JSON parse error: Cannot construct instance of `org.test.dtos.TestChild` (although at least one Creator exists)

Question

I'm getting an error

2020-01-28 18:19:21,311 DEBUG [http-nio-8069-exec-8] ServletInvocableHandlerMethod : Could not resolve parameter [0] in public org.springframework.http.ResponseEntity<org.test.dtos.TestResponse> org.test.controllers.TestController.testRoute(org.test.dtos.TestRequest): JSON parse error: Cannot construct instance of `org.test.dtos.TestChild` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('0'); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `org.test.dtos.TestChild` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('0')
 at [Source: (PushbackInputStream); line: 5, column: 18] (through reference chain: org.test.dtos.TestRequest["children"]->org.test.dtos.TestChildWrapper["child"]->java.util.HashSet[0])
2020-01-28 18:19:21,314 WARN  [http-nio-8069-exec-8] DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot construct instance of `org.test.dtos.TestChild` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('0'); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `org.test.dtos.TestChild` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('0')
 at [Source: (PushbackInputStream); line: 5, column: 18] (through reference chain: org.test.dtos.TestRequest["children"]->org.test.dtos.TestChildWrapper["child"]->java.util.HashSet[0])]

when sending:

<?xml version="1.0" encoding="UTF-8"?>
<TestRequest>
    <children>
        <child>
            <childStuffA>0</childStuffA>
            <childStuffB>0</childStuffB>
            <childStuffC>string</childStuffC>
        </child>
    </children>
    <doubleProperty>0</doubleProperty>
    <id>0</id>
    <longProperty>0</longProperty>
    <stringProperty>string</stringProperty>
</TestRequest>

to the route /test/api/apply

I wrote a sample code on GitHub with the particular issue.

I am using Spring boot 2.2.4-RELEASE and Spring Cloud Hoxton.SR1, you get the pom over there. https://github.com/cmeon/spring-issue-test/tree/master

Avi · Accepted Answer · 2020-01-29 09:34:22Z

Okay I checked your code in github and found the issue, so when you try to deserialise a Collections you have to mention that attribute with @JacksonXmlElementWrapper.

Do add it like below

TestChildWrapper.class

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@AllArgsConstructor
@Data
@NoArgsConstructor
public class TestChildWrapper implements Serializable {

  private static final long serialVersionUID = 1L;

  @JacksonXmlProperty(localName = "child")
  @JacksonXmlElementWrapper(useWrapping = false)
  private Set<TestChild> child = new HashSet<>();
}

It works..

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JSON parse error: Cannot construct instance of `org.test.dtos.TestChild` (although at least one Creator exists)

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TestChildWrapper.class

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