I’ve been doing a fair amount of JSF component writing of late, and, invariably, I miss one or more “minor” details, causing my component to explode in spectacular fashion at runtime. What follows, then, is a check list for writing JSF components, with notes on the differences between the 1.1 and 1.2 versions of the specification.

Table of Contents

• Write the UIComponent Class
• Write the Renderer Class
• Write the Tag Class
• Write the Tag Library Description (.tld)
• Write the faces-config.xml Entries
• Write Facelets .taglib.xml File
• Conclusion

Write the UIComponent Class

• Extend the appropriate UIComponent class
• Define the following properties, changing the the package com.foo to your package, and the component name, Foo to the name of your component:

public static final String COMPONENT_TYPE = "com.foo.Foo"; public static final String RENDERER_TYPE = "com.foo.FooRenderer";

• Define public String getFamily () { return COMPONENT_TYPE; }
• Define default constructor which calls setRendererType(RENDERER_TYPE);
• Define your properties and their getters and setters.

For 1.1:
protected String bar; public String getBar() { if (null != this.bar) { return this.bar ; } ValueBinding _vb = getValueBinding("bar"); return (_vb != null) ? (bar) _vb.getValue(getFacesContext()) : null; }
For 1.2:
protected String bar; public String getBar() { if (null != this.bar) { return this.bar; } ValueExpression _ve = getValueExpression("bar"); return (_ve != null) ? (String) _ve.getValue(getFacesContext().getELContext()) : null; }

• Write the state saving and restoring code:

private Object[] _state = null; public void restoreState(FacesContext _context, Object _state) { this._state = (Object[]) _state; super.restoreState(_context, this._state[0]); bar = (String) this._state[1]; } public Object saveState(FacesContext _context) { if (_state == null) { _state = new Object[2]; } _state[0] = super.saveState(_context); _state[1] = bar; return _state; }

Write the Renderer Class

• Extend Renderer
• Implement encodeBegin(), and/or encodeEnd(). Maybe others, depending on the component’s needs. All of my components, for example, have only need to extend one or the other.

Write the Tag Class

For 1.1

• Extend UIComponentTag
• Define all the properties as String (?)
• Define the following methods (where Foo is your component class):

protected String bar; public String getRendererType() { return Foo.RENDERER_TYPE; } public String getComponentType() { return Foo.COMPONENT_TYPE; } protected void setProperties(UIComponent component) { super.setProperties(component); if (!(component instanceof Foo)) { throw new IllegalStateException("Component " + component.toString() + " not expected type. Expected: com.foo.Foo. Perhaps you're missing a tag?"); } Foo foo = (Foo)component; if (bar!= null) { if (isValueReference(bar)) { ValueBinding vb = Util.getValueBinding(bar); foo.setValueBinding("bar", vb); } else { throw new IllegalStateException("The value for 'bar' must be a ValueBinding."); } } }

For 1.2

• Extend UIComponentElTag
• Define properties as ValueExpression
• Define these methods (where Foo is your component class):

protected ValueExpression bar; public String getComponentType() { return Foo.COMPONENT_TYPE; } public String getRendererType() { return Foo.RENDERER_TYPE; } public ValueExpression getBar() { return bar; } protected void setProperties(UIComponent component) { super.setProperties(component); Foo download = null; try { foo = (Foo) component; } catch (ClassCastException cce) { throw new IllegalStateException("Component " + component.toString() + " not expected type. Expected: com.foo.Foo. Perhaps you're missing a tag?"); } if (bar != null) { foo.setValueExpression("bar", bar); } }

Write the Tag Library Description (.tld)

For 1.1:
<?xml version="1.0" encoding="ISO-8859-1" ?> <!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN" "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd"> <taglib> <tlib-version>1.0</tlib-version> <jsp-version>1.2</jsp-version> <short-name>foo</short-name> <uri>http://foo.com/foo</uri> <description><![CDATA[Your description here]]></description> <tag> <name>foo</name> <tag-class>com.foo.Foo</tag-class> <body-content>JSP</body-content> <description><![CDATA[Your description here]]></description> <attribute> <name>id</name> <required>false</required> <rtexprvalue>true</rtexprvalue> <description> <![CDATA[Your description here.]]> </description> </attribute> <attribute> <name>bar</name> <required>true</required> <rtexprvalue>true</rtexprvalue> <description> <![CDATA[Your description here.]]> </description> </attribute> </tag> </taglib>

For 1.2:
<?xml version="1.0" encoding="UTF-8"?> <taglib xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd" version="2.1"> <description><![CDATA[Your description here]]></description> <tlib-version>1.0</tlib-version> <short-name>foo</short-name> <uri>http://foo.com/foo</uri> <tag> <description><![CDATA[Your description here]]></description> <name>foo</name> <tag-class>com.foo.Foo</tag-class> <body-content>JSP</body-content> <attribute> <description><![CDATA[Your description here]]></description> <name>id</name> <required>false</required> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <description><![CDATA[Your description here]]></description> <name>bar</name> <required>true</required> <deferred-value><type>java.lang.Object</type></deferred-value> </attribute> </taglib>

Write the faces-config.xml Entries

For 1.1:
<?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE faces-config PUBLIC "-//Sun Microsystems, Inc.//DTD JSF Config 1.1//EN" "http://java.sun.com/dtd/web-facesconfig_1_1.dtd"> <faces-config> <component> <component-type>com.foo.Foo</component-type> <component-class>com.foo.component.Foo</component-class> <component-extension> <renderer-type>com.foo.FooRenderer</renderer-type> </component-extension> </component> <render-kit> <renderer> <component-family>com.foo.Foo</component-family> <renderer-type>com.foo.FooRenderer</renderer-type> <renderer-class>com.foo.render.FooRenderer</renderer-class> </renderer> </render-kit> </faces-config>

For 1.2:
<?xml version="1.0"?> <faces-config xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_1_2.xsd" version="1.2"> <component> <description><![CDATA[Your description here]]></description> <display-name>Foo</display-name> <component-type>com.foo.Foo</component-type> <component-class>com.foo.component.Foo</component-class> <component-extension> <renderer-type>com.foo.FooRenderer</renderer-type> </component-extension> </component> <render-kit> <description>Renderkit implementation for the Download component</description> <renderer> <component-family>>com.foo.Foo</component-family> <renderer-type>com.foo.FooRenderer</renderer-type> <renderer-class>com.foo.render.FooRenderer</renderer-class> </renderer> </render-kit>

Write Facelets .taglib.xml File

Optional, but recommended
Name this /META-INF/<component-lib-name>.taglib.xml:
<?xml version="1.0"?> <!DOCTYPE facelet-taglib PUBLIC "-//Sun Microsystems, Inc.//DTD Facelet Taglib 1.0//EN" "http://java.sun.com/dtd/facelet-taglib_1_0.dtd"> <facelet-taglib> <namespace>http://foo.com/foo</namespace> <tag> <tag-name>foo</tag-name> <component> <component-type>com.foo.Foo</component-type> <renderer-type>com.foo.component.Foo</renderer-type> </component> </tag> </facelet-taglib>

Conclusion

That, in a nutshell is what it takes to build a JSF component. I have left out, of course, many, many details in terms of “why” things should be done the way they are. I’m also cognizant that there are differing opinions on how to build a component (for instance, does every component need a separate Renderer? To date, all of my components do, but there’s no reason they have to). Once you throw Ajax into the mix, things get a bit more complicated. My hope is that this helps more people get started. Where there are omissions in these steps, my first suggestion is the excellent JSF: The Complete Reference by Chris Schalk and Ed Burns.

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