- 7.1 Tag Library Components
- 7.2 Example: Simple Prime Tag
- 7.3 Assigning Attributes to Tags
- 7.4 Example: Prime Tag with Variable Length
- 7.5 Including Tag Body in the Tag Output
- 7.6 Example: Heading Tag
- 7.7 Example: Debug Tag
- 7.8 Creating Tag Files
- 7.9 Example: Simple Prime Tag Using Tag Files
- 7.10 Example: Prime Tag with Variable Length Using Tag Files
- 7.11 Example: Heading Tag Using Tag Files
This chapter is from the book
This chapter is from the book
This chapter is from the book
7.6 Example: Heading Tag
Listing 7.11 shows HeadingTag.java, which defines a tag for a heading element that is more flexible than the standard HTML H1 through H6 elements. (Yes, we know that the entire problem could be solved more elegantly with Cascading Style Sheets [CSS] and without the use of a custom tag, but this is for demonstration purposes only, so work with us.) This new element allows a precise font size, a list of preferred font names (the first entry that is available on the client system will be used), a foreground color, a background color, a border, and an alignment (LEFT, CENTER, RIGHT). Only the alignment capability is available with the H1 through H6 elements. The heading is implemented through use of a one-cell table enclosing a SPAN element that has embedded stylesheet attributes.
The doTag method first generates the <TABLE> and <SPAN> start tags, then invokes getJspBody().invoke(null) to instruct the system to include the tag body, and then generates the </SPAN> and </TABLE> tags. We use various setAttributeName methods to handle the attributes like bgColor and fontSize.
Listing 7.12 shows the excerpt from the csajsp-taglib.tld file that defines the heading tag. Listing 7.13 shows heading-1.jsp, which uses the heading tag. Figure 7-3 shows the resulting JSP page.
Listing 7.11. HeadingTag.java
package coreservlets.tags;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.io.*;
/** Heading tag allows the JSP developer to create
* a heading and specify alignment, background color,
* foreground color, font, etc. for that heading.
*/
public class HeadingTag extends SimpleTagSupport {
private String align;
private String bgColor;
private String border;
private String fgColor;
private String font;
private String size;
public void setAlign(String align) {
this.align = align;
}
public void setBgColor(String bgColor) {
this.bgColor = bgColor;
}
public void setBorder(String border) {
this.border = border;
}
public void setFgColor(String fgColor) {
this.fgColor = fgColor;
}
public void setFont(String font) {
this.font = font;
}
public void setSize(String size) {
this.size = size;
}
public void doTag() throws JspException, IOException {
JspWriter out = getJspContext().getOut();
out.print("<TABLE ALIGN=\"" + align + "\"\n" +
" BGCOLOR=\"" + bgColor + "\"\n" +
" BORDER=" + border + "\">\n");
out.print("<TR><TH>");
out.print("<SPAN STYLE=\"color: " + fgColor + ";\n" +
" font-family: " + font + ";\n" +
" font-size: " + size + "px; " +
"\">\n");
// Output content of the body
getJspBody().invoke(null);
out.println("</SPAN></TH></TR></TABLE>" +
"<BR CLEAR=\"ALL\"><BR>");
}
}
Listing 7.12. Excerpt from csajsp-taglib.tld
<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
version="2.0">
<tlib-version>1.0</tlib-version>
<short-name>csajsp-taglib</short-name>
<tag>
<description>Formats enclosed heading</description>
<name>heading</name>
<tag-class>coreservlets.tags.HeadingTag</tag-class>
<body-content>scriptless</body-content>
<attribute>
<name>align</name>
<required>true</required>
</attribute>
<attribute>
<name>bgColor</name>
<required>true</required>
</attribute>
<attribute>
<name>border</name>
<required>true</required>
</attribute>
<attribute>
<name>fgColor</name>
<required>true</required>
</attribute>
<attribute>
<name>font</name>
<required>true</required>
</attribute>
<attribute>
<name>size</name>
<required>true</required>
</attribute>
</tag>
</taglib>
Listing 7.13. heading-1.jsp
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD><TITLE>Headings</TITLE>
<LINK REL=STYLESHEET
HREF="JSP-Styles.css"
TYPE="text/css">
</HEAD>
<BODY>
<%@ taglib uri="/WEB-INF/tlds/csajsp-taglib.tld"
prefix="csajsp" %>
<csajsp:heading align="LEFT" bgColor="CYAN"
border="10" fgColor="BLACK"
font="Arial Black" size="78">
First Heading
</csajsp:heading>
<csajsp:heading align="RIGHT" bgColor="RED"
border="1" fgColor="YELLOW"
font="Times New Roman" size="50">
Second Heading
</csajsp:heading>
<csajsp:heading align="CENTER" bgColor="#C0C0C0"
border="20" fgColor="BLUE"
font="Arial Narrow" size="100">
Third Heading
</csajsp:heading>
</BODY></HTML>
)
Figure 7-3 Result of heading-1.jsp.