傑克遜反序列化陣列與空對象

Question

我有以下JSON：

{"beans":["{}",{"name":"Will"}]} 

和相應POJO類：

public class BeanA { 
    private BeanB[] beans; 
    ...getters/setters 
} 

public class BeanB { 
    private String name; 
    ...getters/setters 
} 

我想傑克遜反序列化到BeanA與BeanBs的陣列，所述第一個元素將只是BeanB的一個實例，第二個元素將是具有名稱屬性集的BeanB實例。

我已經序列化此創建的原始字符串：

BeanA beanA = new BeanA(); 
BeanB beanB = new BeanB(); 
beanB.setName("Will"); 
beanA.setBeans(new BeanB[] {new BeanB(), beanB}); 

這裏是我的objectMapper完整的配置：

this.objectMapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, false); 
this.objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false); 
this.objectMapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY); 

我得到的錯誤是這樣的：

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `BeanB` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('{}') 

Answer 1

使用ObjectMapper#readValue：

BeanA beanA = new BeanA(); 
BeanB beanB = new BeanB(); 
beanB.setName("Will"); 
beanA.setBeans(new BeanB[] {new BeanB(), beanB}); 

ObjectMapper om = new ObjectMapper(); 
om.setSerializationInclusion(JsonInclude.Include.NON_EMPTY); 
String json = om.writeValueAsString(beanA); 
System.out.println(json); 
// output: {"beans":[{},{"name":"Will"}]} 

BeanA deserializedBeanA = om.readValue(json, BeanA.class); 
System.out.println(deserializedBeanA); 
// output: BeanA{beans=[BeanB{name='null'}, BeanB{name='Will'}]}