Json反序列化到使用Jackson的另一个类层次结构

现在我正在和Jackson合作，并且我对它有一些疑问。Json反序列化到使用Jackson的另一个类层次结构

首先。我有两种服务，一种是数据收集和发送服务，另一种是接收这些数据，例如，将其记录到文件中。

所以，第一个服务类层次结构是这样的：

  +----ConcreteC 
     | 
Base ----+----ConcreteA 
     | 
     +----ConcreteB

和第二服务具有类层次结构是这样的：

ConcreteAAdapter extends ConcreteA implements Adapter {} 
ConcreteBAdapter extends ConcreteB implements Adapter {} 
ConcreteCAdapter extends ConcreteC implements Adapter {}

，第一业务一无所知ConcreteXAdapter。

的方法，我发送的第一服务的数据：

Collection<Base> data = new LinkedBlockingQueue<Base>() 
JacksonUtils utils = new JacksonUtils(); 
data.add(new ConcreteA()); 
data.add(new ConcreteB()); 
data.add(new ConcreteC()); 
... 
send(utils.marshall(data)); 
... 

public class JacksonUtils { 

    public byte[] marshall(Collection<Base> data) throws IOException { 
     ByteArrayOutputStream out = new ByteArrayOutputStream() { 
      @Override 
      public byte[] toByteArray() { 
       return buf; 
      } 
     }; 

     getObjectMapper().writeValue(out, data); 
     return out.toByteArray(); 
    } 
    protected ObjectMapper getObjectMapper() { 
     return new ObjectMapper(); 
    } 

    public Object unmarshall(byte[] json) throws IOException { 
     return getObjectMapper().readValue(json, Object.class); 
    } 

    public <T> T unmarshall(InputStream source, TypeReference<T> typeReference) throws IOException { 
     return getObjectMapper().readValue(source, typeReference); 
    } 

    public <T> T unmarshall(byte[] json, TypeReference<T> typeReference) throws IOException { 
     return getObjectMapper().readValue(json, typeReference); 
    } 
}

所以，我想desirialize JSON到收藏ConcreteXAdapter，不进的ConcreteX（ConcreteA -> ConcreteAAdapter, ConcreteB -> ConcreteBAdapter, ConcreteC -> ConcreteCAdapter）系列。在我描述的情况下，我想得到：

Collection [ConcreteAAdapter, ConcreteBAdapter, ConcreteCAdapter]

我该怎么做？

来源

2012-04-26 pbespechnyi

我是如何解决这个问题的。下面是一个例子项目的类图： class diagram

所以我想反序列化后得到ConcreteAAdapter形式ConcreteA。

我的解决方案是扩展ClassNameIdResolver以添加将基类对象反序列化为子类类对象（子类类不增加额外的功能和附加字段）的功能。

这里是一个反序列化创建ObjectMapper代码：

protected ObjectMapper getObjectMapperForDeserialization() { 
     ObjectMapper mapper = new ObjectMapper(); 

     StdTypeResolverBuilder typeResolverBuilder = new ObjectMapper.DefaultTypeResolverBuilder(ObjectMapper.DefaultTyping.OBJECT_AND_NON_CONCRETE); 
     typeResolverBuilder = typeResolverBuilder.inclusion(JsonTypeInfo.As.PROPERTY); 
     typeResolverBuilder.init(JsonTypeInfo.Id.CLASS, new ClassNameIdResolver(SimpleType.construct(Base.class), TypeFactory.defaultInstance()) { 
      private HashMap<Class, Class> classes = new HashMap<Class, Class>() { 
       { 
        put(ConcreteA.class, ConcreteAAdapter.class); 
        put(ConcreteB.class, ConcreteBAdapter.class); 
        put(ConcreteC.class, ConcreteCAdapter.class); 
       } 
      }; 

      @Override 
      public String idFromValue(Object value) { 
       return (classes.containsKey(value.getClass())) ? value.getClass().getName() : null; 
      } 

      @Override 
      public JavaType typeFromId(String id) { 
       try { 
        return classes.get(Class.forName(id)) == null ? super.typeFromId(id) : _typeFactory.constructSpecializedType(_baseType, classes.get(Class.forName(id))); 
       } catch (ClassNotFoundException e) { 
        // todo catch the e 
       } 
       return super.typeFromId(id); 
      } 
     }); 
     mapper.setDefaultTyping(typeResolverBuilder); 
     return mapper; 
    }

这里是序列化创建ObjectMapper代码：

protected ObjectMapper getObjectMapperForSerialization() { 
    ObjectMapper mapper = new ObjectMapper(); 

    StdTypeResolverBuilder typeResolverBuilder = new ObjectMapper.DefaultTypeResolverBuilder(ObjectMapper.DefaultTyping.OBJECT_AND_NON_CONCRETE); 
    typeResolverBuilder = typeResolverBuilder.inclusion(JsonTypeInfo.As.PROPERTY); 
    typeResolverBuilder.init(JsonTypeInfo.Id.CLASS, new ClassNameIdResolver(SimpleType.construct(Base.class), TypeFactory.defaultInstance())); 
    mapper.setDefaultTyping(typeResolverBuilder); 

    return mapper; 
}

测试代码：

public static void main(String[] args) throws IOException { 
    JacksonUtils JacksonUtils = new JacksonUtilsImpl(); 

    Collection<Base> data = new LinkedBlockingQueue<Base>(); 
    data.add(new ConcreteA()); 
    data.add(new ConcreteB()); 
    data.add(new ConcreteC()); 

    String json = JacksonUtils.marshallIntoString(data); 

    System.out.println(json); 

    Collection<? extends Adapter> adapters = JacksonUtils.unmarshall(json, new TypeReference<ArrayList<Adapter>>() {}); 

    for (Adapter adapter : adapters) { 
     System.out.println(adapter.getClass().getName()); 
    } 
}

全部JacksonUtils类的代码：

public class JacksonUtilsImpl implements JacksonUtils { 

    @Override 
    public byte[] marshall(Collection<Base> data) throws IOException { 
     ByteArrayOutputStream out = new ByteArrayOutputStream() { 
      @Override 
      public byte[] toByteArray() { 
       return buf; 
      } 
     }; 

     getObjectMapperForSerialization().writerWithType(new TypeReference<Collection<Base>>() {}).writeValue(out, data); 
     return out.toByteArray(); 
    } 

    @Override 
    public String marshallIntoString(Collection<Base> data) throws IOException { 
     return getObjectMapperForSerialization().writeValueAsString(data); 
    } 

    protected ObjectMapper getObjectMapperForSerialization() { 
     ObjectMapper mapper = new ObjectMapper(); 

     StdTypeResolverBuilder typeResolverBuilder = new ObjectMapper.DefaultTypeResolverBuilder(ObjectMapper.DefaultTyping.OBJECT_AND_NON_CONCRETE); 
     typeResolverBuilder = typeResolverBuilder.inclusion(JsonTypeInfo.As.PROPERTY); 
     typeResolverBuilder.init(JsonTypeInfo.Id.CLASS, new ClassNameIdResolver(SimpleType.construct(Base.class), TypeFactory.defaultInstance())); 
     mapper.setDefaultTyping(typeResolverBuilder); 

     return mapper; 
    } 

    protected ObjectMapper getObjectMapperForDeserialization() { 
     ObjectMapper mapper = new ObjectMapper(); 

     StdTypeResolverBuilder typeResolverBuilder = new ObjectMapper.DefaultTypeResolverBuilder(ObjectMapper.DefaultTyping.OBJECT_AND_NON_CONCRETE); 
     typeResolverBuilder = typeResolverBuilder.inclusion(JsonTypeInfo.As.PROPERTY); 
     typeResolverBuilder.init(JsonTypeInfo.Id.CLASS, new ClassNameIdResolver(SimpleType.construct(Base.class), TypeFactory.defaultInstance()) { 
      private HashMap<Class, Class> classes = new HashMap<Class, Class>() { 
       { 
        put(ConcreteA.class, ConcreteAAdapter.class); 
        put(ConcreteB.class, ConcreteBAdapter.class); 
        put(ConcreteC.class, ConcreteCAdapter.class); 
       } 
      }; 

      @Override 
      public String idFromValue(Object value) { 
       return (classes.containsKey(value.getClass())) ? value.getClass().getName() : null; 
      } 

      @Override 
      public JavaType typeFromId(String id) { 
       try { 
        return classes.get(Class.forName(id)) == null ? super.typeFromId(id) : _typeFactory.constructSpecializedType(_baseType, classes.get(Class.forName(id))); 
       } catch (ClassNotFoundException e) { 
        // todo catch the e 
       } 
       return super.typeFromId(id); 
      } 
     }); 
     mapper.setDefaultTyping(typeResolverBuilder); 
     return mapper; 
    } 

    @Override 
    public Object unmarshall(byte[] json) throws IOException { 
     return getObjectMapperForDeserialization().readValue(json, Object.class); 
    } 

    @Override 
    public <T> T unmarshall(InputStream source, TypeReference<T> typeReference) throws IOException { 
     return getObjectMapperForDeserialization().readValue(source, typeReference); 
    } 

    @Override 
    public <T> T unmarshall(byte[] json, TypeReference<T> typeReference) throws IOException { 
     return getObjectMapperForDeserialization().readValue(json, typeReference); 
    } 

    @Override 
    public <T> Collection<? extends T> unmarshall(String json, Class<? extends Collection<? extends T>> klass) throws IOException { 
     return getObjectMapperForDeserialization().readValue(json, klass); 
    } 


    @Override 
    public <T> Collection<? extends T> unmarshall(String json, TypeReference typeReference) throws IOException { 
     return getObjectMapperForDeserialization().readValue(json, typeReference); 
    } 
}

来源

2012-04-27 10:49:23 pbespechnyi

为此，你需要通过额外的信息在JSON：

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, 
     include=JsonTypeInfo.As.PROPERTY, property="@type") 
class Base { 
... 
}

然后在序列化会加重@type领域：

objectMapper.registerSubtypes(
      new NamedType(ConcreteAAdapter.class, "ConcreteA"), 
      new NamedType(ConcreteBAdapter.class, "ConcreteB"), 
      new NamedType(ConcreteCAdapter.class, "ConcreteC") 
      ); 

// note, that for lists you need to pass TypeReference explicitly 
objectMapper.writerWithType(new TypeReference<List<Base>>() {}) 
    .writeValueAsString(someList); 


    { 
     "@type" : "ConcreteA", 
     ... 
    }

上反序列化将是：

objectMapper.registerSubtypes(
      new NamedType(ConcreteA.class, "ConcreteA"), 
      new NamedType(ConcreteB.class, "ConcreteB"), 
      new NamedType(ConcreteC.class, "ConcreteC") 
      ); 
    objectMapper.readValue(....)

来源

2012-04-26 15:31:00

感谢您的快速回复！我更新了这个问题。简而言之，第一个服务对“ConcreteXAdapter”一无所知。所以问题是如果杰克逊在JSON中发现了'ConcreteX'，那么如何告诉Jackson创建'ConcreteXAdapter'。 – pbespechnyi 2012-04-26 20:20:13

在这种情况下，我会建议手动传递类型（如“@type”：“ConcreteA”），然后根据属性反序列化另一端。即您需要为此实现自定义序列化程序。 – 2012-04-26 20:29:46

所以没有办法做到这一点开箱即用。好的，谢谢你的帮助！ – pbespechnyi 2012-04-26 20:37:14

我发现程序员的方法是最清晰和最容易工作的（下面的例子）。我从他的回答中的信息来一个相关的问题： https://stackoverflow.com/a/6339600/1148030 和相关的博客文章： http://programmerbruce.blogspot.fi/2011/05/deserialize-json-with-jackson-into.html

还检查了这个友好的wiki页面（尤金Retunsky的答案也提到）： http://wiki.fasterxml.com/JacksonPolymorphicDeserialization

另外一个不错的维基页面：http://wiki.fasterxml.com/JacksonMixInAnnotations

下面是一个简单的例子，让您的想法：

配置ObjectMapper这样的：（容易定义为一个内部类）

mapper.getDeserializationConfig().addMixInAnnotations(Base.class, BaseMixin.class); 
    mapper.getSerializationConfig().addMixInAnnotations(Base.class, BaseMixin.class);

例BaseMixin类

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=JsonTypeInfo.As.PROPERTY, property="type") 
@JsonSubTypes({ 
    @JsonSubTypes.Type(value=ConcreteA.class, name="ConcreteA"), 
    @JsonSubTypes.Type(value=ConcreteB.class, name="ConcreteB") 
}) 
private static class BaseMixin { 
}

在第二服务可以定义像这样的BaseMixin：

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=JsonTypeInfo.As.PROPERTY, property="type") 
@JsonSubTypes({ 
    @JsonSubTypes.Type(value=ConcreteAAdapter.class, name="ConcreteA"), 
    @JsonSubTypes.Type(value=ConcreteBAdapter.class, name="ConcreteB") 
}) 
private static class BaseMixin { 
}

来源

2012-12-19 14:48:59

您的解决方案对于第一次看起来更干净和正确。现在我不能说它适合我，因为它很久以前。但无论如何谢谢你的答案！ – pbespechnyi 2012-12-22 22:35:39

Json反序列化到使用Jackson的另一个类层次结构

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