uTools-Manuals/docs/java/javax/xml/xpath/XPathExpression.html

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     javax.xml.xpath 
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<h2 class="title" title="Interface XPathExpression">Interface XPathExpression</h2>
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<hr/> <br/> <pre>public interface <span class="typeNameLabel">XPathExpression</span></pre>
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<p> <span><code>XPathExpression</code>提供对编译的XPath表达式的访问。</span> </p>
<span><a name="XPathExpression-evaluation"></a></span>
<span>  Evaluation of XPath Expressions.     context  If a request is made to evaluate the expression in the absence of a context item, an empty document node will be used for the context. For the purposes of evaluating XPath expressions, a DocumentFragment is treated like a Document node.    variables  If the expression contains a variable reference, its value will be found through the <a href="../../../javax/xml/xpath/XPathVariableResolver.html" title="interface in javax.xml.xpath"><code>XPathVariableResolver</code></a>. An <a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath"><code>XPathExpressionException</code></a> is raised if the variable resolver is undefined or the resolver returns <code>null</code> for the variable. The value of a variable must be immutable through the course of any single evaluation.<p></p>    functions  If the expression contains a function reference, the function will be found through the <a href="../../../javax/xml/xpath/XPathFunctionResolver.html" title="interface in javax.xml.xpath"><code>XPathFunctionResolver</code></a>. An <a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath"><code>XPathExpressionException</code></a> is raised if the function resolver is undefined or the function resolver returns <code>null</code> for the function.<p></p>    QNames  QNames in the expression are resolved against the XPath namespace context.    result  This result of evaluating an expression is converted to an instance of the desired return type. Valid return types are defined in <a href="../../../javax/xml/xpath/XPathConstants.html" title="class in javax.xml.xpath"><code>XPathConstants</code></a>. Conversion to the return type follows XPath conversion rules.<p></p> </span>
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<p> <span>XPath表达式不是线程安全的，不可重入。</span> <span>换句话说，应用程序的责任是确保在任何给定时间从多个线程中使用一个<a href="../../../javax/xml/xpath/XPathExpression.html" title="javax.xml.xpath中的接口"><code>XPathExpression</code></a>对象，并且当调用<code>evaluate</code>方法时，应用程序可能不递归调用<code>evaluate</code>方法。</span> </p>
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<span class="simpleTagLabel">从以下版本开始：</span>
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<dd>
         1.5 
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<span class="seeLabel">另请参见：</span>
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<a href="http://www.w3.org/TR/xpath#section-Expressions">XML Path Language (XPath) Version 1.0, Expressions</a>
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<caption>
<span class="activeTableTab" id="t0"><span>所有方法</span><span class="tabEnd"> </span></span>
<span class="tableTab" id="t2"><span><a href="javascript:show(2);">接口方法</a></span><span class="tabEnd"> </span></span>
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<td class="colFirst"><code><a href="../../../java/lang/String.html" title="class in java.lang">String</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../javax/xml/xpath/XPathExpression.html#evaluate-org.xml.sax.InputSource-">evaluate</a></span>(<a href="../../../org/xml/sax/InputSource.html" title="class in org.xml.sax">InputSource</a> source)</code>
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              计算指定的上下文中，编译的XPath表达式 
             <code>InputSource</code>并返回结果作为 
             <code>String</code> 。 
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<td class="colFirst"><code><a href="../../../java/lang/Object.html" title="class in java.lang">Object</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../javax/xml/xpath/XPathExpression.html#evaluate-org.xml.sax.InputSource-javax.xml.namespace.QName-">evaluate</a></span>(<a href="../../../org/xml/sax/InputSource.html" title="class in org.xml.sax">InputSource</a> source, <a href="../../../javax/xml/namespace/QName.html" title="class in javax.xml.namespace">QName</a> returnType)</code>
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              计算指定的上下文中，编译的XPath表达式 
             <code>InputSource</code>并返回其结果作为指定的类型。 
            </div> </td>
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<td class="colFirst"><code><a href="../../../java/lang/String.html" title="class in java.lang">String</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../javax/xml/xpath/XPathExpression.html#evaluate-java.lang.Object-">evaluate</a></span>(<a href="../../../java/lang/Object.html" title="class in java.lang">Object</a> item)</code>
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              在指定的上下文中评估编译的XPath表达式，并将结果作为 
             <code>String</code> 。 
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<td class="colFirst"><code><a href="../../../java/lang/Object.html" title="class in java.lang">Object</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../javax/xml/xpath/XPathExpression.html#evaluate-java.lang.Object-javax.xml.namespace.QName-">evaluate</a></span>(<a href="../../../java/lang/Object.html" title="class in java.lang">Object</a> item, <a href="../../../javax/xml/namespace/QName.html" title="class in javax.xml.namespace">QName</a> returnType)</code>
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              在指定的上下文中评估编译的XPath表达式，并将结果作为指定的类型返回。 
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<li class="blockList"> <h4>evaluate</h4> <pre><a href="../../../java/lang/Object.html" title="class in java.lang">Object</a> evaluate(<a href="../../../java/lang/Object.html" title="class in java.lang">Object</a> item,
                <a href="../../../javax/xml/namespace/QName.html" title="class in javax.xml.namespace">QName</a> returnType)
         throws <a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></pre>
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<p> <span>在指定的上下文中评估编译的XPath表达式，并将结果作为指定的类型返回。</span> </p>
<p> <span>见<a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a>上下文项计算，变量，函数和QName解析，以及返回类型转换。</span> </p>
<p> <span>如果<code>returnType</code>不是<code>returnType</code>中定义的类型<a href="../../../javax/xml/xpath/XPathConstants.html" title="javax.xml.xpath中的类">之一</a> ，则抛出一个<code>IllegalArgumentException</code> 。</span> </p>
<p> <span>如果<code>null</code>被提供用于值<code>item</code> ，一个空文档将被用于的上下文。</span> <span>如果<code>returnType</code>是<code>null</code> ，那么会抛出一个<code>NullPointerException</code> 。</span> </p>
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<span class="paramLabel">参数</span>
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<code>item</code> - 起始上下文（例如一个节点）。 
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<code>returnType</code> - 所需的返回类型。 
           </dd>
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<span class="returnLabel">结果</span>
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<code>Object</code>是评估表达式并将结果转换为 
            <code>returnType</code>的结果。 
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<span class="throwsLabel">异常</span>
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<code><a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></code> - 如果表达式无法评估。 
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<span><code><a href="../../../java/lang/IllegalArgumentException.html" title="class in java.lang">IllegalArgumentException</a></code> - 如果<code>returnType</code>不是<code>returnType</code>中定义的类型<a href="../../../javax/xml/xpath/XPathConstants.html" title="javax.xml.xpath中的类">之一</a> 。</span>
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<code><a href="../../../java/lang/NullPointerException.html" title="class in java.lang">NullPointerException</a></code> - 如果 
            <code>returnType</code>是 
            <code>null</code> 。 
           </dd>
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<li class="blockList"> <h4>evaluate</h4> <pre><a href="../../../java/lang/String.html" title="class in java.lang">String</a> evaluate(<a href="../../../java/lang/Object.html" title="class in java.lang">Object</a> item)
         throws <a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></pre>
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<p> <span>在指定的上下文中评估编译的XPath表达式，并将结果作为<code>String</code> 。</span> </p>
<p> <span>该方法调用<a href="../../../javax/xml/xpath/XPathExpression.html#evaluate-java.lang.Object-javax.xml.namespace.QName-"><code>evaluate(Object item, QName returnType)</code></a>与<code>returnType</code>的<a href="../../../javax/xml/xpath/XPathConstants.html#STRING"><code>XPathConstants.STRING</code></a> 。</span> </p>
<p> <span>见<a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a>上下文项计算，变量，函数和QName解析，以及返回类型转换。</span> </p>
<p> <span>如果<code>null</code>被提供用于值<code>item</code> ，一个空文档将被用于的上下文。</span> </p>
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<span class="paramLabel">参数</span>
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<code>item</code> - 起始上下文（例如一个节点）。 
           </dd>
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<span class="returnLabel">结果</span>
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<code>String</code>是评估表达式并将结果转换为 
            <code>String</code>的结果。 
           </dd>
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<span class="throwsLabel">异常</span>
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<dd>
<code><a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></code> - 如果表达式无法评估。 
           </dd>
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<li class="blockList"> <h4>evaluate</h4> <pre><a href="../../../java/lang/Object.html" title="class in java.lang">Object</a> evaluate(<a href="../../../org/xml/sax/InputSource.html" title="class in org.xml.sax">InputSource</a> source,
                <a href="../../../javax/xml/namespace/QName.html" title="class in javax.xml.namespace">QName</a> returnType)
         throws <a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></pre>
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<p> <span>计算指定的上下文中，编译的XPath表达式<code>InputSource</code>并返回其结果作为指定的类型。</span> </p>
<p> <span>此方法为<a href="../../../org/xml/sax/InputSource.html" title="在org.xml.sax中的类"><code>InputSource</code></a>构建数据模型，并在结果文档对象上调用<a href="../../../javax/xml/xpath/XPathExpression.html#evaluate-java.lang.Object-javax.xml.namespace.QName-"><code>evaluate(Object item, QName returnType)</code></a> 。</span> </p>
<p> <span>见<a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a>上下文项计算，变量，函数和QName解析，以及返回类型转换。</span> </p>
<p> <span>如果<code>returnType</code>不是<code>returnType</code>中定义的类型<a href="../../../javax/xml/xpath/XPathConstants.html" title="javax.xml.xpath中的类">之一</a> ，那么抛出一个<code>IllegalArgumentException</code> 。</span> </p>
<p> <span>如果<code>source</code>或<code>returnType</code>是<code>null</code> ，那么抛出一个<code>NullPointerException</code> 。</span> </p>
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<dt>
<span class="paramLabel">参数</span>
</dt>
<dd>
<code>source</code> - 评估文件的 
            <code>InputSource</code> 。 
           </dd>
<dd>
<code>returnType</code> - 所需的返回类型。 
           </dd>
<dt>
<span class="returnLabel">结果</span>
</dt>
<dd>
<code>Object</code>是评估表达式并将结果转换为 
            <code>returnType</code>的结果。 
           </dd>
<dt>
<span class="throwsLabel">异常</span>
</dt>
<dd>
<code><a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></code> - 如果表达式无法评估。 
           </dd>
<dd>
<span><code><a href="../../../java/lang/IllegalArgumentException.html" title="class in java.lang">IllegalArgumentException</a></code> - 如果<code>returnType</code>不是<code>returnType</code>中定义的类型<a href="../../../javax/xml/xpath/XPathConstants.html" title="javax.xml.xpath中的类">之一</a> 。</span>
</dd>
<dd>
<code><a href="../../../java/lang/NullPointerException.html" title="class in java.lang">NullPointerException</a></code> - 如果 
            <code>source</code>或 
            <code>returnType</code>是 
            <code>null</code> 。 
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<li class="blockList"> <h4>evaluate</h4> <pre><a href="../../../java/lang/String.html" title="class in java.lang">String</a> evaluate(<a href="../../../org/xml/sax/InputSource.html" title="class in org.xml.sax">InputSource</a> source)
         throws <a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></pre>
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<p> <span>计算指定的上下文中，编译的XPath表达式<code>InputSource</code>并返回结果作为<code>String</code> 。</span> </p>
<p> <span>该方法调用<a href="../../../javax/xml/xpath/XPathExpression.html#evaluate-org.xml.sax.InputSource-javax.xml.namespace.QName-"><code>evaluate(InputSource source, QName returnType)</code></a>与<code>returnType</code>的<a href="../../../javax/xml/xpath/XPathConstants.html#STRING"><code>XPathConstants.STRING</code></a> 。</span> </p>
<p> <span>见<a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a>上下文项计算，变量，函数和QName解析，以及返回类型转换。</span> </p>
<p> <span>如果<code>source</code>是<code>null</code> ，那么会抛出一个<code>NullPointerException</code> 。</span> </p>
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<dt>
<span class="paramLabel">参数</span>
</dt>
<dd>
<code>source</code> - 评估文件的 
            <code>InputSource</code> 。 
           </dd>
<dt>
<span class="returnLabel">结果</span>
</dt>
<dd>
<code>String</code>是评估表达式并将结果转换为 
            <code>String</code>的结果。 
           </dd>
<dt>
<span class="throwsLabel">异常</span>
</dt>
<dd>
<code><a href="../../../javax/xml/xpath/XPathExpressionException.html" title="class in javax.xml.xpath">XPathExpressionException</a></code> - 如果表达式无法评估。 
           </dd>
<dd>
<code><a href="../../../java/lang/NullPointerException.html" title="class in java.lang">NullPointerException</a></code> - 如果 
            <code>source</code>是 
            <code>null</code> 。 
           </dd>
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