Spring Boot中Java反序列化XML时无法构造实例问题

报错信息 #

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of <code>com.example.demo.models.responses.FxRate</code> (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('EU')

问题根源 #

1. XML命名空间未处理：返回的XML所有节点都属于http://www.lb.lt/WebServices/FxRates命名空间，但实体类未配置对应注解，Jackson无法正确识别节点归属
2. 集合节点注解缺失：FxRates中的FxRate集合、FxRate中的CcyAmt集合缺少Jackson XML专属注解，导致Jackson错误将子节点（如<Tp>EU</Tp>）的文本值当作要赋值给FxRate对象的字符串
3. 注解使用错误：xmlns是根节点属性而非子节点，原代码用@JsonProperty标记错误；JsonPropertyOrder配置无效且顺序错误

修正方案及代码 #

1. 修正FxRates类 #

package com.example.demo.models.responses;

import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;

import java.util.List;

@JacksonXmlRootElement(localName = "FxRates", namespace = "http://www.lb.lt/WebServices/FxRates")
public class FxRates {
    // 关闭集合包装，直接解析同名子节点为集合元素
    @JacksonXmlElementWrapper(useWrapping = false)
    @JacksonXmlProperty(localName = "FxRate", namespace = "http://www.lb.lt/WebServices/FxRates")
    private List<FxRate> fxRate;

    // 标记xmlns为节点属性
    @JacksonXmlProperty(isAttribute = true, localName = "xmlns")
    private String xmlns;

    public FxRates() {}

    public FxRates(List<FxRate> fxRate, String xmlns) {
        this.fxRate = fxRate;
        this.xmlns = xmlns;
    }

    // Getter & Setter
    public List<FxRate> getFxRate() {
        return fxRate;
    }

    public void setFxRate(List<FxRate> fxRate) {
        this.fxRate = fxRate;
    }

    public String getXmlns() {
        return xmlns;
    }

    public void setXmlns(String xmlns) {
        this.xmlns = xmlns;
    }
}

2. 修正FxRate类 #

package com.example.demo.models.responses;

import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;

import java.util.List;

public class FxRate {
    @JacksonXmlProperty(localName = "Tp", namespace = "http://www.lb.lt/WebServices/FxRates")
    private String tp;

    @JacksonXmlProperty(localName = "Dt", namespace = "http://www.lb.lt/WebServices/FxRates")
    private String dt;

    @JacksonXmlElementWrapper(useWrapping = false)
    @JacksonXmlProperty(localName = "CcyAmt", namespace = "http://www.lb.lt/WebServices/FxRates")
    private List<CcyAmt> ccyAmt;

    public FxRate() {}

    public FxRate(String tp, String dt, List<CcyAmt> ccyAmt) {
        this.tp = tp;
        this.dt = dt;
        this.ccyAmt = ccyAmt;
    }

    // Getter & Setter
    public String getTp() {
        return tp;
    }

    public void setTp(String tp) {
        this.tp = tp;
    }

    public String getDt() {
        return dt;
    }

    public void setDt(String dt) {
        this.dt = dt;
    }

    public List<CcyAmt> getCcyAmt() {
        return ccyAmt;
    }

    public void setCcyAmt(List<CcyAmt> ccyAmt) {
        this.ccyAmt = ccyAmt;
    }
}

3. 修正CcyAmt类 #

package com.example.demo.models.responses;

import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;

public class CcyAmt {
    @JacksonXmlProperty(localName = "Ccy", namespace = "http://www.lb.lt/WebServices/FxRates")
    private String ccy;

    @JacksonXmlProperty(localName = "Amt", namespace = "http://www.lb.lt/WebServices/FxRates")
    private String amt;

    public CcyAmt() {}

    public CcyAmt(String ccy, String amt) {
        this.ccy = ccy;
        this.amt = amt;
    }

    // Getter & Setter
    public String getCcy() {
        return ccy;
    }

    public void setCcy(String ccy) {
        this.ccy = ccy;
    }

    public String getAmt() {
        return amt;
    }

    public void setAmt(String amt) {
        this.amt = amt;
    }
}

4. 优化Controller中的XmlMapper配置 #

添加忽略未知节点的配置，避免因XML新增节点导致反序列化失败：

XmlMapper xmlMapper = XmlMapper.builder()
        .configure(com.fasterxml.jackson.databind.DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
        .build();

内容的提问来源于stack exchange，提问作者Skully1