ResolutionException when running Spring Boot as Java module

[jollycar]

Problem

I get a ResolutionException on startup when I create a Spring boot application with Spring Initializr with both spring-boot-starter-webflux and spring-boot-starter-web dependencies and I turn the project into a Java module (Project Jigsaw), by adding a module-info.java

module demo {
    requires spring.boot.autoconfigure;
    requires spring.boot;
}

The error:

java.lang.module.ResolutionException: 
Modules jakarta.el and org.apache.tomcat.embed.jasper.el export package javax.el to module spring.boot.starter.web

Cause

When using both spring-boot-starter-webflux and spring-boot-starter-web dependencies, there is a split package: javax.el

This package is present in both jakarta.el-3.0.3.jar and tomcat-embed-el-9.0.30.jar

Versions

Java version: OpenJDK 11.0.4+11 (AdoptOpenJDK Hotspot)
Spring Boot project, from Spring Initializr:
Startup command (from IntelliJ):

/usr/lib/jvm/jdk-11.0.4+11/bin/java -XX:TieredStopAtLevel=1 -noverify -Dspring.output.ansi.enabled=always -Dcom.sun.management.jmxremote -Dspring.jmx.enabled=true -Dspring.liveBeansView.mbeanDomain -Dspring.application.admin.enabled=true -Dfile.encoding=UTF-8 -p /home/ivo/Downloads/demo/target/classes:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter-web/2.2.4.RELEASE/spring-boot-starter-web-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter/2.2.4.RELEASE/spring-boot-starter-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot/2.2.4.RELEASE/spring-boot-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/2.2.4.RELEASE/spring-boot-autoconfigure-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter-logging/2.2.4.RELEASE/spring-boot-starter-logging-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar:/home/ivo/.m2/repository/ch/qos/logback/logback-core/1.2.3/logback-core-1.2.3.jar:/home/ivo/.m2/repository/org/apache/logging/log4j/log4j-to-slf4j/2.12.1/log4j-to-slf4j-2.12.1.jar:/home/ivo/.m2/repository/org/apache/logging/log4j/log4j-api/2.12.1/log4j-api-2.12.1.jar:/home/ivo/.m2/repository/org/slf4j/jul-to-slf4j/1.7.30/jul-to-slf4j-1.7.30.jar:/home/ivo/.m2/repository/jakarta/annotation/jakarta.annotation-api/1.3.5/jakarta.annotation-api-1.3.5.jar:/home/ivo/.m2/repository/org/yaml/snakeyaml/1.25/snakeyaml-1.25.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter-json/2.2.4.RELEASE/spring-boot-starter-json-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.10.2/jackson-databind-2.10.2.jar:/home/ivo/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.10.2/jackson-annotations-2.10.2.jar:/home/ivo/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.10.2/jackson-core-2.10.2.jar:/home/ivo/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jdk8/2.10.2/jackson-datatype-jdk8-2.10.2.jar:/home/ivo/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jsr310/2.10.2/jackson-datatype-jsr310-2.10.2.jar:/home/ivo/.m2/repository/com/fasterxml/jackson/module/jackson-module-parameter-names/2.10.2/jackson-module-parameter-names-2.10.2.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter-tomcat/2.2.4.RELEASE/spring-boot-starter-tomcat-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/9.0.30/tomcat-embed-core-9.0.30.jar:/home/ivo/.m2/repository/org/apache/tomcat/embed/tomcat-embed-el/9.0.30/tomcat-embed-el-9.0.30.jar:/home/ivo/.m2/repository/org/apache/tomcat/embed/tomcat-embed-websocket/9.0.30/tomcat-embed-websocket-9.0.30.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter-validation/2.2.4.RELEASE/spring-boot-starter-validation-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/jakarta/validation/jakarta.validation-api/2.0.2/jakarta.validation-api-2.0.2.jar:/home/ivo/.m2/repository/org/hibernate/validator/hibernate-validator/6.0.18.Final/hibernate-validator-6.0.18.Final.jar:/home/ivo/.m2/repository/org/jboss/logging/jboss-logging/3.4.1.Final/jboss-logging-3.4.1.Final.jar:/home/ivo/.m2/repository/com/fasterxml/classmate/1.5.1/classmate-1.5.1.jar:/home/ivo/.m2/repository/org/springframework/spring-web/5.2.3.RELEASE/spring-web-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/spring-beans/5.2.3.RELEASE/spring-beans-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/spring-webmvc/5.2.3.RELEASE/spring-webmvc-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/spring-aop/5.2.3.RELEASE/spring-aop-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/spring-context/5.2.3.RELEASE/spring-context-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/spring-expression/5.2.3.RELEASE/spring-expression-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter-webflux/2.2.4.RELEASE/spring-boot-starter-webflux-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/boot/spring-boot-starter-reactor-netty/2.2.4.RELEASE/spring-boot-starter-reactor-netty-2.2.4.RELEASE.jar:/home/ivo/.m2/repository/io/projectreactor/netty/reactor-netty/0.9.4.RELEASE/reactor-netty-0.9.4.RELEASE.jar:/home/ivo/.m2/repository/io/netty/netty-codec-http/4.1.45.Final/netty-codec-http-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-common/4.1.45.Final/netty-common-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-buffer/4.1.45.Final/netty-buffer-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-transport/4.1.45.Final/netty-transport-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-resolver/4.1.45.Final/netty-resolver-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-codec/4.1.45.Final/netty-codec-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-codec-http2/4.1.45.Final/netty-codec-http2-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-handler/4.1.45.Final/netty-handler-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-handler-proxy/4.1.45.Final/netty-handler-proxy-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-codec-socks/4.1.45.Final/netty-codec-socks-4.1.45.Final.jar:/home/ivo/.m2/repository/io/netty/netty-transport-native-epoll/4.1.45.Final/netty-transport-native-epoll-4.1.45.Final-linux-x86_64.jar:/home/ivo/.m2/repository/io/netty/netty-transport-native-unix-common/4.1.45.Final/netty-transport-native-unix-common-4.1.45.Final.jar:/home/ivo/.m2/repository/org/glassfish/jakarta.el/3.0.3/jakarta.el-3.0.3.jar:/home/ivo/.m2/repository/org/springframework/spring-webflux/5.2.3.RELEASE/spring-webflux-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/synchronoss/cloud/nio-multipart-parser/1.1.0/nio-multipart-parser-1.1.0.jar:/home/ivo/.m2/repository/org/slf4j/slf4j-api/1.7.30/slf4j-api-1.7.30.jar:/home/ivo/.m2/repository/org/synchronoss/cloud/nio-stream-storage/1.1.3/nio-stream-storage-1.1.3.jar:/home/ivo/.m2/repository/org/springframework/spring-core/5.2.3.RELEASE/spring-core-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/org/springframework/spring-jcl/5.2.3.RELEASE/spring-jcl-5.2.3.RELEASE.jar:/home/ivo/.m2/repository/io/projectreactor/reactor-core/3.3.2.RELEASE/reactor-core-3.3.2.RELEASE.jar:/home/ivo/.m2/repository/org/reactivestreams/reactive-streams/1.0.3/reactive-streams-1.0.3.jar -m demo/com.example.demo.DemoApplication

[bclozel]

Spring Boot provides dependency management and starters for these projects, but the structure of all of these modules is out of our control. You should report the problems to the relevant projects or ask for guidance for those particular cases.

The general advice from the Spring Boot team is to use Java in classpath mode until the ecosystem has caught up.

In this particular instance, the EL dependency issue will be solved in Spring Boot 2.3 with #19550. In the meantime, you can exclude the validation starter (if you don't need it).