📄 组件卷标.htm
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<p>组件卷标</p>
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完成Component的自订，接下来要设定一个自订Tag与之对应，自订Tag的目的，在于设定
Component属性，取得Componenty型态，取得Renderer型态值等；属性的设定包括了设定静态值、设定绑定值、设定验证器等等。<p>
要自订与Component对应的Tag，您可以继承UIComponentTag，例如：</p>
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<b>TextWithCmdTag.java</b></div>
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<pre class="code-java"><span class="code-keyword">package</span> onlyfun.caterpillar;
<span class="code-keyword">import</span> javax.faces.application.Application;
<span class="code-keyword">import</span> javax.faces.component.UIComponent;
<span class="code-keyword">import</span> javax.faces.context.FacesContext;
<span class="code-keyword">import</span> javax.faces.el.ValueBinding;
<span class="code-keyword">import</span> javax.faces.webapp.UIComponentTag;
<span class="code-keyword">public</span> class TextWithCmdTag <span class="code-keyword">extends</span> UIComponentTag {
<span class="code-keyword">private</span> <span class="code-object">String</span> size;
<span class="code-keyword">private</span> <span class="code-object">String</span> value;
<span class="code-keyword">public</span> <span class="code-object">String</span> getComponentType() {
<span class="code-keyword">return</span> <span class="code-quote">"onlyfun.caterpillar.TextWithCmd"</span>;
}
<span class="code-keyword">public</span> <span class="code-object">String</span> getRendererType() {
<span class="code-keyword">return</span> <span class="code-keyword">null</span>;
}
<span class="code-keyword">public</span> void setProperties(UIComponent component) {
<span class="code-keyword">super</span>.setProperties(component);
setStringProperty(component, <span class="code-quote">"size"</span>, size);
setStringProperty(component, <span class="code-quote">"value"</span>, value);
}
<span class="code-keyword">private</span> void setStringProperty(UIComponent component,
<span class="code-object">String</span> attrName, <span class="code-object">String</span> attrValue) {
<span class="code-keyword">if</span>(attrValue == <span class="code-keyword">null</span>)
<span class="code-keyword">return</span>;
<span class="code-keyword">if</span>(isValueReference(attrValue)) {
FacesContext context =
FacesContext.getCurrentInstance();
Application application =
context.getApplication();
ValueBinding binding =
application.createValueBinding(attrValue);
component.setValueBinding(attrName, binding);
}
<span class="code-keyword">else</span> {
component.getAttributes().
put(attrName, attrValue);
}
}
<span class="code-keyword">public</span> void release() {
<span class="code-keyword">super</span>.release();
size = <span class="code-keyword">null</span>;
value = <span class="code-keyword">null</span>;
}
<span class="code-keyword">public</span> <span class="code-object">String</span> getSize() {
<span class="code-keyword">return</span> size;
}
<span class="code-keyword">public</span> void setSize(<span class="code-object">String</span> size) {
<span class="code-keyword">this</span>.size = size;
}
<span class="code-keyword">public</span> <span class="code-object">String</span> getValue() {
<span class="code-keyword">return</span> value;
}
<span class="code-keyword">public</span> void setValue(<span class="code-object">String</span> value) {
<span class="code-keyword">this</span>.value = value;
}
}</pre>
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<p> 首先看到这两个方法：</p>
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<pre class="code-java"><span class="code-keyword">public</span> <span class="code-object">String</span> getComponentType() {
<span class="code-keyword">return</span> <span class="code-quote">"onlyfun.caterpillar.TextWithCmd"</span>;
}
<span class="code-keyword">public</span> <span class="code-object">String</span> getRendererType() {
<span class="code-keyword">return</span> <span class="code-keyword">null</span>;
}</pre>
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<p>
由于我们的Component目前不使用Renderer，所以getRendererType()传回null值，而
getComponentType()在于让JSF取得这个Tag所对应的Component，所传回的值在faces-config.xml中要有定义，例如：</p>
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<pre class="code-java">....
<component>
<component-type>
onlyfun.caterpillar.TextWithCmd
</component-type>
<component-class>
onlyfun.caterpillar.UITextWithCmd
</component-class>
</component>
....</pre>
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<p> 藉由faces-config.xml中的定义，JSF可以得知
onlyfun.caterpillar.TextWithCmd的真正类别，而这样的定义方式很显然的，您可以随时换掉<component-
class>所对应的类别，也就是说，Tag所对应的Component是可以随时替换的。</p>
<p>
在设定Component属性值时，可以由component.getAttributes()取得Map对象，并将卷标属性值存入Map
中，这个Map对象可以在对应的Component中使用getAttributes()取得，例如在上一个主题中的UITextWithCmd中可以如下取得存入Map的size属性：</p>
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<b>UITextWithCmd.java</b></div>
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<pre class="code-java"><span class="code-keyword">package</span> onlyfun.caterpillar;
<span class="code-keyword">import</span> java.io.IOException;
<span class="code-keyword">import</span> java.util.Map;
<span class="code-keyword">import</span> javax.faces.component.UIInput;
<span class="code-keyword">import</span> javax.faces.context.FacesContext;
<span class="code-keyword">import</span> javax.faces.context.ResponseWriter;
<span class="code-keyword">public</span> class UITextWithCmd <span class="code-keyword">extends</span> UIInput {
....
<span class="code-keyword">private</span> void encodeTextField(ResponseWriter writer,
<span class="code-object">String</span> clientId) <span class="code-keyword">throws</span> IOException {
....
<span class="code-object">String</span> size = (<span class="code-object">String</span>) getAttributes().get(<span class="code-quote">"size"</span>);
<span class="code-keyword">if</span>(size != <span class="code-keyword">null</span>) {
writer.writeAttribute(<span class="code-quote">"size"</span>, size, <span class="code-keyword">null</span>);
}
.....
}
....
}</pre>
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<p> 可以使用isValueReference()来测试是否为JSF Expression
Language的绑定语法，如果是的话，则我们必须建立ValueBinding对象，并设定值绑定：</p>
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<pre class="code-java">....
<span class="code-keyword">private</span> void setStringProperty(UIComponent component,
<span class="code-object">String</span> attrName, <span class="code-object">String</span> attrValue) {
<span class="code-keyword">if</span>(attrValue == <span class="code-keyword">null</span>)
<span class="code-keyword">return</span>;
<span class="code-keyword">if</span>(isValueReference(attrValue)) {
FacesContext context =
FacesContext.getCurrentInstance();
Application application =
context.getApplication();
ValueBinding binding =
application.createValueBinding(attrValue);
component.setValueBinding(attrName, binding);
}
<span class="code-keyword">else</span> {
component.getAttributes().
put(attrName, attrValue);
}
}
....</pre>
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<p> 如果是value属性，记得在上一个主题中我们提过，从UIOutput继承下来的getValue()方法可以取得
Component的value设定值，这个值可能是静态的属性设定值，也可能是JSF
Expression的绑定值，预设会先从组件的属性设定值开始找寻，如果找不到，再从绑定值（ValueBinding对象）中找寻。</p>
<p> 最后，我们必须提供自订Tag的tld档：</p>
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<b>textcmd.tld</b></div>
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<pre class="code-java"><?xml version=<span class="code-quote">"1.0"</span> encoding=<span class="code-quote">"UTF-8"</span>?>
<taglib version=<span class="code-quote">"2.0"</span>
xmlns=<span class="code-quote">"http:<span class="code-comment">//java.sun.com/xml/ns/j2ee"</span>
</span> xmlns:xsi=<span class="code-quote">"http:<span class="code-comment">//www.w3.org/2001/XMLSchema-instance"</span>
</span> xsi:schemaLocation=
<span class="code-quote">"http:<span class="code-comment">//java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"</span>>
</span> <tlib-version>1.0</tlib-version>
<jsp-version>2.0</jsp-version>
<<span class="code-object">short</span>-name>textcmd</<span class="code-object">short</span>-name>
<uri>http:<span class="code-comment">//caterpillar.onlyfun.net/textcmd</uri>
</span>
<tag>
<name>textcmd</name>
<tag-class>onlyfun.caterpillar.TextWithCmdTag</tag-class>
<body-content>empty</body-content>
<attribute>
<name>size</name>
</attribute>
<attribute>
<name>value</name>
<required><span class="code-keyword">true</span></required>
</attribute>
</tag>
</taglib></pre>
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