Spring HttpMessageConverter 之 Jackson

    我们在使用Spring MVC 是都有这样的经历，@ResponseBody返回一个JSON格式字符串到前端，或者使用@RequestBody获取前端REST提交的对象，那么Spring MVC 中是如何处理的呢？大体的流程如下：

 

 

  在Spring Web中使用 jackson处理，具体实现类是MappingJackson2HttpMessageConverter. 具体的JSON系列化和反序列化都是有jackson实现的。下面主要介绍一下jackson的使用。

     对日期进行JSON序列化：

/**
 * 
 * @author zhangwei<wei.zw@corp.netease.com>
 * @since 2015年9月18日 下午4:08:08
 * @version v 0.1
 */
public class ContainDateObject {

	private Date startTime;

	private Date endTime;

	public Date getStartTime() {
		return startTime;
	}

	public void setStartTime(Date startTime) {
		this.startTime = startTime;
	}

	public Date getEndTime() {
		return endTime;
	}

	public void setEndTime(Date endTime) {
		this.endTime = endTime;
	}

}

	@Test
	public void testDate() throws JsonProcessingException {
		ContainDateObject cdo = new ContainDateObject();
		cdo.setStartTime(new Date());
		cdo.setEndTime(new Date());
		System.out.println(objectMapper.writeValueAsString(cdo));
	}

 
 结果是:

{"startTime":1442563815734,"endTime":1442563815734}

    这样的结果有的时候是无法接受的，我们有的时候需要一个yyyy-MM-dd HH:mm:ss这样格式的字符串改如何处理呢？这个时候我们就需要制定一个自定义的序列化类；

/**
 * Desc:自定义日期类型序列化类
 * 
 * @author zhangwei<wei.zw@corp.netease.com>
 * @since 2015年9月18日 下午4:12:51
 * @version v 0.1
 */
public class DateJsonSerializer extends JsonSerializer<Date> {

	/**
	 * @see com.fasterxml.jackson.databind.JsonSerializer#serialize(java.lang.Object,
	 *      com.fasterxml.jackson.core.JsonGenerator,
	 *      com.fasterxml.jackson.databind.SerializerProvider)
	 */
	@Override
	public void serialize(Date date, JsonGenerator generator, SerializerProvider provider)
			throws IOException, JsonProcessingException {
		ObjectMapper om = new ObjectMapper();
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		om.writeValue(generator, sdf.format(date));
	}

}

   在需要按照指定格式进行序列化的日期属性上添加注解

	@JsonSerialize(using = DateJsonSerializer.class)
	private Date startTime;

	@JsonSerialize(using = DateJsonSerializer.class)
	private Date endTime;

测试的结果是：

{"startTime":"2015-09-18 16:23:23","endTime":"2015-09-18 16:23:23"}

 这样的结果就比较符合预期了

   反过来，使用这个JSON转换为一个对象时的结果怎样呢？

	@Test
	public void testDate() throws Exception {
		ContainDateObject cdo = new ContainDateObject();
		cdo.setStartTime(new Date());
		cdo.setEndTime(new Date());
		String serializerResult = objectMapper.writeValueAsString(cdo);

		cdo = objectMapper.readValue(serializerResult, ContainDateObject.class);
	}

 结果却是：

com.fasterxml.jackson.databind.exc.InvalidFormatException: Can not construct instance of java.util.Date from String value '2015-09-18 16:26:58': not a valid representation (error: Failed to parse Date value '2015-09-18 16:26:58': Can not parse date "2015-09-18 16:26:58": not compatible with any of standard forms ("yyyy-MM-dd'T'HH:mm:ss.SSSZ", "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", "EEE, dd MMM yyyy HH:mm:ss zzz", "yyyy-MM-dd"))
 at [Source: {"startTime":"2015-09-18 16:26:58","endTime":"2015-09-18 16:26:58"}; line: 1, column: 2] (through reference chain: com.david.demo.jackson.ContainDateObject["startTime"])
	at com.fasterxml.jackson.databind.exc.InvalidFormatException.from(InvalidFormatException.java:55)
	at com.fasterxml.jackson.databind.DeserializationContext.weirdStringException(DeserializationContext.java:883)
	at com.fasterxml.jackson.databind.deser.std.StdDeserializer._parseDate(StdDeserializer.java:750)
	at com.fasterxml.jackson.databind.deser.std.DateDeserializers$DateBasedDeserializer._parseDate(DateDeserializers.java:176)
	at com.fasterxml.jackson.databind.deser.std.DateDeserializers$DateDeserializer.deserialize(DateDeserializers.java:262)
	at com.fasterxml.jackson.databind.deser.std.DateDeserializers$DateDeserializer.deserialize(DateDeserializers.java:246)
	at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:523)
	at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:95)
	at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap.findDeserializeAndSet(BeanPropertyMap.java:285)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:248)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3562)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2578)

  反序列化失败了，这又改如何处理呢？我们同样指定反序列化类

/**
 * Desc:日期类型的反序列化类
 * 
 * @author zhangwei<wei.zw@corp.netease.com>
 * @since 2015年9月18日 下午4:31:02
 * @version v 0.1
 */
public class DateJsonDeserializer extends JsonDeserializer<Date> {

	/**
	 * @see com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser,
	 *      com.fasterxml.jackson.databind.DeserializationContext)
	 */
	@Override
	public Date deserialize(JsonParser parser, DeserializationContext context)
			throws IOException, JsonProcessingException {
		try {
			SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
			return sdf.parse(parser.getValueAsString());
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

}

	@JsonSerialize(using = DateJsonSerializer.class)
	@JsonDeserialize(using = DateJsonDeserializer.class)
	private Date startTime;

	@JsonSerialize(using = DateJsonSerializer.class)
	@JsonDeserialize(using = DateJsonDeserializer.class)
	private Date endTime;

 这样反序列化问题也可以很好地解决了。

    我们再想对象中添加一个个人隐私信息字段 phone;

	@JsonSerialize(using = DateJsonSerializer.class)
	@JsonDeserialize(using = DateJsonDeserializer.class)
	private Date startTime;

	@JsonSerialize(using = DateJsonSerializer.class)
	@JsonDeserialize(using = DateJsonDeserializer.class)
	private Date endTime;

	private String phone;

@Test
	public void testDate() throws Exception {
		ContainDateObject cdo = new ContainDateObject();
		cdo.setStartTime(new Date());
		cdo.setEndTime(new Date());
		cdo.setPhone("13919309243");
		String serializerResult = objectMapper.writeValueAsString(cdo);
		System.out.println(serializerResult);
		objectMapper.readValue(serializerResult, ContainDateObject.class);
	}

 这样序列化的结果是：

{"startTime":"2015-09-18 16:37:34","endTime":"2015-09-18 16:37:34","phone":"13919309243"}

 phone是一个个人隐私信息，如果不想被序列化改如何处理？只需要在该属性上添加一个注解

	@JsonIgnore
	private String phone;

 再次序列化的结果是：

{"startTime":"2015-09-18 16:43:15","endTime":"2015-09-18 16:43:15"}