spring feign with hateos - spring-boot

Question

I am understand more on spring boot with cloud.
It was all fine when I did not not feign dependency to pom.xml. Till then app boot started failing with initially, RelProvider cannot be null! and when I provided linkRelProvider to the depedency. it has not started failing on MessageResolver
exception:
Caused by: java.lang.IllegalArgumentException: MessageResolver must not be null!
at org.springframework.util.Assert.notNull(Assert.java:198) ~[spring-core-5.2.3.RELEASE.jar:5.2.3.RELEASE]
at org.springframework.hateoas.mediatype.hal.Jackson2HalModule$HalLinkListSerializer.<init>(Jackson2HalModule.java:131) ~[spring-hateoas-1.0.3.RELEASE.jar:1.0.3.RELEASE]
at org.springframework.hateoas.mediatype.hal.Jackson2HalModule$HalLinkListSerializer.<init>(Jackson2HalModule.java:121) ~[spring-hateoas-1.0.3.RELEASE.jar:1.0.3.RELEASE]
at org.springframework.hateoas.mediatype.hal.Jackson2HalModule$HalHandlerInstantiator.<init>(Jackson2HalModule.java:753) ~[spring-hateoas-1.0.3.RELEASE.jar:1.0.3.RELEASE]
at org.springframework.hateoas.mediatype.hal.Jackson2HalModule$HalHandlerInstantiator.<init>(Jackson2HalModule.java:738) ~[spring-hateoas-1.0.3.RELEASE.jar:1.0.3.RELEASE]
at org.springframework.hateoas.mediatype.hal.Jackson2HalModule$HalHandlerInstantiator.<init>(Jackson2HalModule.java:722) ~[spring-hateoas-1.0.3.RELEASE.jar:1.0.3.RELEASE]
at org.springframework.cloud.openfeign.hateoas.FeignHalAutoConfiguration.halJacksonHttpMessageConverter(FeignHalAutoConfiguration.java:80) ~[spring-cloud-openfeign-core-2.2.1.RELEASE.jar:2.2.1.RELEASE]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_231]
FeignHalAutoConfiguration sets-up the required dependency which also needs message resolver, which I am struggling to figure out.
pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.2.4.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.test.spring</groupId>
<artifactId>spring-examples</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring-examples</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Hoxton.SR1</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-hateoas</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<!-- <dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency> -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-config</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
<!-- <dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-rest-hal-browser</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.plugin</groupId>
<artifactId>spring-plugin-core</artifactId>
</exclusion>
</exclusions>
</dependency> -->
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-swagger2</artifactId>
<version>2.6.1</version>
</dependency>
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-swagger-ui</artifactId>
<version>2.6.1</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
appConfig.java
package com.test.spring.springexamples;
import java.util.ArrayList;
import java.util.List;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.ResourceBundleMessageSource;
import org.springframework.hateoas.client.LinkDiscoverer;
import org.springframework.hateoas.client.LinkDiscoverers;
import org.springframework.hateoas.mediatype.collectionjson.CollectionJsonLinkDiscoverer;
import org.springframework.hateoas.server.LinkRelationProvider;
import org.springframework.hateoas.server.core.AnnotationLinkRelationProvider;
import org.springframework.plugin.core.SimplePluginRegistry;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.swagger2.annotations.EnableSwagger2;
#Configuration
#EnableSwagger2
public class AppConfig {
#Bean
public ResourceBundleMessageSource messageSource() {
ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
messageSource.setBasename("message");
return messageSource;
}
#Bean
public Docket docket() {
return new Docket(DocumentationType.SWAGGER_2);
}
#Bean
public LinkDiscoverers discoverers() {
List<LinkDiscoverer> plugins = new ArrayList<>();
plugins.add(new CollectionJsonLinkDiscoverer());
return new LinkDiscoverers(SimplePluginRegistry.create(plugins));
}
#Bean
public LinkRelationProvider linkRelationProvider() {
return new AnnotationLinkRelationProvider();
}
}
Please advise what I am doing wrong here.

Answer 1

If you add debug=true to application.properties you will see in your report
HypermediaAutoConfiguration.HypermediaConfiguration:
Did not match:
- #ConditionalOnMissingBean (types: org.springframework.hateoas.client.LinkDiscoverers; SearchStrategy: all) found beans of type 'org.springframework.hateoas.client.LinkDiscoverers' discoverers (OnBeanCondition)
Matched:
- #ConditionalOnClass found required class 'com.fasterxml.jackson.databind.ObjectMapper' (OnClassCondition)
The HypermediaConfiguration backs off because of your custom LinkDiscoverers bean.
Either remove that bean definition or add
#EnableHypermediaSupport(type = EnableHypermediaSupport.HypermediaType.HAL)
On you application class.