Camel升级后Saxon Xslt处理InputStreamCache遇Unexpected EOF异常

我们将Camel从3.14版本升级至4.0.2版本后遇到异常：自3.17版本起Camel会自动启用Stream Caches，原Exchange输入类型为byte[]，现变为InputStreamCache，使用Saxon Xslt组件转换XML数据时出现报错：
net.sf.saxon.trans.XPathException: Error reported by XML parser: Unexpected EOF in prolog

该报错提示转换时输入为空，但实际上InputStreamCache并非空值。完整堆栈信息如下：

net.sf.saxon.trans.XPathException: Error reported by XML parser: Unexpected EOF in prolog
 at [row,col {unknown-source}]: [1,0]
    at net.sf.saxon.pull.StaxBridge.next(StaxBridge.java:205)
    at net.sf.saxon.pull.PullFilter.next(PullFilter.java:98)
    at net.sf.saxon.pull.PullPushTee.next(PullPushTee.java:73)
    at net.sf.saxon.pull.PullConsumer.consume(PullConsumer.java:42)
    at net.sf.saxon.pull.PullPushCopier.copy(PullPushCopier.java:44)
    at net.sf.saxon.pull.PullSource.deliver(PullSource.java:95)
    at net.sf.saxon.pull.ActiveStAXSource.deliver(ActiveStAXSource.java:61)
    at net.sf.saxon.event.Sender.send(Sender.java:104)
    at net.saxon.Controller.makeSourceTree(Controller.java:1306)
    at net.sf.saxon.s9api.XsltTransformer.transform(XsltTransformer.java:342)
    at net.sf.saxon.jaxp.TransformerImpl.transform(TransformerImpl.java:75)
    at org.apache.camel.component.xslt.XsltBuilder.process(XsltBuilder.java:123)
    at org.apache.camel.support.ProcessorEndpoint.onExchange(ProcessorEndpoint.java:93)
    at org.apache.camel.component.xslt.XsltEndpoint.onExchange(XsltEndpoint.java:120)

设置camelContext.setStreamCaching(false);恢复旧行为后一切正常。我们有以下疑问：

• 是否遗漏了Camel的相关配置项以解决该问题？
• 如何准确定位该异常的根本原因？
• 是否有示例或测试验证Saxon Xslt可与InputStreamCache配合使用？

进一步排查发现，路由中提前执行了String body = exchange.getIn().getBody(String.class);，导致InputStreamCache的底层流位置被移至末尾，后续复制到StaxSource时无数据。使用String inBody = MessageHelper.extractBodyAsString(exchange.getIn());或MessageHelper.resetStreamCache(exchange.getIn());可缓解问题，但不确定这是否为InputStreamCache的预期工作方式，Camel相关文档说明较为简略。

内容的提问来源于stack exchange，提问作者Mathias Olausson