发布于 2018-02-07 06:57:49 | 50 次阅读 | 评论: 0 | 来源: 网友投递

这里有新鲜出炉的Java函数式编程,程序狗速度看过来!

Java程序设计语言

java 是一种可以撰写跨平台应用软件的面向对象的程序设计语言,是由Sun Microsystems公司于1995年5月推出的Java程序设计语言和Java平台(即JavaEE(j2ee), JavaME(j2me), JavaSE(j2se))的总称。


这篇文章主要介绍了Java xml出现错误 javax.xml.transform.TransformerException: java.lang.NullPointerException的相关资料,需要的朋友可以参考下

Java xml出现错误 javax.xml.transform.TransformerException: java.lang.NullPointerException解决办法:

利用Java操作XML,在操作XML过程中,执行到最后一步,在利用Transformer进行XML转换时出现NullPointerException错误,出问题的部分代码如下:


 //转换 
TransformerFactory tFactory =TransformerFactory.newInstance(); 
Transformer transformer = tFactory.newTransformer(); 
//需要转换的内存中XML源文件 
DOMSource source = new DOMSource(xmlDoc1); 
//生成的xml文件 
File xmlDoc2 = new File(outPutPath+generateXmlFileName); 
StreamResult result = new StreamResult(xmlDoc2); 
//转换 
transformer.transform(source, result); 

运行到transform函数时出现以下错误(比较长,由于我是利用SWING设计图形界面的,所以会有一些图形界面事件调用的错误):


javax.xml.transform.TransformerException: java.lang.NullPointerException
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transfor
m(TransformerImpl.java:717)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transfor
m(TransformerImpl.java:313)
    at operation.AddNeuronID.addNeuronId(AddNeuronID.java:273)
    at operationUI.AddNeuronIDListener.constructor2Perform(AddNeuronIDListen
er.java:245)
    at operationUI.AddNeuronIDListener.actionPerformed(AddNeuronIDListener.j
ava:85)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2318)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242
)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonL
istener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6041)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
    at java.awt.Component.processEvent(Component.java:5806)
    at java.awt.Container.processEvent(Container.java:2058)
    at java.awt.Component.dispatchEventImpl(Component.java:4413)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Component.dispatchEvent(Component.java:4243)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322
)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
    at java.awt.Container.dispatchEventImpl(Container.java:2102)
    at java.awt.Window.dispatchEventImpl(Window.java:2440)
    at java.awt.Component.dispatchEvent(Component.java:4243)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:273)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:183)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:173)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
Caused by: java.lang.NullPointerException
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters
(ToUnknownStream.java:317)
    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
: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.transfor
mIdentity(TransformerImpl.java:662)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transfor
m(TransformerImpl.java:708)
    ... 29 more
---------
java.lang.NullPointerException
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters
(ToUnknownStream.java:317)
    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
: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.transfor
mIdentity(TransformerImpl.java:662)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transfor
m(TransformerImpl.java:708)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transfor
m(TransformerImpl.java:313)
    at operation.AddNeuronID.addNeuronId(AddNeuronID.java:273)
    at operationUI.AddNeuronIDListener.constructor2Perform(AddNeuronIDListen
er.java:245)
    at operationUI.AddNeuronIDListener.actionPerformed(AddNeuronIDListener.j
ava:85)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:19
95)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.jav
a:2318)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel
.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242
)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonL
istener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6041)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
    at java.awt.Component.processEvent(Component.java:5806)
    at java.awt.Container.processEvent(Container.java:2058)
    at java.awt.Component.dispatchEventImpl(Component.java:4413)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Component.dispatchEvent(Component.java:4243)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322
)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
    at java.awt.Container.dispatchEventImpl(Container.java:2102)
    at java.awt.Window.dispatchEventImpl(Window.java:2440)
    at java.awt.Component.dispatchEvent(Component.java:4243)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
ad.java:273)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
java:183)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:173)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

       一开始我也感到奇怪,transform函数只是把在内存中的XML树转换成文件,为何会出现nullPointer错误呢。上网查了一下,没什么人找到答案,最后在(http://blog.awe.cz/post/english/beware-of-null-text-nodes/)这个blog中找到相当有用的答案.

      其实认真看看出错的信息,会发现有个信息比较重要:


java.lang.NullPointerException
at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters(ToUnknownStream.java:317)
at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(DOM2TO.java:240)

     从这里可以看出是由于com.sun.org.apache.xml.internal.serializer.ToUnknownStream.java文件中的characters函数出错,所在行数是317,到jdk安装目录,找到src,到相应的文件夹serializer中找到ToUnknownStream.java,找到以下函数


/** 
  * Converts the String to a character array and calls the SAX method 
  * characters(char[],int,int); 
  * 
  * @see ExtendedContentHandler#characters(String) 
  */ 
  public void characters(String chars) throws SAXException 
  { 
    final int length = chars.length(); 
    if (length > m_charsBuff.length) 
    { 
      m_charsBuff = new char[length*2 + 1]; 
    } 
    chars.getChars(0, length, m_charsBuff, 0); 
    this.characters(m_charsBuff, 0, length);  
  }  

       很明显,注意int length = chars.length(); 如果参数chars是null的话,调用length函数就会出现nullpoiterException错误。再上一层,com.sun.org.apache.xalan.internal.xsltc.trax下的DOM2TO.java文件的parse函数(240行):


case Node.TEXT_NODE: 
    _handler.characters(node.getNodeValue()); 
    break; 

      在这里,就可以知道characters函数为什么出现null参数了。原因是此结点是文本结点TEXT_NODE,而调用本结点中没有内容(null),当调用getNodeValue时,返回null.

      上升到transform函数,出现结点内容为null,那在DOMSource类中,由于它是在内存中建立起来的XML树,所以肯定是这个XML树中的有一个或多个元素或结点的内容为null。

      OK,问题原因找到。解决办法很简单,DOMSource中有元素或结点为null,那一定是在操作XML时,或者是修改内容,添加元素等等操作,使内容变为null。所以现在需要做的就是找到修改或添加元素内容的代码,把有可能出现null的情况进行处理,如果检测到为null,则不修改XML或不添加此元素。最简单的方法就是用if语句。即setNodeValue(String str)或setTextContent(String str)之前,先查看参数str是否为空(if(str == null)),如果空则不调用此函数。

      而在我的程序中,确实我是把空的内容加入到元素中。代码如下:deviceAndIDMap是一个HashMap,当它调用get时,不存在此主键时,会返回null.


String neuronIdStr = deviceAndIDMap.get(nameContent); 
//更新 
neuronIdElem.getFirstChild().setNodeValue(neuronIdStr); 

    因此我加一下if语句,就可以解决问题了,代码(此代码是在for循环中的,因此用coninue来跳过本次的修改)如下:


String neuronIdStr = deviceAndIDMap.get(nameContent); 
if(neuronIdStr == null) 
{ 
   continue; 
} 
//更新 
neuronIdElem.getFirstChild().setNodeValue(neuronIdStr); 
               

    问题解决!

感谢阅读,希望能帮助到大家,谢谢大家对本站的支持!



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