如何使用Java和Jackson Library对Json String进行多态反序列化？

我有一些类A，B，C它们都inheritance自BaseClass类。

我有一个String json，它包含A，B，C或BaseClass的json表示。

我想有一些方法将此String反序列化为BaseClass（多态反序列化）。 像这样的东西

BaseClass base = ObjectMapper.readValue(jsonString, BaseClass.class); 

jsonString可以是A，B，C或BaseClass中的任何一个的Json String表示。

Answer 1

目前尚不清楚原始海报有什么问题。 我猜这是两件事之一：

1. 未绑定的JSON元素的反序列化问题，因为JSON包含要绑定到Java中的任何内容的元素; 要么

2. 想要实现多态反序列化。

这是第一个问题的解决方案。

 import static org.codehaus.jackson.map.DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES; import org.codehaus.jackson.map.ObjectMapper; public class Foo { public static void main(String[] args) throws Exception { BaseClass base = new BaseClass(); A a = new A(); B b = new B(); C c = new C(); ObjectMapper mapper = new ObjectMapper(); String baseJson = mapper.writeValueAsString(base); System.out.println(baseJson); // {"baseName":"base name"} String aJson = mapper.writeValueAsString(a); System.out.println(aJson); // {"baseName":"base name","aName":"a name"} String bJson = mapper.writeValueAsString(b); System.out.println(bJson); // {"baseName":"base name","bName":"b name"} String cJson = mapper.writeValueAsString(c); System.out.println(cJson); // {"baseName":"base name","cName":"c name"} BaseClass baseCopy = mapper.readValue(baseJson, BaseClass.class); System.out.println(baseCopy); // baseName: base name // BaseClass aCopy = mapper.readValue(aJson, BaseClass.class); // throws UnrecognizedPropertyException: // Unrecognized field "aName", not marked as ignorable // because the JSON contains elements for which no Java field // to bind to was provided. // Need to let Jackson know that not all JSON elements must be bound. // To resolve this, the class can be annotated with // @JsonIgnoreProperties(ignoreUnknown=true) or the ObjectMapper can be // directly configured to not FAIL_ON_UNKNOWN_PROPERTIES mapper = new ObjectMapper(); mapper.configure(FAIL_ON_UNKNOWN_PROPERTIES, false); BaseClass aCopy = mapper.readValue(aJson, BaseClass.class); System.out.println(aCopy); // baseName: base name BaseClass bCopy = mapper.readValue(bJson, BaseClass.class); System.out.println(bCopy); // baseName: base name BaseClass cCopy = mapper.readValue(cJson, BaseClass.class); System.out.println(cCopy); // baseName: base name } } class BaseClass { public String baseName = "base name"; @Override public String toString() {return "baseName: " + baseName;} } class A extends BaseClass { public String aName = "a name"; @Override public String toString() {return super.toString() + ", aName: " + aName;} } class B extends BaseClass { public String bName = "b name"; @Override public String toString() {return super.toString() + ", bName: " + bName;} } class C extends BaseClass { public String cName = "c name"; @Override public String toString() {return super.toString() + ", cName: " + cName;} } 

这是第二个问题的解决方案。

 import org.codehaus.jackson.annotate.JsonSubTypes; import org.codehaus.jackson.annotate.JsonSubTypes.Type; import org.codehaus.jackson.annotate.JsonTypeInfo; import org.codehaus.jackson.map.ObjectMapper; public class Foo { public static void main(String[] args) throws Exception { BaseClass base = new BaseClass(); A a = new A(); B b = new B(); C c = new C(); ObjectMapper mapper = new ObjectMapper(); String baseJson = mapper.writeValueAsString(base); System.out.println(baseJson); // {"type":"BaseClass","baseName":"base name"} String aJson = mapper.writeValueAsString(a); System.out.println(aJson); // {"type":"a","baseName":"base name","aName":"a name"} String bJson = mapper.writeValueAsString(b); System.out.println(bJson); // {"type":"b","baseName":"base name","bName":"b name"} String cJson = mapper.writeValueAsString(c); System.out.println(cJson); // {"type":"c","baseName":"base name","cName":"c name"} BaseClass baseCopy = mapper.readValue(baseJson, BaseClass.class); System.out.println(baseCopy); // baseName: base name BaseClass aCopy = mapper.readValue(aJson, BaseClass.class); System.out.println(aCopy); // baseName: base name, aName: a name BaseClass bCopy = mapper.readValue(bJson, BaseClass.class); System.out.println(bCopy); // baseName: base name, bName: b name BaseClass cCopy = mapper.readValue(cJson, BaseClass.class); System.out.println(cCopy); // baseName: base name, cName: c name } } @JsonTypeInfo( use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type") @JsonSubTypes({ @Type(value = A.class, name = "a"), @Type(value = B.class, name = "b"), @Type(value = C.class, name = "c") }) class BaseClass { public String baseName = "base name"; @Override public String toString() {return "baseName: " + baseName;} } class A extends BaseClass { public String aName = "a name"; @Override public String toString() {return super.toString() + ", aName: " + aName;} } class B extends BaseClass { public String bName = "b name"; @Override public String toString() {return super.toString() + ", bName: " + bName;} } class C extends BaseClass { public String cName = "c name"; @Override public String toString() {return super.toString() + ", cName: " + cName;} } 

相反，目标是反序列化为子类类型而没有专门用于指示子类类型的JSON元素，那么这也是可能的，只要JSON中的某些内容可用于决定子类类型应该是什么。 我在http://programmerbruce.blogspot.com/2011/05/deserialize-json-with-jackson-into.html上发布了这种方法的示例。

Answer 2

你看过谷歌的Gson图书馆吗？ 我认为它可以满足您的需求。

http://code.google.com/p/google-gson/