Maven plugin cannot be resolved

I've searched this problem as the title says but still don't know what I should do. I am trying to build an executable jar file, but one of the plugins maven-assembly-plugin cannot be resolved.

I've tried the https://maven.apache.org/plugins/maven-assembly-plugin/usage.html
but it doesn't work. I put the entire pom.xml file, and the plugin is at the bottom of the file. Any help is highly appreciated.

Here is the error message:

Plugin could not be resolved. Ensure the plugin's groupId, artifactId and 
version are present. Additional information: Plugin 
org.apache.maven.plugins:maven-assembly-plugin:2.2-beta-5 or one of its 
dependencies could not be resolved: Failed to read 
artifact descriptor for org.apache.maven.plugins:maven-assembly-plugin:jar:2.2-beta-5

Here is the 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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>distributed.systems</groupId>
<artifactId>leader.election</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>leader.election</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.6.1</version>
</dependency>
</dependencies>
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>3.1.0</version>
</plugin>
<!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.22.1</version>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>2.5.2</version>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>2.8.2</version>
</plugin>
<!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>3.7.1</version>
</plugin>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<version>3.0.0</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<release>14</release>
</configuration>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>3.3.0</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
<configuration>
<archive>
<manifest>
<mainClass>LeaderElection</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin> 
</plugins>
</pluginManagement>

</build>
</project>

You are possibly using an old Maven version that tries to fetch plugins via HTTP protocol. That has been disabled a few month ago. You must either use a more recent version of Maven or change your local configuration file ~/.m2/settings.xml (or C:\users\you\.m2\settings.xml) to use HTTPS. If there is no such file, you can create it by copying from the example:

<settings xmlns="http://maven.apache.org/SETTINGS/1.1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.1.0 http://maven.apache.org/xsd/settings-1.1.0.xsd">
<profiles>
<profile>
<id>stefan</id>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<repositories>
<repository>
<id>central</id>
<url>https://repo1.maven.org/maven2</url>
<releases>
<updatePolicy>never</updatePolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>  
<repository>
<id>spring-milestones</id>
<url>https://repo.springsource.org/libs-milestone/</url>
<releases>
<updatePolicy>never</updatePolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
<repository>
<id>jboss</id>
<url>https://repository.jboss.org/nexus/content/groups/public/</url>
<releases>
<updatePolicy>never</updatePolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>                
</repositories>    
<pluginRepositories>
<pluginRepository>
<id>central</id>
<url>https://repo1.maven.org/maven2</url>
<releases>
<updatePolicy>never</updatePolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository> 
</pluginRepositories>
</profile>
</profiles>    
</settings>

You have to put the groupId in above the artifactId.

<plugin>
<groupId>org.apache.maven.plugins</groupId>		  
<artifactId>maven-assembly-plugin</artifactId>
<version>3.3.0</version>
<configuration>
<archive>
<manifest>
<mainClass>de.uulm.sp.pvs.sokoban.App</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin>

For this question, I decided to use the downloaded apache maven zip instead of the built-in maven in eclipse.

1. Check if Maven inside eclipse.
   File → New → Other
2. Install m2e.
   Help → Install New Software http://download.eclipse.org/technology/m2e/releases
3. Download the Maven zip and set the environment variables to the main folder.
4. If successful, in cmd, mvn --version command shall see the version of maven and related information.
5. In the downloaded maven folder, create a new folder repository.
6. In the downloaded maven folder, find conf/→ settings.xml. Find the tag <localRepository> and modify the path to the repository folder just created.
7. Windows → Preferences → Maven → Installations → Add → Directory to the downloaded maven folder → Apply
8. Maven → User Settings → Browse the edited settings.xml → OK
9. Restart eclipse.

If all processes are successful, then the plugin issue will be resolved.

reference: https://o7planning.org/en/10101/install-maven-into-eclipse