GenericJsonDeserializer.java

   1 package org.argeo.server.json;
   2
   3 import java.io.IOException;
   4 import java.io.StringWriter;
   5 import java.util.ArrayList;
   6 import java.util.List;
   7
   8 import org.apache.commons.logging.Log;
   9 import org.apache.commons.logging.LogFactory;
  10 import org.argeo.ArgeoException;
  11 import org.codehaus.jackson.JsonFactory;
  12 import org.codehaus.jackson.JsonGenerator;
  13 import org.codehaus.jackson.JsonNode;
  14 import org.codehaus.jackson.JsonParser;
  15 import org.codehaus.jackson.JsonProcessingException;
  16 import org.codehaus.jackson.ObjectCodec;
  17 import org.codehaus.jackson.map.DeserializationContext;
  18 import org.codehaus.jackson.map.JsonDeserializer;
  19 import org.codehaus.jackson.map.ObjectMapper;
  20
  21 public class GenericJsonDeserializer<T> extends JsonDeserializer<T> {
  22         private final static Log log = LogFactory
  23                         .getLog(GenericJsonDeserializer.class);
  24
  25         private JsonFactory jsonFactory = new JsonFactory();
  26         private ObjectCodec objectCodec = new ObjectMapper();
  27         private JsonObjectFactory defaultObjectFactory = new JsonObjectFactoryImpl();
  28
  29         private String typeField = "type";
  30
  31         private List<JsonObjectFactory> objectFactories = new ArrayList<JsonObjectFactory>();
  32
  33         @SuppressWarnings("unchecked")
  34         @Override
  35         public T deserialize(JsonParser parser, DeserializationContext ctxt)
  36                         throws IOException, JsonProcessingException {
  37                 // first read as Json DOM in order to extract the type
  38                 // TODO: optimize with streaming API
  39                 JsonNode root = parser.readValueAsTree();
  40                 String type = root.get(typeField).getTextValue();
  41
  42                 // Write it back as a string
  43                 StringWriter writer = new StringWriter();
  44                 JsonGenerator generator = jsonFactory.createJsonGenerator(writer);
  45                 generator.setCodec(objectCodec);
  46                 generator.writeTree(root);
  47                 String str = writer.toString();
  48
  49                 if (log.isTraceEnabled())
  50                         log.debug("Deserialize object of type=" + type + ", str=" + str);
  51
  52                 JsonObjectFactory objectFactory = null;
  53                 jofs: for (JsonObjectFactory jof : objectFactories) {
  54                         if (jof.supports(type)) {
  55                                 objectFactory = jof;
  56                                 break jofs;
  57                         }
  58                 }
  59
  60                 if (objectFactory == null)
  61                         objectFactory = defaultObjectFactory;
  62
  63                 if (objectFactory == null || !objectFactory.supports(type))
  64                         throw new ArgeoException(
  65                                         "Cannot find JSON object factory for type " + type);
  66
  67                 return (T) objectFactory.readValue(type, str);
  68         }
  69
  70         public void setTypeField(String typeField) {
  71                 this.typeField = typeField;
  72         }
  73
  74         public void setObjectFactories(List<JsonObjectFactory> objectFactories) {
  75                 this.objectFactories = objectFactories;
  76         }
  77
  78         public List<JsonObjectFactory> getObjectFactories() {
  79                 return objectFactories;
  80         }
  81
  82 }