如何用JsonFormat反序列化Jackson Json空字符串到日期

Question

我已经找了很多但仍然没有得到答案到目前为止，任何帮助是非常感谢！

我有一个简单的string到date字段映射，并尝试将JSON字符串读取到Java对象。

@JsonInclude(value=Include.NON_EMPTY)
@JsonFormat(shape=JsonFormat.Shape.STRING, pattern="dd-MMM-yyyy", timezone="PST")
protected Date eolAnnounceDate;

ObjectMapper objectMapper = new ObjectMapper();   
objectMapper.setSerializationInclusion(Include.NON_NULL); 
objectMapper.setSerializationInclusion(Include.NON_EMPTY);

例外情况：

java.lang.IllegalArgumentException：无法解析日期值“null”（格式：“dd-mmm-yyyy”）：不可解析日期：“null”com.fasterxml.jackson.databind.deser.std.dateDeserializer$DateBasedDeserializer._parsedate(DateDeserializers.java:180)com.fasterxml.jackson.databind.deser.std.dateDeserializer$DateDeserializer.deserializer(DateDeserializers.java:279)Atabind.deser.std.CollectionDeserializer.Deserializer.CollectionDeserializer.Deserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.CollectionDeserializer.Collec

谢谢-阿图尔

Answer 1

您的问题不是在JSON中传递了空值。问题是JSON包含一个值为“null”的字符串。

因此，为了解决这个问题，有许多可用的方法。我认为以下两种方法对本案有效。

备选方案1：修复JSON

public class DatePojo {
    @JsonInclude(value= JsonInclude.Include.NON_EMPTY)
    @JsonFormat(shape=JsonFormat.Shape.STRING, pattern="dd-MMM-yyyy", timezone="PST")
    @JsonProperty("date")
    private Date date;
}

@Test
public void testJson() throws IOException {
    String jsonWithValidDate = "{\"date\":\"12-Jun-1982\"}";
    String jsonWithNoDate = "{}";
    String jsonWithNullDate = "{\"date\":null}";

    ObjectMapper mapper = new ObjectMapper();
    final DatePojo pojoWithValidDate = mapper.readValue(jsonWithValidDate, DatePojo.class);
    final DatePojo pojoWithNoDate = mapper.readValue(jsonWithNoDate, DatePojo.class);
    final DatePojo pojoWithNullDate = mapper.readValue(jsonWithNullDate, DatePojo.class);

    Assert.assertNotNull(pojoWithValidDate.date);
    Assert.assertNull(pojoWithNoDate.date);
    Assert.assertNull(pojoWithNullDate.date);
}

@Test(expected = JsonMappingException.class)
public void testInvalidJson() throws IOException {
    String jsonWithNullString = "{\"date\":\"NULL\"}";

    ObjectMapper mapper = new ObjectMapper();
    mapper.readValue(jsonWithNullString, DatePojo.class); // Throws the exception
    Assert.fail();
}

备选方案2：提供处理“null”的自己的转换器

如果无法修复JSON（如备选方案1所述），则可以提供自己的转换器。

像下面这样设置pojo：

public class DatePojo {
    @JsonProperty("date")
    @JsonDeserialize(converter = MyDateConverter.class)
    private Date date;
}

public class MyDateConverter extends StdConverter<String, Date> {
    @Override
    public Date convert(final String value) {
        if (value == null || value.equals("NULL")) {
            return null;
        }
        try {
            return new SimpleDateFormat("dd-MMM-yyyy").parse(value);
        } catch (ParseException e) {
            throw new IllegalStateException("Unable to parse date", e);
        }
    }
}

@Test
public void testJson() throws IOException {
    String jsonWithValidDate = "{\"date\":\"12-Jun-1982\"}";
    String jsonWithNoDate = "{}";
    String jsonWithNullDate = "{\"date\":null}";
    String jsonWithNullString = "{\"date\":\"NULL\"}"; // "NULL"

    ObjectMapper mapper = new ObjectMapper();
    final DatePojo pojoWithValidDate = mapper.readValue(jsonWithValidDate, DatePojo.class);
    final DatePojo pojoWithNoDate = mapper.readValue(jsonWithNoDate, DatePojo.class);
    final DatePojo pojoWithNullDate = mapper.readValue(jsonWithNullDate, DatePojo.class);
    final DatePojo pojoWithNullStr = mapper.readValue(jsonWithNullString, DatePojo.class); // Works

    Assert.assertNotNull(pojoWithValidDate.date);
    Assert.assertNull(pojoWithNoDate.date);
    Assert.assertNull(pojoWithNullDate.date);
    Assert.assertNull(pojoWithNullStr.date); // Works
}

IMO，最好的方法是使用备选方案1，在这里您只需更改JSON。