Jackson反序列化泛型List(使用JavaType将json字符串转换成泛型List)

ObjectMapper mapper = new ObjectMapper();

　　// 排除json字符串中实体类没有的字段
　　objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,false);



String json = "[{"name":"a","password":"345"},{"name":"b","password":"123"}]";
        
//第一种方法
List<User> list = mapper.readValue(json, new TypeReference<List<User>>(){/**/});
        
//第二种方法
JavaType javaType = mapper.getTypeFactory().constructCollectionType(List.class, User.class);
List<User> list2 = mapper.readValue(json, javaType);

Jackson，我感觉是在Java与Json之间相互转换的最快速的框架，当然Google的Gson也很不错，但是参照网上有人的性能测试，看起来还是Jackson比较快一点

Jackson处理一般的JavaBean和Json之间的转换只要使用ObjectMapper 对象的readValue和writeValueAsString两个方法就能实现。但是如果要转换复杂类型Collection如 List<YourBean>，那么就需要先反序列化复杂类型为泛型的Collection Type。

如果是ArrayList<YourBean>那么使用ObjectMapper 的getTypeFactory().constructParametricType(collectionClass, elementClasses);

如果是HashMap<String,YourBean>那么 ObjectMapper 的getTypeFactory().constructParametricType(HashMap.class,String.class, YourBean.class);

public final ObjectMapper mapper = new ObjectMapper(); 
     
    public static void main(String[] args) throws Exception{  
        JavaType javaType = getCollectionType(ArrayList.class, YourBean.class); 
        List<YourBean> lst =  (List<YourBean>)mapper.readValue(jsonString, javaType); 
    }   
       /**   
        * 获取泛型的Collection Type  
        * @param collectionClass 泛型的Collection   
        * @param elementClasses 元素类   
        * @return JavaType Java类型   
        * @since 1.0   
        */   
    public static JavaType getCollectionType(Class<?> collectionClass, Class<?>... elementClasses) {   
        return mapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);   
    }

复杂类型转换

ObjectMapper objectMapper = new ObjectMapper();
// 排除json字符串中实体类没有的字段
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
PledgeCertificate pledgeCertificate;
Pledge pledge = new Pledge();
try {
      pledgeCertificate = objectMapper.readValue(requestBody, PledgeCertificate.class);
      pledge = objectMapper.readValue(requestBody, Pledge.class);
　　   Map<String, Object> map = objectMapper.readValue(requestBody, Map.class);
      String writeValueAsString = objectMapper.writeValueAsString(map.get("obligee"));
      JavaType javaType = objectMapper.getTypeFactory().constructParametricType(List.class, Obligee.class);
      List<Obligee> obligee = objectMapper.readValue(writeValueAsString,javaType);
}catch (IOException e) {
      return “转换错误”;
}

数据格式：（实体类没有obligee字段，先排除）

{
“certificate”:"豫(2016)郑州市不动产权第0026369号",
“debtEnd”: "yyyy-mm-dd",
“debtStart”: "yyyy-mm-dd",
“pledgeType”: "2",
“maxDebtAmount”:88,
“registType”:"0201",
“obligee” :[{
"obligeeType":"1","name":张三","certType":"1","certNo":"4114211..."},{
"obligeeType":"1","name":"李四","certType":"1","certNo":"4114211..."}]
}

{

“certificate”:"豫(2016)郑州市不动产权第0026369号",

“debtEnd”: "yyyy-mm-dd",

“debtStart”: "yyyy-mm-dd",

“pledgeType”: "2",

“maxDebtAmount”:88,

“registType”:"0201",

“obligee” :[{

"obligeeType":"1","name":张三","certType":"1","certNo":"4114211..."},{

"obligeeType":"1","name":"李四","certType":"1","certNo":"4114211..."}]

}