Advance java session 15
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Implementing JSP tag extensions discusses developing custom JSP tags. Custom tags are translated into servlets with tag handlers that operate on the JSP page. There are three types: simple tags without attributes or body; tags with attributes; and tags with body content. Creating a custom tag requires a tag handler class, a Tag Library Descriptor (TLD) file describing the tag, and a JSP page importing and using the tag. The tag handler outputs content or invokes the body. Attributes are handled via set methods, and body content via getJspBody().invoke().
Advance java session 15
- 1. Implementing JSP tag extensions
- 2. Agenda • Understand and use jsp: tags • Developing JSP pages using custom tags
- 3. Use of JSP custom tag • Custom tag is a user defined JSP language element • It is translated into servlet • Tag is converted into operation on tag handler • Container invokes those operation on the JSP page • Three types of tag - Simple tag - Tags with attributes - Tags with body content
- 4. Use of JSP custom tag • Java-based tags - Components of a tag library - Basic tags - Tags that use attributes - Tags that use body content - Tags that optionally use body content • JSP-based tags (tag files) - Components of a tag library - Basic tags - Tags that use attributes - Tags that use body content
- 5. Components that make up a tag library • The Tag Handler Class - Java code that says what to output - Must implement javax.servlet.jsp.tagext.SimpleTag • Usually extends SimpleTagSupport • Goes in same directories as servlet class files and bean • The Tag Library Descriptor File • XML file describing tag name, attributes, and implementing tag handler class - Goes under WEB-IN • The JSP File - Imports a tag library (referencing URL of descriptor file) - Defines tag prefix - Uses tags
- 6. Simple illustration • Create a java class that acts as a tag handler package mytag; import javax.servlet.jsp.tagext.*; import javax.servlet.jsp.*; import java.io.*; public class HelloTag extends SimpleTagSupport { public void doTag() throws JspException, IOException { JspWriter out = getJspContext().getOut(); out.println("Hello Custom Tag!"); } }
- 7. Simple illustration • compile above class and copy it in a directory available in environment variable CLASSPATH. Finally create following tag library file: <Tomcat-Installation-Directory>webappsROOTWEB-INFcustom.tld. <taglib> <tlib-version>1.0</tlib-version> <jsp-version>2.0</jsp-version> <short-name>Example TLD</short-name> <tag> <name>Hello</name> <tag-class>mytag.HelloTag</tag-class> <body-content>empty</body-content> </tag> </taglib>
- 8. Simple illustration • Now it's time to use above defined custom tag Hello in our JSP program as follows <%@ taglib prefix="ex" uri="WEB-INF/custom.tld"%> <html> <head> <title>A sample custom tag</title> </head> <body> <ex:Hello/> </body> </html>
- 9. Accessing tag with body content • Consider you want to define a custom tag named <ex:Hello> and you want to use it in the following fashion with a body: <ex:Hello> This is message body </ex:Hello>
- 10. Tag file package mytag; import javax.servlet.jsp.tagext.*; import javax.servlet.jsp.*; import java.io.*; public class HelloTag extends SimpleTagSupport { StringWriter sw = new StringWriter(); public void doTag() throws JspException, IOException { getJspBody().invoke(sw); getJspContext().getOut().println(sw.toString()); } }
- 11. TLD <taglib> <tlib-version>1.0</tlib-version> <jsp-version>2.0</jsp-version> <short-name>Example TLD with Body</short-name> <tag> <name>Hello</name> <tag-class>com.tutorialspoint.HelloTag</tag-class> <body-content>scriptless</body-content> </tag> </taglib>
- 12. JSP <%@ taglib prefix="ex" uri="WEB-INF/custom.tld"%> <html> <head> <title>A sample custom tag</title> </head> <body> <ex:Hello> This is message body </ex:Hello> </body> </html>
- 13. Elements in TLD
- 14. Summary • For each custom (Java-based) tag, you need - A tag handler class (usually extending SimpleTagSupport - An entry in a Tag Library Descriptor file - A JSP file that imports it, specifies prefix, and uses it • Simple tags - Generate output in doTag, body-content is empty • Attributes - Define setAttributeName method. - Add attribute entries to TLD file. • Body content - body-content is scriptless - doTag calls getJspBody().invoke(null)