使用 Jackson 从 XML 到 POJO 的反序列化问题：没有从字符串值反序列化的字符串参数构造函数/工厂方法
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【中文标题】使用 Jackson 从 XML 到 POJO 的反序列化问题：没有从字符串值反序列化的字符串参数构造函数/工厂方法【英文标题】：Deserialization issue from XML to POJO with Jackson: no String-argument constructor/factory method to deserialize from String value 【发布时间】：2017-05-05 20:14:45 【问题描述】：我有一个 XML 文档，我需要将其转换（反序列化）为 Java POJO。我无法更改 XML 文档的结构。 我使用 Java 8 和 Jackson 框架进行映射。 Gradle 依赖项：
dependencies
compile('com.fasterxml.jackson.dataformat:jackson-dataformat-xml')
compile('org.springframework.boot:spring-boot-starter-freemarker')
compile('org.springframework.boot:spring-boot-starter-web')
providedRuntime('org.springframework.boot:spring-boot-starter-tomcat')
testCompile('org.springframework.boot:spring-boot-starter-test')
包装 XML 文档：
@JacksonXmlRootElement(localName = "rates_response")
public class RatesResponse implements Serializable
private static final long serialVersionUID = 3254688495454519L;
@JacksonXmlProperty(isAttribute = true)
private String b_number = "";
@JacksonXmlProperty(isAttribute = true)
private String l_premium = "";
@JacksonXmlProperty(isAttribute = true)
private String currency = "";
@XmlElement(required = false)
@JacksonXmlProperty
private String c_b_relationship = null;
@JacksonXmlProperty(isAttribute = true)
private String n_of_p_loans = null;
/*
* Key: status_code
* Key: status_explanation
*/
@JacksonXmlElementWrapper
private Map<String, String> message_status = null;
// @XmlElement
@JacksonXmlElementWrapper(useWrapping = false)
private List<RateDetails> rate_details = null;
public RatesResponse()
//GETTERS/SETTERS
Child document (`List<RateDetails> rate_details = null;`):
@JacksonXmlRootElement(localName = "rate_details")
public class RateDetails implements Serializable
private static final long serialVersionUID = 324564684815158619L;
@JacksonXmlProperty
private String r_reference = null;
@JacksonXmlProperty
private String n_of_p_days = null;
@JacksonXmlProperty
private String n_of_instalments = null;
@JacksonXmlProperty
private String n_rate = null;
@JacksonXmlProperty
private String p_p_available = null;
@XmlElement(required = false)
@JacksonXmlProperty
private String i_overrider = null;//not always appears in doc
@JacksonXmlProperty
private String a_fee = null;
@JacksonXmlProperty
private String m_fee = null;
@JacksonXmlProperty
private String t_fees = null;
@JacksonXmlProperty
private String t_c_for_credit = null;
@JacksonXmlProperty
private String d_amount = null;
@JacksonXmlProperty
private String apr = null;
public RateDetails()
//GETTERS/SETTERS
要解析的 XML 文档：
<?xml version="1.0"?>
<!DOCTYPE rates_response SYSTEM "p_f_interface.dtd">
<rates_response b_number="KK5000000000" l_premium="5000.00" currency="GBP" >
<message_status>
<status_code>1000</status_code>
<status_explanation>Success</status_explanation>
</message_status>
<c_b_relationship n_of_p_loans="0"/>
<rate_details>
<r_reference>AS28</r_reference>
<n_of_p_days>28</n_of_p_days>
<n_of_instalments>12</n_of_instalments>
<n_rate>7.00</n_rate>
<p_p_available>NO</p_p_available>
<i_overrider>3.65</i_overrider>
<a_fee>0.00</a_fee>
<m_fee>0.00</m_fee>
<t_fees>0.00</t_fees>
<t_c_for_credit>350.00</t_c_for_credit>
<d_amount>0.00</d_amount>
<apr>16.05</apr>
</rate_details>
</rates_response>
解析文档的方法：
private RatesResponse readRatesDoc()
RatesResponse xmlContainer = null;
ObjectMapper xmlMapper = new XmlMapper();
try
xmlContainer = xmlMapper.readValue(contrUtil.readXmlFile("Rates_Response.xml"), RatesResponse.class);
catch (IOException e)
log.log(Level.SEVERE, "An Exception on parsing XML document", e);
return xmlContainer;
例外：
com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of premium.finance.beanResponse.rates.RateDetails: no String-argument constructor/factory method to deserialize from String value ('16.05')
at [Source: java.io.StringReader@7bd22d0b; line: 1, column: 945] (through reference chain: premium.finance.beanResponse.rates.RatesResponse["rate_details"]->java.util.ArrayList[1])
at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:261) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:1456) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1012) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.ValueInstantiator._createFromStringFallbacks(ValueInstantiator.java:366) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:307) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1278) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:159) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:150) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:277) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:249) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:26) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:499) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:101) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:276) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:140) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.dataformat.xml.deser.WrapperHandlingDeserializer.deserialize(WrapperHandlingDeserializer.java:120) ~[jackson-dataformat-xml-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3789) ~[jackson-databind-2.8.3.jar:2.8.3]
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2833) ~[jackson-databind-2.8.3.jar:2.8.3]
at premium.finance.controller.IndexController.readRatesDoc(IndexController.java:190) [main/:na]
at premium.finance.controller.IndexController.requestIndex(IndexController.java:69) [main/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) [spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:89) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:108) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:784) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:802) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1410) [tomcat-embed-core-8.5.5.jar:8.5.5]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.5.jar:8.5.5]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_91]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_91]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.5.jar:8.5.5]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_91]
第一行说：
no String-argument constructor/factory method to deserialize from String value ('16.05')
它所指的值来自这个标签下：
<apr>16.05</apr>
如果我替换（移动）标签<apr>16.05</apr>，解析器会工作并且不会导致异常。如果我用不同的标签替换标签，仍然会出现同样的异常； 由于某些原因，它仅影响 <rate_details> 包装标签中的最后一个标签。
问题可能是什么？
【问题讨论】：
【参考方案1】：2.10.2 版仍然存在此问题，以下为我修复了此问题。
替换：
ObjectMapper xmlMapper = new XmlMapper();
与：
JacksonXmlModule module = new JacksonXmlModule();
module.setDefaultUseWrapper(false);
XmlMapper xmlMapper = new XmlMapper(module);
来源：
https://github.com/FasterXML/jackson-dataformat-xml/issues/219#issuecomment-286003056
【讨论】：
【参考方案2】：这似乎是一个错误；在这里提交： https://github.com/FasterXML/jackson-dataformat-xml/issues/219
【讨论】：
【参考方案3】：您可以尝试将@JsonCreator 注解添加到您的默认构造函数中，这应该会有所帮助。您的代码中是否有该类的另一个构造函数？
【讨论】：
所以，我将注释添加到我的默认构造函数 RateDetails，但我得到了同样的异常。该类仅包含显式默认构造函数。你还有什么想法吗？以上是关于使用 Jackson 从 XML 到 POJO 的反序列化问题：没有从字符串值反序列化的字符串参数构造函数/工厂方法的主要内容，如果未能解决你的问题，请参考以下文章
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