将JSON反序列化为ArrayList< POJO>用杰克逊 [英] Deserialize JSON to ArrayList<POJO> using Jackson
问题描述
我有一个Java类 MyPojo ，我有兴趣从JSON反序列化。我已经配置了一个特殊的MixIn类， MyPojoDeMixIn ，以帮助我进行反序列化。 MyPojo 只有 int 和字符串实例变量与正确相结合吸气剂和二传手。 MyPojoDeMixIn 看起来像这样：
I have a Java class MyPojo that I am interested in deserializing from JSON. I have configured a special MixIn class, MyPojoDeMixIn, to assist me with the deserialization. MyPojo has only int and String instance variables combined with proper getters and setters. MyPojoDeMixIn looks something like this:
public abstract class MyPojoDeMixIn {
MyPojoDeMixIn(
@JsonProperty("JsonName1") int prop1,
@JsonProperty("JsonName2") int prop2,
@JsonProperty("JsonName3") String prop3) {}
}
在我的测试客户端中，我执行以下操作，但当然它在编译时不起作用时间，因为存在与类型不匹配相关的 JsonMappingException 。
In my test client I do the following, but of course it does not work at compile time because there is a JsonMappingException related to a type mismatch.
ObjectMapper m = new ObjectMapper();
m.getDeserializationConfig().addMixInAnnotations(MyPojo.class,MyPojoDeMixIn.class);
try { ArrayList<MyPojo> arrayOfPojo = m.readValue(response, MyPojo.class); }
catch (Exception e) { System.out.println(e) }
I我知道我可以通过创建一个只有 ArrayList< MyPojo> 的Response对象来缓解这个问题，但是我必须创建这些有些无用的对象对于我想要返回的每一种类型。
I am aware that I could alleviate this issue by creating a "Response" object that has only an ArrayList<MyPojo> in it, but then I would have to create these somewhat useless objects for every single type I want to return.
我也在线查看了 JacksonInFiveMinutes 但是很难理解有关 Map< A，B> 以及它与我的问题的关系。如果你不能说，我是Java的新手，来自Obj-C背景。他们特别提到：
I also looked online at JacksonInFiveMinutes but had a terrible time understanding the stuff about Map<A,B> and how it relates to my issue. If you cannot tell, I'm entirely new to Java and come from an Obj-C background. They specifically mention:
除了绑定到POJO和简单类型之外，还有一个
的额外变体：绑定到通用（类型）容器。
这种情况需要特殊处理，因为所谓的类型擦除
（由Java用来实现有点向后兼容的
方式的泛型），这会阻止你使用像
这样的东西.class（不编译）。
In addition to binding to POJOs and "simple" types, there is one additional variant: that of binding to generic (typed) containers. This case requires special handling due to so-called Type Erasure (used by Java to implement generics in somewhat backwards compatible way), which prevents you from using something like Collection.class (which does not compile).
因此，如果你想将数据绑定到Map中，你需要使用：
So if you want to bind data into a Map you will need to use:
Map<String,User> result = mapper.readValue(src, new TypeReference<Map<String,User>>() { });
如何直接反序列化为 ArrayList ？
How can I deserialize directly to ArrayList?
推荐答案
您可以使用 TypeReference 包装直接反序列化到列表。示例方法：
You can deserialize directly to a list by using the TypeReference wrapper. An example method:
public static <T> T fromJSON(final TypeReference<T> type,
final String jsonPacket) {
T data = null;
try {
data = new ObjectMapper().readValue(jsonPacket, type);
} catch (Exception e) {
// Handle the problem
}
return data;
}
因此使用：
final String json = "";
Set<POJO> properties = fromJSON(new TypeReference<Set<POJO>>() {}, json);
。
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