（尽管至少存在一个 Creator）：没有字符串参数构造函数/工厂方法可以从字符串值（'12'）反序列化答案

【问题标题】：(although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('12')（尽管至少存在一个 Creator）：没有字符串参数构造函数/工厂方法可以从字符串值（'12'）反序列化
【发布时间】：2020-11-11 15:44:04
【问题描述】：

以下方法 convertToObject 使用 Jackson 将 XML 转换为 Object。我收到以下错误：

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `com.test.Student` 
(although at least one Creator exists):no String-argument constructor/factory method to deserialize from String value ('12')

以下是核心类：

    private Students convertToObject(String xml) {
    XmlMapper xmlMapper = new XmlMapper();
    Students matchedObjects = null;

    try {
         System.out.println(xml);
         matchedObjects = xmlMapper.readValue(xml, Students.class);
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }

    System.out.println(matchedObjects);

    return matchedObjects;
}

这是输入 XML：

<students>
<student><id>12</id><surname>DOE</surname><givenName>JOHN</givenName><marks>98.928</marks></student>
<student><id>13</id><surname>PRICE</surname><givenName>MIKE</givenName><marks>90.8444</marks> </student>
</students>

这是两个 POJO：

@Getter @Setter @AllArgsConstructor @NoArgsConstructor @ToString
@JacksonXmlRootElement(localName = "student")
public class Student {
    String id;
    String givenName;
    String surname;
    String marks;
}

@Getter @Setter @AllArgsConstructor @NoArgsConstructor @ToString
@JacksonXmlRootElement(localName = "students")
public class Students {
    @JacksonXmlProperty(localName = "student")
    private List<Student> student;
}

这是pom文件中的依赖。

    <dependency>
        <groupId>com.fasterxml.jackson.dataformat</groupId>
        <artifactId>jackson-dataformat-xml</artifactId>
        <version>2.11.1</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.11.1</version>
    </dependency>

【问题讨论】：

标签： java json xml jackson

【解决方案1】：

您不需要Students 包装类。将此XML 有效负载反序列化为List<Student>：

CollectionType studentsListType = xmlMapper.getTypeFactory().constructCollectionType(List.class, Student.class);
List<Student> students = xmlMapper.readValue(xmlFile, studentsListType);

【讨论】：