Java client: decouple JSON handling

modules/swagger-codegen/src/main/resources/Java/JSON.mustache

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+package {{invokerPackage}};
+
+import com.fasterxml.jackson.annotation.*;
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.datatype.joda.*;
+
+import java.io.IOException;
+
+public class JSON {
+  private ObjectMapper mapper;
+
+  public JSON() {
+    mapper = new ObjectMapper();
+    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
+    mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
+    mapper.registerModule(new JodaModule());
+	}
+
+  /**
+   * Serialize the given Java object into JSON string.
+   */
+  public String serialize(Object obj) throws ApiException {
+    try {
+      if (obj != null)
+        return mapper.writeValueAsString(obj);
+      else
+        return null;
+    } catch (Exception e) {
+      throw new ApiException(400, e.getMessage());
+    }
+  }
+
+  /**
+   * Deserialize the given JSON string to Java object.
+   *
+   * @param body The JSON string
+   * @param returnType The type to deserialize inot
+   * @return The deserialized Java object
+   */
+  public <T> T deserialize(String body, TypeRef returnType) throws ApiException {
+    JavaType javaType = mapper.constructType(returnType.getType());
+    try {
+      return mapper.readValue(body, javaType);
+    } catch (IOException e) {
+      if (returnType.getType().equals(String.class))
+        return (T) body;
+      else
+        throw new ApiException(500, e.getMessage(), null, body);
+    }
+  }
+}