Example of calling Xero API using JSON format via Resteasy client with custom ObjectMapper

gistfile1.java

ResteasyClient client = new ResteasyClientBuilder().httpEngine(engine).build();
//  XXX For JSON dates. Not applicable when using XML API
client.register(new XeroObjectMapperContextResolver());

XeroObjectMapperContextResolver.java

import java.text.DateFormat;
import java.text.FieldPosition;
import java.text.ParsePosition;
import java.util.Date;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.ws.rs.ext.ContextResolver;

import org.codehaus.jackson.map.ObjectMapper;

public class XeroObjectMapperContextResolver implements ContextResolver<ObjectMapper>
{
    private final ObjectMapper xeroObjectMapper;
    
    public XeroObjectMapperContextResolver()
    {
        xeroObjectMapper = new ObjectMapper();
        
        DateFormat df = new DateFormat()
        {
            private static final long serialVersionUID = 1L;
            
            private final Pattern PATTERN = Pattern.compile("/Date\\((\\d+)\\)/");
            
            @Override
            public StringBuffer format(Date date,
                    StringBuffer toAppendTo, FieldPosition fieldPosition)
            {
                throw new UnsupportedOperationException();
            }
            
            @Override
            public Date parse(String source, ParsePosition pos)
            {
                Matcher matcher = PATTERN.matcher(source);
                
                if (matcher.find())
                {
                    String timeValue = matcher.group(1);
                    
                    long time = Long.parseLong(timeValue);
                    
                    pos.setIndex(source.length());
                    
                    return new Date(time);
                }
                
                return null;
            }
            
            @Override
            public Object clone()
            {
                //  We're thread safe
                return this;
            }
        };
        
        //  This will only work for responses, not for requests
        xeroObjectMapper.setDeserializationConfig(
                xeroObjectMapper.getDeserializationConfig().withDateFormat(df));
    }
    @Override
    public ObjectMapper getContext(Class<?> objectType)
    {
        return xeroObjectMapper;
    }
}