jspintro8.html

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<a name="wp71179"> </a><div class="pCellBody">
<code class="cCode">&lt;jsp:setProperty name=&quot;</code><code class="cVariable">beanName</code><code class="cCode">&quot;</code>
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<a name="wp71184"> </a><div class="pCellBody">
<code class="cCode">&nbsp;&nbsp;property=&quot;</code><code class="cVariable">propName</code><code class="cCode">&quot; &gt;</code>
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<a name="wp71185"> </a><div class="pCellBody">
<code class="cCode">&nbsp;&nbsp;&lt;jsp:attribute name=&quot;</code>value<code class="cCode">&quot;&gt;<br />&nbsp;&nbsp;&nbsp;&nbsp;</code><code class="cVariable">expression<br /></code><code class="cCode">&nbsp;&nbsp;&lt;/jsp:attribute&gt;</code>
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<a name="wp71189"> </a><div class="pCellBody">
<code class="cCode">&lt;/jsp:setProperty&gt;</code>
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    <td><a name="wp81236"> </a><div class="pCellBody">
1. <code class="cVariable">beanName</code> must be the same as that specified for the <code class="cCode">id</code> attribute in a <code class="cCode">useBean</code> element. 
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<a name="wp81237"> </a><div class="pCellBody">
2. There must be a <code class="cVariable">setPropName</code><code class="cCode"> </code>method in the JavaBeans component.
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<a name="wp70814"> </a><div class="pCellBody">
3. <code class="cVariable">paramName</code> must be a request parameter name.
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<p class="pBody">
</p>
<a name="wp70817"> </a><p class="pBody">
A property set from a constant string or request parameter must have a type listed in <a  href="JSPIntro8.html#wp70827">Table 12-4</a>. Since both a constant and request parameter are strings, the Web container automatically converts the value to the property's type; the conversion applied is shown in the table. 
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<a name="wp76920"> </a><p class="pBody">
<code class="cCode">String</code> values can be used to assign values to a property that has a <code class="cCode">PropertyEditor</code> class. When that is the case, the <code class="cCode">setAsText(String)</code> method is used. A conversion failure arises if the method throws an <code class="cCode">IllegalArgumentException</code>. 
</p>
<a name="wp76921"> </a><p class="pBody">
The value assigned to an indexed property must be an array, and the rules just described apply to the elements. </p><div align="left">
<table border="1" summary="Valid Property Value Assignments from String Values" id="wp70827">
  <caption><a name="wp70827"> </a><div class="pTableTitle">
Table 12-4   Valid Property Value Assignments from String Values&nbsp;
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</caption>
  <tr align="center">    <th><a name="wp70831"> </a><div class="pCellHeading">
Property Type
</div>
</th>
    <th><a name="wp70833"> </a><div class="pCellHeading">
Conversion on String Value
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</th>
</tr>
  <tr align="left">    <td><a name="wp70835"> </a><div class="pCellBody">
Bean Property
</div>
</td>
    <td><a name="wp70837"> </a><div class="pCellBody">
Uses<code class="cCode"> setAsText(</code><code class="cVariable">string-literal</code><code class="cCode">)</code>
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  <tr align="left">    <td><a name="wp70839"> </a><div class="pCellBody">
<code class="cCode">boolean</code> or <code class="cCode">Boolean</code>
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</td>
    <td><a name="wp70841"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.Boolean.valueOf(String)</code>
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<code class="cCode">byte</code> or <code class="cCode">Byte</code>
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</td>
    <td><a name="wp70845"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.Byte.valueOf(String)</code>
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<code class="cCode">char</code> or <code class="cCode">Character</code>
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    <td><a name="wp70849"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.String.charAt(0)</code>
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<code class="cCode">double</code> or <code class="cCode">Double</code>
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    <td><a name="wp70853"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.Double.valueOf(String)</code>
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<code class="cCode">int</code> or <code class="cCode">Integer</code>
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</td>
    <td><a name="wp70857"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.Integer.valueOf(String)</code>
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<code class="cCode">float</code> or <code class="cCode">Float</code>
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</td>
    <td><a name="wp70861"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.Float.valueOf(String)</code>
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  <tr align="left">    <td><a name="wp70863"> </a><div class="pCellBody">
<code class="cCode">long</code> or <code class="cCode">Long</code>
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</td>
    <td><a name="wp70865"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.Long.valueOf(String)</code>
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</td>
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  <tr align="left">    <td><a name="wp70867"> </a><div class="pCellBody">
<code class="cCode">short</code> or <code class="cCode">Short</code> 
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</td>
    <td><a name="wp70869"> </a><div class="pCellBody">
As indicated in <code class="cCode">java.lang.Short.valueOf(String)</code>
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<code class="cCode">Object</code>
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    <td><a name="wp70873"> </a><div class="pCellBody">
new <code class="cCode">String(</code><code class="cVariable">string-literal</code><code class="cCode">)</code>
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<p class="pBody">
</p>
<a name="wp70875"> </a><p class="pBody">
You use an expression to set the value of a property whose type is a compound Java programming language type. The type returned from an expression must match or be castable to the type of the property. 
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<a name="wp74344"> </a><p class="pBody">
The Duke's Bookstore application demonstrates how to use the <code class="cCode">setProperty</code> element to set the current book from a request parameter in the database helper bean in <code class="cCode"><a  href="../examples/web/bookstore2/web/bookdetails.txt" target="_blank">bookstore2/web/bookdetails.jsp</a></code>:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
&lt;c:set var=&quot;bid&quot; value=&quot;${param.bookId}&quot;/&gt;
&lt;jsp:setProperty name=&quot;bookDB&quot; property=&quot;bookId&quot;
&nbsp;&nbsp;value=&quot;${bid}&quot; /&gt;<a name="wp76923"> </a>
</pre></div>
<a name="wp70886"> </a><p class="pBody">
The following fragment from the page <code class="cCode"><a  href="../examples/web/bookstore2/web/bookshowcart.txt" target="_blank">bookstore2/web/bookshowcart.jsp</a></code> illustrates how to initialize a <code class="cCode">BookDB</code> bean with a <code class="cCode">database</code> object. Because the initialization is nested in a <code class="cCode">useBean</code> element, it is only executed when the bean is created.
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
&lt;jsp:useBean id=&quot;bookDB&quot; class=&quot;database.BookDB&quot; scope=&quot;page&quot;&gt;
&nbsp;&nbsp;&lt;jsp:setProperty name=&quot;bookDB&quot; property=&quot;database&quot; 
&nbsp;&nbsp;&nbsp;&nbsp;value=&quot;${bookDBAO}&quot; /&gt;
&lt;/jsp:useBean&gt;<a name="wp74308"> </a>
</pre></div>
<a name="wp74296"> </a><h3 class="pHeading2">
Retrieving JavaBeans Component Properties
</h3>
<a name="wp70891"> </a><p class="pBody">
The main way to retrieve JavaBeans component properties is with the JSP expression language. Thus, to retrieve a book title, the Duke's Bookstore application uses the following expression:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
${bookDB.bookDetails.title}<a name="wp75014"> </a>
</pre></div>
<a name="wp75009"> </a><p class="pBody">
Another way to retrieve component properties is to use the <code class="cCode">jsp:getProperty</code> element. This element converts the value of the property into a <code class="cCode">String</code> and inserts the value into the response stream:
</p>
<div class="pPreformattedRelative"><pre class="pPreformattedRelative">
<code class="cCode">&lt;jsp:getProperty name=&quot;</code><code class="cVariable">beanName</code><code class="cCode">&quot; property=&quot;</code><code class="cVariable">propName</code><code class="cCode">&quot;/&gt;</code><a name="wp70893"> </a>
</pre></div>
<a name="wp70895"> </a><p class="pBody">
Note that <code class="cVariable">beanName</code> must be the same as that specified for the <code class="cCode">id</code> attribute in a <code class="cCode">useBean</code> element, and there must be a <code class="cCode">get</code><code class="cVariable">PropName</code> method in the JavaBeans component. Although the preferred approach to getting properties is to use an EL expression, the <code class="cCode">getProperty</code> element is available if you need to disable expression evaluation.
</p>
    </blockquote>

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