Jackson Json 并没有这样的方法错误

Question

我正在尝试使用 jackson 来序列化和反序列化 POJO。从 POJO 转为 JSON 效果很好，但反之则不行。

我有一个 POJO

public class Event {
  private String kind;

  public String getKind() {
    return kind;
  }

  public void setKind(String kind) {
    this.kind = kind;
  }
}

为了运行和测试，我运行包 calendar.model；

Event event = new Event();
event.setKind("This is a kind");
String json = objectMapper.writeValueAsString(event); 
// RETURNS: "{\"kind\":\"This is a kind\"}"

objectMapper.readValue(json, Event.class);

抛出异常

java.lang.NoSuchMethodError: com.fasterxml.jackson.core.JsonParser.getValueAsString()Ljava/lang/String;
at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:24)
at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:11)
at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375)
at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2796)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1942)
at calendar.controller.RootController.details(RootController.java:59)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:100)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:604)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:565)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)

我已经尽我所能让 JSON 到 POJO 工作，但它不会。如果我从 JSON 映射到 Map 类型，它确实有效。

感谢您的帮助

编辑

这是我的依赖项中杰克逊的一个 grep

± > mvn dependency:tree | grep jackson                                                                                                                       -I- 
[INFO] +- com.google.http-client:google-http-client-jackson2:jar:1.13.1-beta:compile
[INFO] |  \- com.fasterxml.jackson.core:jackson-core:jar:2.0.5:compile
[INFO] |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.1.1:compile
[INFO] |  |  +- com.fasterxml.jackson.dataformat:jackson-dataformat-xml:jar:2.1.1:compile
[INFO] |  |  |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.1.1:compile
[INFO] |  |  |  +- com.fasterxml.jackson.module:jackson-module-jaxb-annotations:jar:2.1.0:compile

貌似除了jackson2之外没有其他版本的jackson了。

正在运行的完整方法是一个弹簧控制器方法。

@RequestMapping(value = "/")
  public Event root() throws IOException {
    Event event = new Event();
    event.setKind("This is a kind");
    String json = objectMapper.writeValueAsString(event);
    // RETURNS: "{\"kind\":\"This is a kind\"}"

    Event mapped = objectMapper.readValue(json, Event.class);
    return mapped;
  }

Answer 1

看起来问题是您获得了不兼容的jackson-core 和jackson-databind 版本 - jackson-core 2.0.5 被引入，但我相信至少需要 2.1.0。

异常的第一行告诉你它找不到方法JsonParser.getValueAsString()，查看2.0.5的API文档，该方法确实不存在。好像是在2.1.0中添加的。

因此，您需要修复依赖关系 - 很可能通过排除 2.0.5 并包括 2.1.0 来解决。