烦人的cxf unexpected element 异常

1.背景

当cxf传输的数据对象结构变化时,比如请求对象减少了字段,响应对象增加了字段,在jaxb unmarsh时会抛出异常,导致接口访问失败.

javax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"name"). Expected elements are <{}name>

上面这是一个典型的unexpected element异常,如果cxf客户端请求中多了一个name属性,或者cxf服务端响应中多了一个name属性,都会导致此异常.

2.源代码分析

翻了下源代码:

com.sun.xml.bind.v2.runtime.unmarshaller.StructureLoader#childElement检查是否是新增属性

 @Override
public void childElement(UnmarshallingContext.State state, TagName arg) throws SAXException {
    ChildLoader child = childUnmarshallers.get(arg.uri,arg.local);
    if(child==null) {//检查是否新增属性
        child = catchAll;
        if(child==null) {
            super.childElement(state,arg);
            return;
        }
    }

    state.loader = child.loader;
    state.receiver = child.receiver;
}

在com.sun.xml.bind.v2.runtime.unmarshaller.Loader中检查是否处理此问题

 public void childElement(UnmarshallingContext.State state, TagName ea) throws SAXException {
    // notify the error, then recover by ignoring the whole element.
    reportUnexpectedChildElement(ea, true);
    state.loader = Discarder.INSTANCE;
    state.receiver = null;
}

@SuppressWarnings({"StringEquality"})
protected final void reportUnexpectedChildElement(TagName ea, boolean canRecover) throws SAXException {
    if(canRecover && !UnmarshallingContext.getInstance().parent.hasEventHandler())
    //这里默认会有个EventHandler,不会直接忽略此问题
        // this error happens particurly often (when input documents contain a lot of unexpected elements to be ignored),
        // so don't bother computing all the messages and etc if we know that
        // there's no event handler to receive the error in the end. See #286 
        return;
     //下面的代码抛出异常
    if(ea.uri!=ea.uri.intern() || ea.local!=ea.local.intern())
        reportError(Messages.UNINTERNED_STRINGS.format(), canRecover );
    else
        reportError(Messages.UNEXPECTED_ELEMENT.format(ea.uri,ea.local,computeExpectedElements()), canRecover );
}

在org.apache.cxf.jaxb.io.DataReaderImpl#createUnmarshaller中设置了EventHandler,注意这里的veventHandler,默认是没有的.

if (setEventHandler) {
            um.setEventHandler(new WSUIDValidationHandler(veventHandler));
}

org.apache.cxf.jaxb.io.DataReaderImpl.WSUIDValidationHandler的代码很简单:

private static class WSUIDValidationHandler implements ValidationEventHandler {
    ValidationEventHandler origHandler;
    WSUIDValidationHandler(ValidationEventHandler o) {
        origHandler = o;
    }

    public boolean handleEvent(ValidationEvent event) {
        String msg = event.getMessage();
        System.out.println("WSUIDValidationHandler"+msg);
        if (msg != null
                && msg.contains(":Id")
                && (msg.startsWith("cvc-type.3.1.1: ")
                || msg.startsWith("cvc-type.3.2.2: ")
                || msg.startsWith("cvc-complex-type.3.1.1: ")
                || msg.startsWith("cvc-complex-type.3.2.2: "))) {
            return true;
        }
        if (origHandler != null) {
            return origHandler.handleEvent(event);
        }
        return false;
    }
}

先自己处理,自己处理不了的交给origHandler,那我们只需要自己构建一个javax.xml.bind.ValidationEventHandler来专门处理unexpected element异常,问题就得到了解决.

org.apache.cxf.jaxb.io.DataReaderImpl#setProperty中有段代码:

veventHandler = (ValidationEventHandler)m.getContextualProperty("jaxb-validation-event-handler");
       if (veventHandler == null) {
           veventHandler = databinding.getValidationEventHandler();
       }

如果配置了jaxb-validation-event-handler属性,就可以让我们自己的javax.xml.bind.ValidationEventHandler来处理此异常.也可以设置setEventHandler为false,不设置异常处理器,忽略所有unmarsh异常,不过这样我感觉太暴力了点,这样做也忽略了org.apache.cxf.jaxb.io.DataReaderImpl.WSUIDValidationHandler的逻辑,点儿都不科学.

3.实现

上面分析清楚了,实现就很简单,实现javax.xml.bind.ValidationEventHandler

public class IgnoreUnexpectedElementValidationEventHandler implements ValidationEventHandler {
        private static final Logger logger = LoggerFactory.getLogger(IgnoreUnexpectedElementValidationEventHandler.class);

        @Override
        public boolean handleEvent(ValidationEvent event) {
                String msg = event.getMessage();
                if (msg != null && msg.startsWith("unexpected element")) {
                    logger.warn("{}", msg);
                    return true;
             }
              return false;
        }
}

在cxf:bus中配置下就ok

  <cxf:bus>
    <cxf:properties>
        <entry key="jaxb-validation-event-handler">
            <bean class="IgnoreUnexpectedElementValidationEventHandler"/>
        </entry>
    </cxf:properties>
</cxf:bus>

建议只在线上环境启用此东东,线下还是不要开启,早点发现问题是好事.