?? 自訂轉換器.htm
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<p>自訂轉換器</p>
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除了使用標準的轉換器之外，您還可以自行定制您的轉換器，您可以實作javax.faces.convert.Converter接口，這個接口有兩個要實作的方法：<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
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<pre class="code-java"><span class="code-keyword">public</span> <span class="code-object">Object</span> getAsObject(FacesContext context,
UIComponent component,
<span class="code-object">String</span> str);
<span class="code-keyword">public</span> <span class="code-object">String</span> getAsString(FacesContext context,
UIComponent component,
<span class="code-object">Object</span> obj);</pre>
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<p>
簡單的說，第一個方法會接收從客戶端經由HTTP傳來的字符串數據，您在第一個方法中將之轉換為您的自訂對象，這個自訂對象將會自動設定給您指定的Bean對象；第二個方法就是將從您的Bean對象得到的對象轉換為字符串，如此才能藉由HTTP傳回給客戶端。</p>
<p> 直接以一個簡單的例子來作說明，假設您有一個User類別：</p>
<ul>
<li>User.java </li>
</ul>
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<b>User.java</b></div>
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<pre class="code-java"><span class="code-keyword">package</span> onlyfun.caterpillar;
<span class="code-keyword">public</span> class User {
<span class="code-keyword">private</span> <span class="code-object">String</span> firstName;
<span class="code-keyword">private</span> <span class="code-object">String</span> lastName;
<span class="code-keyword">public</span> <span class="code-object">String</span> getFirstName() {
<span class="code-keyword">return</span> firstName;
}
<span class="code-keyword">public</span> void setFirstName(<span class="code-object">String</span> firstName) {
<span class="code-keyword">this</span>.firstName = firstName;
}
<span class="code-keyword">public</span> <span class="code-object">String</span> getLastName() {
<span class="code-keyword">return</span> lastName;
}
<span class="code-keyword">public</span> void setLastName(<span class="code-object">String</span> lastName) {
<span class="code-keyword">this</span>.lastName = lastName;
}
}</pre>
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<p> 這個User類別是我們轉換器的目標對象，而您有一個GuestBean類別：</p>
<ul>
<li>GuestBean.java </li>
</ul>
<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
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<b>GuestBean.java</b></div>
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<pre class="code-java"><span class="code-keyword">package</span> onlyfun.caterpillar;
<span class="code-keyword">public</span> class GuestBean {
<span class="code-keyword">private</span> User user;
<span class="code-keyword">public</span> void setUser(User user) {
<span class="code-keyword">this</span>.user = user;
}
<span class="code-keyword">public</span> User getUser() {
<span class="code-keyword">return</span> user;
}
}</pre>
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<p>
這個Bean上的屬性直接傳回或接受User型態的參數，我們來實作一個簡單的轉換器，為HTTP字符串與User對象進行轉換：</p>
<ul>
<li>UserConverter.java </li>
</ul>
<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<div class="codeHeader" style="BORDER-BOTTOM-STYLE: solid">
<b>UserConverter.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.component.UIComponent;
<span class="code-keyword">import</span> javax.faces.context.FacesContext;
<span class="code-keyword">import</span> javax.faces.convert.Converter;
<span class="code-keyword">import</span> javax.faces.convert.ConverterException;
<span class="code-keyword">public</span> class UserConverter <span class="code-keyword">implements</span> Converter {
<span class="code-keyword">public</span> <span class="code-object">Object</span> getAsObject(FacesContext context,
UIComponent component,
<span class="code-object">String</span> str)
<span class="code-keyword">throws</span> ConverterException {
<span class="code-object">String</span>[] strs = str.split(<span class="code-quote">","</span>);
User user = <span class="code-keyword">new</span> User();
<span class="code-keyword">try</span> {
user.setFirstName(strs[0]);
user.setLastName(strs[1]);
}
<span class="code-keyword">catch</span>(Exception e) {
<span class="code-comment">// 轉換錯誤，簡單的丟出例外
</span> <span class="code-keyword">throw</span> <span class="code-keyword">new</span> ConverterException();
}
<span class="code-keyword">return</span> user;
}
<span class="code-keyword">public</span> <span class="code-object">String</span> getAsString(FacesContext context,
UIComponent component,
<span class="code-object">Object</span> obj)
<span class="code-keyword">throws</span> ConverterException {
<span class="code-object">String</span> firstName = ((User) obj).getFirstName();
<span class="code-object">String</span> lastName = ((User) obj).getLastName();
<span class="code-keyword">return</span> firstName + <span class="code-quote">","</span> + lastName;
}
}</pre>
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<p> 實作完成這個轉換器，我們要告訴JSF這件事，這是在faces-config.xml中完成注冊：</p>
<ul>
<li>faces-config.xml </li>
</ul>
<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
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<b>faces-config.xml</b></div>
<div class="codeContent">
<pre class="code-java"><?xml version=<span class="code-quote">"1.0"</span>?>
<!DOCTYPE faces-config PUBLIC
<span class="code-quote">"-<span class="code-comment">//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.0//EN"</span>
</span> <span class="code-quote">"http:<span class="code-comment">//java.sun.com/dtd/web-facesconfig_1_0.dtd"</span>>
</span>
<faces-config>
<navigation-rule>
<from-view-id>/*</from-view-id>
<navigation-<span class="code-keyword">case</span>>
<from-outcome>show</from-outcome>
<to-view-id>/pages/index.jsp</to-view-id>
</navigation-<span class="code-keyword">case</span>>
</navigation-rule>
<converter>
<converter-id>onlyfun.caterpillar.User</converter-id>
<converter-class>
onlyfun.caterpillar.UserConverter
</converter-class>
</converter>
<managed-bean>
<managed-bean-name>guest</managed-bean-name>
<managed-bean-class>
onlyfun.caterpillar.GuestBean
</managed-bean-class>
<managed-bean-scope>session</managed-bean-scope>
</managed-bean>
</faces-config></pre>
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<p> 注冊轉換器時，需提供轉換器識別（Converter
ID）與轉換器類別，接下來要在JSF頁面中使用轉換器的話，就是指定所要使用的轉換器識別，例如：</p>
<ul>
<li>index.jsp </li>
</ul>
<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
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<b>index.jsp</b></div>
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<pre class="code-java"><%@ taglib uri=<span class="code-quote">"http:<span class="code-comment">//java.sun.com/jsf/core"</span> prefix="f" %>
</span> <%@ taglib uri=<span class="code-quote">"http:<span class="code-comment">//java.sun.com/jsf/html"</span> prefix="h" %>
</span> <%@page contentType=<span class="code-quote">"text/html;charset=Big5"</span>%>
<f:view>
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<title>自訂轉換器</title>
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Guest名稱是：<b>
<h:outputText value=<span class="code-quote">"#{guest.user}"</span>
converter=<span class="code-quote">"onlyfun.caterpillar.User"</span>/>
</b>
<h:form>
<h:inputText id=<span class="code-quote">"userField"</span>
value=<span class="code-quote">"#{guest.user}"</span>
converter=<span class="code-quote">"onlyfun.caterpillar.User"</span>/>
<h:message <span class="code-keyword">for</span>=<span class="code-quote">"userField"</span> style=<span class="code-quote">"color:red"</span>/>
<br>
<h:commandButton value=<span class="code-quote">"送出"</span> action=<span class="code-quote">"show"</span>/>
</h:form>
</body>
</html>
</f:view></pre>
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<p> 您也可以<f:converter>卷標并使用converterId屬性來指定轉換器，例如：</p>
<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<div class="codeContent">
<pre class="code-java"><h:inputText id=<span class="code-quote">"userField"</span> value=<span class="code-quote">"#{guest.user}"</span>>
<f:converter converterId=<span class="code-quote">"onlyfun.caterpillar.User"</span>/>
</h:inputText></pre>
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<p>
除了向JSF注冊轉換器之外，還有一個方式可以不用注冊，就是直接在Bean上提供一個取得轉換器的方法，例如：</p>
<ul>
<li>GuestBean.java </li>
</ul>
<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<div class="codeHeader" style="BORDER-BOTTOM-STYLE: solid">
<b>GuestBean.java</b></div>
<div class="codeContent">
<pre class="code-java"><span class="code-keyword">package</span> onlyfun.caterpillar;
<span class="code-keyword">import</span> javax.faces.convert.Converter;
<span class="code-keyword">public</span> class GuestBean {
<span class="code-keyword">private</span> User user;
<span class="code-keyword">private</span> Converter converter = <span class="code-keyword">new</span> UserConverter();
<span class="code-keyword">public</span> void setUser(User user) {
<span class="code-keyword">this</span>.user = user;
}
<span class="code-keyword">public</span> User getUser() {
<span class="code-keyword">return</span> user;
}
<span class="code-keyword">public</span> Converter getConverter() {
<span class="code-keyword">return</span> converter;
}
}</pre>
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<p> 之后可以直接結合 JSF Expression Language 來指定轉換器：</p>
<div class="code" style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<div class="codeContent">
<pre class="code-java"><h:inputText id=<span class="code-quote">"userField"</span>
value=<span class="code-quote">"#{guest.user}"</span>
converter=<span class="code-quote">"#{guest.converter}"</span>/></pre>
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