如何反序列化浮点值与杰克逊

Question

本地化的小数点分隔符，我用Jackson分析输入流包含经纬度值，如这里：

{ 
    "name": "product 23", 
    "latitude": "52,48264", 
    "longitude": "13,31822" 
} 

出于某种原因，服务器使用 逗号作为

产生InvalidFormatException的小数点分隔符。由于我无法更改服务器输出格式，因此我想教授Jackson的ObjectMapper来处理这些情况。下面是相关代码：

public static Object getProducts(final String inputStream) { 
    ObjectMapper objectMapper = new ObjectMapper(); 
    try { 
     return objectMapper.readValue(inputStream, 
       new TypeReference<Product>() {} 
     ); 
    } catch (UnrecognizedPropertyException e) { 
     e.printStackTrace(); 
    } catch (InvalidFormatException e) { 
     e.printStackTrace(); 
    } catch (JsonMappingException e) { 
     e.printStackTrace(); 
    } catch (JsonParseException e) { 
     e.printStackTrace(); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
    return null; 
} 

这里是POJO：

import com.fasterxml.jackson.annotation.JsonProperty; 

public class Product { 

    @JsonProperty("name") 
    public String name; 
    @JsonProperty("latitude") 
    public float latitude; 
    @JsonProperty("longitude") 
    public float longitude; 

} 

我怎么能告诉杰克逊，这些坐标值都配有德文场所？

---

我想a custom deserializer for the specific fields as discussed here将是要走的路。我起草了这一点：

public class GermanFloatDeserializer extends JsonDeserializer<Float> { 

    @Override 
    public Float deserialize(JsonParser parser, DeserializationContext context) 
      throws IOException { 
     // TODO Do some comma magic 
     return floatValue; 
    } 

} 

然后POJO是这样的：

import com.fasterxml.jackson.annotation.JsonProperty; 

public class Product { 

    @JsonProperty("name") 
    public String name; 
    @JsonDeserialize(using = GermanFloatDeserializer.class, as = Float.class) 
    @JsonProperty("latitude") 
    public float latitude; 
    @JsonDeserialize(using = GermanFloatDeserializer.class, as = Float.class) 
    @JsonProperty("longitude") 
    public float longitude; 

} 

Answer 1

我想出了以下解决方案：

public class FlexibleFloatDeserializer extends JsonDeserializer<Float> { 

    @Override 
    public Float deserialize(JsonParser parser, DeserializationContext context) 
      throws IOException { 
     String floatString = parser.getText(); 
     if (floatString.contains(",")) { 
      floatString = floatString.replace(",", "."); 
     } 
     return Float.valueOf(floatString); 
    } 

} 

...

public class Product { 

    @JsonProperty("name") 
    public String name; 
    @JsonDeserialize(using = FlexibleFloatDeserializer.class) 
    @JsonProperty("latitude") 
    public float latitude; 
    @JsonDeserialize(using = FlexibleFloatDeserializer.class) 
    @JsonProperty("longitude") 
    public float longitude; 

} 

我仍然想知道为什么我会这么做不能工作当我指定返回值类为as = Float.class可以在documentation of JsonDeserialize中找到。它看起来好像我应该使用一种或另一种，但不是两种。无论如何，该文档还声称，当using =定义as =将被忽略：

如果使用（）也用于它的优先级（因为它直接指定解串器，而这将仅被用于定位解串器）并且此注释属性的值将被忽略。

Answer 2

在接受答案的所有方面，有一种方法可以去掉这些@JsonDeserialize注释。

您需要在ObjectMapper中注册自定义的反序列化器。

继教程from official web-site你只是这样做：如果你使用Spring启动还有一个更简单的方法

ObjectMapper mapper = new ObjectMapper(); 
    SimpleModule testModule = new SimpleModule(
      "DoubleCustomDeserializer", 
      new com.fasterxml.jackson.core.Version(1, 0, 0, null)) 
      .addDeserializer(Double.class, new JsonDeserializer<Double>() { 
       @Override 
       public Double deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException { 
        String valueAsString = jp.getValueAsString(); 
        if (StringUtils.isEmpty(valueAsString)) { 
         return null; 
        } 

        return Double.parseDouble(valueAsString.replaceAll(",", "\\.")); 
       } 
      }); 
    mapper.registerModule(testModule); 

。只需在您的配置类的地方定义Jackson2ObjectMapperBuilder豆：

@Bean 
public Jackson2ObjectMapperBuilder jacksonBuilder() { 
    Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder(); 

    builder.deserializerByType(Double.class, new JsonDeserializer<Double>() { 
     @Override 
     public Double deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException { 
      String valueAsString = jp.getValueAsString(); 
      if (StringUtils.isEmpty(valueAsString)) { 
       return null; 
      } 

      return Double.parseDouble(valueAsString.replaceAll(",", "\\.")); 
     } 
    }); 

    builder.applicationContext(applicationContext); 
    return builder; 
} 

和定制HttpMessageConverter增加的WebMvcConfigurerAdapter消息转换列表：

messageConverters.add(new MappingJackson2HttpMessageConverter(jacksonBuilder().build())); 

Answer 3

比其他拟议的答案，这需要更多的通用解决方案注册每种类型的单个解串器，将提供定制的DefaultDeserializationContext至ObjectMapper。

下实现（这是由DefaultDeserializationContext.Impl启发）工作对我来说：

class LocalizedDeserializationContext extends DefaultDeserializationContext { 
    private final NumberFormat format; 

    public LocalizedDeserializationContext(Locale locale) { 
     // Passing `BeanDeserializerFactory.instance` because this is what happens at 
     // 'jackson-databind-2.8.1-sources.jar!/com/fasterxml/jackson/databind/ObjectMapper.java:562'. 
     this(BeanDeserializerFactory.instance, DecimalFormat.getNumberInstance(locale)); 
    } 

    private LocalizedDeserializationContext(DeserializerFactory factory, NumberFormat format) { 
     super(factory, null); 
     this.format = format; 
    } 

    private LocalizedDeserializationContext(DefaultDeserializationContext src, DeserializationConfig config, JsonParser parser, InjectableValues values, NumberFormat format) { 
     super(src, config, parser, values); 
     this.format = format; 
    } 

    @Override 
    public DefaultDeserializationContext with(DeserializerFactory factory) { 
     return new LocalizedDeserializationContext(factory, format); 
    } 

    @Override 
    public DefaultDeserializationContext createInstance(DeserializationConfig config, JsonParser parser, InjectableValues values) { 
     return new LocalizedDeserializationContext(this, config, parser, values, format); 
    } 

    @Override 
    public Object handleWeirdStringValue(Class<?> targetClass, String value, String msg, Object... msgArgs) throws IOException { 
     // This method is called when default deserialization fails. 
     if (targetClass == float.class || targetClass == Float.class) { 
      return parseNumber(value).floatValue(); 
     } 
     if (targetClass == double.class || targetClass == Double.class) { 
      return parseNumber(value).doubleValue(); 
     } 
     // TODO Handle `targetClass == BigDecimal.class`? 
     return super.handleWeirdStringValue(targetClass, value, msg, msgArgs); 
    } 

    // Is synchronized because `NumberFormat` isn't thread-safe. 
    private synchronized Number parseNumber(String value) throws IOException { 
     try { 
      return format.parse(value); 
     } catch (ParseException e) { 
      throw new IOException(e); 
     } 
    } 
} 

现在设置你的对象映射你想要的locale：

Locale locale = Locale.forLanguageTag("da-DK"); 
ObjectMapper objectMapper = new ObjectMapper(null, 
              null, 
              new LocalizedDeserializationContext(locale)); 

如果你使用Spring RestTemplate，你可以设置为使用objectMapper像这样：

RestTemplate template = new RestTemplate(); 
template.setMessageConverters(
    Collections.singletonList(new MappingJackson2HttpMessageConverter(objectMapper)) 
); 

请注意，该值必须在JSON文档中表示为一个字符串（即，因为例如， {"number": 2,2}无效JSON将无法​​解析。