Jackson 踩坑

Jackson 反序列化对象冲突

Jackson 反序列化对象时，如果所需反序列化对象 Setter 存在重载，则会提示错误。

Code 如下：

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;

public class MyTest {
    @Test
    public void jacksonTest() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(new MyClass(1, "aaa"));
        MyClass w = mapper.readValue(json, MyClass.class);
        System.out.println(w.getCode());
        System.out.println(w.getName());
    }
}

class MyClass {
    private int code;
    private String name;

    MyClass(int code, String name) {
        this.code = code;
        this.name = name;
    }

    public MyClass() {
    }

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public void setCode(short code) {
        this.code = (int) code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

错误信息如下：

com.fasterxml.jackson.databind.JsonMappingException: Conflicting setter definitions for property "code": wode#setCode(1 params) vs wode#setCode(1 params)
 at [Source: (String)"{"code":1,"name":"aaa"}"; line: 1, column: 1]

	at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:306)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:268)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
	at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:142)
	at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:476)
	at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:4389)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4198)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3205)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3173)
	at MyTest.JacksonTest(MyTest.java:11)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	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$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: java.lang.IllegalArgumentException: Conflicting setter definitions for property "code": wode#setCode(1 params) vs wode#setCode(1 params)
	at com.fasterxml.jackson.databind.introspect.POJOPropertyBuilder.getSetter(POJOPropertyBuilder.java:497)
	at com.fasterxml.jackson.databind.introspect.POJOPropertyBuilder.getPrimaryType(POJOPropertyBuilder.java:338)
	at com.fasterxml.jackson.databind.introspect.POJOPropertyBuilder.getRawPrimaryType(POJOPropertyBuilder.java:358)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.filterBeanProps(BeanDeserializerFactory.java:633)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.addBeanProps(BeanDeserializerFactory.java:503)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.buildBeanDeserializer(BeanDeserializerFactory.java:234)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.createBeanDeserializer(BeanDeserializerFactory.java:143)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer2(DeserializerCache.java:411)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer(DeserializerCache.java:349)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:264)
	... 30 more

从报错信息中可以得知，产生错误的根本原因是存在两个 Setter。Jackson 反序列化时，不确定应该选用哪个 Setter 才会产生这个问题。

解决方案

方案一：采用 Gson / fastjson (原因还有待分析源码)

方案二：添加注解，注明反序列化所需setter

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import org.junit.Test;

public class MyTest {
    @Test
    public void jacksonTest() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(new MyClass(1, "aaa"));
        MyClass w = mapper.readValue(json, MyClass.class);
        System.out.println(w.getCode());
        System.out.println(w.getName());
    }
}

class MyClass {
    private int code;
    private String name;

    MyClass(int code, String name) {
        this.code = code;
        this.name = name;
    }

    public MyClass() {
    }

    public int getCode() {
        return code;
    }

    @JsonDeserialize
    public void setCode(int code) {
        this.code = code;
    }

    public void setCode(short code) {
        this.code = (int) code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}