解决json串和实体类字段不一致的问题

这里我们对json串和实体类字段不一致的情况进行一个测试：

首先，我们建立一个实体类：这里简单定义了name,sex,age三个属性，以及get set tostring方法。

public class Student { private String name ; private String sex ; private Integer age ; public String getName () { return name ; } public String getSex () { return sex ; } public Integer getAge () { return age ; } public void setName ( String name ) { this . name = name ; } public void setSex ( String sex ) { this . sex = sex ; } public void setAge ( Integer age ) { this . age = age ; } @Override public String toString () { return "Student [name=" + name + ", sex=" + sex + ", age=" + age + "]" ; } }

首先用fastjson进行测试：

当字段少于实体类字段：正常通过，没有的字段会被赋予默认值

//fastjson 少字段 @Test public void testFastjson01 () { String jsonStr = "{\"age\":18,\"name\":\"zhangsan\"}" ; Student stu = JSON . parseObject ( jsonStr , Student . class ); System . out . println ( stu ); // Student [name=zhangsan, sex=null, age=18] }

当字段多于实体类字段：正常通过，没有的字段不会被反序列化到对象中

//fastjson 多字段 @Test public void testFastjson02 () { String jsonStr = "{\"age\":20,\"name\":\"lisi\",\"sex\":\"男\",\"hobby\":\"basketball\"}" ; Student stu = JSON . parseObject ( jsonStr , Student . class ); System . out . println ( stu ); // Student [name=lisi, sex=男, age=20] }

再用jackson进行测试：

当字段少于实体类字段：正常通过，没有的字段会被赋予默认值

//jackson 少字段 @Test public void testJackson01 () throws Exception { String jsonStr = "{\"age\":18,\"name\":\"zhangsan\"}" ; ObjectMapper om = new ObjectMapper (); Student stu = om . readValue ( jsonStr , Student . class ); System . out . println ( stu ); // Student [name=zhangsan, sex=null, age=18] }

当字段多于实体类字段：

//jackson 多字段 @Test public void testJackson02 () throws Exception { String jsonStr = "{\"age\":20,\"name\":\"lisi\",\"sex\":\"男\",\"hobby\":\"basketball\"}" ; ObjectMapper om = new ObjectMapper (); Student stu = om . readValue ( jsonStr , Student . class ); System . out . println ( stu ); }

此时会报错，这个错翻译过来就是，一个无法识别的field。

com . fasterxml . jackson . databind . exc . UnrecognizedPropertyException : Unrecognized field "hobby" ( class com . cyj . demo03 . Student ), not marked as ignorable ( 3 known properties : "name" , "sex" , "age" ]) at [ Source : { "age" : 20 , "name" : "lisi" , "sex" : "男" , "hobby" : "basketball" }; line : 1 , column : 44 ] ( through reference chain : com . cyj . demo03 . Student [ "hobby" ]) at com . fasterxml . jackson . databind . exc . UnrecognizedPropertyException . from ( UnrecognizedPropertyException . java : 51 ) at com . fasterxml . jackson . databind . DeserializationContext . reportUnknownProperty ( DeserializationContext . java : 817 ) at com . fasterxml . jackson . databind . deser . std . StdDeserializer . handleUnknownProperty ( StdDeserializer . java : 958 ) at com . fasterxml . jackson . databind . deser . BeanDeserializerBase . handleUnknownProperty ( BeanDeserializerBase . java : 1324 ) at com . fasterxml . jackson . databind . deser . BeanDeserializerBase . handleUnknownVanilla ( BeanDeserializerBase . java : 1302 ) at com . fasterxml . jackson . databind . deser . BeanDeserializer . vanillaDeserialize ( BeanDeserializer . java : 249 ) at com . fasterxml . jackson . databind . deser . BeanDeserializer . deserialize ( BeanDeserializer . java : 136 ) at com . fasterxml . jackson . databind . ObjectMapper . _readMapAndClose ( ObjectMapper . java : 3564 ) at com . fasterxml . jackson . databind . ObjectMapper . readValue ( ObjectMapper . java : 2580 ) at com . cyj . demo03 . TestJson . testJackson02 ( TestJson . java : 40 ) at sun . reflect . NativeMethodAccessorImpl . invoke0 ( Native Method ) at sun . reflect . NativeMethodAccessorImpl . invoke ( NativeMethodAccessorImpl . java : 62 ) at sun . reflect . DelegatingMethodAccessorImpl . invoke ( DelegatingMethodAccessorImpl . java : 43 ) at java . lang . reflect . Method . invoke ( Method . java : 497 ) at org . junit . runners . model . FrameworkMethod$1 . runReflectiveCall ( FrameworkMethod . java : 50 ) at org . junit . internal . runners . model . ReflectiveCallable . run ( ReflectiveCallable . java : 12 ) at org . junit . runners . model . FrameworkMethod . invokeExplosively ( FrameworkMethod . java : 47 ) at org . junit . internal . runners . statements . InvokeMethod . evaluate ( InvokeMethod . java : 17 ) at org . junit . runners . ParentRunner . runLeaf ( ParentRunner . java : 325 ) at org . junit . runners . BlockJUnit4ClassRunner . runChild ( BlockJUnit4ClassRunner . java : 78 ) at org . junit . runners . BlockJUnit4ClassRunner . runChild ( BlockJUnit4ClassRunner . java : 57 ) at org . junit . runners . ParentRunner$3 . run ( ParentRunner . java : 290 ) at org . junit . runners . ParentRunner$1 . schedule ( ParentRunner . java : 71 ) at org . junit . runners . ParentRunner . runChildren ( ParentRunner . java : 288 ) at org . junit . runners . ParentRunner . access$000 ( ParentRunner . java : 58 ) at org . junit . runners . ParentRunner$2 . evaluate ( ParentRunner . java : 268 ) at org . junit . runners . ParentRunner . run ( ParentRunner . java : 363 ) at org . eclipse . jdt . internal . junit4 . runner . JUnit4TestReference . run ( JUnit4TestReference . java : 86 ) at org . eclipse . jdt . internal . junit . runner . TestExecution . run ( TestExecution . java : 38 ) at org . eclipse . jdt . internal . junit . runner . RemoteTestRunner . runTests ( RemoteTestRunner . java : 538 ) at org . eclipse . jdt . internal . junit . runner . RemoteTestRunner . runTests ( RemoteTestRunner . java : 760 ) at org . eclipse . jdt . internal . junit . runner . RemoteTestRunner . run ( RemoteTestRunner . java : 460 ) at org . eclipse . jdt . internal . junit . runner . RemoteTestRunner . main ( RemoteTestRunner . java : 206 )

由此可见，在默认情况下，jackson是不支持json串的字段多于实体类字段的，但是，jackson也提供了解决方案，我们在实体类上，添加注解@JsonIgnoreProperties，这个注解有一个ignoreUnknown属性，默认值为false，我们可以将它改为true,这样jackson在反序列化的时候，就会忽略掉不存在的属性了。（@JsonIgnoreProperties(ignoreUnknown = true)）

补充：json字段名不一致的问题

1.场景

项目开发过程中，有时候可能要对接第三方平台，可能就会存在字段名不一样的问题，而双方的字段名不一致， 而代码开发已经有一段时间勒，如果就因为字段名不一样的问题，双方改成属性名一致，这样改动量太大，也不保险，下面我来接手一下，针对这种场景，如果解决。

假设： 系统通过http对接，传的是json。有一个参数"名称"

第三方平台：name

开发环境：userName

直接通过实体类映射，不用说肯定有问题

2.解决方法

@JsonProperty ( "name" ) private String userName ;

在实体类的属性上增加一个注解就可以解决这种问题。

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。如有错误或未考虑完全的地方，望不吝赐教。

原文链接：https://blog.csdn.net/MrHamster/article/details/85268990

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