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POAdding XMLAdapter causes NullPointerException in JAXBContext.newInstance method
 

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  1. POAdding XMLAdapter causes NullPointerException in JAXBContext.newInstance method
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    <p>I'm in the process of learning JAXB and wanted to try out some adapters. When I added one to my very simple class it caused the JAXBContext.newInstance() call to throw a NullPointerException. Note that the adapter isn't strictly necessary. If I comment out the @XmlJavaTypeAdapter(MapTypeAdaptor.class) annotation the code works. But that doesn't help me learn how to use adapters... Adding MapType.class and MapTypeEntry.class to JAXBContext.getInstance() didn't fix the problem either.</p> <p>I would really appreciate any advice on what I'm doing wrong. Thanks!</p> <p>Here's the Java object I'm marshaling:</p> <pre><code>import java.util.List; import java.util.Map; import javax.xml.bind.annotation.XmlRootElement; import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter; import com.s5a.api.models.jaxb.MapTypeAdaptor; @XmlAccessorType(XmlAccessType.FIELD) @XmlRootElement public class TestCollections { @XmlJavaTypeAdapter(MapTypeAdaptor.class) // &lt;---Adding this line causes the error private Map&lt;String, Object&gt; oneColor; public Map&lt;String, Object&gt; getColor() { return oneColor; } public void setColor(Map&lt;String, Object&gt; oneColor) { this.oneColor = oneColor; } public List&lt;String&gt; getListOfColors() { return listOfColors; } public void setListOfColors(List&lt;String&gt; listOfColors) { this.listOfColors = listOfColors; } private List&lt;String&gt; listOfColors; } </code></pre> <p>Here's the adapter:</p> <pre><code>import java.util.ArrayList; import java.util.HashMap; import java.util.Map; import java.util.Map.Entry; import javax.xml.bind.annotation.adapters.XmlAdapter; public class MapTypeAdaptor extends XmlAdapter&lt;MapType, Map&lt;String, Object&gt;&gt; { @Override public MapType marshal(Map&lt;String, Object&gt; map) throws Exception { ArrayList&lt;MapEntryType&gt; entries = new ArrayList&lt;MapEntryType&gt;(); MapType mapType = new MapType(); if (map != null &amp;&amp; map.entrySet() != null){ for (Entry&lt;String, Object&gt; entry : map.entrySet()) { MapEntryType mapEntryType = new MapEntryType(); if (entry != null){ mapEntryType.setKey(entry.getKey()); mapEntryType.setValue(entry.getValue()); } entries.add(mapEntryType); } mapType.setEntries(entries); } return mapType; } @Override public Map&lt;String, Object&gt; unmarshal(MapType map) throws Exception { HashMap&lt;String, Object&gt; hashMap = new HashMap&lt;String, Object&gt;(); if (map != null){ for (MapEntryType entryType : map.getEntries()) { if (entryType != null){ hashMap.put(entryType.getKey(), entryType.getValue()); } } } return hashMap; } } </code></pre> <p>Here's the MapType class:</p> <pre><code>import java.util.ArrayList; import java.util.List; public class MapType { private List&lt;MapEntryType&gt; mapEntries = new ArrayList&lt;MapEntryType&gt;(); public List&lt;MapEntryType&gt; getEntries() { return mapEntries; } public void setEntries(List&lt;MapEntryType&gt; mapEntries) { this.mapEntries = mapEntries; } } </code></pre> <p>And here's the MapEntryType class:</p> <pre><code>import javax.xml.bind.annotation.XmlAccessType; import javax.xml.bind.annotation.XmlAccessorType; import javax.xml.bind.annotation.XmlAttribute; import javax.xml.bind.annotation.XmlValue; @XmlAccessorType(XmlAccessType.FIELD) public class MapEntryType { @XmlAttribute private String key; @XmlValue private Object value; public String getKey() { return key; } public void setKey(String key) { this.key = key; } public Object getValue() { return value; } public void setValue(Object value) { this.value = value; } } </code></pre> <p>Finally, my unit test:</p> <pre><code>@Test public void shouldReturnXMLRepresentation() throws Exception { TestCollections test = new TestCollections(); HashMap&lt;String, Object&gt; color1 = new HashMap&lt;String, Object&gt;(); color1.put("blue", new Integer(50)); HashMap&lt;String, Object&gt; color2 = new HashMap&lt;String, Object&gt;(); color2.put("red", "red is the 2nd color"); ArrayList&lt;Map&lt;String, Object&gt;&gt; colors = new ArrayList&lt;Map&lt;String, Object&gt;&gt;(); colors.add(color1); colors.add(color2); test.setColor(color1); ArrayList&lt;String&gt; listofstrings = new ArrayList&lt;String&gt;(); listofstrings.add("foo"); listofstrings.add("bar"); test.setListOfColors(listofstrings); String xmlRepresentaion = genXML(test); assertTrue(xmlRepresentaion != null); assertTrue(xmlRepresentaion.length() &gt; 0); } private String genXML(Object object) throws Exception{ StringWriter writer = new StringWriter(); try { /* I tried the following, but it also throw an NPE JAXBContext jc = JAXBContext.newInstance(TestCollections.class, MapType.class, MapTypeEntry.class); */ JAXBContext jc = JAXBContext.newInstance(TestCollections.class); //&lt;-- NPE Marshaller marshaller = jc.createMarshaller(); marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true); marshaller.marshal(object, writer); }catch (Exception e){ System.out.println("Error marshalling: " + e.getMessage()); e.printStackTrace(System.out); throw e; } System.out.println(writer.toString()); return writer.toString(); } </code></pre>
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    1. COI have noticed that JAXBExceptions have a "unique" format where e.toString() gives you information that e.getMessage() does not. The NPE is almost certainly caused by some other error; someone doesn't have a no-arg constructor or something along those lines.
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    2. COThanks Kyle, that's good to know but didn't provide any new information in this case. The toString() method returns the same NPE with no additional message.
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      1. USrzrelyea
    3. COI'm having the same issue... the Object type of the Map seems to be the problem. Changing to Map<String, String> fixed the problem. However, I'm still looking for a solution since I'd like to transparently serialize various types like String, Number, Date.
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      1. USRaman
 

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