`maven compile` can not find package when they are installed in ~/.m2 - maven

Question

I am trying to learn how to build a maven project.
this is my ./src/main/java/Hello.java
import com.google.code.gson.*;
public class Hello{
public static void main(String[] args) {
System.out.println("Hello world");
}
}
This file does't do something actually, I just want to learn how to import a 3rd library.
this is my ./pom.xml
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.5</version>
</dependency>
So, I try to execute mvn compile.
But there is an error:
package com.google.code.gson does not exist
But in my ~/.m2/repository
$ tree -L 3 ~/.m2/repository/com/google/code/gson
/Users/apple/.m2/repository/com/google/code/gson
├── 2.8.5
│   ├── gson-2.8.5.jar.lastUpdated
│   └── gson-2.8.5.pom.lastUpdated
├── gson
│   └── 2.8.5
│   ├── _remote.repositories
│   ├── gson-2.8.5.jar
│   ├── gson-2.8.5.jar.sha1
│   ├── gson-2.8.5.pom
│   └── gson-2.8.5.pom.sha1
I seems that mvn don't add ~/.m2/repository to my classpath, How to fix this?
$ mvn -v
Apache Maven 3.6.0 (97c98ec64a1fdfee7767ce5ffb20918da4f719f3; 2018-10-25T02:41:47+08:00)
Maven home: /Users/apple/Downloads/apache-maven-3.6.0
Java version: 10, vendor: Oracle Corporation, runtime: /Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home
Default locale: en_CN, platform encoding: UTF-8
OS name: "mac os x", version: "10.12.6", arch: "x86_64", family: "mac"

Answer 1

According to GSON javadoc , there is no package called com.google.code.gson.*. The root package starts from com.google.gson . So change to :
import com.google.gson.*;
What you see in the <groupId> has nothing to do with the package name. Always refer to the javadoc or its source codes for the package name.