如何解决Jackson反序列化MismatchedInputException异常？

错误核心原因 #

存在两个致命问题导致反序列化失败：

1. 数据类型不匹配：API返回的是单个JSON对象（以{开头），但你强行用Forecast[]数组类型接收，Jackson无法将单个对象转换为数组，直接抛出MismatchedInputException。
2. POJO与JSON结构完全脱节：你定义的Forecast类字段（number/name等）和返回的JSON结构（外层properties包含updated/units等字段）完全对应不上，即使解决数组问题，也无法正确映射数据。

步骤1：重构POJO匹配JSON结构 #

根据返回的JSON层级，创建对应的Java类：

1.1 顶层响应类（对应外层JSON对象） #

@JsonIgnoreProperties(ignoreUnknown = true)
public class ForecastResponse {
    private Properties properties;

    // Getter & Setter
    public Properties getProperties() {
        return properties;
    }

    public void setProperties(Properties properties) {
        this.properties = properties;
    }
}

1.2 Properties类（对应properties字段） #

@JsonIgnoreProperties(ignoreUnknown = true)
public class Properties {
    private String updated;
    private String units;
    private String forecastGenerator;
    private String generatedAt;
    private String updateTime;
    private String validTimes;
    private Elevation elevation;

    // Getters & Setters
    public String getUpdated() { return updated; }
    public void setUpdated(String updated) { this.updated = updated; }
    public String getUnits() { return units; }
    public void setUnits(String units) { this.units = units; }
    public String getForecastGenerator() { return forecastGenerator; }
    public void setForecastGenerator(String forecastGenerator) { this.forecastGenerator = forecastGenerator; }
    public String getGeneratedAt() { return generatedAt; }
    public void setGeneratedAt(String generatedAt) { this.generatedAt = generatedAt; }
    public String getUpdateTime() { return updateTime; }
    public void setUpdateTime(String updateTime) { this.updateTime = updateTime; }
    public String getValidTimes() { return validTimes; }
    public void setValidTimes(String validTimes) { this.validTimes = validTimes; }
    public Elevation getElevation() { return elevation; }
    public void setElevation(Elevation elevation) { this.elevation = elevation; }
}

1.3 Elevation类（对应elevation子字段） #

@JsonIgnoreProperties(ignoreUnknown = true)
public class Elevation {
    private String unitCode;
    private double value;

    // Getters & Setters
    public String getUnitCode() { return unitCode; }
    public void setUnitCode(String unitCode) { this.unitCode = unitCode; }
    public double getValue() { return value; }
    public void setValue(double value) { this.value = value; }
}

步骤2：修正Controller接收逻辑 #

把RestTemplate的返回类型改为ForecastResponse，不再使用数组：

@Controller
@RequestMapping("/test")
public class ConsumeController {
    RestTemplate restTemplate = new RestTemplate();

    @RequestMapping("/show")
    public ModelAndView showForecast() {
        ModelAndView mv = new ModelAndView();
        mv.setViewName("show");

        // 改为接收单个ForecastResponse对象
        ResponseEntity<ForecastResponse> responseEntity = restTemplate.getForEntity("https://api.golde.gov", ForecastResponse.class);
        ForecastResponse responseBody = responseEntity.getBody();

        // 将响应对象传入视图
        mv.addObject("forecastData", responseBody);

        System.out.println("data: " + responseBody);
        return mv;
    }
}

步骤3：调整JSP展示逻辑 #

根据新的数据结构修改EL表达式，示例如下：

<p>Forecast Details:</p>
<div>
    <p>Last Updated: ${forecastData.properties.updated}</p>
    <p>Units: ${forecastData.properties.units}</p>
    <p>Elevation: ${forecastData.properties.elevation.value} ${forecastData.properties.elevation.unitCode}</p>
    <!-- 其他字段可按需添加 -->
</div>

额外说明 #

• @JsonIgnoreProperties(ignoreUnknown = true)：确保API返回未定义的额外字段时，Jackson不会抛出反序列化错误。
• 如果你原本期望API返回Forecast数组，需要确认API的正确端点——当前调用的https://api.golde.gov返回的是单个对象，并非数组。

内容的提问来源于stack exchange，提问作者Khanh Luong Van