转换为pojo时简单的json结构抛出错误

Question

我正在尝试将 json 字符串转换为 java pojo，但在解析时收到此错误：

org.codehaus.jackson.map.JsonMappingException: Can not instantiate value of type [simple type, class com.json.pojo.Userdatum] from JSON String; no single-String constructor/factory method
    at org.codehaus.jackson.map.deser.std.StdValueInstantiator._createFromStringFallbacks(StdValueInstantiator.java:379)
    at org.codehaus.jackson.map.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:268)
    at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromString(BeanDeserializer.java:765)
    at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:585)
    at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2732)
    at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1863)
    at com.json.pojo.ParseJson.main(ParseJson.java:21)

这是我的转换代码：

package com.json.pojo;

import java.io.IOException;

import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.annotate.JsonAutoDetect.Visibility;
import org.codehaus.jackson.annotate.JsonMethod;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.ObjectMapper;

public class ParseJson {

    public static void main(String args[]){

        String str = "\"userdata\": [  {\"userid\": \"user1\",\"title\": \"Next weeks preview\", \"date\": \"19/12/2013\",\"time\": \"15:00\"}";
        org.codehaus.jackson.map.ObjectMapper mapper = new org.codehaus.jackson.map.ObjectMapper();     
        mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

        try {
            com.json.pojo.Userdatum user = mapper.readValue(str, com.json.pojo.Userdatum.class);
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

还有我的pojo：

package com.json.pojo;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.annotation.Generated;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@Generated("com.googlecode.jsonschema2pojo")
@JsonPropertyOrder({
"userdata"
})
public class UserData {

@JsonProperty("userdata")
private List<Userdatum> userdata = new ArrayList<Userdatum>();
private Map<String, Object> additionalProperties = new HashMap<String, Object>();

@JsonProperty("userdata")
public List<Userdatum> getUserdata() {
return userdata;
}

@JsonProperty("userdata")
public void setUserdata(List<Userdatum> userdata) {
this.userdata = userdata;
}

@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}

@JsonAnySetter
public void setAdditionalProperties(String name, Object value) {
this.additionalProperties.put(name, value);
}

}


package com.json.pojo;

import java.util.HashMap;
import java.util.Map;
import javax.annotation.Generated;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@Generated("com.googlecode.jsonschema2pojo")
@JsonPropertyOrder({
"userid",
"title",
"date",
"time"
})
public class Userdatum {

@JsonProperty("userid")
private String userid;
@JsonProperty("title")
private String title;
@JsonProperty("date")
private String date;
@JsonProperty("time")
private String time;
private Map<String, Object> additionalProperties = new HashMap<String, Object>();

@JsonProperty("userid")
public String getUserid() {
return userid;
}

@JsonProperty("userid")
public void setUserid(String userid) {
this.userid = userid;
}

@JsonProperty("title")
public String getTitle() {
return title;
}

@JsonProperty("title")
public void setTitle(String title) {
this.title = title;
}

@JsonProperty("date")
public String getDate() {
return date;
}

@JsonProperty("date")
public void setDate(String date) {
this.date = date;
}

@JsonProperty("time")
public String getTime() {
return time;
}

@JsonProperty("time")
public void setTime(String time) {
this.time = time;
}

@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}

@JsonAnySetter
public void setAdditionalProperties(String name, Object value) {
this.additionalProperties.put(name, value);
}

}

生成的 pojo 一定有问题，但看起来是正确的？

Answer 1

这可行，出于某种原因，即使我的属性与 json 属性匹配，我也需要使用 @JsonProperty，但我认为它们不是必需的。

package com.json.pojo;

import java.io.IOException;

import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.annotate.JsonAutoDetect.Visibility;
import org.codehaus.jackson.annotate.JsonMethod;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.ObjectMapper;

public class ParseJson {

    public static void main(String args[]){

        String str = "{ \"userdata\": [  {\"userid\": \"user1\",\"title\": \"Next weeks preview\", \"date\": \"19/12/2013\",\"time\": \"15:00\"} ] }";

        org.codehaus.jackson.map.ObjectMapper mapper = new org.codehaus.jackson.map.ObjectMapper();     
        mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, true);

        try {
            com.json.pojo.RequestBean user = mapper.readValue(str, com.json.pojo.RequestBean.class);

            System.out.println(user.getToAdd().size());
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

package com.json.pojo;

import java.io.Serializable;
import java.util.List;

import org.codehaus.jackson.annotate.JsonIgnoreProperties;
import org.codehaus.jackson.annotate.JsonProperty;
import org.codehaus.jackson.map.annotate.JsonSerialize;

@JsonSerialize(include = JsonSerialize.Inclusion.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class RequestBean implements Serializable {

    @JsonProperty("userdata")
    private List<SimpleBean> userdata;

    public List<SimpleBean> getToAdd() {
        return userdata;
    }

    public void setToAdd(List<SimpleBean> toAdd) {
        this.userdata = toAdd;
    }


    // constructors, getters, setters
}

package com.json.pojo;

import java.io.Serializable;

import org.codehaus.jackson.annotate.JsonIgnoreProperties;
import org.codehaus.jackson.annotate.JsonProperty;
import org.codehaus.jackson.map.annotate.JsonSerialize;

@JsonSerialize(include = JsonSerialize.Inclusion.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class SimpleBean implements Serializable {

    @JsonProperty("userid")
    private String userid;
    @JsonProperty("title")
    private String title;
    @JsonProperty("date")
    private String date;
    @JsonProperty("time")
    private String time;

    public String getUserid() {
        return userid;
    }
    public void setUserid(String userid) {
        this.userid = userid;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getDate() {
        return date;
    }
    public void setDate(String date) {
        this.date = date;
    }
    public String getTime() {
        return time;
    }
    public void setTime(String time) {
        this.time = time;
    }


}