Question

我有一个XML对象，当我用

将其转换为字符串时

public static String XMLElementToString(Document doc, Element e) {
    // --- Output XML ---
    try {
        TransformerFactory transFactory = TransformerFactory.newInstance();
        Transformer transformer = transFactory.newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");

        StringWriter buffer = new StringWriter();
        Result result = new StreamResult(buffer);
        Source source = null;
        if (e != null) {
            transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
            source = new DOMSource(e);
        } else {
            source = new DOMSource(doc);
        }
        transformer.transform(source, result); // <-- Error occurs here

        buffer.flush();
        return buffer.toString();

    } catch (TransformerException ex) {
        System.out.println("exception: " + ex.getMessage());            
    }
    return "";
}

我的一个对象出错了。使用断点并查看xml对象我不能说为什么，尽管TransformerException确实说包含的异常是一个空指针异常。它适用于我在同一个程序中的其他相关对象，但我不知道如何调试它。

[[编辑]] 这是堆栈跟踪：

ERROR:  ''
javax.xml.transform.TransformerException: java.lang.NullPointerException
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:716)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:313)
at com.protocase.utils.StringHelpers.XMLElementToString(StringHelpers.java:132)
at com.protocase.io.PDWriter.writePD(PDWriter.java:49)
at com.protocase.io.PDWriter.writePDA(PDWriter.java:26)
at com.protocase.viewer.JDesigner.OnSaveAs(JDesigner.java:1364)
at com.protocase.viewer.JDesigner.access$000(JDesigner.java:106)
at com.protocase.viewer.JDesigner$34.actionPerformed(JDesigner.java:722)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
at java.awt.Component.processMouseEvent(Component.java:6288)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6053)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4651)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:643)
at java.awt.EventQueue.access$000(EventQueue.java:84)
at java.awt.EventQueue$1.run(EventQueue.java:602)
at java.awt.EventQueue$1.run(EventQueue.java:600)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:616)
at java.awt.EventQueue$2.run(EventQueue.java:614)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:613)
at com.protocase.viewer.EventQueueProxy.dispatchEvent(JDesigner.java:2338)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Caused by: java.lang.NullPointerException
at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters(ToUnknownStream.java:338)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:240)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:132)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:94)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(TransformerImpl.java:661)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:707)
    ... 45 more
---------
java.lang.NullPointerException
at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters(ToUnknownStream.java:338)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:240)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:226)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:132)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:94)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(TransformerImpl.java:661)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:707)
at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(TransformerImpl.java:313)
at com.protocase.utils.StringHelpers.XMLElementToString(StringHelpers.java:132)
at com.protocase.io.PDWriter.writePD(PDWriter.java:49)
at com.protocase.io.PDWriter.writePDA(PDWriter.java:26)
at com.protocase.viewer.JDesigner.OnSaveAs(JDesigner.java:1364)
at com.protocase.viewer.JDesigner.access$000(JDesigner.java:106)
at com.protocase.viewer.JDesigner$34.actionPerformed(JDesigner.java:722)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
at java.awt.Component.processMouseEvent(Component.java:6288)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6053)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4651)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:643)
at java.awt.EventQueue.access$000(EventQueue.java:84)
at java.awt.EventQueue$1.run(EventQueue.java:602)
at java.awt.EventQueue$1.run(EventQueue.java:600)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:616)
at java.awt.EventQueue$2.run(EventQueue.java:614)
at java.security.AccessController.doPrivileged(Native Method)
at     java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:613)
at com.protocase.viewer.EventQueueProxy.dispatchEvent(JDesigner.java:2338)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

我猜这个错误是你的一个对象，因为该对象不是有效的XML，或者因为XML有一个空（null）文本节点而不是空字符串值。

请参阅java.lang.NullPointerException

at com.sun.org.apache.xml.internal.serializer. ToUnknownStream.characters(ToUnknownStream.java:338)

基于@Sajan Chandran评论中的链接：

http://dotcommers.wordpress.com/2008/10/22/javaxxmltransformtransformerexception-javalangnullpointerexception-how-to-solve/

如果你看一下，你会看到代码。

public void characters(String chars) throws SAXException
{
  final int length = chars.length();

由于空文本节点，char.length()的问题为零。

正如其所述，要解决此问题，只需确保所有XML节点都具有字符串值而不是“null”值。

如果这不起作用，您可以发布导致引发异常的XML对象的示例。此外，您是否可以检查对象是否是有效的XML，以及字符实体等是否已正确编码。

Answer 2

基本上同意其他答案，除了：

问题是您的doc或e数据中包含 null （不为空）字符内容的文本节点结构

虽然Kiran的帖子（由Sajan链接）很有用，但我很确定他错误地说“chars.length（）为零，因为尝试了一个空文本节点插入。” chars.length()不是零;对chars.length()的调用引发了NPE，因为chars为空。

要找到问题，请在此处添加方法调用：

    if (e != null) {
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        source = new DOMSource(e);
        checkForNullTextNodes(e); // ADDED
    } else {
        source = new DOMSource(doc);
        checkForNullTextNodes(doc);  // ADDED
    }
    transformer.transform(source, result); // <-- Error occurs here

然后将checkForNullTextNodes(node)定义为:(伪代码）

遍历每个节点n的树
检查每个文本节点是否有空字符数据

E.g。（仍然是半伪代码）

 if (n.getType() == org.w3c.dom.Node.TEXT_NODE && n.getNodeValue() == null) {
     throw new Exception("Text node with null content: " +
         path to this node);
 }

这应该可以帮助您找出具有空字符内容的任何文本节点的位置，这可以帮助您找出它们的来源。无论如何，这些doc或e结构在哪里被创建？

Answer 3

我同意另一个答案，这是我用来摆脱null节点的代码

public void deleteNullNode(Node racine)
    {
        NodeList nl = racine.getChildNodes();
        for (int i = 0; i < nl.getLength(); i++)
        {
            if (nl.item(i).getNodeType() == Node.TEXT_NODE && nl.item(i).getNodeValue() == null)
            {
                nl.item(i).getParentNode().removeChild(nl.item(i));
            }
            else
            {
                deleteNullNode(nl.item(i));
            }
        }
    }

在编写字符串时，如何调试导致转换错误的xml对象？

3 个答案: