Error message when trying to implement Swagger in my Java Spring API

Question

After adding Swagger in my API made with Spring, i'm getting the following error message when running :

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2020-05-15 13:51:39.631 ERROR 13804 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

***************************
APPLICATION FAILED TO START
***************************

Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

    org.springframework.data.rest.core.support.UnwrappingRepositoryInvokerFactory.<init>(UnwrappingRepositoryInvokerFactory.java:57)

The following method did not exist:

    'org.springframework.plugin.core.PluginRegistry org.springframework.plugin.core.PluginRegistry.of(java.util.List)'

The method's class, org.springframework.plugin.core.PluginRegistry, is available from the following locations:

    jar:file:/home/gabriel/.m2/repository/org/springframework/plugin/spring-plugin-core/1.2.0.RELEASE/spring-plugin-core-1.2.0.RELEASE.jar!/org/springframework/plugin/core/PluginRegistry.class

It was loaded from the following location:

    file:/home/gabriel/.m2/repository/org/springframework/plugin/spring-plugin-core/1.2.0.RELEASE/spring-plugin-core-1.2.0.RELEASE.jar


Action:

Correct the classpath of your application so that it contains a single, compatible version of org.springframework.plugin.core.PluginRegistry


Process finished with exit code 1

My pom.xml file :

<?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>2.2.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.tropicalia</groupId>
    <artifactId>users_api</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>users_api</name>
    <description>1st users API with Spring</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

        <dependencies>

<dependency>
    <groupId>org.springframework.plugin</groupId>
    <artifactId>spring-plugin-core</artifactId>
    <version>1.2.0.RELEASE</version>
</dependency>
<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger2</artifactId>
    <version>2.9.2</version>
</dependency>
<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger-ui</artifactId>
    <version>2.9.2</version>
</dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-rest</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-rest-hal-browser</artifactId>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.8</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.modelmapper</groupId>
            <artifactId>modelmapper</artifactId>
            <version>2.3.5</version>
        </dependency>

        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct</artifactId>
            <version>1.3.1.Final</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.xmlunit</groupId>
            <artifactId>xmlunit-core</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <annotationProcessorPaths>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>1.3.1.Final</version>
                        </path>
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                            <version>1.18.8</version>
                        </path>
                    </annotationProcessorPaths>
                </configuration>
            </plugin>


        </plugins>
    </build>

</project>

Coding wise, i think everything is alright. I'm almost sure that the solution to this problem is in the dependencies of the maven file.

I tried some solutions that i've found online but none of them worked, would be grateful if someone could share some knowledge with me on this one.

Answer 1

So i've found the solution to the problem and it was all about incompatibility between the versions of the software i'm using in my api.

I changed my spring version to 2.3.0 and added the following dependency on my pom file :

<dependency>
      <groupId>org.javassist</groupId>
      <artifactId>javassist</artifactId>
      <version>3.23.1-GA</version>
    </dependency>

Credit : https://github.com/spring-projects/spring-boot/issues/14610

Answer 2

The following dependency can be removed from your POM file:

<dependency>
    <groupId>org.springframework.plugin</groupId>
    <artifactId>spring-plugin-core</artifactId>
    <version>1.2.0.RELEASE</version>
</dependency>

This dependency is already a transitive dependency of the Swagger dependencies (compile scope). Adding this dependency separately creates conflict with the spring-boot-starter-data-rest dependency at runtime. By removing it from your POM file, you allow Maven to pick the correct version (which will be the one compatible with Spring Boot, since it is the latest). Currently the version is forced to 1.2.0.RELEASE, while Spring Boot probably requires 2.0.0.RELEASE.

Swagger only requires the following dependencies in your POM file:

<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger2</artifactId>
    <version>2.9.2</version>
</dependency>
<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger-ui</artifactId>
    <version>2.9.2</version>
</dependency>

In case your application does require the spring-plugin-core dependency, you can bump the version instead of removing it. Adding an exclusion for it to the Swagger dependencies would then also be the proper thing to do.