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JsonMappingException:找不到[simple type, class car.Car$Parts]类型的合适构造函数

by @Hooli

java json jackson jackson-modules jackson-dataformat-xml

我正在尝试将此XML反序列化为Parts对象:

<Parts>
    <Part>
                <Name>gearbox</Name>
                <Year>1990</Year>
    </Part>
    <Part>
                <Name>wheel</Name>
                <Year>2000</Year>
    </Part>
</Parts>

Car.java:

package problem.car;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Car {

    @JsonInclude(JsonInclude.Include.NON_NULL)
    @JsonPropertyOrder({
        "Parts"
    })
    public class Parts {

        @JsonProperty("parts")
        private List<Part> parts = new ArrayList<>();

        @JsonProperty("parts")
        public List<Part> getParts() {
            return parts;
        }

        @JsonProperty("parts")
        public void setParts(List<Part> parts) {
            this.parts = parts;
        }

    }

    @JsonInclude(JsonInclude.Include.NON_NULL)
    @JsonPropertyOrder({
        "Name",
        "Year"
    })
    public class Part {

        @JsonProperty("Name")
        private String Name;
        @JsonProperty("Year")
        private String Year;

        @JsonProperty("Name")
        public String getName() {
            return Name;
        }

        @JsonProperty("Name")
        public void setName(String Name) {
            this.Name = Name;
        }

        @JsonProperty("Year")
        public String getYear() {
            return Year;
        }

        @JsonProperty("Year")
        public void setYear(String Year) {
            this.Year = Year;
        }

    }

    public static void main(String args[]) {
        try {
            String xml = "<Parts>\n"
                    + " <Part>\n"
                    + "             <Name>gearbox</Name>\n"
                    + "             <Year>1990</Year>\n"
                    + " </Part>\n"
                    + " <Part>\n"
                    + "             <Name>wheel</Name>\n"
                    + "             <Year>2000</Year>\n"
                    + " </Part>\n"
                    + "</Parts>";
          Parts parts = (Parts) deserialize(Parts.class, xml);

        } catch (IOException ex) {
            Logger.getLogger(Car.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public static final Object deserialize(final Class clazz, final String xml) throws IOException {
        ObjectMapper xmlMapper = new XmlMapper();
        xmlMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssz"));
        Object object;
        try {
            object = xmlMapper.readValue(xml, clazz);
        } catch (com.fasterxml.jackson.databind.exc.InvalidFormatException ex) {
            xmlMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd"));
            object = xmlMapper.readValue(xml, clazz);
        }
        return object;
    }
}

我的代码没有看到任何问题,但为什么它一直给我以下内容呢?

com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class problem.car.Car$Parts]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)

2个答案

3 by @DwB

<h2>The answer</h2> Part类是一个嵌套的非静态类。 为了实例化它,你必须有一个外部类的实例。

Here is an inner class tutorial

<h2>I-hate-reading answer</h2> 将Part和Parts类移动到自己的java文件,名为Part.java和Parts.java。

0 by @Alex Stybaev

尝试用大写编写它,就像在类体中一样:

@XmlType(name = "Parts", propOrder = {
    "Part"  
})

因为jackson反序列化区分大小写。


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