如何使用jackson将json转换为java中的POJO [英] How to convert json into POJO in java using jackson

问题描述

我正在使用spring 3.1.2，我需要将一个json对象解析为POJO。
这是我需要解析的json：

I'm using spring 3.1.2 and I need to parse a json object into POJO. This is the json that I need to parse:

{
"Person" : {
    "id" : "2"
 },
"Dog" : {
    "dateOfBirth" : "2012-08-20 00:00:00",
    "price" : "10.00"
    }
}

我需要转换这个json对象（由两个对象组合而成）到一个POJO中，这里是：

I need to convert this json object (which is combined from two objects) into one POJO, here it is:

public class MyClass{
     public MyClass(){}
     public MyClass(String personsId, TimeStamp dogsDateOfBirth, BigDecimal dogsPrice){
     .... // assign each parameter to the appropriate field
     }
     private String personsId;
     private TimeStamp dogsDateOfBirth;
     private BigDecimal dogsPrice;
     //... Getters and Setters for each field
}

For那件事我用 ObjectMapper mapper = new ObjectMapper（）;
现在因为我有几个json对象，我的代码看起来像这样：

For that matter I used ObjectMapper mapper = new ObjectMapper(); Now since I have several json objects my code looks like this:

    String json = ... ;// A json with several objects as above
    JsonNode tree = mapper.readTree(json);
    Iterator<JsonNode> iter = tree.path("data").getElements();
    while (iter.hasNext()){
        JsonNode node = iter.next();
        MyClass myClass = mapper.readValue(node, MyClass.class);
        ... // do something with myClass object
    }

当我运行这个 - 我得到以下异常：

When I run this - I get the following exception:

org.codehaus.jackson.map.JsonMappingException: No suitable constructor found for type [simple type, class ...MyClass]: can not instantiate from JSON object (need to add/enable type information?)

我试图创建一个简单的POJO - Person ：

I tried to create a simple POJO - Person:

public class Person{
        private String id;          
        public Person(){}
        public Person(String id){
            this.id = id;
         }
         ... // Getter and Setter
    }

并执行以下操作：

Person person = mapper.readValue(node.path("Person"), Person.class);

我得到这个（相同）例外：

I get this (same) exception:

org.codehaus.jackson.map.JsonMappingException: No suitable constructor found for type [simple type, class ...Person]: can not instantiate from JSON object (need to add/enable type information?)

我试着读一些关于类型信息 - 但无法理解它是如何帮助我的。

I tried to read some about the type information - but couldn't understand how it can help me here.

如何将此json转换为我的POJO？

How can I convert this json into my POJO?

谢谢。

推荐答案

我做的是这样的：
我创建了一个包含Person对象和Dog对象的新类，这些类需要是静态的（我发现它这里）。
以下是课程：

What I did was this: I created a new class that holds a Person object and Dog object, these classes needs to be static ( I found it here ). Here are the classes:

public static class MyNewClass{
    private Person person;
    private Dog dog;
    ... // two constructors and getters and setters

 public static class Person{
     private String id;
     ... // two constructors and getters and setters
 }
 public static class Dog{
     private String dateOfBirth;
     private String price;
     ... // two constructors and getters and setters
  }
}

现在我的代码如下所示：

Now my code looks like this:

    JsonNode tree = mapper.readTree(jsonString);
    Iterator<JsonNode> iter = tree.path("data").getElements();
    while (iter.hasNext()){
        JsonNode node = iter.next();
        Person person = mapper.readValue(node.path("Person"), Person.class);
        Dog dog = mapper.readValue(node.path("Dog"), Dog.class);
        MyNewClass myNewClass = new MyNewClass(person , dog);
        ... //Do something with it
    }

我仍然想要在没有创建这两个对象（人和狗）的情况下这样做 - 现在已经足够了 - 但如果有人有想法 - 我想在这里！

I still want to do it without creating these two objects ( Person and Dog ) - That'a good enough for now - but if someone have an idea - I would like to here!

谢谢。

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