Cannot deserialize value of type `java.time.OffsetDateTime` from String in openapi client

I have a spring boot application with a java client generated via the gradle plugin:

openApiGenerate {
    generatorName = "java"
    inputSpec = specsYml
    outputDir = "$buildDir/generated".toString()
    apiPackage = "com.customapi.api"
    invokerPackage = "com.customapi.invoker"
    modelPackage = "com.customapi.model"
    configOptions = [
        dateLibrary: "java8",
        library    : "resttemplate"
    ]
}

I have chosen "java8" as dateLibrary as that seems to be the preferred one for a project with java 1.8.

With that generated client I'm executing a request that returns an object that holds a timestamp.
I get the following error:

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    ...
Caused by: org.springframework.web.client.RestClientException: Error while extracting response for type [class com.customapi.model.Info] and content type [application/json];
    ...
Caused by: org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize value of type `java.time.OffsetDateTime` from String "2020-07-21T12:12:23.000+0200": ...
   ...
...
Caused by: com.fasterxml.jackson.databind.exc.InvalidFormatException: Cannot deserialize value of type `java.time.OffsetDateTime` from String "2020-07-21T12:12:23.000+0200": Failed to deserialize java.time.OffsetDateTime: (java.time.format.DateTimeParseException) Text '2020-07-21T12:12:23.000+0200' could not be parsed at index 23
 at [Source: (ByteArrayInputStream); line: 1, column: 84] (through reference chain: com.customapi.model.Info["buildTimestamp"])
	at com.fasterxml.jackson.databind.exc.InvalidFormatException.from(InvalidFormatException.java:67) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.DeserializationContext.weirdStringException(DeserializationContext.java:1679) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.DeserializationContext.handleWeirdStringValue(DeserializationContext.java:935) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.datatype.jsr310.deser.JSR310DeserializerBase._handleDateTimeException(JSR310DeserializerBase.java:86) ~[jackson-datatype-jsr310-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.datatype.jsr310.deser.InstantDeserializer.deserialize(InstantDeserializer.java:218) ~[jackson-datatype-jsr310-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.datatype.jsr310.deser.InstantDeserializer.deserialize(InstantDeserializer.java:50) ~[jackson-datatype-jsr310-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:369) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4218) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3267) ~[jackson-databind-2.10.3.jar:2.10.3]
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:269) ~[spring-web-5.2.7.RELEASE.jar:5.2.7.RELEASE]
	... 17 common frames omitted
Caused by: java.time.format.DateTimeParseException: Text '2020-07-21T12:12:23.000+0200' could not be parsed at index 23
	at java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:1949) ~[na:1.8.0_151]
	at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1777) ~[na:1.8.0_151]
	at com.fasterxml.jackson.datatype.jsr310.deser.InstantDeserializer.deserialize(InstantDeserializer.java:212) ~[jackson-datatype-jsr310-2.10.3.jar:2.10.3]
	... 24 common frames omitted

The relevant parts of the Info class in question:

...
@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", date = "2020-07-26T14:09:54.137+02:00[Europe/Berlin]")
public class Info {
    ...
    public static final String JASON_PROPERTY_BUILD_TIMESTAMP = "buildTimestamp";
    private OffsetDateTime buildTimestamp;
    ...
    public Info buildTimestamp(OffsetDateTime buildTimestamp) {
        this.buildTimestamp = buildTimestamp;
        return this;
    }

    public void setBuildTimestamp(OffsetDateTime buildTimestamp) {
        this.buildTimestamp = buildTimestamp;
    }
    ...
}

Both setter methods accept OffsetDateTime objects and have no annotations so the conversion must happen elsewhere. The input String again is "2020-07-21T12:12:23.000+0200".
relevant dependencies are

ext {
    swagger_annotations_version = "1.5.22"
    jackson_version = "2.10.3"
    jackson_databind_version = "2.10.3"
    jackson_databind_nullable_version = "0.2.1"
}

dependencies {
    compile "io.swagger:swagger-annotations:$swagger_annotations_version"
    compile "com.fasterxml.jackson.core:jackson-core:$jackson_version"
    compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
    compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
    compile "com.fasterxml.jackson.jaxrs:jackson-jaxrs-json-provider:$jackson_version"
    compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
    compile "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:$jackson_version"
}

There seem to be a lot of problems with jackson and java 8 and most solutions on this site seem to be adding annotations. But I doubt that modifying generated code is the proper solution. Did I overlook an important parameter when generating the client? Does the server supply the wrong format? How can I investigate this?

Update:

When I switch dateLibrary to legacy it works, so I think I receive the correct data.

There is a bug in the (jaxrs) server generator https://github.com/swagger-api/swagger-codegen/issues/3648#issuecomment-244056314 that has the server send out wrongly formatted (without colon) date-time. My solution was to use the legacy dateLibrary for the client which can handle the wrong format.

Following my comment in the question, I realize you don't need a Jackson annotation. You just need to adjust the setter. Here is a basic demo:

Assume the following class:

import java.time.OffsetDateTime;
//import com.fasterxml.jackson.annotation.JsonSetter;
import java.time.format.DateTimeFormatter;

public class MyOdt {
    
    private OffsetDateTime odt;

    public OffsetDateTime getOdt() {
        return odt;
    }

    //@JsonSetter("odt")
    public void setOdt(String odtString) {
        final String pattern = "yyyy-MM-dd'T'HH:mm:ss.SSSxx";
        DateTimeFormatter dtfB = DateTimeFormatter.ofPattern(pattern);
        this.odt = OffsetDateTime.parse(odtString, dtfB);
    }
    
}

The class will be created from a JSON fragment such as this:

String jsonTest = "{ \"odt\" : \"2020-07-21T12:12:23.000+0200\" }";

The object mapper:

ObjectMapper objectMapper = new ObjectMapper()
        .registerModule(new JavaTimeModule())
        .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

MyOdt odtTest = objectMapper.readValue(jsonTest, MyOdt.class);

For reference, here is the original comment in the question:

> An observation: That is not a valid string to be parsed by OffsetDateTime.parse() because the default datetime format expects the offset to have a colon in it: +02:00. So, this works: OffsetDateTime.parse("2020-07-21T12:12:23.000+02:00")

I was helped by switching dateLibrary to java8-localdatetime

See also here.