加入微信接口中时间类型的序列化转换类，供转换json使用

weixin-java-mp/src/main/java/me/chanjar/weixin/mp/util/json/WxLongTimeJsonSerializer.java

@@ -0,0 +1,24 @@
+package me.chanjar.weixin.mp.util.json;
+
+import java.io.IOException;
+import java.text.SimpleDateFormat;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+
+/**
+ * Created by Binary Wang on 2016/7/13.
+ */
+public class WxLongTimeJsonSerializer extends JsonSerializer<Long> {
+  private static SimpleDateFormat DF = new SimpleDateFormat(
+      "yyyy-MM-dd hh:mm:ss");
+
+  @Override
+  public void serialize(Long value, JsonGenerator gen,
+      SerializerProvider serializers)
+      throws IOException, JsonProcessingException {
+    gen.writeString(DF.format(value * 1000));
+  }
+}