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这是对我之前的问题Extract specific value from complex JSON in java的扩展 。我得到了解决方案，但我想尝试从带有 bean 类的 json 字符串中提取 3 个值。对于给定的 json 结构。json结构在链接中。

我正在使用以下代码调用杰克逊：

mainbean obj = mapper.readValue(file, mainbean.class);
System.out.println(obj.clientPayload.e.h.getAk());

我已经为 mainbean 类的整个层次结构生成了 POJO：

public class mainbean {
    public Cpld cp;

    public Cpld getCp() {
        return Cp;
    }

    public void setCp(Cpld cp) {
        this.cp= cp;
    }
    public SPL getSp() {
        return sp;
    }
    public void setSp(SPL sp) {
        this.sp= sp;
    }
    private SPL sp;
    @Override
    public String toString() {
        return "mainbean [cp=" + cp+ "]";
    }
}

其次是CPLD类

public class Cpld {
    public E e;

    public E getE() {
        return e;
    }

    public void setE(E e) {
        this.e = e;
    }
    public String toString(){
        return "E string" + e;
    }
}

然后e课

public class E {
    public H h;

    public H getH() {
        return h;
    }
    public void setH(H h) {
        this.h = h;
    }
    public C c;
    public B b;
    public TT tt;
    public C getC() {
        return c;
    }
    public void setC(C c) {
        this.c = c;
    }
    public B getB() {
        return b;
    }
    public void setB(B b) {
        this.b = b;
    }
    public TT getTt() {
        return tt;
    }
    public void setTt(TT tt) {
        this.tt = tt;
    }
}

等等......我遇到了一个例外

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [simple type, class JsonPath.Cpld] from JSON String; no single-String constructor/factory method (through reference chain: JsonPath.mainbean["clientPayload"])
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator._createFromStringFallbacks(StdValueInstantiator.java:419)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:295)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromString(BeanDeserializer.java:405)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:117)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:336)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:89)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:290)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:112)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2577)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1764)

谁能在这里为我指明正确的方向...在此先感谢您的帮助

更新：Json 文件：从 java 中的复杂 JSON 中提取特定值

4

2 回答 2

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Just add an empty constructor to your Clpd class

于 2013-12-11T22:49:07.137 回答
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因为顶部 JSON 对象的值CP是 JSON 对象的字符串表示形式，而不是 JSON 对象本身，所以您的Cpld类需要一个显式构造函数，该构造函数接受一个字符串并将其反序列化为该对象的属性。

于 2013-06-23T18:01:11.443 回答