object[]</type>
        </attribute>
        <attribute>
            <name>rows</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
            <type>java.util.Object[]</type>
        </attribute>
    </tag>

Answer 1

TimSparq wrote:
Cool, thanks for the input/advice, evanfets.
Yeah, my plan was now that I have a basic understanding of the mechanics of what's going on in the tags, I'll go and look into what ready-made stuff there is out there (like you suggest, JSTL).
And thanks for the advice regarding styles, exceptions and the return value. All appreciated.
I'll be taking a look into the tag files too.
Thanks again.Just another option on the styles. One thing I have done in similar situations is to generate a lot of class names and automatically apply them to the correct spot. Example:
<table class="reportTable">
  <thead class="reportTableHead">
    <tr class="rtHeadRow"><th class="rtOddColumn">...</th><th class="rtEvenColumn">...</th></tr>
  <thead>
  <tbody class="reportTableBody">
    <tr class="rtOddRow"><td class="rtOddColumn">...</td><td class="rtEvenColumn">...</td></tr>
    <tr class="rtEvenRow"><td class="rtOddColumn">...</td><td class="rtEvenColumn">...</td></tr>
  </tbody>
</table>This gives the web developer a large selection of selectors to work on:
table.reportTable -> Edit the entire table
table.reportTable tr -> Configure all rows in the table
table.reportTable tr.rtOddRow -> Configure the odd rows in the table
table.reportTable tr.rtOddRow td.rtEvenColumn -> Configure just the even columns in an odd row
etc...
You just communicate the class names that can be used and then the web designer generates a CSS to fit his needs.