转换返回空指针异常，但参数不为空？

Question

我正在生成一个KML文件，在我使用transformer API的时候，我得到了NullPointerException异常。下面是我引用的代码：

TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(kml);
            StreamResult result = new StreamResult(new File("src/mapa/mapa.kml"));
            System.out.print("DESPRES DE CREAR RESULT\n");
            if(source == null)
                System.out.print("SOURCE IS NULL");
            if(result == null)
                System.out.print("RESULT IS NULL");
            transformer.transform(source, result);
            System.out.print("AFTER TRASNFORM\n");

它不会打印任何空的System.outs，但是也不会打印最后一个。为什么它会给我NPE？

例外：

DESPRES DE CREAR RESULT
ERROR:  ''
javax.xml.transform.TransformerException: java.lang.NullPointerException
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at Joc.crearMapa(Joc.java:199)
    at MastersOfWar.main(MastersOfWar.java:18)
Caused by: java.lang.NullPointerException
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(Unknown Source)
    ... 4 more
---------
java.lang.NullPointerException
    at com.sun.org.apache.xml.internal.serializer.ToUnknownStream.characters(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.DOM2TO.parse(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transformIdentity(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at com.sun.org.apache.xalan.internal.xsltc.trax.TransformerImpl.transform(Unknown Source)
    at Joc.crearMapa(Joc.java:199)
    at MastersOfWar.main(MastersOfWar.java:18)

Answer 1

尝试下面的代码

System.out.print(transformerFactory.newTransformer());

它可能返回null，使您的transformer对象为null。