那些遇到过的问题

使用Jackson将Json反序列化为另一个类层次结构

pbe*_*nyi 22 java serialization json jackson deserialization

现在我和杰克逊一起工作,我对此有一些疑问.

首先.我有两个服务,第一个是数据收集和发送服务,第二个接收这些数据,例如,将其记录到文件中.

所以,第一个服务有类层次结构,如下所示:

         +----ConcreteC
         |
Base ----+----ConcreteA
         |
         +----ConcreteB
Run Code Online (Sandbox Code Playgroud)

第二个服务有类层次结构,如下所示:

ConcreteAAdapter extends ConcreteA implements Adapter {}
ConcreteBAdapter extends ConcreteB implements Adapter {}
ConcreteCAdapter extends ConcreteC implements Adapter {}
Run Code Online (Sandbox Code Playgroud)

第一个服务一无所知ConcreteXAdapter.

我在第一个服务上发送数据的方式:

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);
    }
}
Run Code Online (Sandbox Code Playgroud)

所以,我想将json想象成Collection ConcreteXAdapter,而不是集合ConcreteX(ConcreteA -> ConcreteAAdapter, ConcreteB -> ConcreteBAdapter, ConcreteC -> ConcreteCAdapter).在我描述的情况下我想得到:

Collection [ConcreteAAdapter, ConcreteBAdapter, ConcreteCAdapter]
Run Code Online (Sandbox Code Playgroud)

我怎样才能做到这一点？

Eug*_*sky 29

为此,您需要在JSON中传递其他信息:

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

然后在序列化时,它将添加@type字段:

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",
      ...
    }
Run Code Online (Sandbox Code Playgroud)

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(....)
Run Code Online (Sandbox Code Playgroud)

更多信息:http://wiki.fasterxml.com/JacksonPolymorphicDeserialization

  • @Eugene有支持:只使用`@JsonTypeName`和'As.NAME' - 不是类名,如果它们不同的话.然后,您需要注册子类型(通过调用`ObjectMapper.registerSubtypes()`或使用@JsonSubTypes注释). (2认同)

pbe*_*nyi 17

我是怎么解决这个问题的 这是一个示例项目的类图: 类图

所以我希望在反序列ConcreteAAdapter化ConcreteA后得到表单.

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型对象的功能(子类型不添加额外的功能和附加字段).

这是ObjectMapper为反序列化创建的代码:

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;
    }
Run Code Online (Sandbox Code Playgroud)

这是一个ObjectMapper为序列化创建的代码:

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;
}
Run Code Online (Sandbox Code Playgroud)

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());
    }
}
Run Code Online (Sandbox Code Playgroud)

JacksonUtils类的完整代码:

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);
    }
}
Run Code Online (Sandbox Code Playgroud)

Pet*_*erg 11

我发现programmerbruce的方法是最清晰,最容易上手的(下面的例子).我从他对相关问题的回答中得到了相关信息:https: //stackoverflow.com/a/6339600/1148030 和相关的博文:http: //programmerbruce.blogspot.fi/2011/05/deserialize-json-with -jackson-into.html

另请查看这个友好的维基页面(也在Eugene Retunsky的回答中提到):http://wiki.fasterxml.com/JacksonPolymorphicDeserialization

另一个不错的维基页面:http://wiki.fasterxml.com/JacksonMixInAnnotations

这是一个简短的例子来给你这个想法:

像这样配置ObjectMapper:

    mapper.getDeserializationConfig().addMixInAnnotations(Base.class, BaseMixin.class);
    mapper.getSerializationConfig().addMixInAnnotations(Base.class, BaseMixin.class);
Run Code Online (Sandbox Code Playgroud)

示例BaseMixin类(易于定义为内部类.)

@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 {
}
Run Code Online (Sandbox Code Playgroud)

在第二个服务上,您可以像这样定义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 {
}
Run Code Online (Sandbox Code Playgroud)

归档时间：

查看次数：

39140 次

最近记录：

6 年，1 月 前
如何阻止Jackson序列化多态类型的注释属性？ 14
更多相关链接
相关归档
为什么我在Java中获得NoClassDefFoundError？ 505
从另一个线程在主线程中运行代码 302
Apache POI锁定标题行 70
PageRequest构造函数已被弃用 48
将Django Rest Framework与序列化程序一起使用时的AttributeError 31
在Perl中,检查json解码的布尔值 15
使用Web Matrix助手进行C#JSON解码 10
设置Jackson功能WRITE_DATES_AS_TIMESTAMPS在Spring Boot中不起作用 7
杰克逊:解析自定义偏移日期时间 6
从枚举标志转换CSV,反之亦然 5
难疑归档
什么是JSONP,为什么创建它？ 2040
如何在Java中声明和初始化数组？ 1946
2048游戏的最佳算法是什么？ 1893
如何在Git中检索当前提交的哈希值？ 1788
<button>与<input type ="button"/>.哪个用？ 1588
短路Array.forEach就像调用break 1429
Memcached与Redis？ 1398
如何在HTTP POST请求中发送参数？ 1396
如何删除旧的Docker容器 1162
如何在同一分支上的两个不同提交之间区分相同的文件？ 1077