Error finding io.netty package, but it's in pom file

June 10, 2023

I created just a barebones ‘Hello World’ project to try to resolve this. The pom file is like this:

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>untitled2</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <repositories>
        <repository>
            <id>central</id>
            <name>Maven Central</name>
            <url>https://repo1.maven.org/maven2/</url>
        </repository>
    </repositories>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>io.netty</groupId>
                <artifactId>netty-all</artifactId>
                <version>4.1.93.Final</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

</project>

with the main class looking like this:

package org.example;

import io.netty.bootstrap.ServerBootstrap;

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}

I have the import statement in there unused so it will try to build with that dependency when I run mvn clean install -U.

Here is the terminal output from running that command:

PS ~\Java\untitled2> mvn clean install -U
[INFO] Scanning for projects...
[INFO]
[INFO] -----------------------< org.example:untitled2 >------------------------
[INFO] Building untitled2 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- clean:3.2.0:clean (default-clean) @ untitled2 ---
[INFO] Deleting ~\Java\untitled2\target
[INFO]
[INFO] --- resources:3.3.0:resources (default-resources) @ untitled2 ---
[INFO] Copying 0 resource
[INFO]
[INFO] --- compiler:3.10.1:compile (default-compile) @ untitled2 ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to ~\Java\untitled2\target\classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /~/Java/untitled2/src/main/java/org/example/Main.java:[3,26] package io.netty.bootstrap does not exist
[INFO] 1 error
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  0.511 s
[INFO] Finished at: 2023-06-09T23:21:42-05:00
[INFO] ------------------------------------------------------------------------
[WARNING]
[WARNING] Plugin validation issues were detected in 2 plugin(s)
[WARNING]
[WARNING]  * org.apache.maven.plugins:maven-compiler-plugin:3.10.1
[WARNING]  * org.apache.maven.plugins:maven-resources-plugin:3.3.0
[WARNING]
[WARNING] For more or less details, use 'maven.plugin.validation' property with one of the values (case insensitive): [BRIEF, DEFAULT, VERBOSE]
[WARNING]
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.10.1:compile (default-compile) on project untitled2: Compilation failure
[ERROR] /~/Java/untitled2/src/main/java/org/example/Main.java:[3,26] package io.netty.bootstrap does not exist
[ERROR]
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
PS ~\Java\untitled2>

I have a settings folder in the .m2 repo, but it’s pretty basic from what I’ve seen:

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">

    <localRepository>${user.home}/.m2/repository</localRepository>

    <profiles>
        <profile>
            <id>default</id>
            <repositories>
                <repository>
                    <id>central</id>
                    <name>Maven Central</name>
                    <url>https://repo1.maven.org/maven2/</url>
                </repository>
            </repositories>
        </profile>
    </profiles>


    <activeProfiles>
        <activeProfile>default</activeProfile>
    </activeProfiles>
</settings>

I’ve also tried this in the IntelliJ IDE, where I’ve tried reloading project and invalidating cache in hopes for a different outcome.

If I delete the .m2 folder, a bunch of dependencies of other projects will get downloaded okay. It seems it’s just io.netty, and I believe okhttp3 that I know of that this happens to. I triple check all of the versions, and that they are available in the maven central repository, they just don’t get downloaded to the .m2 folder / used like the other dependencies do.

>Solution :

Change your pom file to this

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <groupId>org.example</groupId>
   <artifactId>untitled2</artifactId>
   <version>1.0-SNAPSHOT</version>

   <properties>
      <maven.compiler.source>11</maven.compiler.source>
      <maven.compiler.target>11</maven.compiler.target>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>

   <repositories>
      <repository>
         <id>central</id>
         <name>Maven Central</name>
         <url>https://repo1.maven.org/maven2/</url>
      </repository>
   </repositories>

   <dependencies>
      <dependency>
         <groupId>io.netty</groupId>
         <artifactId>netty-all</artifactId>
         <version>4.1.93.Final</version>
      </dependency>
   </dependencies>
</project>

Declare the dependencies without the dependencyManagement tag. This should work fine. dependencyManagement is just a declaration, and it does not really add a dependency. You can read more on the difference here.