Using the XPath Filter

此组件定义了一个基于 XPath 的消息过滤器。内部，这些组件使用一个包装 AbstractXPathMessageSelector 实例的 MessageFilter。

This component defines an XPath-based message filter. Internally, these components uses a MessageFilter that wraps an instance of AbstractXPathMessageSelector.

有关详细信息，请参阅 Filter。

See Filter for further details.

要使用 XPath 过滤器，您至少必须通过声明 xpath-expression 元素或在 xpath-expression-ref 属性中引用 XPath 表达式来提供一个 XPath 表达式。

to use the XPath filter you must, at a minimum, provide an XPath expression either by declaring the xpath-expression element or by referencing an XPath Expression in the xpath-expression-ref attribute.

如果提供的 XPath 表达式计算得出一个 boolean 值，则不需要其他配置参数。然而，如果 XPath 表达式计算得出一个 String，您应设置 match-value 属性，对其比对计算结果。

If the provided XPath expression evaluates to a boolean value, no further configuration parameters are necessary. However, if the XPath expression evaluates to a String, you should set the match-value attribute, against which the evaluation result is matched.

match-type 有三个选项：

match-type has three options:

exact: Correspond to equals on java.lang.String. The underlying implementation uses a StringValueTestXPathMessageSelector
case-insensitive: Correspond to equals-ignore-case on java.lang.String. The underlying implementation uses a StringValueTestXPathMessageSelector
regex: Matches operations one java.lang.String. The underlying implementation uses a RegexTestXPathMessageSelector

当提供 regex 的 'match-type' 值时，随 match-value 属性一起提供的 value 必须是一个有效的正则表达式。

When providing a 'match-type' value of 'regex', the value provided with the match-value attribute must be a valid regular expression.

以下示例显示了 xpath-filter 元素的所有可用属性：

The following example shows all the available attributes for the xpath-filter element:

<int-xml:xpath-filter discard-channel=""                      1
                      id=""                                   2
                      input-channel=""                        3
                      match-type="exact"                      4
                      match-value=""                          5
                      output-channel=""                       6
                      throw-exception-on-rejection="false"    7
                      xpath-expression-ref="">                8
    <int-xml:xpath-expression ... />                          9
    <int:poller ... />                                        10
</int-xml:xpath-filter>

1	Message channel where you want rejected messages to be sent. Optional.
2	ID for the underlying bean definition. Optional.
3	The receiving message channel of this endpoint. Optional.
4	Type of match to apply between the XPath evaluation result and the `match-value`. The default is `exact`. Optional.
5	String value to be matched against the XPath evaluation result. If you do not set this attribute, the XPath evaluation must produce a boolean result. Optional.
6	The channel to which messages that matched the filter criteria are dispatched. Optional.
7	By default, this property is set to `false` and rejected messages (those did not match the filter criteria) are silently dropped. However, if set to `true`, message rejection results in an error condition and an exception being propagated upstream to the caller. Optional.
8	Reference to an XPath expression instance to evaluate.
9	This child element sets the XPath expression to be evaluated. If you do not include this element, you must set the `xpath-expression-ref` attribute. Also, you can include only one `xpath-expression` element.
10	A poller to use with the XPath filter. Optional.