FWK005 parse may not be called while parsing.


最近在使用javax.xml.parsers.DocumentBuilder解析xml文件的时候偶尔会出错:

org.xml.sax.SAXException: FWK005 parse may not be called while parsing.
        at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:263)
        at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:284)
        at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:208)
...

跟踪了一下代码,发现这个异常是在com.sun.org.apache.xerces.internal.parsers.DTDConfiguration.parse(DTDConfiguration.java:546)抛出来的。该段代码结构如下:

if(fParseInProgress) {
    throw new XNIException("FWK005 parse may not be called while parsing.");
}

fParseInProgress = true;

// 解析xml文件

finally {
    fParseInProgress = false;
}

从程序逻辑来看,如果当前DocumentBuilder对象正在转换文档,此时再次请求转换文档,那么直接抛出XNIException(“FWK005 parse may not be called while parsing.”);异常。

这个问题也比较好解决,一种是对转换xml文档的方法,增加synchronized关键字,这样子不会有两个线程同时访问方法。

还有一种方法是创建一个DocumentBuilder类型的ThreadLocal变量,这样子每个线程都拥有自己的DocumentBuilder对象,能够同时转换多个xml文件。代码如下:

private static ThreadLocal docBuildeIns = new ThreadLocal() {
    protected DocumentBuilder initialValue() {
        try {
            return DocumentBuilderFactory.newInstance().newDocumentBuilder();
        } catch (ParserConfigurationException e) {
            String msg = "DocumentBuilder 对象初始化失败!";
            log.error(msg, e);
            throw new IllegalStateException(msg, e);
        }
    }
};

解析xml文件时的调用方法:

docBuildIns.get().parse(File);

get()方法返回此线程局部变量的当前线程副本中的值。如果变量没有用于当前线程的值,则先将其初始化为调用 initialValue() 方法返回的值。

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