HowTo: How to create JAX_WS WebMethod which returns a complex type, by example java.util.HashMap

In simple words, you can't do this directly. The only way is use of workaround.

But one by one. I decided to write this post after reading a few threads on Oracle's Forum. By example this thread: https://forums.oracle.com/message/7015500. I found also many other posts with issues "what to do when WebMethod returns null value instedad of complex type" - which is a typical symptom when you try to return an unacceptable type.

As says Java EE 6 Tutorial:

"JAX-WS delegates the mapping of Java programming language types to and from XML definitions to JAXB. Application developers don’t need to know the details of these mappings but should be aware that not every class in the Java language can be used as a method parameter or return type in JAX-WS."

next we have a list of Schema-to-Java mappings:

XML Schema Type	Java Data Type
xsd:string	java.lang.String
xsd:integer	java.math.BigInteger
xsd:int	int
xsd.long	long
xsd:short	short
xsd:decimal	java.math.BigDecimal
xsd:float	float
xsd:double	double
xsd:boolean	boolean
xsd:byte	byte
xsd:QName	javax.xml.namespace.QName
xsd:dateTime	javax.xml.datatype.XMLGregorianCalendar
xsd:base64Binary	byte[]
xsd:hexBinary	byte[]
xsd:unsignedInt	long
xsd:unsignedShort	int
xsd:unsignedByte	short
xsd:time	javax.xml.datatype.XMLGregorianCalendar
xsd:date	javax.xml.datatype.XMLGregorianCalendar
xsd:g	javax.xml.datatype.XMLGregorianCalendar
xsd:anySimpleType	java.lang.Object
xsd:anySimpleType	java.lang.String
xsd:duration	javax.xml.datatype.Duration
xsd:NOTATION	javax.xml.namespace.QName

and Java-to-Schema mappings:

Java Class	XML Data Type
java.lang.String	xs:string
java.math.BigInteger	xs:integer
java.math.BigDecimal	xs:decimal
java.util.Calendar	xs:dateTime
java.util.Date	xs:dateTime
javax.xml.namespace.QName	xs:QName
java.net.URI	xs:string
javax.xml.datatype.XMLGregorianCalendar	xs:anySimpleType
javax.xml.datatype.Duration	xs:duration
java.lang.Object	xs:anyType
java.awt.Image	xs:base64Binary
javax.activation.DataHandler	xs:base64Binary
javax.xml.transform.Source	xs:base64Binary
java.util.UUID	xs:string

If your desired type wasn't listed above, you have to come up with some workaround. For types like lists and maps you can convert those types to array of simple java types. By example:

/**
* We need return Map<String,String> but because we can't do this, 
* we would use workaround and return an two-dimensional array of Strings
*/

@WebMethod()
@WebResult(name="MyMethod",targetNamespace="http://my-java-planet.blogspot.com/my-java-planet")
public String[][] MyMethod(
        @WebParam(name="Symbol",targetNamespace="http://my-java-planet.blogspot.com/my-java-planet") 
        String projectSymbol,             
        @WebParam(name="Year",targetNamespace="http://my-java-planet.blogspot.com/my-java-planet") 
        String projectYear)
{

      try
      {
             LinkedHashMap<String,String> re = getData(projectSymbol, projectYear); 
             
             String ra[][] = new String[re.size()][2]; 
             int i = 0; 
             for(Map.Entry<String,String> entry : re.entrySet())
             { 
                         ra[i][0] = entry.getKey(); 
                         ra[i][1] = entry.getValue(); 
                         i++; 
             } 
             return ra; 
      } 
      catch (Exception ex) 
      { 
             String methodName=Thread.currentThread().getStackTrace()[1].getMethodName();
             logger.severe("Exception "+ex.getMessage()+" in "+methodName );
             String re[][] = new String[][]{{"ERROR",ex.getMessage()}};
      }
}